r360308 - [c++20] Implement P0846R0: allow (ADL-only) calls to template-ids whose

Richard Smith via cfe-commits cfe-commits at lists.llvm.org
Tue Aug 13 19:29:54 PDT 2019


On Tue, 13 Aug 2019 at 18:09, Alex L via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Hi Richard,
>
> Did you get a chance to look at the issue that was reported by Akira? It's
> causing a lot of pain on our end.
>

Sorry, I missed that email. I'll take a look tomorrow.


> Thanks,
> Alex
>
>
>
> On Mon, 8 Jul 2019 at 18:27, Akira Hatanaka via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
>
>> Hi Richard,
>>
>> It looks like this patch is causing clang to reject the following code,
>> which used to compile fine:
>>
>> $ cat test.cpp
>> typedef __attribute__((__ext_vector_type__(2))) float vector_float2;
>>
>> bool foo123(vector_float2 &A, vector_float2 &B)
>> {
>>   return A.x < B.x && B.y > A.y;
>> }
>>
>> On May 8, 2019, at 8:31 PM, Richard Smith via cfe-commits <
>> cfe-commits at lists.llvm.org> wrote:
>>
>> Author: rsmith
>> Date: Wed May  8 20:31:27 2019
>> New Revision: 360308
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=360308&view=rev
>> Log:
>> [c++20] Implement P0846R0: allow (ADL-only) calls to template-ids whose
>> template name is not visible to unqualified lookup.
>>
>> In order to support this without a severe degradation in our ability to
>> diagnose typos in template names, this change significantly restructures
>> the way we handle template-id-shaped syntax for which lookup of the
>> template name finds nothing.
>>
>> Instead of eagerly diagnosing an undeclared template name, we now form a
>> placeholder template-name representing a name that is known to not find
>> any templates. When the parser sees such a name, it attempts to
>> disambiguate whether we have a less-than comparison or a template-id.
>> Any diagnostics or typo-correction for the name are delayed until its
>> point of use.
>>
>> The upshot should be a small improvement of our diagostic quality
>> overall: we now take more syntactic context into account when trying to
>> resolve an undeclared identifier on the left hand side of a '<'. In
>> fact, this works well enough that the backwards-compatible portion (for
>> an undeclared identifier rather than a lookup that finds functions but
>> no function templates) is enabled in all language modes.
>>
>> Added:
>>    cfe/trunk/test/SemaCXX/cxx2a-adl-only-template-id.cpp
>> Modified:
>>    cfe/trunk/include/clang/AST/ASTContext.h
>>    cfe/trunk/include/clang/AST/DeclarationName.h
>>    cfe/trunk/include/clang/AST/TemplateName.h
>>    cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td
>>    cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>>    cfe/trunk/include/clang/Basic/TemplateKinds.h
>>    cfe/trunk/include/clang/Parse/Parser.h
>>    cfe/trunk/include/clang/Sema/Sema.h
>>    cfe/trunk/lib/AST/ASTContext.cpp
>>    cfe/trunk/lib/AST/ASTImporter.cpp
>>    cfe/trunk/lib/AST/ASTStructuralEquivalence.cpp
>>    cfe/trunk/lib/AST/ItaniumMangle.cpp
>>    cfe/trunk/lib/AST/ODRHash.cpp
>>    cfe/trunk/lib/AST/TemplateName.cpp
>>    cfe/trunk/lib/Parse/ParseDecl.cpp
>>    cfe/trunk/lib/Parse/ParseDeclCXX.cpp
>>    cfe/trunk/lib/Parse/ParseExprCXX.cpp
>>    cfe/trunk/lib/Parse/ParseTemplate.cpp
>>    cfe/trunk/lib/Parse/ParseTentative.cpp
>>    cfe/trunk/lib/Parse/Parser.cpp
>>    cfe/trunk/lib/Sema/SemaCXXScopeSpec.cpp
>>    cfe/trunk/lib/Sema/SemaDecl.cpp
>>    cfe/trunk/lib/Sema/SemaDeclCXX.cpp
>>    cfe/trunk/lib/Sema/SemaExpr.cpp
>>    cfe/trunk/lib/Sema/SemaExprCXX.cpp
>>    cfe/trunk/lib/Sema/SemaOverload.cpp
>>    cfe/trunk/lib/Sema/SemaTemplate.cpp
>>    cfe/trunk/lib/Serialization/ASTReader.cpp
>>    cfe/trunk/lib/Serialization/ASTWriter.cpp
>>    cfe/trunk/test/CXX/basic/basic.lookup/basic.lookup.unqual/p3.cpp
>>    cfe/trunk/test/CXX/drs/dr2xx.cpp
>>    cfe/trunk/test/CXX/drs/dr6xx.cpp
>>    cfe/trunk/test/CXX/temp/temp.spec/temp.explicit/p5.cpp
>>    cfe/trunk/test/FixIt/typo-crash.cpp
>>    cfe/trunk/test/Misc/diag-template-diffing.cpp
>>    cfe/trunk/test/Modules/module-private.cpp
>>    cfe/trunk/test/Modules/submodules-merge-defs.cpp
>>    cfe/trunk/test/Parser/cxx-ambig-init-templ.cpp
>>    cfe/trunk/test/Parser/cxx-template-argument.cpp
>>    cfe/trunk/test/Parser/cxx-template-decl.cpp
>>    cfe/trunk/test/SemaCXX/alias-template.cpp
>>    cfe/trunk/test/SemaCXX/class.cpp
>>    cfe/trunk/test/SemaCXX/destructor.cpp
>>    cfe/trunk/test/SemaCXX/invalid-member-expr.cpp
>>    cfe/trunk/test/SemaCXX/typo-correction.cpp
>>    cfe/trunk/test/SemaTemplate/dependent-base-classes.cpp
>>    cfe/trunk/test/SemaTemplate/dependent-template-recover.cpp
>>    cfe/trunk/test/SemaTemplate/rdar9173693.cpp
>>    cfe/trunk/test/SemaTemplate/recovery-crash.cpp
>>    cfe/trunk/tools/libclang/CIndex.cpp
>>    cfe/trunk/www/cxx_status.html
>>
>> Modified: cfe/trunk/include/clang/AST/ASTContext.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/ASTContext.h?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/AST/ASTContext.h (original)
>> +++ cfe/trunk/include/clang/AST/ASTContext.h Wed May  8 20:31:27 2019
>> @@ -1977,6 +1977,7 @@ public:
>>
>>   TemplateName getOverloadedTemplateName(UnresolvedSetIterator Begin,
>>                                          UnresolvedSetIterator End) const;
>> +  TemplateName getAssumedTemplateName(DeclarationName Name) const;
>>
>>   TemplateName getQualifiedTemplateName(NestedNameSpecifier *NNS,
>>                                         bool TemplateKeyword,
>>
>> Modified: cfe/trunk/include/clang/AST/DeclarationName.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/DeclarationName.h?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/AST/DeclarationName.h (original)
>> +++ cfe/trunk/include/clang/AST/DeclarationName.h Wed May  8 20:31:27 2019
>> @@ -863,4 +863,24 @@ struct DenseMapInfo<clang::DeclarationNa
>>
>> } // namespace llvm
>>
>> +// The definition of AssumedTemplateStorage is factored out of
>> TemplateName to
>> +// resolve a cyclic dependency between it and DeclarationName (via Type).
>> +namespace clang {
>> +
>> +/// A structure for storing the information associated with a name that
>> has
>> +/// been assumed to be a template name (despite finding no
>> TemplateDecls).
>> +class AssumedTemplateStorage : public UncommonTemplateNameStorage {
>> +  friend class ASTContext;
>> +
>> +  AssumedTemplateStorage(DeclarationName Name)
>> +      : UncommonTemplateNameStorage(Assumed, 0), Name(Name) {}
>> +  DeclarationName Name;
>> +
>> +public:
>> +  /// Get the name of the template.
>> +  DeclarationName getDeclName() const { return Name; }
>> +};
>> +
>> +} // namespace clang
>> +
>> #endif // LLVM_CLANG_AST_DECLARATIONNAME_H
>>
>> Modified: cfe/trunk/include/clang/AST/TemplateName.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/TemplateName.h?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/AST/TemplateName.h (original)
>> +++ cfe/trunk/include/clang/AST/TemplateName.h Wed May  8 20:31:27 2019
>> @@ -31,6 +31,7 @@ class NamedDecl;
>> class NestedNameSpecifier;
>> enum OverloadedOperatorKind : int;
>> class OverloadedTemplateStorage;
>> +class AssumedTemplateStorage;
>> class PartialDiagnostic;
>> struct PrintingPolicy;
>> class QualifiedTemplateName;
>> @@ -46,6 +47,7 @@ class UncommonTemplateNameStorage {
>> protected:
>>   enum Kind {
>>     Overloaded,
>> +    Assumed, // defined in DeclarationName.h
>>     SubstTemplateTemplateParm,
>>     SubstTemplateTemplateParmPack
>>   };
>> @@ -78,6 +80,12 @@ public:
>>              : nullptr;
>>   }
>>
>> +  AssumedTemplateStorage *getAsAssumedTemplateName()  {
>> +    return Bits.Kind == Assumed
>> +             ? reinterpret_cast<AssumedTemplateStorage *>(this)
>> +             : nullptr;
>> +  }
>> +
>>   SubstTemplateTemplateParmStorage *getAsSubstTemplateTemplateParm() {
>>     return Bits.Kind == SubstTemplateTemplateParm
>>              ? reinterpret_cast<SubstTemplateTemplateParmStorage *>(this)
>> @@ -194,6 +202,10 @@ public:
>>     /// A set of overloaded template declarations.
>>     OverloadedTemplate,
>>
>> +    /// An unqualified-id that has been assumed to name a function
>> template
>> +    /// that will be found by ADL.
>> +    AssumedTemplate,
>> +
>>     /// A qualified template name, where the qualification is kept
>>     /// to describe the source code as written.
>>     QualifiedTemplate,
>> @@ -215,6 +227,7 @@ public:
>>   TemplateName() = default;
>>   explicit TemplateName(TemplateDecl *Template);
>>   explicit TemplateName(OverloadedTemplateStorage *Storage);
>> +  explicit TemplateName(AssumedTemplateStorage *Storage);
>>   explicit TemplateName(SubstTemplateTemplateParmStorage *Storage);
>>   explicit TemplateName(SubstTemplateTemplateParmPackStorage *Storage);
>>   explicit TemplateName(QualifiedTemplateName *Qual);
>> @@ -236,7 +249,7 @@ public:
>>   TemplateDecl *getAsTemplateDecl() const;
>>
>>   /// Retrieve the underlying, overloaded function template
>> -  // declarations that this template name refers to, if known.
>> +  /// declarations that this template name refers to, if known.
>>   ///
>>   /// \returns The set of overloaded function templates that this template
>>   /// name refers to, if known. If the template name does not refer to a
>> @@ -244,6 +257,10 @@ public:
>>   /// refers to a single template, returns NULL.
>>   OverloadedTemplateStorage *getAsOverloadedTemplate() const;
>>
>> +  /// Retrieve information on a name that has been assumed to be a
>> +  /// template-name in order to permit a call via ADL.
>> +  AssumedTemplateStorage *getAsAssumedTemplateName() const;
>> +
>>   /// Retrieve the substituted template template parameter, if
>>   /// known.
>>   ///
>>
>> Modified: cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td (original)
>> +++ cfe/trunk/include/clang/Basic/DiagnosticParseKinds.td Wed May  8
>> 20:31:27 2019
>> @@ -744,7 +744,8 @@ def err_typename_refers_to_non_type_temp
>> def err_expected_type_name_after_typename : Error<
>>   "expected an identifier or template-id after '::'">;
>> def err_explicit_spec_non_template : Error<
>> -  "explicit %select{specialization|instantiation}0 of non-template %1
>> %2">;
>> +  "explicit %select{specialization|instantiation}0 of "
>> +  "%select{non-|undeclared }3template %1 %2">;
>>
>> def err_default_template_template_parameter_not_template : Error<
>>   "default template argument for a template template parameter must be a
>> class "
>>
>> Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
>> +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Wed May  8
>> 20:31:27 2019
>> @@ -3963,6 +3963,15 @@ def err_template_member_noparams : Error
>> def err_template_tag_noparams : Error<
>>   "extraneous 'template<>' in declaration of %0 %1">;
>>
>> +def warn_cxx17_compat_adl_only_template_id : Warning<
>> +  "use of function template name with no prior function template "
>> +  "declaration in function call with explicit template arguments "
>> +  "is incompatible with C++ standards before C++2a">,
>> +  InGroup<CXXPre2aCompat>, DefaultIgnore;
>> +def ext_adl_only_template_id : ExtWarn<
>> +  "use of function template name with no prior declaration in function
>> call "
>> +  "with explicit template arguments is a C++2a extension">,
>> InGroup<CXX2a>;
>> +
>> // C++ Template Argument Lists
>> def err_template_missing_args : Error<
>>   "use of "
>>
>> Modified: cfe/trunk/include/clang/Basic/TemplateKinds.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/TemplateKinds.h?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Basic/TemplateKinds.h (original)
>> +++ cfe/trunk/include/clang/Basic/TemplateKinds.h Wed May  8 20:31:27 2019
>> @@ -21,7 +21,8 @@ enum TemplateNameKind {
>>   /// The name does not refer to a template.
>>   TNK_Non_template = 0,
>>   /// The name refers to a function template or a set of overloaded
>> -  /// functions that includes at least one function template.
>> +  /// functions that includes at least one function template, or (in
>> C++20)
>> +  /// refers to a set of non-template functions but is followed by a '<'.
>>   TNK_Function_template,
>>   /// The name refers to a template whose specialization produces a
>>   /// type. The template itself could be a class template, template
>> @@ -42,7 +43,11 @@ enum TemplateNameKind {
>>   /// whether the template name is assumed to refer to a type template or
>> a
>>   /// function template depends on the context in which the template
>>   /// name occurs.
>> -  TNK_Dependent_template_name
>> +  TNK_Dependent_template_name,
>> +  /// Lookup for the name failed, but we're assuming it was a template
>> name
>> +  /// anyway. In C++20, this is mandatory in order to parse ADL-only
>> function
>> +  /// template specialization calls.
>> +  TNK_Undeclared_template,
>> };
>>
>> }
>>
>> Modified: cfe/trunk/include/clang/Parse/Parser.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Parse/Parser.h?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Parse/Parser.h (original)
>> +++ cfe/trunk/include/clang/Parse/Parser.h Wed May  8 20:31:27 2019
>> @@ -2303,13 +2303,18 @@ private:
>>   /// Doesn't consume tokens.
>>   TPResult
>>   isCXXDeclarationSpecifier(TPResult BracedCastResult = TPResult::False,
>> -                            bool *HasMissingTypename = nullptr);
>> +                            bool *InvalidAsDeclSpec = nullptr);
>>
>>   /// Given that isCXXDeclarationSpecifier returns \c TPResult::True or
>>   /// \c TPResult::Ambiguous, determine whether the decl-specifier would
>> be
>>   /// a type-specifier other than a cv-qualifier.
>>   bool isCXXDeclarationSpecifierAType();
>>
>> +  /// Determine whether the current token sequence might be
>> +  ///   '<' template-argument-list '>'
>> +  /// rather than a less-than expression.
>> +  TPResult isTemplateArgumentList(unsigned TokensToSkip);
>> +
>>   /// Determine whether an identifier has been tentatively declared as a
>>   /// non-type. Such tentative declarations should not be found to name a
>> type
>>   /// during a tentative parse, but also should not be annotated as a
>> non-type.
