r290792 - [c++17] Implement P0522R0 as written. This allows a template template argument

Erik Pilkington via cfe-commits cfe-commits at lists.llvm.org
Sun Jan 1 07:28:21 PST 2017


> On Dec 31, 2016, at 4:41 PM, Richard Smith via cfe-commits <cfe-commits at lists.llvm.org> wrote:
> 
> Author: rsmith
> Date: Sat Dec 31 15:41:23 2016
> New Revision: 290792
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=290792&view=rev
> Log:
> [c++17] Implement P0522R0 as written. This allows a template template argument
> to be specified for a template template parameter whenever the parameter is at
> least as specialized as the argument (when there's an obvious and correct
> mapping from uses of the parameter to uses of the argument). For example, a
> template with more parameters can be passed to a template template parameter
> with fewer, if those trailing parameters have default arguments.
> 
> This is disabled by default, despite being a DR resolution, as it's fairly
> broken in its current state: there are no partial ordering rules to cope with
> template template parameters that have different parameter lists, meaning that
> code that attempts to decompose template-ids based on arity can hit unavoidable
> ambiguity issues.
> 
> The diagnostics produced on a non-matching argument are also pretty bad right
> now, but I aim to improve them in a subsequent commit.
> 
> Added:
>    cfe/trunk/test/SemaTemplate/temp_arg_template_cxx1z.cpp
> Modified:
>    cfe/trunk/include/clang/Basic/LangOptions.def
>    cfe/trunk/include/clang/Driver/Options.td
>    cfe/trunk/include/clang/Sema/Sema.h
>    cfe/trunk/lib/Driver/Tools.cpp
>    cfe/trunk/lib/Frontend/CompilerInvocation.cpp
>    cfe/trunk/lib/Sema/SemaTemplate.cpp
>    cfe/trunk/lib/Sema/SemaTemplateDeduction.cpp
>    cfe/trunk/test/SemaTemplate/temp_arg_template.cpp
>    cfe/trunk/www/cxx_status.html
> 
> Modified: cfe/trunk/include/clang/Basic/LangOptions.def
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/LangOptions.def?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/include/clang/Basic/LangOptions.def (original)
> +++ cfe/trunk/include/clang/Basic/LangOptions.def Sat Dec 31 15:41:23 2016
> @@ -134,6 +134,7 @@ LANGOPT(NoBuiltin         , 1, 0, "disab
> LANGOPT(NoMathBuiltin     , 1, 0, "disable math builtin functions")
> LANGOPT(GNUAsm            , 1, 1, "GNU-style inline assembly")
> LANGOPT(CoroutinesTS      , 1, 0, "C++ coroutines TS")
> +LANGOPT(RelaxedTemplateTemplateArgs, 1, 0, "C++17 relaxed matching of tempalte template arguments")
> 
> BENIGN_LANGOPT(ThreadsafeStatics , 1, 1, "thread-safe static initializers")
> LANGOPT(POSIXThreads      , 1, 0, "POSIX thread support")
> 
> Modified: cfe/trunk/include/clang/Driver/Options.td
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Driver/Options.td?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/include/clang/Driver/Options.td (original)
> +++ cfe/trunk/include/clang/Driver/Options.td Sat Dec 31 15:41:23 2016
> @@ -1088,6 +1088,11 @@ def fapplication_extension : Flag<["-"],
>   HelpText<"Restrict code to those available for App Extensions">;
> def fno_application_extension : Flag<["-"], "fno-application-extension">,
>   Group<f_Group>;
> +def frelaxed_template_template_args : Flag<["-"], "frelaxed-template-template-args">,
> +  Flags<[CC1Option]>, HelpText<"Enable C++17 relaxed template template argument matching">,
> +  Group<f_Group>;
> +def fno_relaxed_template_template_args : Flag<["-"], "fno-relaxed-template-template-args">,
> +  Group<f_Group>;
> def fsized_deallocation : Flag<["-"], "fsized-deallocation">, Flags<[CC1Option]>,
>   HelpText<"Enable C++14 sized global deallocation functions">, Group<f_Group>;
> def fno_sized_deallocation: Flag<["-"], "fno-sized-deallocation">, Group<f_Group>;
> 
> Modified: cfe/trunk/include/clang/Sema/Sema.h
