[clang] [Clang][Sema] Fix the lambda call expression inside of a type alias declaration (PR #82310)
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Tue Feb 20 01:26:39 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Younan Zhang (zyn0217)
<details>
<summary>Changes</summary>
This patch attempts to fix the lambda call expression inside of a type alias declaration from two aspects:
1. Defer the lambda call expression building until after we have sufficient template arguments. This avoids the overeager (and often wrong) semantic checking before the type alias instantiation.
2. Properly obtain template arguments involving a template type alias for constraint checking.
It is unfortunate that a `TypeAliasTemplateDecl` (or a `TypeAliasDecl`) is never a `DeclContext`, nor does it have an associated specialization Decl from which we could collect these template arguments. Thus, I added a new CodeSynthesisContext to record template arguments for alias declarations.
Fixes https://github.com/llvm/llvm-project/issues/70601
Fixes https://github.com/llvm/llvm-project/issues/76674
Fixes https://github.com/llvm/llvm-project/issues/79555
Fixes https://github.com/llvm/llvm-project/issues/81145
Note that this doesn't involve the fix for https://github.com/llvm/llvm-project/issues/23317. That seems different, and I'd like to leave it as a follow-up.
---
Full diff: https://github.com/llvm/llvm-project/pull/82310.diff
10 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+5)
- (modified) clang/include/clang/AST/DeclCXX.h (+4)
- (modified) clang/include/clang/Sema/Sema.h (+9)
- (modified) clang/lib/Frontend/FrontendActions.cpp (+2)
- (modified) clang/lib/Sema/SemaConcept.cpp (+8-4)
- (modified) clang/lib/Sema/SemaTemplate.cpp (+7-3)
- (modified) clang/lib/Sema/SemaTemplateInstantiate.cpp (+95-3)
- (modified) clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (+5)
- (modified) clang/lib/Sema/TreeTransform.h (+31)
- (added) clang/test/SemaTemplate/alias-template-with-lambdas.cpp (+82)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 649ad655905af2..7988912faa2075 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -267,6 +267,11 @@ Bug Fixes to C++ Support
was only accepted at namespace scope but not at local function scope.
- Clang no longer tries to call consteval constructors at runtime when they appear in a member initializer.
(`#782154 <https://github.com/llvm/llvm-project/issues/82154>`_`)
+- Clang now supports direct lambda calls inside of a type alias template declarations.
+ This addresses (`#70601 <https://github.com/llvm/llvm-project/issues/70601>`_),
+ (`#76674 <https://github.com/llvm/llvm-project/issues/76674>`_),
+ (`#79555 <https://github.com/llvm/llvm-project/issues/79555>`_),
+ (`#81145 <https://github.com/llvm/llvm-project/issues/81145>`_), and so on.
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
index 9cebaff63bb0db..7aed4d5cbc002e 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -1869,6 +1869,10 @@ class CXXRecordDecl : public RecordDecl {
DL.MethodTyInfo = TS;
}
+ void setLambdaDependencyKind(unsigned Kind) {
+ getLambdaData().DependencyKind = Kind;
+ }
+
void setLambdaIsGeneric(bool IsGeneric) {
assert(DefinitionData && DefinitionData->IsLambda &&
"setting lambda property of non-lambda class");
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index e9cd42ae777df5..5847b0301a4ca4 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -9622,6 +9622,9 @@ class Sema final {
/// We are building deduction guides for a class.
BuildingDeductionGuides,
+
+ /// We are instantiating a type alias template declaration.
+ TypeAliasTemplateInstantiation,
} Kind;
/// Was the enclosing context a non-instantiation SFINAE context?
@@ -9812,6 +9815,12 @@ class Sema final {
FunctionDecl *Entity, ExceptionSpecification,
SourceRange InstantiationRange = SourceRange());
+ /// Note that we are instantiating a type alias template declaration.
+ InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
+ TypeAliasTemplateDecl *Template,
+ ArrayRef<TemplateArgument> TemplateArgs,
+ SourceRange InstantiationRange = SourceRange());
+
/// Note that we are instantiating a default argument in a
/// template-id.
InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
diff --git a/clang/lib/Frontend/FrontendActions.cpp b/clang/lib/Frontend/FrontendActions.cpp
index b9ed5dedfa4223..43d6e2230fb129 100644
--- a/clang/lib/Frontend/FrontendActions.cpp
+++ b/clang/lib/Frontend/FrontendActions.cpp
@@ -426,6 +426,8 @@ class DefaultTemplateInstCallback : public TemplateInstantiationCallback {
return "BuildingBuiltinDumpStructCall";
case CodeSynthesisContext::BuildingDeductionGuides:
return "BuildingDeductionGuides";
+ case Sema::CodeSynthesisContext::TypeAliasTemplateInstantiation:
+ return "TypeAliasTemplateInstantiation";
}
return "";
}
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 2878e4d31ee8fe..5908b941f21a7d 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -614,10 +614,14 @@ bool Sema::SetupConstraintScope(
// reference the original primary template.
// We walk up the instantiated template chain so that nested lambdas get
// handled properly.
- for (FunctionTemplateDecl *FromMemTempl =
- PrimaryTemplate->getInstantiatedFromMemberTemplate();
- FromMemTempl;
- FromMemTempl = FromMemTempl->getInstantiatedFromMemberTemplate()) {
+ // Note that we shall not collect instantiated parameters from
+ // 'intermediate' transformed function templates but the primary template
+ // for which we have built up the template arguments relative to. Otherwise,
+ // we may have mismatched template parameter depth!
+ if (FunctionTemplateDecl *FromMemTempl =
+ PrimaryTemplate->getInstantiatedFromMemberTemplate()) {
+ while (FromMemTempl->getInstantiatedFromMemberTemplate())
+ FromMemTempl = FromMemTempl->getInstantiatedFromMemberTemplate();
if (addInstantiatedParametersToScope(FD, FromMemTempl->getTemplatedDecl(),
Scope, MLTAL))
return true;
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 9e516da2aa27a1..85962afb8899e9 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -4016,9 +4016,13 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
if (Inst.isInvalid())
return QualType();
- CanonType = SubstType(Pattern->getUnderlyingType(),
- TemplateArgLists, AliasTemplate->getLocation(),
- AliasTemplate->getDeclName());
+ InstantiatingTemplate InstTemplate(
+ *this, /*PointOfInstantiation=*/AliasTemplate->getBeginLoc(),
+ /*Template=*/AliasTemplate,
+ /*TemplateArgs=*/TemplateArgLists.getInnermost());
+ CanonType =
+ SubstType(Pattern->getUnderlyingType(), TemplateArgLists,
+ AliasTemplate->getLocation(), AliasTemplate->getDeclName());
if (CanonType.isNull()) {
// If this was enable_if and we failed to find the nested type
// within enable_if in a SFINAE context, dig out the specific
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 371378485626c2..a94b48ecd13ffb 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -282,7 +282,7 @@ Response HandleFunctionTemplateDecl(const FunctionTemplateDecl *FTD,
return Response::ChangeDecl(FTD->getLexicalDeclContext());
}
-Response HandleRecordDecl(const CXXRecordDecl *Rec,
+Response HandleRecordDecl(Sema &SemaRef, const CXXRecordDecl *Rec,
MultiLevelTemplateArgumentList &Result,
ASTContext &Context,
bool ForConstraintInstantiation) {
@@ -313,9 +313,75 @@ Response HandleRecordDecl(const CXXRecordDecl *Rec,
// This is to make sure we pick up the VarTemplateSpecializationDecl that this
// lambda is defined inside of.
- if (Rec->isLambda())
+ if (Rec->isLambda()) {
if (const Decl *LCD = Rec->getLambdaContextDecl())
return Response::ChangeDecl(LCD);
+ // Attempt to retrieve the template arguments for a using alias declaration.
+ // This is necessary for constraint checking, since we always keep
+ // constraints relative to the primary template.