>> @@ -2994,7 +2999,6 @@ private:
>>                                UnqualifiedId &TemplateName,
>>                                bool AllowTypeAnnotation = true);
>>   void AnnotateTemplateIdTokenAsType(bool IsClassName = false);
>> -  bool IsTemplateArgumentList(unsigned Skip = 0);
>>   bool ParseTemplateArgumentList(TemplateArgList &TemplateArgs);
>>   ParsedTemplateArgument ParseTemplateTemplateArgument();
>>   ParsedTemplateArgument ParseTemplateArgument();
>>
>> Modified: cfe/trunk/include/clang/Sema/Sema.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Sema.h?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Sema/Sema.h (original)
>> +++ cfe/trunk/include/clang/Sema/Sema.h Wed May  8 20:31:27 2019
>> @@ -1823,7 +1823,8 @@ public:
>>     NC_NestedNameSpecifier,
>>     NC_TypeTemplate,
>>     NC_VarTemplate,
>> -    NC_FunctionTemplate
>> +    NC_FunctionTemplate,
>> +    NC_UndeclaredTemplate,
>>   };
>>
>>   class NameClassification {
>> @@ -1871,6 +1872,12 @@ public:
>>       return Result;
>>     }
>>
>> +    static NameClassification UndeclaredTemplate(TemplateName Name) {
>> +      NameClassification Result(NC_UndeclaredTemplate);
>> +      Result.Template = Name;
>> +      return Result;
>> +    }
>> +
>>     NameClassificationKind getKind() const { return Kind; }
>>
>>     ParsedType getType() const {
>> @@ -1885,7 +1892,7 @@ public:
>>
>>     TemplateName getTemplateName() const {
>>       assert(Kind == NC_TypeTemplate || Kind == NC_FunctionTemplate ||
>> -             Kind == NC_VarTemplate);
>> +             Kind == NC_VarTemplate || Kind == NC_UndeclaredTemplate);
>>       return Template;
>>     }
>>
>> @@ -1897,6 +1904,8 @@ public:
>>         return TNK_Function_template;
>>       case NC_VarTemplate:
>>         return TNK_Var_template;
>> +      case NC_UndeclaredTemplate:
>> +        return TNK_Undeclared_template;
>>       default:
>>         llvm_unreachable("unsupported name classification.");
>>       }
>> @@ -6256,7 +6265,8 @@ public:
>>                                      bool AllowDependent = true);
>>   bool hasAnyAcceptableTemplateNames(LookupResult &R,
>>                                      bool AllowFunctionTemplates = true,
>> -                                     bool AllowDependent = true);
>> +                                     bool AllowDependent = true,
>> +                                     bool AllowNonTemplateFunctions =
>> false);
>>   /// Try to interpret the lookup result D as a template-name.
>>   ///
>>   /// \param D A declaration found by name lookup.
>> @@ -6268,10 +6278,20 @@ public:
>>                                    bool AllowFunctionTemplates = true,
>>                                    bool AllowDependent = true);
>>
>> +  enum class AssumedTemplateKind {
>> +    /// This is not assumed to be a template name.
>> +    None,
>> +    /// This is assumed to be a template name because lookup found
>> nothing.
>> +    FoundNothing,
>> +    /// This is assumed to be a template name because lookup found one
>> or more
>> +    /// functions (but no function templates).
>> +    FoundFunctions,
>> +  };
>>   bool LookupTemplateName(LookupResult &R, Scope *S, CXXScopeSpec &SS,
>>                           QualType ObjectType, bool EnteringContext,
>>                           bool &MemberOfUnknownSpecialization,
>> -                          SourceLocation TemplateKWLoc =
>> SourceLocation());
>> +                          SourceLocation TemplateKWLoc =
>> SourceLocation(),
>> +                          AssumedTemplateKind *ATK = nullptr);
>>
>>   TemplateNameKind isTemplateName(Scope *S,
>>                                   CXXScopeSpec &SS,
>> @@ -6282,6 +6302,20 @@ public:
>>                                   TemplateTy &Template,
>>                                   bool &MemberOfUnknownSpecialization);
>>
>> +  /// Try to resolve an undeclared template name as a type template.
>> +  ///
>> +  /// Sets II to the identifier corresponding to the template name, and
>> updates
>> +  /// Name to a corresponding (typo-corrected) type template name and
>> TNK to
>> +  /// the corresponding kind, if possible.
>> +  void ActOnUndeclaredTypeTemplateName(Scope *S, TemplateTy &Name,
>> +                                       TemplateNameKind &TNK,
>> +                                       SourceLocation NameLoc,
>> +                                       IdentifierInfo *&II);
>> +
>> +  bool resolveAssumedTemplateNameAsType(Scope *S, TemplateName &Name,
>> +                                        SourceLocation NameLoc,
>> +                                        bool Diagnose = true);
>> +
>>   /// Determine whether a particular identifier might be the name in a
>> C++1z
>>   /// deduction-guide declaration.
>>   bool isDeductionGuideName(Scope *S, const IdentifierInfo &Name,
>> @@ -6391,14 +6425,11 @@ public:
>>                               TemplateArgumentListInfo &TemplateArgs);
>>
>>   TypeResult
>> -  ActOnTemplateIdType(CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
>> +  ActOnTemplateIdType(Scope *S, CXXScopeSpec &SS, SourceLocation
>> TemplateKWLoc,
>>                       TemplateTy Template, IdentifierInfo *TemplateII,
>> -                      SourceLocation TemplateIILoc,
>> -                      SourceLocation LAngleLoc,
>> -                      ASTTemplateArgsPtr TemplateArgs,
>> -                      SourceLocation RAngleLoc,
>> -                      bool IsCtorOrDtorName = false,
>> -                      bool IsClassName = false);
>> +                      SourceLocation TemplateIILoc, SourceLocation
>> LAngleLoc,
>> +                      ASTTemplateArgsPtr TemplateArgs, SourceLocation
>> RAngleLoc,
>> +                      bool IsCtorOrDtorName = false, bool IsClassName =
>> false);
>>
>>   /// Parsed an elaborated-type-specifier that refers to a template-id,
>>   /// such as \c class T::template apply<U>.
>>
>> Modified: cfe/trunk/lib/AST/ASTContext.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ASTContext.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/AST/ASTContext.cpp (original)
>> +++ cfe/trunk/lib/AST/ASTContext.cpp Wed May  8 20:31:27 2019
>> @@ -5226,6 +5226,11 @@ ASTContext::getNameForTemplate(TemplateN
>>     return DeclarationNameInfo((*Storage->begin())->getDeclName(),
>> NameLoc);
>>   }
>>
>> +  case TemplateName::AssumedTemplate: {
>> +    AssumedTemplateStorage *Storage = Name.getAsAssumedTemplateName();
>> +    return DeclarationNameInfo(Storage->getDeclName(), NameLoc);
>> +  }
>> +
>>   case TemplateName::DependentTemplate: {
>>     DependentTemplateName *DTN = Name.getAsDependentTemplateName();
>>     DeclarationName DName;
>> @@ -5273,7 +5278,8 @@ TemplateName ASTContext::getCanonicalTem
>>   }
>>
>>   case TemplateName::OverloadedTemplate:
>> -    llvm_unreachable("cannot canonicalize overloaded template");
>> +  case TemplateName::AssumedTemplate:
>> +    llvm_unreachable("cannot canonicalize unresolved template");
>>
>>   case TemplateName::DependentTemplate: {
>>     DependentTemplateName *DTN = Name.getAsDependentTemplateName();
>> @@ -7620,6 +7626,13 @@ ASTContext::getOverloadedTemplateName(Un
>>   return TemplateName(OT);
>> }
>>
>> +/// Retrieve a template name representing an unqualified-id that has been
>> +/// assumed to name a template for ADL purposes.
>> +TemplateName ASTContext::getAssumedTemplateName(DeclarationName Name)
>> const {
>> +  auto *OT = new (*this) AssumedTemplateStorage(Name);
>> +  return TemplateName(OT);
>> +}
>> +
>> /// Retrieve the template name that represents a qualified
>> /// template name such as \c std::vector.
>> TemplateName
>>
>> Modified: cfe/trunk/lib/AST/ASTImporter.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ASTImporter.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/AST/ASTImporter.cpp (original)
>> +++ cfe/trunk/lib/AST/ASTImporter.cpp Wed May  8 20:31:27 2019
>> @@ -8126,6 +8126,14 @@ Expected<TemplateName> ASTImporter::Impo
>>                                                ToTemplates.end());
>>   }
>>
>> +  case TemplateName::AssumedTemplate: {
>> +    AssumedTemplateStorage *FromStorage =
>> From.getAsAssumedTemplateName();
>> +    auto DeclNameOrErr = Import_New(FromStorage->getDeclName());
>> +    if (!DeclNameOrErr)
>> +      return DeclNameOrErr.takeError();
>> +    return ToContext.getAssumedTemplateName(*DeclNameOrErr);
>> +  }
>> +
>>   case TemplateName::QualifiedTemplate: {
>>     QualifiedTemplateName *QTN = From.getAsQualifiedTemplateName();
>>     auto QualifierOrErr = Import_New(QTN->getQualifier());
>>
>> Modified: cfe/trunk/lib/AST/ASTStructuralEquivalence.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ASTStructuralEquivalence.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/AST/ASTStructuralEquivalence.cpp (original)
>> +++ cfe/trunk/lib/AST/ASTStructuralEquivalence.cpp Wed May  8 20:31:27
>> 2019
>> @@ -180,6 +180,12 @@ static bool IsStructurallyEquivalent(Str
>>     return I1 == E1 && I2 == E2;
>>   }
>>
>> +  case TemplateName::AssumedTemplate: {
>> +    AssumedTemplateStorage *TN1 = N1.getAsAssumedTemplateName(),
>> +                           *TN2 = N1.getAsAssumedTemplateName();
>> +    return TN1->getDeclName() == TN2->getDeclName();
>> +  }
>> +
>>   case TemplateName::QualifiedTemplate: {
>>     QualifiedTemplateName *QN1 = N1.getAsQualifiedTemplateName(),
>>                           *QN2 = N2.getAsQualifiedTemplateName();
>>
>> Modified: cfe/trunk/lib/AST/ItaniumMangle.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ItaniumMangle.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/AST/ItaniumMangle.cpp (original)
>> +++ cfe/trunk/lib/AST/ItaniumMangle.cpp Wed May  8 20:31:27 2019
>> @@ -1891,6 +1891,7 @@ void CXXNameMangler::mangleType(Template
>>     break;
>>
>>   case TemplateName::OverloadedTemplate:
>> +  case TemplateName::AssumedTemplate:
>>     llvm_unreachable("can't mangle an overloaded template name as a
>> <type>");
>>
>>   case TemplateName::DependentTemplate: {
>> @@ -2030,6 +2031,7 @@ bool CXXNameMangler::mangleUnresolvedTyp
>>     }
>>
>>     case TemplateName::OverloadedTemplate:
>> +    case TemplateName::AssumedTemplate:
>>     case TemplateName::DependentTemplate:
>>       llvm_unreachable("invalid base for a template specialization type");
>>
>>
>> Modified: cfe/trunk/lib/AST/ODRHash.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ODRHash.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/AST/ODRHash.cpp (original)
>> +++ cfe/trunk/lib/AST/ODRHash.cpp Wed May  8 20:31:27 2019
>> @@ -140,6 +140,7 @@ void ODRHash::AddTemplateName(TemplateNa
>>     break;
>>   // TODO: Support these cases.
>>   case TemplateName::OverloadedTemplate:
>> +  case TemplateName::AssumedTemplate:
>>   case TemplateName::QualifiedTemplate:
>>   case TemplateName::DependentTemplate:
>>   case TemplateName::SubstTemplateTemplateParm:
>>
>> Modified: cfe/trunk/lib/AST/TemplateName.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/TemplateName.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/AST/TemplateName.cpp (original)
>> +++ cfe/trunk/lib/AST/TemplateName.cpp Wed May  8 20:31:27 2019
>> @@ -66,6 +66,8 @@ TemplateName::TemplateName(void *Ptr) {
>> TemplateName::TemplateName(TemplateDecl *Template) : Storage(Template) {}
>> TemplateName::TemplateName(OverloadedTemplateStorage *Storage)
>>     : Storage(Storage) {}
>> +TemplateName::TemplateName(AssumedTemplateStorage *Storage)
>> +    : Storage(Storage) {}
>> TemplateName::TemplateName(SubstTemplateTemplateParmStorage *Storage)
>>     : Storage(Storage) {}
>> TemplateName::TemplateName(SubstTemplateTemplateParmPackStorage *Storage)
>> @@ -87,6 +89,8 @@ TemplateName::NameKind TemplateName::get
>>     = Storage.get<UncommonTemplateNameStorage*>();
>>   if (uncommon->getAsOverloadedStorage())
>>     return OverloadedTemplate;
>> +  if (uncommon->getAsAssumedTemplateName())
>> +    return AssumedTemplate;
>>   if (uncommon->getAsSubstTemplateTemplateParm())
>>     return SubstTemplateTemplateParm;
>>   return SubstTemplateTemplateParmPack;
>> @@ -113,6 +117,14 @@ OverloadedTemplateStorage *TemplateName:
>>   return nullptr;
>> }
>>
>> +AssumedTemplateStorage *TemplateName::getAsAssumedTemplateName() const {
>> +  if (UncommonTemplateNameStorage *Uncommon =
>> +          Storage.dyn_cast<UncommonTemplateNameStorage *>())
>> +    return Uncommon->getAsAssumedTemplateName();
>> +
>> +  return nullptr;
>> +}
>> +
>> SubstTemplateTemplateParmStorage *
>> TemplateName::getAsSubstTemplateTemplateParm() const {
>>   if (UncommonTemplateNameStorage *uncommon =
>> @@ -230,7 +242,9 @@ TemplateName::print(raw_ostream &OS, con
>>   } else if (SubstTemplateTemplateParmPackStorage *SubstPack
>>                                         =
>> getAsSubstTemplateTemplateParmPack())
>>     OS << *SubstPack->getParameterPack();
>> -  else {
>> +  else if (AssumedTemplateStorage *Assumed = getAsAssumedTemplateName())
>> {
>> +    Assumed->getDeclName().print(OS, Policy);
>> +  } else {
>>     OverloadedTemplateStorage *OTS = getAsOverloadedTemplate();
>>     (*OTS->begin())->printName(OS);
>>   }
>>
>> Modified: cfe/trunk/lib/Parse/ParseDecl.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseDecl.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Parse/ParseDecl.cpp (original)
>> +++ cfe/trunk/lib/Parse/ParseDecl.cpp Wed May  8 20:31:27 2019
>> @@ -2916,6 +2916,7 @@ Parser::DiagnoseMissingSemiAfterTagDefin
>>       case Sema::NC_Expression:
>>       case Sema::NC_VarTemplate:
>>       case Sema::NC_FunctionTemplate:
>> +      case Sema::NC_UndeclaredTemplate:
>>         // Might be a redeclaration of a prior entity.
>>         break;
>>       }
>> @@ -3386,7 +3387,8 @@ void Parser::ParseDeclarationSpecifiers(
>>       // type-name
>>     case tok::annot_template_id: {
>>       TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
>> -      if (TemplateId->Kind != TNK_Type_template) {
>> +      if (TemplateId->Kind != TNK_Type_template &&
>> +          TemplateId->Kind != TNK_Undeclared_template) {
>>         // This template-id does not refer to a type name, so we're
>>         // done with the type-specifiers.
>>         goto DoneWithDeclSpec;
>>
>> Modified: cfe/trunk/lib/Parse/ParseDeclCXX.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseDeclCXX.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Parse/ParseDeclCXX.cpp (original)
>> +++ cfe/trunk/lib/Parse/ParseDeclCXX.cpp Wed May  8 20:31:27 2019
>> @@ -597,10 +597,11 @@ bool Parser::ParseUsingDeclarator(Declar
>>
>>   // Parse nested-name-specifier.