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Sema.h?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/include/clang/Sema/Sema.h (original)
> +++ cfe/trunk/include/clang/Sema/Sema.h Sat Dec 31 15:41:23 2016
> @@ -6719,6 +6719,9 @@ public:
>   bool isMoreSpecializedThanPrimary(VarTemplatePartialSpecializationDecl *T,
>                                     sema::TemplateDeductionInfo &Info);
> 
> +  bool isTemplateTemplateParameterAtLeastAsSpecializedAs(
> +      TemplateParameterList *P, TemplateDecl *AArg, SourceLocation Loc);
> +
>   void MarkUsedTemplateParameters(const TemplateArgumentList &TemplateArgs,
>                                   bool OnlyDeduced,
>                                   unsigned Depth,
> 
> Modified: cfe/trunk/lib/Driver/Tools.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/Tools.cpp?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Driver/Tools.cpp (original)
> +++ cfe/trunk/lib/Driver/Tools.cpp Sat Dec 31 15:41:23 2016
> @@ -6020,6 +6020,13 @@ void Clang::ConstructJob(Compilation &C,
>                     options::OPT_fno_assume_sane_operator_new))
>     CmdArgs.push_back("-fno-assume-sane-operator-new");
> 
> +  // -frelaxed-template-template-args is off by default, as it is a severe
> +  // breaking change until a corresponding change to template partial ordering
> +  // is provided.
> +  if (Args.hasFlag(options::OPT_frelaxed_template_template_args,
> +                   options::OPT_fno_relaxed_template_template_args, false))
> +    CmdArgs.push_back("-frelaxed-template-template-args");
> +
>   // -fsized-deallocation is off by default, as it is an ABI-breaking change for
>   // most platforms.
>   if (Args.hasFlag(options::OPT_fsized_deallocation,
> 
> Modified: cfe/trunk/lib/Frontend/CompilerInvocation.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Frontend/CompilerInvocation.cpp?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Frontend/CompilerInvocation.cpp (original)
> +++ cfe/trunk/lib/Frontend/CompilerInvocation.cpp Sat Dec 31 15:41:23 2016
> @@ -1960,6 +1960,8 @@ static void ParseLangArgs(LangOptions &O
>   if (!Opts.NoBuiltin)
>     getAllNoBuiltinFuncValues(Args, Opts.NoBuiltinFuncs);
>   Opts.NoMathBuiltin = Args.hasArg(OPT_fno_math_builtin);
> +  Opts.RelaxedTemplateTemplateArgs =
> +      Args.hasArg(OPT_frelaxed_template_template_args);
>   Opts.SizedDeallocation = Args.hasArg(OPT_fsized_deallocation);
>   Opts.AlignedAllocation =
>       Args.hasFlag(OPT_faligned_allocation, OPT_fno_aligned_allocation,
> 
> Modified: cfe/trunk/lib/Sema/SemaTemplate.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaTemplate.cpp?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaTemplate.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaTemplate.cpp Sat Dec 31 15:41:23 2016
> @@ -5585,6 +5585,10 @@ ExprResult Sema::CheckTemplateArgument(N
>   return Arg;
> }
> 
> +static void DiagnoseTemplateParameterListArityMismatch(
> +    Sema &S, TemplateParameterList *New, TemplateParameterList *Old,
> +    Sema::TemplateParameterListEqualKind Kind, SourceLocation TemplateArgLoc);
> +
> /// \brief Check a template argument against its corresponding
> /// template template parameter.
> ///
> @@ -5601,6 +5605,9 @@ bool Sema::CheckTemplateArgument(Templat
>     return false;
>   }
> 
> +  if (Template->isInvalidDecl())
> +    return true;
> +
>   // C++0x [temp.arg.template]p1:
>   //   A template-argument for a template template-parameter shall be
>   //   the name of a class template or an alias template, expressed as an
> @@ -5628,6 +5635,25 @@ bool Sema::CheckTemplateArgument(Templat
>   if (Param->isExpandedParameterPack())
>     Params = Param->getExpansionTemplateParameters(ArgumentPackIndex);
> 
> +  // C++1z [temp.arg.template]p3: (DR 150)
> +  //   A template-argument matches a template template-parameter P when P
> +  //   is at least as specialized as the template-argument A.