+ if (ForConstraintInstantiation && !SemaRef.CodeSynthesisContexts.empty()) {
+ for (auto &CSC : llvm::reverse(SemaRef.CodeSynthesisContexts)) {
+ if (CSC.Kind != Sema::CodeSynthesisContext::SynthesisKind::
+ TypeAliasTemplateInstantiation)
+ continue;
+ auto *TATD = cast<TypeAliasTemplateDecl>(CSC.Entity),
+ *CurrentTATD = TATD;
+ FunctionDecl *LambdaCallOperator = Rec->getLambdaCallOperator();
+ // Retrieve the 'primary' template for a lambda call operator. It's
+ // unfortunate that we only have the mappings of call operators rather
+ // than lambda classes.
+ while (true) {
+ auto *FTD = dyn_cast_if_present<FunctionTemplateDecl>(
+ LambdaCallOperator->getDescribedTemplate());
+ if (FTD && FTD->getInstantiatedFromMemberTemplate()) {
+ LambdaCallOperator =
+ FTD->getInstantiatedFromMemberTemplate()->getTemplatedDecl();
+ } else if (auto *Prev = cast<CXXMethodDecl>(LambdaCallOperator)
+ ->getInstantiatedFromMemberFunction())
+ LambdaCallOperator = Prev;
+ else
+ break;
+ }
+ // Same applies for type alias Decl. We perform this to obtain the
+ // "canonical" template parameter depths.
+ while (TATD->getInstantiatedFromMemberTemplate())
+ TATD = TATD->getInstantiatedFromMemberTemplate();
+ // Tell if we're currently inside of a lambda expression that is
+ // surrounded by a using alias declaration. e.g.
+ // template <class> using type = decltype([](auto) { ^ }());
+ // By checking if:
+ // 1. The lambda expression and the using alias declaration share the
+ // same declaration context.
+ // 2. They have the same template depth.
+ // Then we assume the template arguments from the using alias
+ // declaration are essential for constraint instantiation. We have to do
+ // so since a TypeAliasTemplateDecl (or a TypeAliasDecl) is never a
+ // DeclContext, nor does it have an associated specialization Decl from
+ // which we could collect these template arguments.
+ if (cast<CXXRecordDecl>(LambdaCallOperator->getDeclContext())
+ ->getTemplateDepth() == TATD->getTemplateDepth() &&
+ getLambdaAwareParentOfDeclContext(LambdaCallOperator) ==
+ TATD->getDeclContext()) {
+ Result.addOuterTemplateArguments(CurrentTATD,
+ CSC.template_arguments(),
+ /*Final=*/false);
+ // Visit the parent of the current type alias declaration rather than
+ // the lambda thereof. We have the following case:
+ // struct S {
+ // template <class> using T = decltype([]<Concept> {} ());
+ // };
+ // void foo() {
+ // S::T var;
+ // }
+ // The instantiated lambda expression (which we're visiting at 'var')
+ // has a function DeclContext 'foo' rather than the Record DeclContext
+ // S. This seems to be an oversight that we may want to set a Sema
+ // Context from the CXXScopeSpec before substituting into T to me.
+ return Response::ChangeDecl(CurrentTATD->getDeclContext());
+ }
+ }
+ }
+ }
return Response::UseNextDecl(Rec);
}
@@ -412,7 +478,8 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
R = HandleFunction(Function, Result, Pattern, RelativeToPrimary,
ForConstraintInstantiation);
} else if (const auto *Rec = dyn_cast<CXXRecordDecl>(CurDecl)) {
- R = HandleRecordDecl(Rec, Result, Context, ForConstraintInstantiation);
+ R = HandleRecordDecl(*this, Rec, Result, Context,
+ ForConstraintInstantiation);
} else if (const auto *CSD =
dyn_cast<ImplicitConceptSpecializationDecl>(CurDecl)) {
R = HandleImplicitConceptSpecializationDecl(CSD, Result);
@@ -469,6 +536,7 @@ bool Sema::CodeSynthesisContext::isInstantiationRecord() const {
case BuildingBuiltinDumpStructCall:
case LambdaExpressionSubstitution:
case BuildingDeductionGuides:
+ case TypeAliasTemplateInstantiation:
return false;
// This function should never be called when Kind's value is Memoization.