>>   IdentifierInfo *LastII = nullptr;
>> -  ParseOptionalCXXScopeSpecifier(D.SS, nullptr,
>> /*EnteringContext=*/false,
>> -                                 /*MayBePseudoDtor=*/nullptr,
>> -                                 /*IsTypename=*/false,
>> -                                 /*LastII=*/&LastII);
>> +  if (ParseOptionalCXXScopeSpecifier(D.SS, nullptr,
>> /*EnteringContext=*/false,
>> +                                     /*MayBePseudoDtor=*/nullptr,
>> +                                     /*IsTypename=*/false,
>> +                                     /*LastII=*/&LastII))
>> +    return true;
>>   if (D.SS.isInvalid())
>>     return true;
>>
>> @@ -1111,7 +1112,8 @@ TypeResult Parser::ParseBaseTypeSpecifie
>>
>>   // Parse optional nested-name-specifier
>>   CXXScopeSpec SS;
>> -  ParseOptionalCXXScopeSpecifier(SS, nullptr, /*EnteringContext=*/false);
>> +  if (ParseOptionalCXXScopeSpecifier(SS, nullptr,
>> /*EnteringContext=*/false))
>> +    return true;
>>
>>   BaseLoc = Tok.getLocation();
>>
>> @@ -1135,7 +1137,8 @@ TypeResult Parser::ParseBaseTypeSpecifie
>>   if (Tok.is(tok::annot_template_id)) {
>>     TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
>>     if (TemplateId->Kind == TNK_Type_template ||
>> -        TemplateId->Kind == TNK_Dependent_template_name) {
>> +        TemplateId->Kind == TNK_Dependent_template_name ||
>> +        TemplateId->Kind == TNK_Undeclared_template) {
>>       AnnotateTemplateIdTokenAsType(/*IsClassName*/true);
>>
>>       assert(Tok.is(tok::annot_typename) && "template-id -> type
>> failed");
>> @@ -1554,6 +1557,36 @@ void Parser::ParseClassSpecifier(tok::To
>>
>>   TemplateParameterLists *TemplateParams = TemplateInfo.TemplateParams;
>>
>> +  auto RecoverFromUndeclaredTemplateName = [&](IdentifierInfo *Name,
>> +                                               SourceLocation NameLoc,
>> +                                               SourceRange
>> TemplateArgRange,
>> +                                               bool KnownUndeclared) {
>> +    Diag(NameLoc, diag::err_explicit_spec_non_template)
>> +        << (TemplateInfo.Kind ==
>> ParsedTemplateInfo::ExplicitInstantiation)
>> +        << TagTokKind << Name << TemplateArgRange << KnownUndeclared;
>> +
>> +    // Strip off the last template parameter list if it was empty, since
>> +    // we've removed its template argument list.
>> +    if (TemplateParams && TemplateInfo.LastParameterListWasEmpty) {
>> +      if (TemplateParams->size() > 1) {
>> +        TemplateParams->pop_back();
>> +      } else {
>> +        TemplateParams = nullptr;
>> +        const_cast<ParsedTemplateInfo &>(TemplateInfo).Kind =
>> +            ParsedTemplateInfo::NonTemplate;
>> +      }
>> +    } else if (TemplateInfo.Kind ==
>> ParsedTemplateInfo::ExplicitInstantiation) {
>> +      // Pretend this is just a forward declaration.
>> +      TemplateParams = nullptr;
>> +      const_cast<ParsedTemplateInfo &>(TemplateInfo).Kind =
>> +          ParsedTemplateInfo::NonTemplate;
>> +      const_cast<ParsedTemplateInfo &>(TemplateInfo).TemplateLoc =
>> +          SourceLocation();
>> +      const_cast<ParsedTemplateInfo &>(TemplateInfo).ExternLoc =
>> +          SourceLocation();
>> +    }
>> +  };
>> +
>>   // Parse the (optional) class name or simple-template-id.
>>   IdentifierInfo *Name = nullptr;
>>   SourceLocation NameLoc;
>> @@ -1574,38 +1607,26 @@ void Parser::ParseClassSpecifier(tok::To
>>         // try to give any location information for the list.
>>         LAngleLoc = RAngleLoc = SourceLocation();
>>       }
>> -
>> -      Diag(NameLoc, diag::err_explicit_spec_non_template)
>> -          << (TemplateInfo.Kind ==
>> ParsedTemplateInfo::ExplicitInstantiation)
>> -          << TagTokKind << Name << SourceRange(LAngleLoc, RAngleLoc);
>> -
>> -      // Strip off the last template parameter list if it was empty,
>> since
>> -      // we've removed its template argument list.
>> -      if (TemplateParams && TemplateInfo.LastParameterListWasEmpty) {
>> -        if (TemplateParams->size() > 1) {
>> -          TemplateParams->pop_back();
>> -        } else {
>> -          TemplateParams = nullptr;
>> -          const_cast<ParsedTemplateInfo&>(TemplateInfo).Kind
>> -            = ParsedTemplateInfo::NonTemplate;
>> -        }
>> -      } else if (TemplateInfo.Kind
>> -                                ==
>> ParsedTemplateInfo::ExplicitInstantiation) {
>> -        // Pretend this is just a forward declaration.
>> -        TemplateParams = nullptr;
>> -        const_cast<ParsedTemplateInfo&>(TemplateInfo).Kind
>> -          = ParsedTemplateInfo::NonTemplate;
>> -        const_cast<ParsedTemplateInfo&>(TemplateInfo).TemplateLoc
>> -          = SourceLocation();
>> -        const_cast<ParsedTemplateInfo&>(TemplateInfo).ExternLoc
>> -          = SourceLocation();
>> -      }
>> +      RecoverFromUndeclaredTemplateName(
>> +          Name, NameLoc, SourceRange(LAngleLoc, RAngleLoc), false);
>>     }
>>   } else if (Tok.is(tok::annot_template_id)) {
>>     TemplateId = takeTemplateIdAnnotation(Tok);
>>     NameLoc = ConsumeAnnotationToken();
>>
>> -    if (TemplateId->Kind != TNK_Type_template &&
>> +    if (TemplateId->Kind == TNK_Undeclared_template) {
>> +      // Try to resolve the template name to a type template.
>> +      Actions.ActOnUndeclaredTypeTemplateName(getCurScope(),
>> TemplateId->Template,
>> +                                              TemplateId->Kind, NameLoc,
>> Name);
>> +      if (TemplateId->Kind == TNK_Undeclared_template) {
>> +        RecoverFromUndeclaredTemplateName(
>> +            Name, NameLoc,
>> +            SourceRange(TemplateId->LAngleLoc, TemplateId->RAngleLoc),
>> true);
>> +        TemplateId = nullptr;
>> +      }
>> +    }
>> +
>> +    if (TemplateId && TemplateId->Kind != TNK_Type_template &&
>>         TemplateId->Kind != TNK_Dependent_template_name) {
>>       // The template-name in the simple-template-id refers to
>>       // something other than a class template. Give an appropriate
>> @@ -1616,7 +1637,7 @@ void Parser::ParseClassSpecifier(tok::To
>>
>>       // FIXME: Name may be null here.
>>       Diag(TemplateId->LAngleLoc,
>> diag::err_template_spec_syntax_non_template)
>> -        << TemplateId->Name << static_cast<int>(TemplateId->Kind) <<
>> Range;
>> +          << TemplateId->Name << static_cast<int>(TemplateId->Kind) <<
>> Range;
>>
>>       DS.SetTypeSpecError();
>>       SkipUntil(tok::semi, StopBeforeMatch);
>> @@ -3451,7 +3472,8 @@ void Parser::ParseConstructorInitializer
>> MemInitResult Parser::ParseMemInitializer(Decl *ConstructorDecl) {
>>   // parse '::'[opt] nested-name-specifier[opt]
>>   CXXScopeSpec SS;
>> -  ParseOptionalCXXScopeSpecifier(SS, nullptr, /*EnteringContext=*/false);
>> +  if (ParseOptionalCXXScopeSpecifier(SS, nullptr,
>> /*EnteringContext=*/false))
>> +    return true;
>>
>>   // : identifier
>>   IdentifierInfo *II = nullptr;
>> @@ -3477,11 +3499,14 @@ MemInitResult Parser::ParseMemInitialize
>>                                            ? takeTemplateIdAnnotation(Tok)
>>                                            : nullptr;
>>     if (TemplateId && (TemplateId->Kind == TNK_Type_template ||
>> -                       TemplateId->Kind == TNK_Dependent_template_name))
>> {
>> +                       TemplateId->Kind == TNK_Dependent_template_name ||
>> +                       TemplateId->Kind == TNK_Undeclared_template)) {
>>       AnnotateTemplateIdTokenAsType(/*IsClassName*/true);
>>       assert(Tok.is(tok::annot_typename) && "template-id -> type
>> failed");
>>       TemplateTypeTy = getTypeAnnotation(Tok);
>>       ConsumeAnnotationToken();
>> +      if (!TemplateTypeTy)
>> +        return true;
>>     } else {
>>       Diag(Tok, diag::err_expected_member_or_base_name);
>>       return true;
>>
>> Modified: cfe/trunk/lib/Parse/ParseExprCXX.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseExprCXX.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Parse/ParseExprCXX.cpp (original)
>> +++ cfe/trunk/lib/Parse/ParseExprCXX.cpp Wed May  8 20:31:27 2019
>> @@ -487,6 +487,14 @@ bool Parser::ParseOptionalCXXScopeSpecif
>>                                                         EnteringContext,
>>                                                         Template,
>>                                               MemberOfUnknownSpecialization))
>> {
>> +        // If lookup didn't find anything, we treat the name as a
>> template-name
>> +        // anyway. C++20 requires this, and in prior language modes it
>> improves
>> +        // error recovery. But before we commit to this, check that we
>> actually
>> +        // have something that looks like a template-argument-list next.
>> +        if (!IsTypename && TNK == TNK_Undeclared_template &&
>> +            isTemplateArgumentList(1) == TPResult::False)
>> +          break;
>> +
>>         // We have found a template name, so annotate this token
>>         // with a template-id annotation. We do not permit the
>>         // template-id to be translated into a type annotation,
>> @@ -501,7 +509,7 @@ bool Parser::ParseOptionalCXXScopeSpecif
>>       }
>>
>>       if (MemberOfUnknownSpecialization && (ObjectType || SS.isSet()) &&
>> -          (IsTypename || IsTemplateArgumentList(1))) {
>> +          (IsTypename || isTemplateArgumentList(1) == TPResult::True)) {
>>         // We have something like t::getAs<T>, where getAs is a
>>         // member of an unknown specialization. However, this will only
>>         // parse correctly as a template, so suggest the keyword
>> 'template'
>> @@ -2138,9 +2146,15 @@ bool Parser::ParseUnqualifiedIdTemplateI
>>                                    TemplateKWLoc.isValid(), Id,
>>                                    ObjectType, EnteringContext, Template,
>>                                    MemberOfUnknownSpecialization);
>> +      // If lookup found nothing but we're assuming that this is a
>> template
>> +      // name, double-check that makes sense syntactically before
>> committing
>> +      // to it.
>> +      if (TNK == TNK_Undeclared_template &&
>> +          isTemplateArgumentList(0) == TPResult::False)
>> +        return false;
>>
>>       if (TNK == TNK_Non_template && MemberOfUnknownSpecialization &&
>> -          ObjectType && IsTemplateArgumentList()) {
>> +          ObjectType && isTemplateArgumentList(0) == TPResult::True) {
>>         // We have something like t->getAs<T>(), where getAs is a
>>         // member of an unknown specialization. However, this will only
>>         // parse correctly as a template, so suggest the keyword
>> 'template'
>> @@ -2244,11 +2258,9 @@ bool Parser::ParseUnqualifiedIdTemplateI
>>   ASTTemplateArgsPtr TemplateArgsPtr(TemplateArgs);
>>
>>   // Constructor and destructor names.
>> -  TypeResult Type
>> -    = Actions.ActOnTemplateIdType(SS, TemplateKWLoc,
>> -                                  Template, Name, NameLoc,
>> -                                  LAngleLoc, TemplateArgsPtr, RAngleLoc,
>> -                                  /*IsCtorOrDtorName=*/true);
>> +  TypeResult Type = Actions.ActOnTemplateIdType(
>> +      getCurScope(), SS, TemplateKWLoc, Template, Name, NameLoc,
>> LAngleLoc,
>> +      TemplateArgsPtr, RAngleLoc, /*IsCtorOrDtorName=*/true);
>>   if (Type.isInvalid())
>>     return true;
>>
>>
>> Modified: cfe/trunk/lib/Parse/ParseTemplate.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseTemplate.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Parse/ParseTemplate.cpp (original)
>> +++ cfe/trunk/lib/Parse/ParseTemplate.cpp Wed May  8 20:31:27 2019
>> @@ -1031,6 +1031,8 @@ bool Parser::AnnotateTemplateIdToken(Tem
>>     // If we failed to parse the template ID but skipped ahead to a >,
>> we're not
>>     // going to be able to form a token annotation.  Eat the '>' if
>> present.
>>     TryConsumeToken(tok::greater);
>> +    // FIXME: Annotate the token stream so we don't produce the same
>> errors
>> +    // again if we're doing this annotation as part of a tentative parse.
>>     return true;
>>   }
>>
>> @@ -1039,13 +1041,15 @@ bool Parser::AnnotateTemplateIdToken(Tem
>>   // Build the annotation token.
>>   if (TNK == TNK_Type_template && AllowTypeAnnotation) {
>>     TypeResult Type = Actions.ActOnTemplateIdType(
>> -        SS, TemplateKWLoc, Template, TemplateName.Identifier,
>> +        getCurScope(), SS, TemplateKWLoc, Template,
>> TemplateName.Identifier,
>>         TemplateNameLoc, LAngleLoc, TemplateArgsPtr, RAngleLoc);
>>     if (Type.isInvalid()) {
>>       // If we failed to parse the template ID but skipped ahead to a >,
>> we're
>>       // not going to be able to form a token annotation.  Eat the '>' if
>>       // present.
>>       TryConsumeToken(tok::greater);
>> +      // FIXME: Annotate the token stream so we don't produce the same
>> errors
>> +      // again if we're doing this annotation as part of a tentative
>> parse.
>>       return true;
>>     }
>>
>> @@ -1108,14 +1112,16 @@ void Parser::AnnotateTemplateIdTokenAsTy
>>
>>   TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
>>   assert((TemplateId->Kind == TNK_Type_template ||
>> -          TemplateId->Kind == TNK_Dependent_template_name) &&
>> +          TemplateId->Kind == TNK_Dependent_template_name ||
>> +          TemplateId->Kind == TNK_Undeclared_template) &&
>>          "Only works for type and dependent templates");
>>
>>   ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),
>>                                      TemplateId->NumArgs);
>>
>>   TypeResult Type
>> -    = Actions.ActOnTemplateIdType(TemplateId->SS,
>> +    = Actions.ActOnTemplateIdType(getCurScope(),
>> +                                  TemplateId->SS,
>>                                   TemplateId->TemplateKWLoc,
>>                                   TemplateId->Template,
>>                                   TemplateId->Name,
>> @@ -1272,36 +1278,6 @@ ParsedTemplateArgument Parser::ParseTemp
>>                                 ExprArg.get(), Loc);
>> }
>>
>> -/// Determine whether the current tokens can only be parsed as a
>> -/// template argument list (starting with the '<') and never as a '<'
>> -/// expression.
>> -bool Parser::IsTemplateArgumentList(unsigned Skip) {
>> -  struct AlwaysRevertAction : TentativeParsingAction {
>> -    AlwaysRevertAction(Parser &P) : TentativeParsingAction(P) { }
>> -    ~AlwaysRevertAction() { Revert(); }
>> -  } Tentative(*this);
>> -
>> -  while (Skip) {
>> -    ConsumeAnyToken();
>> -    --Skip;
>> -  }
>> -
>> -  // '<'
>> -  if (!TryConsumeToken(tok::less))
>> -    return false;
>> -
>> -  // An empty template argument list.