> +  if (getLangOpts().RelaxedTemplateTemplateArgs) {
> +    // Quick check for the common case:
> +    //   If P contains a parameter pack, then A [...] matches P if each of A's
> +    //   template parameters matches the corresponding template parameter in
> +    //   the template-parameter-list of P.
> +    if (TemplateParameterListsAreEqual(
> +            Template->getTemplateParameters(), Params, false,
> +            TPL_TemplateTemplateArgumentMatch, Arg.getLocation()))
> +      return false;
> +
> +    if (isTemplateTemplateParameterAtLeastAsSpecializedAs(Params, Template,
> +                                                          Arg.getLocation()))
> +      return false;
> +    // FIXME: Produce better diagnostics for deduction failures.
> +  }
> +
>   return !TemplateParameterListsAreEqual(Template->getTemplateParameters(),
>                                          Params,
>                                          true,
> @@ -5839,7 +5865,7 @@ static bool MatchTemplateParameterKind(S
>     return false;
>   }
> 
> -  // Check that both are parameter packs are neither are parameter packs.
> +  // Check that both are parameter packs or neither are parameter packs.
>   // However, if we are matching a template template argument to a
>   // template template parameter, the template template parameter can have
>   // a parameter pack where the template template argument does not.
> 
> Modified: cfe/trunk/lib/Sema/SemaTemplateDeduction.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaTemplateDeduction.cpp?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaTemplateDeduction.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaTemplateDeduction.cpp Sat Dec 31 15:41:23 2016
> @@ -1898,11 +1898,11 @@ DeduceTemplateArguments(Sema &S, Templat
>         return NumberOfArgumentsMustMatch ? Sema::TDK_TooFewArguments
>                                           : Sema::TDK_Success;
> 
> -      if (Args[ArgIdx].isPackExpansion()) {
> -        // FIXME: We follow the logic of C++0x [temp.deduct.type]p22 here,
> -        // but applied to pack expansions that are template arguments.
> +      // C++1z [temp.deduct.type]p9:
> +      //   During partial ordering, if Ai was originally a pack expansion [and]
> +      //   Pi is not a pack expansion, template argument deduction fails.
> +      if (Args[ArgIdx].isPackExpansion())
>         return Sema::TDK_MiscellaneousDeductionFailure;
> -      }
> 
>       // Perform deduction for this Pi/Ai pair.
>       if (Sema::TemplateDeductionResult Result
> @@ -1965,7 +1965,8 @@ DeduceTemplateArguments(Sema &S,
>                         TemplateDeductionInfo &Info,
>                         SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
>   return DeduceTemplateArguments(S, TemplateParams, ParamList.asArray(),
> -                                 ArgList.asArray(), Info, Deduced, false);
> +                                 ArgList.asArray(), Info, Deduced,
> +                                 /*NumberOfArgumentsMustMatch*/false);
> }
> 
> /// \brief Determine whether two template arguments are the same.
> @@ -4581,13 +4582,13 @@ UnresolvedSetIterator Sema::getMostSpeci
> /// Determine whether one partial specialization, P1, is at least as
> /// specialized than another, P2.
> ///
> -/// \tparam PartialSpecializationDecl The kind of P2, which must be a
> -/// {Class,Var}Template{PartialSpecialization,}Decl.
> +/// \tparam TemplateLikeDecl The kind of P2, which must be a
> +/// TemplateDecl or {Class,Var}TemplatePartialSpecializationDecl.
> /// \param T1 The injected-class-name of P1 (faked for a variable template).
> /// \param T2 The injected-class-name of P2 (faked for a variable template).