>> -  if (Tok.is(tok::greater))
>> -    return true;
>> -
>> -  // See whether we have declaration specifiers, which indicate a type.
>> -  while (isCXXDeclarationSpecifier() == TPResult::True)
>> -    ConsumeAnyToken();
>> -
>> -  // If we have a '>' or a ',' then this is a template argument list.
>> -  return Tok.isOneOf(tok::greater, tok::comma);
>> -}
>> -
>> /// ParseTemplateArgumentList - Parse a C++ template-argument-list
>> /// (C++ [temp.names]). Returns true if there was an error.
>> ///
>>
>> Modified: cfe/trunk/lib/Parse/ParseTentative.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseTentative.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Parse/ParseTentative.cpp (original)
>> +++ cfe/trunk/lib/Parse/ParseTentative.cpp Wed May  8 20:31:27 2019
>> @@ -1178,12 +1178,17 @@ public:
>> /// be either a decl-specifier or a function-style cast, and
>> TPResult::Error
>> /// if a parsing error was found and reported.
>> ///
>> -/// If HasMissingTypename is provided, a name with a dependent scope
>> specifier
>> -/// will be treated as ambiguous if the 'typename' keyword is missing.
>> If this
>> -/// happens, *HasMissingTypename will be set to 'true'. This will also
>> be used
>> -/// as an indicator that undeclared identifiers (which will trigger a
>> later
>> -/// parse error) should be treated as types. Returns TPResult::Ambiguous
>> in
>> -/// such cases.
>> +/// If InvalidAsDeclSpec is not null, some cases that would be
>> ill-formed as
>> +/// declaration specifiers but possibly valid as some other kind of
>> construct
>> +/// return TPResult::Ambiguous instead of TPResult::False. When this
>> happens,
>> +/// the intent is to keep trying to disambiguate, on the basis that we
>> might
>> +/// find a better reason to treat this construct as a declaration later
>> on.
>> +/// When this happens and the name could possibly be valid in some other
>> +/// syntactic context, *InvalidAsDeclSpec is set to 'true'. The current
>> cases
>> +/// that trigger this are:
>> +///
>> +///   * When parsing X::Y (with no 'typename') where X is dependent
>> +///   * When parsing X<Y> where X is undeclared
>> ///
>> ///         decl-specifier:
>> ///           storage-class-specifier
>> @@ -1281,7 +1286,7 @@ public:
>> ///
>> Parser::TPResult
>> Parser::isCXXDeclarationSpecifier(Parser::TPResult BracedCastResult,
>> -                                  bool *HasMissingTypename) {
>> +                                  bool *InvalidAsDeclSpec) {
>>   switch (Tok.getKind()) {
>>   case tok::identifier: {
>>     // Check for need to substitute AltiVec __vector keyword
>> @@ -1321,7 +1326,7 @@ Parser::isCXXDeclarationSpecifier(Parser
>>         // argument is an error, and was probably intended to be a type.
>>         return GreaterThanIsOperator ? TPResult::True : TPResult::False;
>>       case ANK_Unresolved:
>> -        return HasMissingTypename ? TPResult::Ambiguous :
>> TPResult::False;
>> +        return InvalidAsDeclSpec ? TPResult::Ambiguous : TPResult::False;
>>       case ANK_Success:
>>         break;
>>       }
>> @@ -1342,7 +1347,7 @@ Parser::isCXXDeclarationSpecifier(Parser
>>     }
>>
>>     // We annotated this token as something. Recurse to handle whatever
>> we got.
>> -    return isCXXDeclarationSpecifier(BracedCastResult,
>> HasMissingTypename);
>> +    return isCXXDeclarationSpecifier(BracedCastResult,
>> InvalidAsDeclSpec);
>>   }
>>
>>   case tok::kw_typename:  // typename T::type
>> @@ -1350,7 +1355,7 @@ Parser::isCXXDeclarationSpecifier(Parser
>>     // recurse to handle whatever we get.
>>     if (TryAnnotateTypeOrScopeToken())
>>       return TPResult::Error;
>> -    return isCXXDeclarationSpecifier(BracedCastResult,
>> HasMissingTypename);
>> +    return isCXXDeclarationSpecifier(BracedCastResult,
>> InvalidAsDeclSpec);
>>
>>   case tok::coloncolon: {    // ::foo::bar
>>     const Token &Next = NextToken();
>> @@ -1365,7 +1370,7 @@ Parser::isCXXDeclarationSpecifier(Parser
>>     // recurse to handle whatever we get.
>>     if (TryAnnotateTypeOrScopeToken())
>>       return TPResult::Error;
>> -    return isCXXDeclarationSpecifier(BracedCastResult,
>> HasMissingTypename);
>> +    return isCXXDeclarationSpecifier(BracedCastResult,
>> InvalidAsDeclSpec);
>>
>>     // decl-specifier:
>>     //   storage-class-specifier
>> @@ -1471,6 +1476,16 @@ Parser::isCXXDeclarationSpecifier(Parser
>>
>>   case tok::annot_template_id: {
>>     TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
>> +    // If lookup for the template-name found nothing, don't assume we
>> have a
>> +    // definitive disambiguation result yet.
>> +    if (TemplateId->Kind == TNK_Undeclared_template &&
>> InvalidAsDeclSpec) {
>> +      // 'template-id(' can be a valid expression but not a valid decl
>> spec if
>> +      // the template-name is not declared, but we don't consider this
>> to be a
>> +      // definitive disambiguation. In any other context, it's an error
>> either
>> +      // way.
>> +      *InvalidAsDeclSpec = NextToken().is(tok::l_paren);
>> +      return TPResult::Ambiguous;
>> +    }
>>     if (TemplateId->Kind != TNK_Type_template)
>>       return TPResult::False;
>>     CXXScopeSpec SS;
>> @@ -1499,19 +1514,19 @@ Parser::isCXXDeclarationSpecifier(Parser
>>           TPResult TPR = TPResult::False;
>>           if (!isIdentifier)
>>             TPR = isCXXDeclarationSpecifier(BracedCastResult,
>> -                                            HasMissingTypename);
>> +                                            InvalidAsDeclSpec);
>>
>>           if (isIdentifier ||
>>               TPR == TPResult::True || TPR == TPResult::Error)
>>             return TPResult::Error;
>>
>> -          if (HasMissingTypename) {
>> +          if (InvalidAsDeclSpec) {
>>             // We can't tell whether this is a missing 'typename' or a
>> valid
>>             // expression.
>> -            *HasMissingTypename = true;
>> +            *InvalidAsDeclSpec = true;
>>             return TPResult::Ambiguous;
>>           } else {
>> -            // In MS mode, if HasMissingTypename is not provided, and
>> the tokens
>> +            // In MS mode, if InvalidAsDeclSpec is not provided, and the
>> tokens
>>             // are or the form *) or &) *> or &> &&>, this can't be an
>> expression.
>>             // The typename must be missing.
>>             if (getLangOpts().MSVCCompat) {
>> @@ -1547,8 +1562,7 @@ Parser::isCXXDeclarationSpecifier(Parser
>>                        ? TPResult::True
>>                        : TPResult::False;
>>           case ANK_Unresolved:
>> -            return HasMissingTypename ? TPResult::Ambiguous
>> -                                      : TPResult::False;
>> +            return InvalidAsDeclSpec ? TPResult::Ambiguous :
>> TPResult::False;
>>           case ANK_Success:
>>             break;
>>           }
>> @@ -1556,8 +1570,7 @@ Parser::isCXXDeclarationSpecifier(Parser
>>           // Annotated it, check again.
>>           assert(Tok.isNot(tok::annot_cxxscope) ||
>>                  NextToken().isNot(tok::identifier));
>> -          return isCXXDeclarationSpecifier(BracedCastResult,
>> -                                           HasMissingTypename);
>> +          return isCXXDeclarationSpecifier(BracedCastResult,
>> InvalidAsDeclSpec);
>>         }
>>       }
>>       return TPResult::False;
>> @@ -2029,3 +2042,56 @@ Parser::TPResult Parser::TryParseBracket
>>
>>   return TPResult::Ambiguous;
>> }
>> +
>> +/// Determine whether we might be looking at the '<'
>> template-argument-list '>'
>> +/// of a template-id or simple-template-id, rather than a less-than
>> comparison.
>> +/// This will often fail and produce an ambiguity, but should never be
>> wrong
>> +/// if it returns True or False.
>> +Parser::TPResult Parser::isTemplateArgumentList(unsigned TokensToSkip) {
>> +  if (!TokensToSkip) {
>> +    if (Tok.isNot(tok::less))
>> +      return TPResult::False;
>> +    if (NextToken().is(tok::greater))
>> +      return TPResult::True;
>> +  }
>> +
>> +  RevertingTentativeParsingAction PA(*this);
>> +
>> +  while (TokensToSkip) {
>> +    ConsumeAnyToken();
>> +    --TokensToSkip;
>> +  }
>> +
>> +  if (!TryConsumeToken(tok::less))
>> +    return TPResult::False;
>> +
>> +  bool InvalidAsTemplateArgumentList = false;
>> +  while (true) {
>> +    // We can't do much to tell an expression apart from a
>> template-argument,
>> +    // but one good distinguishing factor is that a "decl-specifier" not
>> +    // followed by '(' or '{' can't appear in an expression.
>> +    if (isCXXDeclarationSpecifier(
>> +            TPResult::False, &InvalidAsTemplateArgumentList) ==
>> TPResult::True)
>> +      return TPResult::True;
>> +
>> +    // That didn't help, try the next template-argument.
>> +    SkipUntil({tok::comma, tok::greater, tok::greatergreater,
>> +               tok::greatergreatergreater},
>> +              StopAtSemi | StopBeforeMatch);
>> +    switch (Tok.getKind()) {
>> +    case tok::comma:
>> +      ConsumeToken();
>> +      break;
>> +
>> +    case tok::greater:
>> +    case tok::greatergreater:
>> +    case tok::greatergreatergreater:
>> +      if (InvalidAsTemplateArgumentList)
>> +        return TPResult::False;
>> +      return TPResult::Ambiguous;
>> +
>> +    default:
>> +      return TPResult::False;
>> +    }
>> +  }
>> +}
>>
>> Modified: cfe/trunk/lib/Parse/Parser.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/Parser.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Parse/Parser.cpp (original)
>> +++ cfe/trunk/lib/Parse/Parser.cpp Wed May  8 20:31:27 2019
>> @@ -315,6 +315,14 @@ bool Parser::SkipUntil(ArrayRef<tok::Tok
>>       else
>>         SkipUntil(tok::r_brace);
>>       break;
>> +    case tok::question:
>> +      // Recursively skip ? ... : pairs; these function as brackets. But
>> +      // still stop at a semicolon if requested.
>> +      ConsumeToken();
>> +      SkipUntil(tok::colon,
>> +                SkipUntilFlags(unsigned(Flags) &
>> +                               unsigned(StopAtCodeCompletion |
>> StopAtSemi)));
>> +      break;
>>
>>     // Okay, we found a ']' or '}' or ')', which we think should be
>> balanced.
>>     // Since the user wasn't looking for this token (if they were, it
>> would
>> @@ -1600,6 +1608,20 @@ Parser::TryAnnotateName(bool IsAddressOf
>>       Actions.ClassifyName(getCurScope(), SS, Name, NameLoc, Next,
>>                            IsAddressOfOperand, SS.isEmpty() ? CCC :
>> nullptr);
>>
>> +  // If name lookup found nothing and we guessed that this was a
>> template name,
>> +  // double-check before committing to that interpretation. C++20
>> requires that
>> +  // we interpret this as a template-id if it can be, but if it can't
>> be, then
>> +  // this is an error recovery case.
>> +  if (Classification.getKind() == Sema::NC_UndeclaredTemplate &&
>> +      isTemplateArgumentList(1) == TPResult::False) {
>> +    // It's not a template-id; re-classify without the '<' as a hint.
>> +    Token FakeNext = Next;
>> +    FakeNext.setKind(tok::unknown);
>> +    Classification =
>> +        Actions.ClassifyName(getCurScope(), SS, Name, NameLoc, FakeNext,
>> +                             IsAddressOfOperand, SS.isEmpty() ? CCC :
>> nullptr);
>> +  }
>> +
>>   switch (Classification.getKind()) {
>>   case Sema::NC_Error:
>>     return ANK_Error;
>> @@ -1668,7 +1690,8 @@ Parser::TryAnnotateName(bool IsAddressOf
>>     }
>>     LLVM_FALLTHROUGH;
>>   case Sema::NC_VarTemplate:
>> -  case Sema::NC_FunctionTemplate: {
>> +  case Sema::NC_FunctionTemplate:
>> +  case Sema::NC_UndeclaredTemplate: {
>>     // We have a type, variable or function template followed by '<'.
>>     ConsumeToken();
>>     UnqualifiedId Id;
>> @@ -1791,7 +1814,8 @@ bool Parser::TryAnnotateTypeOrScopeToken
>>     } else if (Tok.is(tok::annot_template_id)) {
>>       TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
>>       if (TemplateId->Kind != TNK_Type_template &&
>> -          TemplateId->Kind != TNK_Dependent_template_name) {
>> +          TemplateId->Kind != TNK_Dependent_template_name &&
>> +          TemplateId->Kind != TNK_Undeclared_template) {
>>         Diag(Tok, diag::err_typename_refers_to_non_type_template)
>>           << Tok.getAnnotationRange();
>>         return true;
>> @@ -1890,6 +1914,8 @@ bool Parser::TryAnnotateTypeOrScopeToken
>>     }
>>
>>     // If this is a template-id, annotate with a template-id or type
>> token.
>> +    // FIXME: This appears to be dead code. We already have formed
>> template-id
>> +    // tokens when parsing the scope specifier; this can never form a
>> new one.
>>     if (NextToken().is(tok::less)) {
>>       TemplateTy Template;
>>       UnqualifiedId TemplateName;
>> @@ -1900,14 +1926,19 @@ bool Parser::TryAnnotateTypeOrScopeToken
>>               /*hasTemplateKeyword=*/false, TemplateName,
>>               /*ObjectType=*/nullptr, /*EnteringContext*/false, Template,
>>               MemberOfUnknownSpecialization)) {
>> -        // Consume the identifier.
>> -        ConsumeToken();
>> -        if (AnnotateTemplateIdToken(Template, TNK, SS, SourceLocation(),
>> -                                    TemplateName)) {
>> -          // If an unrecoverable error occurred, we need to return true
>> here,
>> -          // because the token stream is in a damaged state.  We may not
>> return
>> -          // a valid identifier.
>> -          return true;
>> +        // Only annotate an undeclared template name as a template-id if
>> the
>> +        // following tokens have the form of a template argument list.
>> +        if (TNK != TNK_Undeclared_template ||
>> +            isTemplateArgumentList(1) != TPResult::False) {
>> +          // Consume the identifier.
>> +          ConsumeToken();
>> +          if (AnnotateTemplateIdToken(Template, TNK, SS,
>> SourceLocation(),
>> +                                      TemplateName)) {
>> +            // If an unrecoverable error occurred, we need to return
>> true here,
>> +            // because the token stream is in a damaged state.  We may
>> not
>> +            // return a valid identifier.
>> +            return true;
>> +          }
>>         }
>>       }
>>     }
>>
>> Modified: cfe/trunk/lib/Sema/SemaCXXScopeSpec.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaCXXScopeSpec.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaCXXScopeSpec.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaCXXScopeSpec.cpp Wed May  8 20:31:27 2019
>> @@ -888,7 +888,7 @@ bool Sema::IsInvalidUnlessNestedName(Sco
>> bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,
>>                                        CXXScopeSpec &SS,
>>                                        SourceLocation TemplateKWLoc,
>> -                                       TemplateTy Template,
>> +                                       TemplateTy OpaqueTemplate,
>>                                        SourceLocation TemplateNameLoc,
>>                                        SourceLocation LAngleLoc,
>>                                        ASTTemplateArgsPtr TemplateArgsIn,
>> @@ -898,11 +898,13 @@ bool Sema::ActOnCXXNestedNameSpecifier(S
>>   if (SS.isInvalid())
>>     return true;
>>
>> +  TemplateName Template = OpaqueTemplate.get();
>> +
>>   // Translate the parser's template argument list in our AST format.
>>   TemplateArgumentListInfo TemplateArgs(LAngleLoc, RAngleLoc);
>>   translateTemplateArguments(TemplateArgsIn, TemplateArgs);
>>
>> -  DependentTemplateName *DTN =
>> Template.get().getAsDependentTemplateName();
>> +  DependentTemplateName *DTN = Template.getAsDependentTemplateName();
>>   if (DTN && DTN->isIdentifier()) {
>>     // Handle a dependent template specialization for which we cannot
>> resolve
>>     // the template name.
>> @@ -930,23 +932,28 @@ bool Sema::ActOnCXXNestedNameSpecifier(S
>>     return false;
>>   }
>>
>> -  TemplateDecl *TD = Template.get().getAsTemplateDecl();
>> -  if (Template.get().getAsOverloadedTemplate() || DTN ||
>> +  // If we assumed an undeclared identifier was a template name, try to
>> +  // typo-correct it now.
>> +  if (Template.getAsAssumedTemplateName() &&
>> +      resolveAssumedTemplateNameAsType(S, Template, TemplateNameLoc))
>> +    return true;
>> +
>> +  TemplateDecl *TD = Template.getAsTemplateDecl();
>> +  if (Template.getAsOverloadedTemplate() || DTN ||
>>       isa<FunctionTemplateDecl>(TD) || isa<VarTemplateDecl>(TD)) {
>>     SourceRange R(TemplateNameLoc, RAngleLoc);
>>     if (SS.getRange().isValid())
>>       R.setBegin(SS.getRange().getBegin());
>>
>>     Diag(CCLoc, diag::err_non_type_template_in_nested_name_specifier)
>> -      << (TD && isa<VarTemplateDecl>(TD)) << Template.get() << R;
>> -    NoteAllFoundTemplates(Template.get());
>> +      << (TD && isa<VarTemplateDecl>(TD)) << Template << R;
>> +    NoteAllFoundTemplates(Template);
>>     return true;
>>   }
>>
>>   // We were able to resolve the template name to an actual template.
>>   // Build an appropriate nested-name-specifier.
>> -  QualType T =
>> -      CheckTemplateIdType(Template.get(), TemplateNameLoc, TemplateArgs);
>> +  QualType T = CheckTemplateIdType(Template, TemplateNameLoc,
>> TemplateArgs);
>>   if (T.isNull())
>>     return true;
>>
>> @@ -954,7 +961,7 @@ bool Sema::ActOnCXXNestedNameSpecifier(S
>>   // nested name specifiers.
>>   if (!T->isDependentType() && !T->getAs<TagType>()) {
>>     Diag(TemplateNameLoc, diag::err_nested_name_spec_non_tag) << T;
>> -    NoteAllFoundTemplates(Template.get());
>> +    NoteAllFoundTemplates(Template);
>>     return true;
>>   }
>>
>>
>> Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaDecl.cpp Wed May  8 20:31:27 2019
>> @@ -917,6 +917,16 @@ Corrected:
>>       }
>>     }
>>
>> +    if (getLangOpts().CPlusPlus2a && !SS.isSet() && NextToken.is(tok::less))
>> {
>> +      // In C++20 onwards, this could be an ADL-only call to a function
>> +      // template, and we're required to assume that this is a template
>> name.
>> +      //
>> +      // FIXME: Find a way to still do typo correction in this case.
>> +      TemplateName Template =
>> +          Context.getAssumedTemplateName(NameInfo.getName());
>> +      return NameClassification::UndeclaredTemplate(Template);
>> +    }
>> +
>>     // In C, we first see whether there is a tag type by the same name, in
>>     // which case it's likely that the user just forgot to write "enum",
>>     // "struct", or "union".
>> @@ -1045,52 +1055,62 @@ Corrected:
>>
>>   if (getLangOpts().CPlusPlus && NextToken.is(tok::less) &&
>>       (IsFilteredTemplateName ||
>> -       hasAnyAcceptableTemplateNames(Result,
>> /*AllowFunctionTemplates=*/true,
>> -                                     /*AllowDependent=*/false))) {
>> +       hasAnyAcceptableTemplateNames(
>> +           Result, /*AllowFunctionTemplates=*/true,
>> +           /*AllowDependent=*/false,
>> +           /*AllowNonTemplateFunctions*/ !SS.isSet() &&
>> +               getLangOpts().CPlusPlus2a))) {
>>     // C++ [temp.names]p3:
>>     //   After name lookup (3.4) finds that a name is a template-name or
>> that
>>     //   an operator-function-id or a literal- operator-id refers to a
>> set of
>>     //   overloaded functions any member of which is a function template
>> if
>>     //   this is followed by a <, the < is always taken as the delimiter
>> of a
>>     //   template-argument-list and never as the less-than operator.
>> +    // C++2a [temp.names]p2:
>> +    //   A name is also considered to refer to a template if it is an
>> +    //   unqualified-id followed by a < and name lookup finds either one
>> +    //   or more functions or finds nothing.
>>     if (!IsFilteredTemplateName)
>>       FilterAcceptableTemplateNames(Result);
>>
>> -    if (!Result.empty()) {
>> -      bool IsFunctionTemplate;
>> -      bool IsVarTemplate;
>> -      TemplateName Template;
>> -      if (Result.end() - Result.begin() > 1) {
>> -        IsFunctionTemplate = true;
>> -        Template = Context.getOverloadedTemplateName(Result.begin(),
>> -                                                     Result.end());
>> -      } else {
>> -        auto *TD = cast<TemplateDecl>(getAsTemplateNameDecl(
>> -            *Result.begin(), /*AllowFunctionTemplates=*/true,
>> -            /*AllowDependent=*/false));
>> -        IsFunctionTemplate = isa<FunctionTemplateDecl>(TD);
>> -        IsVarTemplate = isa<VarTemplateDecl>(TD);
>> -
>> -        if (SS.isSet() && !SS.isInvalid())
>> -          Template =
>> -              Context.getQualifiedTemplateName(SS.getScopeRep(),
>> -
>>                                               /*TemplateKeyword=*/false,
>> TD);
>> -        else
>> -          Template = TemplateName(TD);
>> -      }
>> -
>> -      if (IsFunctionTemplate) {
>> -        // Function templates always go through overload resolution, at
>> which
>> -        // point we'll perform the various checks (e.g., accessibility)
>> we need
>> -        // to based on which function we selected.
>> -        Result.suppressDiagnostics();
>> +    bool IsFunctionTemplate;
>> +    bool IsVarTemplate;
>> +    TemplateName Template;
>> +    if (Result.end() - Result.begin() > 1) {
>> +      IsFunctionTemplate = true;
>> +      Template = Context.getOverloadedTemplateName(Result.begin(),
>> +                                                   Result.end());
>> +    } else if (!Result.empty()) {
>> +      auto *TD = cast<TemplateDecl>(getAsTemplateNameDecl(
>> +          *Result.begin(), /*AllowFunctionTemplates=*/true,
>> +          /*AllowDependent=*/false));
>> +      IsFunctionTemplate = isa<FunctionTemplateDecl>(TD);
>> +      IsVarTemplate = isa<VarTemplateDecl>(TD);
>> +
>> +      if (SS.isSet() && !SS.isInvalid())
>> +        Template =
>> +            Context.getQualifiedTemplateName(SS.getScopeRep(),
>> +                                             /*TemplateKeyword=*/false,
>> TD);
>> +      else
>> +        Template = TemplateName(TD);
>> +    } else {
>> +      // All results were non-template functions. This is a function
>> template
>> +      // name.
>> +      IsFunctionTemplate = true;
>> +      Template = Context.getAssumedTemplateName(NameInfo.getName());
>> +    }
>>
>> -        return NameClassification::FunctionTemplate(Template);
>> -      }
>> +    if (IsFunctionTemplate) {
>> +      // Function templates always go through overload resolution, at
>> which
>> +      // point we'll perform the various checks (e.g., accessibility) we
>> need
>> +      // to based on which function we selected.
>> +      Result.suppressDiagnostics();
>>
>> -      return IsVarTemplate ? NameClassification::VarTemplate(Template)
>> -                           : NameClassification::TypeTemplate(Template);
>> +      return NameClassification::FunctionTemplate(Template);
>>     }
>> +
>> +    return IsVarTemplate ? NameClassification::VarTemplate(Template)
>> +                         : NameClassification::TypeTemplate(Template);
>>   }
>>
>>   NamedDecl *FirstDecl = (*Result.begin())->getUnderlyingDecl();
>>
>> Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclCXX.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaDeclCXX.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp Wed May  8 20:31:27 2019
>> @@ -3881,6 +3881,8 @@ Sema::BuildMemInitializer(Decl *Construc
>>
>>   if (TemplateTypeTy) {
>>     BaseType = GetTypeFromParser(TemplateTypeTy, &TInfo);
>> +    if (BaseType.isNull())
>> +      return true;
>>   } else if (DS.getTypeSpecType() == TST_decltype) {
>>     BaseType = BuildDecltypeType(DS.getRepAsExpr(),
>> DS.getTypeSpecTypeLoc());
>>   } else if (DS.getTypeSpecType() == TST_decltype_auto) {
>>
>> Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaExpr.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaExpr.cpp Wed May  8 20:31:27 2019
>> @@ -2065,11 +2065,12 @@ bool Sema::DiagnoseEmptyLookup(Scope *S,
>>       // is in the wrong place to recover. Suggest the typo
>>       // correction, but don't make it a fix-it since we're not going
>>       // to recover well anyway.
>> -      AcceptableWithoutRecovery =
>> -          isa<TypeDecl>(UnderlyingND) ||
>> isa<ObjCInterfaceDecl>(UnderlyingND);
>> +      AcceptableWithoutRecovery = isa<TypeDecl>(UnderlyingND) ||
>> +                                  getAsTypeTemplateDecl(UnderlyingND) ||
>> +                                  isa<ObjCInterfaceDecl>(UnderlyingND);
>>     } else {
>> -      // FIXME: We found a keyword or a type. Suggest it, but don't
>> provide a
>> -      // fix-it because we aren't able to recover.
>> +      // FIXME: We found a keyword. Suggest it, but don't provide a
>> fix-it
>> +      // because we aren't able to recover.
>>       AcceptableWithoutRecovery = true;
>>     }
>>
>> @@ -2221,8 +2222,10 @@ Sema::ActOnIdExpression(Scope *S, CXXSco
>>     // this becomes a performance hit, we can work harder to preserve
>> those
>>     // results until we get here but it's likely not worth it.
>>     bool MemberOfUnknownSpecialization;
>> +    AssumedTemplateKind AssumedTemplate;
>>     if (LookupTemplateName(R, S, SS, QualType(),
>> /*EnteringContext=*/false,
>> -                           MemberOfUnknownSpecialization, TemplateKWLoc))
>> +                           MemberOfUnknownSpecialization, TemplateKWLoc,
>> +                           &AssumedTemplate))
>>       return ExprError();
>>
>>     if (MemberOfUnknownSpecialization ||
>> @@ -5518,7 +5521,24 @@ tryImplicitlyCaptureThisIfImplicitMember
>> ExprResult Sema::ActOnCallExpr(Scope *Scope, Expr *Fn, SourceLocation
>> LParenLoc,
>>                                MultiExprArg ArgExprs, SourceLocation
>> RParenLoc,
>>                                Expr *ExecConfig) {
>> -  return BuildCallExpr(Scope, Fn, LParenLoc, ArgExprs, RParenLoc,
>> ExecConfig);
>> +  ExprResult Call =
>> +      BuildCallExpr(Scope, Fn, LParenLoc, ArgExprs, RParenLoc,
>> ExecConfig);
>> +  if (Call.isInvalid())
>> +    return Call;
>> +
>> +  // Diagnose uses of the C++20 "ADL-only template-id call" feature in
>> earlier
>> +  // language modes.
>> +  if (auto *ULE = dyn_cast<UnresolvedLookupExpr>(Fn)) {
>> +    if (ULE->hasExplicitTemplateArgs() &&
>> +        ULE->decls_begin() == ULE->decls_end()) {
>> +      Diag(Fn->getExprLoc(), getLangOpts().CPlusPlus2a
>> +                                 ?
>> diag::warn_cxx17_compat_adl_only_template_id
>> +                                 : diag::ext_adl_only_template_id)
>> +          << ULE->getName();
>> +    }
>> +  }
>> +
>> +  return Call;
>> }
>>
>> /// BuildCallExpr - Handle a call to Fn with the specified array of
>> arguments.
>>
>> Modified: cfe/trunk/lib/Sema/SemaExprCXX.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExprCXX.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaExprCXX.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaExprCXX.cpp Wed May  8 20:31:27 2019
>> @@ -7074,7 +7074,8 @@ ExprResult Sema::ActOnPseudoDestructorEx
>>     TemplateIdAnnotation *TemplateId = SecondTypeName.TemplateId;
>>     ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),
>>                                        TemplateId->NumArgs);
>> -    TypeResult T = ActOnTemplateIdType(TemplateId->SS,
>> +    TypeResult T = ActOnTemplateIdType(S,
>> +                                       TemplateId->SS,
>>                                        TemplateId->TemplateKWLoc,
>>                                        TemplateId->Template,
>>                                        TemplateId->Name,
>> @@ -7126,7 +7127,8 @@ ExprResult Sema::ActOnPseudoDestructorEx
>>       TemplateIdAnnotation *TemplateId = FirstTypeName.TemplateId;
>>       ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),
>>                                          TemplateId->NumArgs);
>> -      TypeResult T = ActOnTemplateIdType(TemplateId->SS,
>> +      TypeResult T = ActOnTemplateIdType(S,
>> +                                         TemplateId->SS,
>>                                          TemplateId->TemplateKWLoc,
>>                                          TemplateId->Template,
>>                                          TemplateId->Name,
>>
>> Modified: cfe/trunk/lib/Sema/SemaOverload.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaOverload.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaOverload.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaOverload.cpp Wed May  8 20:31:27 2019
>> @@ -12017,7 +12017,8 @@ bool Sema::buildOverloadedCallSet(Scope
>>     // We don't perform ADL for implicit declarations of builtins.
>>     // Verify that this was correctly set up.