> -template<typename PartialSpecializationDecl>
> +template<typename TemplateLikeDecl>
> static bool isAtLeastAsSpecializedAs(Sema &S, QualType T1, QualType T2,
> -                                     PartialSpecializationDecl *P2,
> +                                     TemplateLikeDecl *P2,
>                                      TemplateDeductionInfo &Info) {
>   // C++ [temp.class.order]p1:
>   //   For two class template partial specializations, the first is at least as
> @@ -4729,6 +4730,72 @@ bool Sema::isMoreSpecializedThanPrimary(
>   return true;
> }
> 
> +bool Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs(
> +     TemplateParameterList *P, TemplateDecl *AArg, SourceLocation Loc) {
> +  // C++1z [temp.arg.template]p4: (DR 150)
> +  //   A template template-parameter P is at least as specialized as a
> +  //   template template-argument A if, given the following rewrite to two
> +  //   function templates...
> +
> +  // Rather than synthesize function templates, we merely perform the
> +  // equivalent partial ordering by performing deduction directly on
> +  // the template parameter lists of the template template parameters.
> +  //
> +  //   Given an invented class template X with the template parameter list of
> +  //   A (including default arguments):
> +  TemplateName X = Context.getCanonicalTemplateName(TemplateName(AArg));
> +  TemplateParameterList *A = AArg->getTemplateParameters();
> +
> +  //    - Each function template has a single function parameter whose type is
> +  //      a specialization of X with template arguments corresponding to the
> +  //      template parameters from the respective function template
> +  SmallVector<TemplateArgument, 8> AArgs;
> +  Context.getInjectedTemplateArgs(A, AArgs);
> +
> +  // Check P's arguments against A's parameter list. This will fill in default
> +  // template arguments as needed. AArgs are already correct by construction.
> +  // We can't just use CheckTemplateIdType because that will expand alias
> +  // templates.
> +  SmallVector<TemplateArgument, 4> PArgs;
> +  {
> +    SFINAETrap Trap(*this);
> +
> +    Context.getInjectedTemplateArgs(P, PArgs);
> +    TemplateArgumentListInfo PArgList(P->getLAngleLoc(), P->getRAngleLoc());
> +    for (unsigned I = 0, N = P->size(); I != N; ++I) {
> +      // Unwrap packs that getInjectedTemplateArgs wrapped around pack
> +      // expansions, to form an "as written" argument list.
> +      TemplateArgument Arg = PArgs[I];
> +      if (Arg.getKind() == TemplateArgument::Pack) {
> +        assert(Arg.pack_size() == 1 && Arg.pack_begin()->isPackExpansion());
> +        Arg = *Arg.pack_begin();
> +      }
> +      PArgList.addArgument(getTrivialTemplateArgumentLoc(
> +          Arg, QualType(), P->getParam(I)->getLocation()));
> +    }
> +    PArgs.clear();
> +
> +    // C++1z [temp.arg.template]p3:
> +    //   If the rewrite produces an invalid type, then P is not at least as
> +    //   specialized as A.
> +    if (CheckTemplateArgumentList(AArg, Loc, PArgList, false, PArgs) ||
> +        Trap.hasErrorOccurred())
> +      return false;
> +  }
> +
> +  QualType AType = Context.getTemplateSpecializationType(X, AArgs);
> +  QualType PType = Context.getTemplateSpecializationType(X, PArgs);
> +
> +  SmallVector<DeducedTemplateArgument, 4> Deduced;
> +  Deduced.resize(A->size());

Looks like Deduced is unused here!

> +
> +  //   ... the function template corresponding to P is at least as specialized
> +  //   as the function template corresponding to A according to the partial
> +  //   ordering rules for function templates.