>>     FunctionDecl *F;
>> -    if (ULE->decls_begin() + 1 == ULE->decls_end() &&
>> +    if (ULE->decls_begin() != ULE->decls_end() &&
>> +        ULE->decls_begin() + 1 == ULE->decls_end() &&
>>         (F = dyn_cast<FunctionDecl>(*ULE->decls_begin())) &&
>>         F->getBuiltinID() && F->isImplicit())
>>       llvm_unreachable("performing ADL for builtin");
>> @@ -12201,10 +12202,9 @@ ExprResult Sema::BuildOverloadedCallExpr
>>   OverloadingResult OverloadResult =
>>       CandidateSet.BestViableFunction(*this, Fn->getBeginLoc(), Best);
>>
>> -  return FinishOverloadedCallExpr(*this, S, Fn, ULE, LParenLoc, Args,
>> -                                  RParenLoc, ExecConfig, &CandidateSet,
>> -                                  &Best, OverloadResult,
>> -                                  AllowTypoCorrection);
>> +  return FinishOverloadedCallExpr(*this, S, Fn, ULE, LParenLoc, Args,
>> RParenLoc,
>> +                                  ExecConfig, &CandidateSet, &Best,
>> +                                  OverloadResult, AllowTypoCorrection);
>> }
>>
>> static bool IsOverloaded(const UnresolvedSetImpl &Functions) {
>>
>> Modified: cfe/trunk/lib/Sema/SemaTemplate.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaTemplate.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaTemplate.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaTemplate.cpp Wed May  8 20:31:27 2019
>> @@ -130,10 +130,15 @@ void Sema::FilterAcceptableTemplateNames
>>
>> bool Sema::hasAnyAcceptableTemplateNames(LookupResult &R,
>>                                          bool AllowFunctionTemplates,
>> -                                         bool AllowDependent) {
>> -  for (LookupResult::iterator I = R.begin(), IEnd = R.end(); I != IEnd;
>> ++I)
>> +                                         bool AllowDependent,
>> +                                         bool AllowNonTemplateFunctions)
>> {
>> +  for (LookupResult::iterator I = R.begin(), IEnd = R.end(); I != IEnd;
>> ++I) {
>>     if (getAsTemplateNameDecl(*I, AllowFunctionTemplates, AllowDependent))
>>       return true;
>> +    if (AllowNonTemplateFunctions &&
>> +        isa<FunctionDecl>((*I)->getUnderlyingDecl()))
>> +      return true;
>> +  }
>>
>>   return false;
>> }
>> @@ -171,11 +176,25 @@ TemplateNameKind Sema::isTemplateName(Sc
>>
>>   QualType ObjectType = ObjectTypePtr.get();
>>
>> +  AssumedTemplateKind AssumedTemplate;
>>   LookupResult R(*this, TName, Name.getBeginLoc(), LookupOrdinaryName);
>>   if (LookupTemplateName(R, S, SS, ObjectType, EnteringContext,
>> -                         MemberOfUnknownSpecialization))
>> +                         MemberOfUnknownSpecialization, SourceLocation(),
>> +                         &AssumedTemplate))
>> +    return TNK_Non_template;
>> +
>> +  if (AssumedTemplate != AssumedTemplateKind::None) {
>> +    TemplateResult =
>> TemplateTy::make(Context.getAssumedTemplateName(TName));
>> +    // Let the parser know whether we found nothing or found functions;
>> if we
>> +    // found nothing, we want to more carefully check whether this is
>> actually
>> +    // a function template name versus some other kind of undeclared
>> identifier.
>> +    return AssumedTemplate == AssumedTemplateKind::FoundNothing
>> +               ? TNK_Undeclared_template
>> +               : TNK_Function_template;
>> +  }
>> +
>> +  if (R.empty())
>>     return TNK_Non_template;
>> -  if (R.empty()) return TNK_Non_template;
>>
>>   NamedDecl *D = nullptr;
>>   if (R.isAmbiguous()) {
>> @@ -325,7 +344,11 @@ bool Sema::LookupTemplateName(LookupResu
>>                               QualType ObjectType,
>>                               bool EnteringContext,
>>                               bool &MemberOfUnknownSpecialization,
>> -                              SourceLocation TemplateKWLoc) {
>> +                              SourceLocation TemplateKWLoc,
>> +                              AssumedTemplateKind *ATK) {
>> +  if (ATK)
>> +    *ATK = AssumedTemplateKind::None;
>> +
>>   Found.setTemplateNameLookup(true);
>>
>>   // Determine where to perform name lookup
>> @@ -405,6 +428,32 @@ bool Sema::LookupTemplateName(LookupResu
>>   if (Found.isAmbiguous())
>>     return false;
>>
>> +  if (ATK && !SS.isSet() && ObjectType.isNull() &&
>> TemplateKWLoc.isInvalid()) {
>> +    // C++2a [temp.names]p2:
>> +    //   A name is also considered to refer to a template if it is an
>> +    //   unqualified-id followed by a < and name lookup finds either one
>> or more
>> +    //   functions or finds nothing.
>> +    //
>> +    // To keep our behavior consistent, we apply the "finds nothing"
>> part in
>> +    // all language modes, and diagnose the empty lookup in
>> ActOnCallExpr if we
>> +    // successfully form a call to an undeclared template-id.
>> +    bool AllFunctions =
>> +        getLangOpts().CPlusPlus2a &&
>> +        std::all_of(Found.begin(), Found.end(), [](NamedDecl *ND) {
>> +          return isa<FunctionDecl>(ND->getUnderlyingDecl());
>> +        });
>> +    if (AllFunctions || (Found.empty() && !IsDependent)) {
>> +      // If lookup found any functions, or if this is a name that can
>> only be
>> +      // used for a function, then strongly assume this is a function
>> +      // template-id.
>> +      *ATK = (Found.empty() && Found.getLookupName().isIdentifier())
>> +                 ? AssumedTemplateKind::FoundNothing
>> +                 : AssumedTemplateKind::FoundFunctions;
>> +      Found.clear();
>> +      return false;
>> +    }
>> +  }
>> +
>>   if (Found.empty() && !IsDependent) {
>>     // If we did not find any names, attempt to correct any typos.
>>     DeclarationName Name = Found.getLookupName();
>> @@ -418,13 +467,13 @@ bool Sema::LookupTemplateName(LookupResu
>>     if (TypoCorrection Corrected =
>>             CorrectTypo(Found.getLookupNameInfo(), Found.getLookupKind(),
>> S,
>>                         &SS, FilterCCC, CTK_ErrorRecovery, LookupCtx)) {
>> -      Found.setLookupName(Corrected.getCorrection());
>>       if (auto *ND = Corrected.getFoundDecl())
>>         Found.addDecl(ND);
>>       FilterAcceptableTemplateNames(Found);
>>       if (Found.isAmbiguous()) {
>>         Found.clear();
>>       } else if (!Found.empty()) {
>> +        Found.setLookupName(Corrected.getCorrection());
>>         if (LookupCtx) {
>>           std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
>>           bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
>> @@ -436,8 +485,6 @@ bool Sema::LookupTemplateName(LookupResu
>>           diagnoseTypo(Corrected, PDiag(diag::err_no_template_suggest) <<
>> Name);
>>         }
>>       }
>> -    } else {
>> -      Found.setLookupName(Name);
>>     }
>>   }
>>
>> @@ -3348,14 +3395,65 @@ QualType Sema::CheckTemplateIdType(Templ
>>   return Context.getTemplateSpecializationType(Name, TemplateArgs,
>> CanonType);
>> }
>>
>> -TypeResult
>> -Sema::ActOnTemplateIdType(CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
>> -                          TemplateTy TemplateD, IdentifierInfo
>> *TemplateII,
>> -                          SourceLocation TemplateIILoc,
>> -                          SourceLocation LAngleLoc,
>> -                          ASTTemplateArgsPtr TemplateArgsIn,
>> -                          SourceLocation RAngleLoc,
>> -                          bool IsCtorOrDtorName, bool IsClassName) {
>> +void Sema::ActOnUndeclaredTypeTemplateName(Scope *S, TemplateTy
>> &ParsedName,
>> +                                           TemplateNameKind &TNK,
>> +                                           SourceLocation NameLoc,
>> +                                           IdentifierInfo *&II) {
>> +  assert(TNK == TNK_Undeclared_template && "not an undeclared template
>> name");
>> +
>> +  TemplateName Name = ParsedName.get();
>> +  auto *ATN = Name.getAsAssumedTemplateName();
>> +  assert(ATN && "not an assumed template name");
>> +  II = ATN->getDeclName().getAsIdentifierInfo();
>> +
>> +  if (!resolveAssumedTemplateNameAsType(S, Name, NameLoc,
>> /*Diagnose*/false)) {
>> +    // Resolved to a type template name.
>> +    ParsedName = TemplateTy::make(Name);
>> +    TNK = TNK_Type_template;
>> +  }
>> +}
>> +
>> +bool Sema::resolveAssumedTemplateNameAsType(Scope *S, TemplateName &Name,
>> +                                            SourceLocation NameLoc,
>> +                                            bool Diagnose) {
>> +  // We assumed this undeclared identifier to be an (ADL-only) function
>> +  // template name, but it was used in a context where a type was
>> required.
>> +  // Try to typo-correct it now.
>> +  AssumedTemplateStorage *ATN = Name.getAsAssumedTemplateName();
>> +  assert(ATN && "not an assumed template name");
>> +
>> +  LookupResult R(*this, ATN->getDeclName(), NameLoc, LookupOrdinaryName);
>> +  struct CandidateCallback : CorrectionCandidateCallback {
>> +    bool ValidateCandidate(const TypoCorrection &TC) override {
>> +      return TC.getCorrectionDecl() &&
>> +             getAsTypeTemplateDecl(TC.getCorrectionDecl());
>> +    }
>> +    std::unique_ptr<CorrectionCandidateCallback> clone() override {
>> +      return llvm::make_unique<CandidateCallback>(*this);
>> +    }
>> +  } FilterCCC;
>> +
>> +  TypoCorrection Corrected =
>> +      CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), S, nullptr,
>> +                  FilterCCC, CTK_ErrorRecovery);
>> +  if (Corrected && Corrected.getFoundDecl()) {
>> +    diagnoseTypo(Corrected, PDiag(diag::err_no_template_suggest)
>> +                                << ATN->getDeclName());
>> +    Name = TemplateName(Corrected.getCorrectionDeclAs<TemplateDecl>());
>> +    return false;
>> +  }
>> +
>> +  if (Diagnose)
>> +    Diag(R.getNameLoc(), diag::err_no_template) << R.getLookupName();
>> +  return true;
>> +}
>> +
>> +TypeResult Sema::ActOnTemplateIdType(
>> +    Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
>> +    TemplateTy TemplateD, IdentifierInfo *TemplateII,
>> +    SourceLocation TemplateIILoc, SourceLocation LAngleLoc,
>> +    ASTTemplateArgsPtr TemplateArgsIn, SourceLocation RAngleLoc,
>> +    bool IsCtorOrDtorName, bool IsClassName) {
>>   if (SS.isInvalid())
>>     return true;
>>
>> @@ -3396,6 +3494,9 @@ Sema::ActOnTemplateIdType(CXXScopeSpec &
>>   }
>>
>>   TemplateName Template = TemplateD.get();
>> +  if (Template.getAsAssumedTemplateName() &&
>> +      resolveAssumedTemplateNameAsType(S, Template, TemplateIILoc))
>> +    return true;
>>
>>   // Translate the parser's template argument list in our AST format.
>>   TemplateArgumentListInfo TemplateArgs(LAngleLoc, RAngleLoc);
>> @@ -4141,7 +4242,6 @@ ExprResult Sema::BuildTemplateIdExpr(con
>>   //       vs template<class T, class U> void f(U);
>>
>>   // These should be filtered out by our callers.
>> -  assert(!R.empty() && "empty lookup results when building templateid");
>>   assert(!R.isAmbiguous() && "ambiguous lookup when building templateid");
>>
>>   // Non-function templates require a template argument list.
>>
>> Modified: cfe/trunk/lib/Serialization/ASTReader.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Serialization/ASTReader.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Serialization/ASTReader.cpp (original)
>> +++ cfe/trunk/lib/Serialization/ASTReader.cpp Wed May  8 20:31:27 2019
>> @@ -8745,6 +8745,11 @@ ASTReader::ReadTemplateName(ModuleFile &
>>     return Context.getOverloadedTemplateName(Decls.begin(), Decls.end());
>>   }
>>
>> +  case TemplateName::AssumedTemplate: {
>> +    DeclarationName Name = ReadDeclarationName(F, Record, Idx);
>> +    return Context.getAssumedTemplateName(Name);
>> +  }
>> +
>>   case TemplateName::QualifiedTemplate: {
>>     NestedNameSpecifier *NNS = ReadNestedNameSpecifier(F, Record, Idx);
>>     bool hasTemplKeyword = Record[Idx++];
>>
>> Modified: cfe/trunk/lib/Serialization/ASTWriter.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Serialization/ASTWriter.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Serialization/ASTWriter.cpp (original)
>> +++ cfe/trunk/lib/Serialization/ASTWriter.cpp Wed May  8 20:31:27 2019
>> @@ -5877,6 +5877,12 @@ void ASTRecordWriter::AddTemplateName(Te
>>     break;
>>   }
>>
>> +  case TemplateName::AssumedTemplate: {
>> +    AssumedTemplateStorage *ADLT = Name.getAsAssumedTemplateName();
>> +    AddDeclarationName(ADLT->getDeclName());
>> +    break;
>> +  }
>> +
>>   case TemplateName::QualifiedTemplate: {
>>     QualifiedTemplateName *QualT = Name.getAsQualifiedTemplateName();
>>     AddNestedNameSpecifier(QualT->getQualifier());
>>
>> Modified: cfe/trunk/test/CXX/basic/basic.lookup/basic.lookup.unqual/p3.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/basic/basic.lookup/basic.lookup.unqual/p3.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/CXX/basic/basic.lookup/basic.lookup.unqual/p3.cpp
>> (original)
>> +++ cfe/trunk/test/CXX/basic/basic.lookup/basic.lookup.unqual/p3.cpp Wed
>> May  8 20:31:27 2019
>> @@ -1,25 +1,67 @@
>> // RUN: %clang_cc1 -fsyntax-only -verify %s
>> -// expected-no-diagnostics
>> +// RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify %s
>> +// RUN: %clang_cc1 -std=c++2a -fsyntax-only -verify %s
>>
>> -typedef int f;
>> +typedef int fn;
>>
>> namespace N0 {
>> -  struct A {
>> -    friend void f();
>> +  struct A {
>> +    friend void fn();
>>     void g() {
>> -      int i = f(1);
>> +      int i = fn(1);
>>     }
>>   };
>> }
>>
>> namespace N1 {
>> -  struct A {
>> -    friend void f(A &);
>> +  struct A {
>> +    friend void fn(A &);
>>     operator int();
>>     void g(A a) {
>> -      // ADL should not apply to the lookup of 'f', it refers to the
>> typedef
>> +      // ADL should not apply to the lookup of 'fn', it refers to the
>> typedef
>>       // above.
>> -      int i = f(a);
>> +      int i = fn(a);
>>     }
>>   };
>> }
>> +
>> +namespace std_example {
>> +  int h; // expected-note {{non-template declaration}}
>> +  void g();
>> +#if __cplusplus <= 201703L
>> +  // expected-note at -2 {{non-template declaration}}
>> +#endif
>> +  namespace N {
>> +    struct A {};
>> +    template<class T> int f(T);
>> +    template<class T> int g(T);
>> +#if __cplusplus <= 201703L
>> +    // expected-note at -2 {{here}}
>> +#endif
>> +    template<class T> int h(T); // expected-note {{here}}
>> +  }
>> +
>> +  int x = f<N::A>(N::A());
>> +#if __cplusplus <= 201703L
>> +  // expected-warning at -2 {{C++2a extension}}
>> +#endif
>> +  int y = g<N::A>(N::A());
>> +#if __cplusplus <= 201703L
>> +  // expected-error at -2 {{'g' does not name a template but is followed
>> by template arguments; did you mean 'N::g'?}}
>> +#endif
>> +  int z = h<N::A>(N::A()); // expected-error {{'h' does not name a
>> template but is followed by template arguments; did you mean 'N::h'?}}
>> +}
>> +
>> +namespace AnnexD_example {
>> +  struct A {};
>> +  void operator<(void (*fp)(), A);
>> +  void f() {}
>> +  int main() {
>> +    A a;
>> +    f < a;
>> +#if __cplusplus > 201703L
>> +    // expected-error at -2 {{expected '>'}}
>> +#endif
>> +    (f) < a;
>> +  }
>> +}
>>
>> Modified: cfe/trunk/test/CXX/drs/dr2xx.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/drs/dr2xx.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/CXX/drs/dr2xx.cpp (original)
>> +++ cfe/trunk/test/CXX/drs/dr2xx.cpp Wed May  8 20:31:27 2019
>> @@ -2,6 +2,7 @@
>> // RUN: %clang_cc1 -std=c++11 %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>> // RUN: %clang_cc1 -std=c++14 %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>> // RUN: %clang_cc1 -std=c++17 %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>> +// RUN: %clang_cc1 -std=c++2a %s -verify -fexceptions -fcxx-exceptions
>> -pedantic-errors
>>
>> // PR13819 -- __SIZE_TYPE__ is incompatible.
>> typedef __SIZE_TYPE__ size_t; // expected-error 0-1 {{extension}}
>> @@ -434,7 +435,7 @@ namespace dr239 { // dr239: yes
>> namespace dr241 { // dr241: yes
>>   namespace A {
>>     struct B {};
>> -    template <int X> void f(); // expected-note 2{{candidate}}
>> +    template <int X> void f(); // expected-note 3{{candidate}}
>>     template <int X> void g(B);
>>   }
>>   namespace C {
>> @@ -442,8 +443,8 @@ namespace dr241 { // dr241: yes
>>     template <class T> void g(T t); // expected-note {{candidate}}
>>   }
>>   void h(A::B b) {
>> -    f<3>(b); // expected-error {{undeclared identifier}}
>> -    g<3>(b); // expected-error {{undeclared identifier}}
>> +    f<3>(b); // expected-error 0-1{{C++2a extension}} expected-error
>> {{no matching}}
>> +    g<3>(b); // expected-error 0-1{{C++2a extension}}
>>     A::f<3>(b); // expected-error {{no matching}}
>>     A::g<3>(b);
>>     C::f<3>(b); // expected-error {{no matching}}
>>
>> Modified: cfe/trunk/test/CXX/drs/dr6xx.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/drs/dr6xx.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/CXX/drs/dr6xx.cpp (original)
>> +++ cfe/trunk/test/CXX/drs/dr6xx.cpp Wed May  8 20:31:27 2019
>> @@ -1048,10 +1048,13 @@ namespace dr686 { // dr686: yes
>>   template<struct R {} *> struct Y; // expected-error {{cannot be defined
>> in a type specifier}}
>> }
>>
>> -namespace dr687 { // dr687 still open
>> +namespace dr687 { // dr687 (9 c++20, but the issue is still considered
>> open)
>>   template<typename T> void f(T a) {
>> -    // FIXME: This is valid in C++20.
>> -    g<int>(a); // expected-error {{undeclared}} expected-error {{'('}}
>> +    // This is valid in C++20.
>> +    g<int>(a);
>> +#if __cplusplus <= 201703L
>> +    // expected-error at -2 {{C++2a extension}}
>> +#endif
>>
>>     // This is not.
>>     template g<int>(a); // expected-error {{expected expression}}
>>
>> Modified: cfe/trunk/test/CXX/temp/temp.spec/temp.explicit/p5.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/temp/temp.spec/temp.explicit/p5.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/CXX/temp/temp.spec/temp.explicit/p5.cpp (original)
>> +++ cfe/trunk/test/CXX/temp/temp.spec/temp.explicit/p5.cpp Wed May  8
>> 20:31:27 2019
>> @@ -8,7 +8,10 @@ namespace N {
>>   };
>> }
>>
>> -template class Z<int>; // expected-error{{explicit instantiation of
>> non-template class 'Z'}}
>> +template class Z<int>; // expected-error{{explicit instantiation of
>> undeclared template class 'Z'}}
>> +
>> +struct Q;
>> +template class Q<int>; // expected-error{{explicit instantiation of
>> non-template class 'Q'}}
>>
>> // FIXME: This example from the standard is wrong; note posted to CWG
>> reflector
>> // on 10/27/2009
>>
>> Modified: cfe/trunk/test/FixIt/typo-crash.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/FixIt/typo-crash.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/FixIt/typo-crash.cpp (original)
>> +++ cfe/trunk/test/FixIt/typo-crash.cpp Wed May  8 20:31:27 2019
>> @@ -1,14 +1,8 @@
>> // RUN: %clang_cc1 -fsyntax-only -verify %s
>>
>> -// FIXME: The diagnostics and recovery here are very, very poor.
>> -
>> // PR10355
>> -template<typename T> void template_id1() { // expected-note
>> {{'template_id1' declared here}} \
>> -  // expected-note {{possible target for call}}
>> -  template_id2<> t; // expected-error {{no template named
>> 'template_id2'; did you mean 'template_id1'?}} \
>> -  // expected-error {{expected ';' after expression}} \
>> -  // expected-error {{reference to overloaded function could not be
>> resolved; did you mean to call it?}} \
>> -  // expected-error {{use of undeclared identifier 't'}}
>> +template<typename T> void template_id1() {
>> +  template_id2<> t; // expected-error-re {{no template named
>> 'template_id2'{{$}}}}
>>  }
>>
>> // FIXME: It would be nice if we could get this correction right.
>>
>> Modified: cfe/trunk/test/Misc/diag-template-diffing.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Misc/diag-template-diffing.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/Misc/diag-template-diffing.cpp (original)
>> +++ cfe/trunk/test/Misc/diag-template-diffing.cpp Wed May  8 20:31:27 2019
>> @@ -394,7 +394,7 @@ template<double* ...A> class class_ptrs
>> void set13(class_ptrs<&a13, &b13>) {}
>> void test13() {
>>   set13(class_ptrs<&c13>());
>> -  set13(class_ptrss<&a13, &b13, &d13>());
>> +  set13(class_ptrs<&a13, &b13, &d13>());
>> }
>> // CHECK-ELIDE-NOTREE: no matching function for call to 'set13'
>> // CHECK-ELIDE-NOTREE: candidate function not viable: no known conversion
>> from 'class_ptrs<&c13, (no argument)>' to 'class_ptrs<&a13, &b13>' for 1st
>> argument
>>
>> Modified: cfe/trunk/test/Modules/module-private.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/module-private.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/Modules/module-private.cpp (original)
>> +++ cfe/trunk/test/Modules/module-private.cpp Wed May  8 20:31:27 2019
>> @@ -18,9 +18,7 @@ int test_broken() {
>>   int *ip = 0;
>>   f1(ip); // expected-error{{use of undeclared identifier 'f1'}}
>>
>> -  vector<int> vec; // expected-error{{use of undeclared identifier
>> 'vector'}} \
>> -  // expected-error{{expected '(' for function-style cast or type
>> construction}} \
>> -  // expected-error{{use of undeclared identifier 'vec'}}
>> +  vector<int> vec; // expected-error{{no template named 'vector'}}
>>
>>   VisibleStruct vs;
>>   vs.field = 0; // expected-error{{no member named 'field' in
>> 'VisibleStruct'}}
>>
>> Modified: cfe/trunk/test/Modules/submodules-merge-defs.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/submodules-merge-defs.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/Modules/submodules-merge-defs.cpp (original)
>> +++ cfe/trunk/test/Modules/submodules-merge-defs.cpp Wed May  8 20:31:27
>> 2019
>> @@ -29,7 +29,7 @@ B::Inner2 pre_bi; // expected-error +{{m
>> // expected-note at defs.h:4 +{{here}}
>> // expected-note at defs.h:17 +{{here}}
>> void pre_bfi(B b) { // expected-error +{{must be imported}}
>> -  b.f<int>(); // expected-error +{{}}
>> +  b.f<int>();
>> }
>>
>> C_Base<1> pre_cb1; // expected-error +{{must be imported}}
>> @@ -48,7 +48,7 @@ int pre_e = E(0); // expected-error {{mu
>> // expected-note at defs.h:32 +{{here}}
>>
>> int pre_ff = F<int>().f(); // expected-error +{{must be imported}}
>> -int pre_fg = F<int>().g<int>(); // expected-error +{{must be imported}}
>> expected-error 2{{expected}}
>> +int pre_fg = F<int>().g<int>(); // expected-error +{{must be imported}}
>> // expected-note at defs.h:34 +{{here}}
>>
>> G::A pre_ga // expected-error +{{must be imported}}
>>
>> Modified: cfe/trunk/test/Parser/cxx-ambig-init-templ.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Parser/cxx-ambig-init-templ.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/Parser/cxx-ambig-init-templ.cpp (original)
>> +++ cfe/trunk/test/Parser/cxx-ambig-init-templ.cpp Wed May  8 20:31:27
>> 2019
>> @@ -31,7 +31,7 @@ struct S {
>>
>>   void f2a(
>>     // T3<int> here is a parameter type, so must be declared before it is
>> used.
>> -    int k1 = c < b, T3 < int > x = 0 // expected-error {{unexpected end
>> of default argument expression}}
>> +    int k1 = c < b, T3 < int > x = 0 // expected-error {{no template
>> named 'T3'}}
>>   );
>>
>>   template<typename, int=0> struct T3 { T3(int); operator int(); };
>>
>> Modified: cfe/trunk/test/Parser/cxx-template-argument.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Parser/cxx-template-argument.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/Parser/cxx-template-argument.cpp (original)
>> +++ cfe/trunk/test/Parser/cxx-template-argument.cpp Wed May  8 20:31:27
>> 2019
>> @@ -60,33 +60,32 @@ namespace pr16225add {
>>   template<int N1, int N2> struct ABC2 {};
>>
>>   template<class T1, typename T2> struct foo :
>> -    UnknownBase<T1,T2> // expected-error {{unknown template name
>> 'UnknownBase'}}
>> +    UnknownBase<T1,T2> // expected-error {{no template named
>> 'UnknownBase'}}
>>   { };
>>
>>   template<class T1, typename T2> struct foo2 :
>> -    UnknownBase<T1,T2>, // expected-error {{unknown template name
>> 'UnknownBase'}}
>> +    UnknownBase<T1,T2>, // expected-error {{no template named
>> 'UnknownBase'}}
>>     Known<T1>  // expected-error {{too few template arguments for class
>> template 'Known'}}
>>   { };
>>
>>   template<class T1, typename T2> struct foo3 :
>> -    UnknownBase<T1,T2,ABC<T2,T1> > // expected-error {{unknown template
>> name 'UnknownBase'}}
>> +    UnknownBase<T1,T2,ABC<T2,T1> > // expected-error {{no template named
>> 'UnknownBase'}}
>>   { };
>>
>>   template<class T1, typename T2> struct foo4 :
>> -    UnknownBase<T1,ABC<T2> >, // expected-error {{unknown template name
>> 'UnknownBase'}} \
>> -                              // expected-error {{too few template
>> arguments for class template 'ABC'}}
>> +    UnknownBase<T1,ABC<T2> >, // expected-error {{too few template
>> arguments for class template 'ABC'}}
>>     Known<T1>  // expected-error {{too few template arguments for class
>> template 'Known'}}
>>   { };
>>
>>   template<class T1, typename T2> struct foo5 :
>> -    UnknownBase<T1,T2,ABC<T2,T1>> // expected-error {{unknown template
>> name 'UnknownBase'}}
>> +    UnknownBase<T1,T2,ABC<T2,T1>> // expected-error {{no template named
>> 'UnknownBase'}}
>> #if __cplusplus <= 199711L
>>     // expected-error at -2 {{use '> >'}}
>> #endif
>>   { };
>>
>>   template<class T1, typename T2> struct foo6 :
>> -    UnknownBase<T1,ABC<T2,T1>>, // expected-error {{unknown template
>> name 'UnknownBase'}}
>> +    UnknownBase<T1,ABC<T2,T1>>, // expected-error {{no template named
>> 'UnknownBase'}}
>> #if __cplusplus <= 199711L
>>     // expected-error at -2 {{use '> >'}}
>> #endif
>> @@ -94,32 +93,32 @@ namespace pr16225add {
>>   { };
>>
>>   template<class T1, typename T2, int N> struct foo7 :
>> -    UnknownBase<T1,T2,(N>1)> // expected-error {{unknown template name
>> 'UnknownBase'}}
>> +    UnknownBase<T1,T2,(N>1)> // expected-error {{no template named
>> 'UnknownBase'}}
>>   { };
>>
>>   template<class T1, typename T2> struct foo8 :
>> -    UnknownBase<X<int,int>,X<int,int>> // expected-error {{unknown
>> template name 'UnknownBase'}}
>> +    UnknownBase<X<int,int>,X<int,int>> // expected-error {{no template
>> named 'UnknownBase'}}
>> #if __cplusplus <= 199711L
>>     // expected-error at -2 {{use '> >'}}
>> #endif
>>   { };
>>
>>   template<class T1, typename T2> struct foo9 :
>> -    UnknownBase<Known<int,int>,X<int,int>> // expected-error {{unknown
>> template name 'UnknownBase'}}
>> +    UnknownBase<Known<int,int>,X<int,int>> // expected-error {{no
>> template named 'UnknownBase'}}
>> #if __cplusplus <= 199711L
>>     // expected-error at -2 {{use '> >'}}
>> #endif
>>   { };
>>
>>   template<class T1, typename T2> struct foo10 :
>> -    UnknownBase<Known<int,int>,X<int,X<int,int>>> // expected-error
>> {{unknown template name 'UnknownBase'}}
>> +    UnknownBase<Known<int,int>,X<int,X<int,int>>> // expected-error {{no
>> template named 'UnknownBase'}}
>> #if __cplusplus <= 199711L
>>     // expected-error at -2 {{use '> >'}}
>> #endif
>>   { };
>>
>>   template<int N1, int N2> struct foo11 :
>> -    UnknownBase<2<N1,N2<4> // expected-error {{unknown template name
>> 'UnknownBase'}}
>> +    UnknownBase<2<N1,N2<4> // expected-error {{no template named
>> 'UnknownBase'}}
>>   { };
>>
>> }
>>
>> Modified: cfe/trunk/test/Parser/cxx-template-decl.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Parser/cxx-template-decl.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/Parser/cxx-template-decl.cpp (original)
>> +++ cfe/trunk/test/Parser/cxx-template-decl.cpp Wed May  8 20:31:27 2019
>> @@ -128,8 +128,13 @@ void f2() {
>>
>>
>> // PR3844
>> -template <> struct S<int> { }; // expected-error{{explicit
>> specialization of non-template struct 'S'}}
>> -template <> union U<int> { }; // expected-error{{explicit specialization
>> of non-template union 'U'}}
>> +template <> struct S<int> { }; // expected-error{{explicit
>> specialization of undeclared template struct 'S'}}
>> +template <> union U<int> { }; // expected-error{{explicit specialization
>> of undeclared template union 'U'}}
>> +
>> +struct SS;
>> +union UU;
>> +template <> struct SS<int> { }; // expected-error{{explicit
>> specialization of non-template struct 'SS'}}
>> +template <> union UU<int> { }; // expected-error{{explicit
>> specialization of non-template union 'UU'}}
>>
>> namespace PR6184 {
>>   namespace N {
>> @@ -230,11 +235,11 @@ struct base { };
>>
>> struct t1 : base<int,
>>   public:  // expected-error {{expected expression}}
>> -};  // expected-error {{expected class name}}
>> +};
>> // expected-error at -1 {{expected '{' after base class list}}
>> struct t2 : base<int,
>>   public  // expected-error {{expected expression}}
>> -};  // expected-error {{expected class name}}
>> +};
>> // expected-error at -1 {{expected '{' after base class list}}
>>
>> }
>>
>> Modified: cfe/trunk/test/SemaCXX/alias-template.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/alias-template.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/alias-template.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/alias-template.cpp Wed May  8 20:31:27 2019
>> @@ -112,11 +112,8 @@ namespace StdExample {
>>   template<typename T> using handler_t = void (*)(T);
>>   extern handler_t<int> ignore;
>>   extern void (*ignore)(int);
>> -  // FIXME: we recover as if cell is an undeclared variable. the
>> diagnostics are terrible!