> +  TemplateDeductionInfo Info(Loc, A->getDepth());
> +  return isAtLeastAsSpecializedAs(*this, PType, AType, AArg, Info);
> +}
> +
> static void
> MarkUsedTemplateParameters(ASTContext &Ctx,
>                            const TemplateArgument &TemplateArg,
> 
> Modified: cfe/trunk/test/SemaTemplate/temp_arg_template.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaTemplate/temp_arg_template.cpp?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/test/SemaTemplate/temp_arg_template.cpp (original)
> +++ cfe/trunk/test/SemaTemplate/temp_arg_template.cpp Sat Dec 31 15:41:23 2016
> @@ -6,11 +6,12 @@ template<template<typename T> class X> s
> 
> template<template<typename T, int I> class X> struct B; // expected-note{{previous template template parameter is here}}
> 
> -template<template<int I> class X> struct C;  // expected-note{{previous non-type template parameter with type 'int' is here}}
> +template<template<int I> class X> struct C;  // expected-note 2{{previous non-type template parameter with type 'int' is here}}
> 
> template<class> struct X; // expected-note{{too few template parameters in template template argument}}
> template<int N> struct Y; // expected-note{{template parameter has a different kind in template argument}}
> template<long N> struct Ylong; // expected-note{{template non-type parameter has a different type 'long' in template argument}}
> +template<const int &N> struct Yref; // expected-note{{template non-type parameter has a different type 'const int &' in template argument}}
> 
> namespace N {
>   template<class> struct Z;
> @@ -27,6 +28,7 @@ A<TooMany> *a5; // expected-error{{templ
> B<X> *a6; // expected-error{{template template argument has different template parameters than its corresponding template template parameter}}
> C<Y> *a7;
> C<Ylong> *a8; // expected-error{{template template argument has different template parameters than its corresponding template template parameter}}
> +C<Yref> *a9; // expected-error{{template template argument has different template parameters than its corresponding template template parameter}}
> 
> template<typename T> void f(int);
> 
> 
> Added: cfe/trunk/test/SemaTemplate/temp_arg_template_cxx1z.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaTemplate/temp_arg_template_cxx1z.cpp?rev=290792&view=auto
> ==============================================================================
> --- cfe/trunk/test/SemaTemplate/temp_arg_template_cxx1z.cpp (added)
> +++ cfe/trunk/test/SemaTemplate/temp_arg_template_cxx1z.cpp Sat Dec 31 15:41:23 2016
> @@ -0,0 +1,102 @@
> +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++1z -frelaxed-template-template-args %s
> +
> +// expected-note at temp_arg_template_cxx1z.cpp:* 1+{{}}
> +
> +template<template<int> typename> struct Ti;
> +template<template<int...> typename> struct TPi;
> +template<template<int, int...> typename> struct TiPi;
> +template<template<int..., int...> typename> struct TPiPi; // FIXME: Why is this not ill-formed?
> +
> +template<typename T, template<T> typename> struct tT0;
> +template<template<typename T, T> typename> struct Tt0;
> +
> +template<template<typename> typename> struct Tt;
> +template<template<typename, typename...> typename> struct TtPt;
> +
> +template<int> struct i;
> +template<int, int = 0> struct iDi;
> +template<int, int> struct ii;
> +template<int...> struct Pi;
> +template<int, int, int...> struct iiPi;
> +
> +template<int, typename = int> struct iDt;
> +template<int, typename> struct it;
> +
> +template<typename T, T v> struct t0;
> +
> +template<typename...> struct Pt;
> +
> +namespace IntParam {
> +  using ok = Pt<Ti<i>,
> +        Ti<iDi>,
> +        Ti<Pi>,
> +        Ti<iDt>>;
> +  using err1 = Ti<ii>; // expected-error {{different template parameters}}
> +  using err2 = Ti<iiPi>; // expected-error {{different template parameters}}
> +  using err3 = Ti<t0>; // expected-error {{different template parameters}}
> +  using err4 = Ti<it>; // expected-error {{different template parameters}}
> +}
> +
> +// These are accepted by the backwards-compatibility "parameter pack in
> +// parameter matches any number of parameters in arguments" rule.
> +namespace IntPackParam {
> +  using ok = TPi<Pi>;
> +  using ok_compat = Pt<TPi<i>, TPi<iDi>, TPi<ii>, TPi<iiPi>>;
> +  using err1 = TPi<t0>; // expected-error {{different template parameters}}
> +  using err2 = TPi<iDt>; // expected-error {{different template parameters}}
> +  using err3 = TPi<it>; // expected-error {{different template parameters}}
> +}
> +
> +namespace IntAndPackParam {
> +  using ok = TiPi<Pi>;
> +  using ok_compat = Pt<TiPi<ii>, TiPi<iDi>, TiPi<iiPi>>;
> +  using err = TiPi<iDi>;
> +}
> +
> +namespace DependentType {
> +  using ok = Pt<tT0<int, i>, tT0<int, iDi>>;
> +  using err1 = tT0<int, ii>; // expected-error {{different template parameters}}
> +  using err2 = tT0<short, i>; // FIXME: should this be OK?