>> -  template<typename T> using cell = pair<T*, cell<T>*>; //
>> expected-error {{use of undeclared identifier 'cell'}} \
>> -
>>                                                           expected-error
>> {{'T' does not refer to a value}} \
>> -                                                           expected-note
>> {{declared here}} \
>> -
>>                                                           expected-error
>> {{expected ';' after alias declaration}}
>> +  // FIXME: we recover as if cell is an undeclared variable template
>> +  template<typename T> using cell = pair<T*, cell<T>*>; //
>> expected-error {{use of undeclared identifier 'cell'}} expected-error
>> {{expected expression}}
>> }
>>
>> namespace Access {
>>
>> Modified: cfe/trunk/test/SemaCXX/class.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/class.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/class.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/class.cpp Wed May  8 20:31:27 2019
>> @@ -138,7 +138,7 @@ struct S
>> // Don't crash on this bogus code.
>> namespace pr6629 {
>>   template<class T1, class T2> struct foo :
>> -    bogus<foo<T1,T2> > // expected-error {{unknown template name
>> 'bogus'}}
>> +    bogus<foo<T1,T2> > // expected-error {{no template named 'bogus'}}
>>   { };
>>
>>   template<> struct foo<unknown,unknown> { // expected-error {{undeclared
>> identifier 'unknown'}}
>>
>> Added: cfe/trunk/test/SemaCXX/cxx2a-adl-only-template-id.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/cxx2a-adl-only-template-id.cpp?rev=360308&view=auto
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/cxx2a-adl-only-template-id.cpp (added)
>> +++ cfe/trunk/test/SemaCXX/cxx2a-adl-only-template-id.cpp Wed May  8
>> 20:31:27 2019
>> @@ -0,0 +1,67 @@
>> +// RUN: %clang_cc1 -std=c++2a -verify %s
>> +
>> +namespace N {
>> +  struct Q {};
>> +  template<typename> int f(Q);
>> +  template<int> int f(Q);
>> +  template<typename> int g(Q);
>> +  template<int> int g(Q);
>> +
>> +  template<int> int some_long_name(Q); // expected-note {{here}}
>> +}
>> +N::Q q;
>> +int g();
>> +
>> +int h();
>> +template<int> int h(...);
>> +int h(int);
>> +
>> +// OK, these find the above functions by ADL.
>> +int a = f<int>(q);
>> +int b(f<int>(q));
>> +int c(f<0>(q));
>> +int d = g<int>(q);
>> +
>> +int e = h<0>(q); // ok, found by unqualified lookup
>> +
>> +void fn() {
>> +  f<0>(q);
>> +  int f;
>> +  f<0>(q); // expected-error {{invalid operands to binary expression}}
>> +}
>> +
>> +void disambig() {
>> +  // FIXME: It's unclear whether ending the template argument at the >
>> inside the ?: is correct here (see DR579).
>> +  f<true ? 1 > 2 : 3>(q); // expected-error {{expected ':'}}
>> expected-note {{to match}} expected-error {{expected expression}}
>> +
>> +  f < 1 + 3 > (q); // ok, function call
>> +}
>> +
>> +bool typo(int something) { // expected-note 4{{declared here}}
>> +  // FIXME: We shouldn't suggest the N:: for an ADL call if the
>> candidate can be found by ADL.
>> +  some_logn_name<3>(q); // expected-error {{did you mean
>> 'N::some_long_name'?}}
>> +  somethign < 3 ? h() > 4 : h(0); // expected-error {{did you mean
>> 'something'}}
>> +  // This is parsed as a comparison on the left of a ?: expression.
>> +  somethign < 3 ? h() + 4 : h(0); // expected-error {{did you mean
>> 'something'}}
>> +  // This is parsed as an ADL-only template-id call.
>> +  somethign < 3 ? h() + 4 : h(0) >(0); // expected-error {{undeclared
>> identifier 'somethign'}}
>> +  bool k(somethign < 3); // expected-error {{did you mean 'something'}}
>> +  return somethign < 3; // expected-error {{did you mean 'something'}}
>> +}
>> +
>> +// Ensure that treating undeclared identifiers as template names doesn't
>> cause
>> +// problems.
>> +struct W<int> {}; // expected-error {{undeclared template struct 'W'}}
>> +X<int>::Y xy; // expected-error {{no template named 'X'}}
>> +void xf(X<int> x); // expected-error {{no template named 'X'}}
>> +struct A : X<int> { // expected-error {{no template named 'X'}}
>> +  A() : X<int>() {} // expected-error {{no template named 'X'}}
>> +};
>> +
>> +// Similarly for treating overload sets of functions as template names.
>> +struct g<int> {}; // expected-error {{'g' refers to a function template}}
>> +g<int>::Y xy; // expected-error {{no template named 'g'}} FIXME lies
>> +void xf(g<int> x); // expected-error {{variable has incomplete type
>> 'void'}} expected-error 1+{{}} expected-note {{}}
>> +struct B : g<int> { // expected-error {{expected class name}}
>> +  B() : g<int>() {} // expected-error {{expected class member or base
>> class name}}
>> +};
>>
>> Modified: cfe/trunk/test/SemaCXX/destructor.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/destructor.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/destructor.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/destructor.cpp Wed May  8 20:31:27 2019
>> @@ -99,7 +99,7 @@ struct Y {
>> namespace PR6421 {
>>   class T; // expected-note{{forward declaration}}
>>
>> -  class QGenericArgument // expected-note{{declared here}}
>> +  class QGenericArgument
>>   {
>>     template<typename U>
>>     void foo(T t) // expected-error{{variable has incomplete type}}
>> @@ -108,8 +108,7 @@ namespace PR6421 {
>>     void disconnect()
>>     {
>>       T* t;
>> -      bob<QGenericArgument>(t); // expected-error{{undeclared identifier
>> 'bob'}} \
>> -      // expected-error{{does not refer to a value}}
>> +      bob<QGenericArgument>(t); // expected-error{{undeclared identifier
>> 'bob'}}
>>     }
>>   };
>> }
>>
>> Modified: cfe/trunk/test/SemaCXX/invalid-member-expr.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/invalid-member-expr.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/invalid-member-expr.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/invalid-member-expr.cpp Wed May  8 20:31:27
>> 2019
>> @@ -53,7 +53,10 @@ namespace test3 {
>> namespace rdar11293995 {
>>
>> struct Length {
>> -  explicit Length(PassRefPtr<CalculationValue>); // expected-error {{no
>> template named 'PassRefPtr}} expected-error {{undeclared identifier
>> 'CalculationValue'}}
>> +  // FIXME: We try to annotate the template-id here during tentative
>> parsing,
>> +  // and fail, then try again during the actual parse. This results in
>> the same
>> +  // diagnostic being produced twice. :(
>> +  explicit Length(PassRefPtr<CalculationValue>); // expected-error
>> 2{{undeclared identifier 'CalculationValue'}}
>> };
>>
>> struct LengthSize {
>>
>> Modified: cfe/trunk/test/SemaCXX/typo-correction.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/typo-correction.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/typo-correction.cpp (original)
>> +++ cfe/trunk/test/SemaCXX/typo-correction.cpp Wed May  8 20:31:27 2019
>> @@ -438,7 +438,7 @@ namespace PR17394 {
>>     long zzzzzzzzzz;
>>   };
>>   class B : private A {};
>> -  B zzzzzzzzzy<>; // expected-error {{expected ';' after top level
>> declarator}}{}
>> +  B zzzzzzzzzy<>; // expected-error {{template specialization requires
>> 'template<>'}} expected-error {{no variable template matches
>> specialization}}
>> }
>>
>> namespace correct_fields_in_member_funcs {
>>
>> Modified: cfe/trunk/test/SemaTemplate/dependent-base-classes.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaTemplate/dependent-base-classes.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaTemplate/dependent-base-classes.cpp (original)
>> +++ cfe/trunk/test/SemaTemplate/dependent-base-classes.cpp Wed May  8
>> 20:31:27 2019
>> @@ -9,7 +9,7 @@ template<typename T, typename U>
>> struct X1 : T::apply<U> { }; // expected-error{{use 'template' keyword to
>> treat 'apply' as a dependent template name}}
>>
>> template<typename T>
>> -struct X2 : vector<T> { }; // expected-error{{unknown template name
>> 'vector'}}
>> +struct X2 : vector<T> { }; // expected-error{{no template named
>> 'vector'}}
>>
>> namespace PR6031 {
>>   template<typename T>
>>
>> Modified: cfe/trunk/test/SemaTemplate/dependent-template-recover.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaTemplate/dependent-template-recover.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaTemplate/dependent-template-recover.cpp (original)
>> +++ cfe/trunk/test/SemaTemplate/dependent-template-recover.cpp Wed May  8
>> 20:31:27 2019
>> @@ -7,7 +7,7 @@ struct X {
>>
>>     t->operator+<U const, 1>(1); // expected-error{{use 'template'
>> keyword to treat 'operator +' as a dependent template name}}
>>     t->f1<int const, 2>(1); // expected-error{{use 'template' keyword to
>> treat 'f1' as a dependent template name}}
>> -    t->f1<3, int const>(1); // expected-error{{missing 'template'
>> keyword prior to dependent template name 'f1'}}
>> +    t->f1<3, int const>(1); // expected-error{{use 'template' keyword to
>> treat 'f1' as a dependent template name}}
>>
>>     T::getAs<U>(); // expected-error{{use 'template' keyword to treat
>> 'getAs' as a dependent template name}}
>>     t->T::getAs<U>(); // expected-error{{use 'template' keyword to treat
>> 'getAs' as a dependent template name}}
>> @@ -15,7 +15,7 @@ struct X {
>>     (*t).f2<N>(); // expected-error{{missing 'template' keyword prior to
>> dependent template name 'f2'}}
>>     (*t).f2<0>(); // expected-error{{missing 'template' keyword prior to
>> dependent template name 'f2'}}
>>     T::f2<0>(); // expected-error{{missing 'template' keyword prior to
>> dependent template name 'f2'}}
>> -    T::f2<0, int>(0); // expected-error{{missing 'template' keyword
>> prior to dependent template name 'f2'}}
>> +    T::f2<0, int>(0); // expected-error{{use 'template' keyword to treat
>> 'f2' as a dependent template name}}
>>
>>     T::foo<N < 2 || N >= 4>(); // expected-error{{missing 'template'
>> keyword prior to dependent template name 'foo'}}
>>
>> @@ -24,7 +24,7 @@ struct X {
>>     T::foo<T::bar < 1>(); // expected-error{{missing 'template' keyword
>> prior to dependent template name 'foo'}}
>>     T::foo < T::bar<1>(); // expected-error{{missing 'template' keyword
>> prior to dependent template name 'bar'}}
>>
>> -    // Prefer to diagonse a missing 'template' keyword rather than
>> finding a non-template name.
>> +    // Prefer to diagnose a missing 'template' keyword rather than
>> finding a non-template name.
>>     xyz < T::foo < 1 > (); // expected-error{{missing 'template' keyword
>> prior to dependent template name 'foo'}}
>>     T::foo < xyz < 1 > (); // expected-error{{missing 'template' keyword
>> prior to dependent template name 'foo'}}
>>
>> @@ -83,12 +83,12 @@ template<int N, typename T> void f(T t)
>>   T::g<mb>(0);
>>
>>   // ... but this one must be a template-id.
>> -  T::g<mb, int>(0); // expected-error {{missing 'template' keyword prior
>> to dependent template name 'g'}}
>> +  T::g<mb, int>(0); // expected-error {{use 'template' keyword to treat
>> 'g' as a dependent template name}} expected-error {{no matching function}}
>> }
>>
>> struct Y {
>>   template <int> void f(int);
>> -  template <int = 0> static void g(int); // expected-warning
>> 0-1{{extension}}
>> +  template <int = 0> static void g(int); // expected-warning
>> 0-1{{extension}} expected-note {{candidate}}
>> };
>> void q() { void (*p)(int) = Y::g; }
>> template void f<0>(Y); // expected-note {{in instantiation of}}
>>
>> Modified: cfe/trunk/test/SemaTemplate/rdar9173693.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaTemplate/rdar9173693.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaTemplate/rdar9173693.cpp (original)
>> +++ cfe/trunk/test/SemaTemplate/rdar9173693.cpp Wed May  8 20:31:27 2019
>> @@ -2,5 +2,8 @@
>>
>> // <rdar://problem/9173693>
>> template< bool C > struct assert { };
>> -template< bool > struct assert_arg_pred_impl { }; // expected-note 3
>> {{declared here}}
>> -template< typename Pred > assert<false> assert_not_arg( void (*)(Pred),
>> typename assert_arg_pred<Pred>::type ); // expected-error 5 {{}}
>> +// FIXME: We diagnose the same problem multiple times here because we
>> have no
>> +// way to indicate in the token stream that we already tried to annotate
>> a
>> +// template-id and we failed.
>> +template< bool > struct assert_arg_pred_impl { }; // expected-note 4
>> {{declared here}}
>> +template< typename Pred > assert<false> assert_not_arg( void (*)(Pred),
>> typename assert_arg_pred<Pred>::type ); // expected-error 6 {{}}
>>
>> Modified: cfe/trunk/test/SemaTemplate/recovery-crash.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaTemplate/recovery-crash.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaTemplate/recovery-crash.cpp (original)
>> +++ cfe/trunk/test/SemaTemplate/recovery-crash.cpp Wed May  8 20:31:27
>> 2019
>> @@ -28,12 +28,12 @@ namespace PR16134 {
>> namespace PR16225 {
>>   template <typename T> void f();
>>   template <typename C> void g(C*) {
>> -    struct LocalStruct : UnknownBase<Mumble, C> { };  // expected-error
>> {{unknown template name 'UnknownBase'}} \
>> -                                                      // expected-error
>> {{use of undeclared identifier 'Mumble'}}
>> +    struct LocalStruct : UnknownBase<Mumble, C> { };  // expected-error
>> {{use of undeclared identifier 'Mumble'}}
>>     f<LocalStruct>();
>> #if __cplusplus <= 199711L
>>     // expected-warning at -2 {{template argument uses local type
>> 'LocalStruct'}}
>> #endif
>> +    struct LocalStruct2 : UnknownBase<C> { };  // expected-error {{no
>> template named 'UnknownBase'}}
>>   }
>>   struct S;
>>   void h() {
>>
>> Modified: cfe/trunk/tools/libclang/CIndex.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/tools/libclang/CIndex.cpp?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/tools/libclang/CIndex.cpp (original)
>> +++ cfe/trunk/tools/libclang/CIndex.cpp Wed May  8 20:31:27 2019
>> @@ -1430,6 +1430,10 @@ bool CursorVisitor::VisitTemplateName(Te
>>
>>     return false;
>>
>> +  case TemplateName::AssumedTemplate:
>> +    // FIXME: Visit DeclarationName?
>> +    return false;
>> +
>>   case TemplateName::DependentTemplate:
>>     // FIXME: Visit nested-name-specifier.
>>     return false;
>>
>> Modified: cfe/trunk/www/cxx_status.html
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/www/cxx_status.html?rev=360308&r1=360307&r2=360308&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/www/cxx_status.html (original)
>> +++ cfe/trunk/www/cxx_status.html Wed May  8 20:31:27 2019
>> @@ -893,7 +893,7 @@ as the draft C++2a standard evolves.
>>     <tr>
>>       <td>ADL and function templates that are not visible</td>
>>       <td><a href="http://wg21.link/p0846r0">P0846R0</a></td>
>> -      <td class="none" align="center">No</td>
>> +      <td class="svn" align="center">SVN</td>
>>     </tr>
>>     <tr>
>>       <td><tt>const</tt> mismatch with defaulted copy constructor</td>
>>
>>
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>>
>>
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