> +  using err2a = tT0<long long, i>; // FIXME: should this be OK (if long long is larger than int)?
> +  using err2b = tT0<void*, i>; // expected-error {{different template parameters}}
> +  using err3 = tT0<short, t0>; // expected-error {{different template parameters}}
> +
> +  using ok2 = Tt0<t0>;
> +  using err4 = Tt0<it>; // expected-error {{different template parameters}}
> +}
> +
> +namespace Auto {
> +  template<template<int> typename T> struct TInt {};
> +  template<template<int*> typename T> struct TIntPtr {};
> +  template<template<auto> typename T> struct TAuto {};
> +  template<template<auto*> typename T> struct TAutoPtr {};
> +  template<auto> struct Auto;
> +  template<auto*> struct AutoPtr;
> +  template<int> struct Int;
> +  template<int*> struct IntPtr;
> +
> +  TInt<Auto> ia;
> +  TInt<AutoPtr> iap; // FIXME: ill-formed
> +  TInt<Int> ii;
> +  TInt<IntPtr> iip; // expected-error {{different template parameters}}
> +
> +  TIntPtr<Auto> ipa;
> +  TIntPtr<AutoPtr> ipap;
> +  TIntPtr<Int> ipi; // expected-error {{different template parameters}}
> +  TIntPtr<IntPtr> ipip;
> +
> +  TAuto<Auto> aa;
> +  TAuto<AutoPtr> aap; // FIXME: ill-formed
> +  TAuto<Int> ai; // FIXME: ill-formed
> +  TAuto<IntPtr> aip; // FIXME: ill-formed
> +
> +  TAutoPtr<Auto> apa;
> +  TAutoPtr<AutoPtr> apap;
> +  TAutoPtr<Int> api; // FIXME: ill-formed
> +  TAutoPtr<IntPtr> apip; // FIXME: ill-formed
> +
> +  int n;
> +  template<auto A, decltype(A) B = &n> struct SubstFailure;
> +  TInt<SubstFailure> isf; // expected-error {{different template parameters}}
> +  TIntPtr<SubstFailure> ipsf; // expected-error {{different template parameters}}
> +}
> 
> Modified: cfe/trunk/www/cxx_status.html
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/www/cxx_status.html?rev=290792&r1=290791&r2=290792&view=diff
> ==============================================================================
> --- cfe/trunk/www/cxx_status.html (original)
> +++ cfe/trunk/www/cxx_status.html Sat Dec 31 15:41:23 2016
> @@ -733,7 +733,7 @@ as the draft C++1z standard evolves.
>     <tr>
>       <td>Matching template template parameters to compatible arguments</td>
>       <td><a href="http://wg21.link/p0522r0">P0522R0</a></td>
> -      <td class="none" align="center">No <a href="#p0522">(12)</a></td>
> +      <td class="partial" align="center">Partial <a href="#p0522">(12)</a></td>
>     </tr>
>     <tr>
>       <td>Removing deprecated dynamic exception specifications</td>
> @@ -763,8 +763,12 @@ left to right in the callee. As a result
> functions using expression syntax are no longer guaranteed to be destroyed in
> reverse construction order in that ABI.
> </span><br>
> -<span id="p0522">(12): This is the resolution to a Defect Report, so will be
> -applied to all language versions.
> +<span id="p0522">(12): Despite being the the resolution to a Defect Report, this
> +feature is disabled by default in all language versions, and can be enabled
> +explicitly with the flag <tt>-frelaxed-template-template-args</tt>. The change
> +to the standard lacks a corresponding change for template partial ordering,
> +resulting in ambiguity errors for reasonable and previously-valid code. This
> +issue is expected to be rectified soon.
> </span>
> </p>
> </details>
> 
> 
> _______________________________________________
> cfe-commits mailing list
> cfe-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits



More information about the cfe-commits mailing list