@@ -614,6 +682,15 @@ Sema::InstantiatingTemplate::InstantiatingTemplate(
PointOfInstantiation, InstantiationRange, Param, Template,
TemplateArgs) {}
+Sema::InstantiatingTemplate::InstantiatingTemplate(
+ Sema &SemaRef, SourceLocation PointOfInstantiation,
+ TypeAliasTemplateDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
+ SourceRange InstantiationRange)
+ : InstantiatingTemplate(
+ SemaRef, Sema::CodeSynthesisContext::TypeAliasTemplateInstantiation,
+ PointOfInstantiation, InstantiationRange, /*Entity=*/Template,
+ nullptr, TemplateArgs) {}
+
Sema::InstantiatingTemplate::InstantiatingTemplate(
Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateDecl *Template,
NamedDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
@@ -1131,6 +1208,8 @@ void Sema::PrintInstantiationStack() {
Diags.Report(Active->PointOfInstantiation,
diag::note_building_deduction_guide_here);
break;
+ case CodeSynthesisContext::TypeAliasTemplateInstantiation:
+ break;
}
}
}
@@ -1208,6 +1287,7 @@ std::optional<TemplateDeductionInfo *> Sema::isSFINAEContext() const {
break;
case CodeSynthesisContext::Memoization:
+ case CodeSynthesisContext::TypeAliasTemplateInstantiation:
break;
}
@@ -1479,6 +1559,18 @@ namespace {
SubstTemplateTypeParmPackTypeLoc TL,
bool SuppressObjCLifetime);
+ CXXRecordDecl::LambdaDependencyKind
+ ComputeLambdaDependency(LambdaScopeInfo *LSI) {
+ auto &CCS = SemaRef.CodeSynthesisContexts.back();
+ if (CCS.Kind ==
+ Sema::CodeSynthesisContext::TypeAliasTemplateInstantiation) {
+ unsigned TypeAliasDeclDepth = CCS.Entity->getTemplateDepth();
+ if (TypeAliasDeclDepth >= TemplateArgs.getNumSubstitutedLevels())
+ return CXXRecordDecl::LambdaDependencyKind::LDK_AlwaysDependent;
+ }
+ return inherited::ComputeLambdaDependency(LSI);
+ }
+
ExprResult TransformLambdaExpr(LambdaExpr *E) {
LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
Sema::ConstraintEvalRAII<TemplateInstantiator> RAII(*this);
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 9c696e072ba4a7..2d8675690972ff 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1083,6 +1083,11 @@ TemplateDeclInstantiator::VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D) {
return nullptr;
TypeAliasDecl *Pattern = D->getTemplatedDecl();
+ Sema::InstantiatingTemplate InstTemplate(
+ SemaRef, Pattern->getTypeSourceInfo()->getTypeLoc().getBeginLoc(), D,
+ D->getTemplateDepth() >= TemplateArgs.getNumSubstitutedLevels()
+ ? ArrayRef<TemplateArgument>()
+ : TemplateArgs.getInnermost());
TypeAliasTemplateDecl *PrevAliasTemplate = nullptr;
if (getPreviousDeclForInstantiation<TypedefNameDecl>(Pattern)) {
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index a32a585531873a..41633646863536 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -767,6 +767,12 @@ class TreeTransform {
/// the body.
StmtResult SkipLambdaBody(LambdaExpr *E, Stmt *Body);
+ CXXRecordDecl::LambdaDependencyKind
+ ComputeLambdaDependency(LambdaScopeInfo *LSI) {
+ return static_cast<CXXRecordDecl::LambdaDependencyKind>(
+ LSI->Lambda->getLambdaDependencyKind());
+ }
+
QualType TransformReferenceType(TypeLocBuilder &TLB, ReferenceTypeLoc TL);
StmtResult TransformCompoundStmt(CompoundStmt *S, bool IsStmtExpr);
@@ -13905,6 +13911,31 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
/*IsInstantiation*/ true);
SavedContext.pop();
+ // Recompute the dependency of the lambda so that we can defer the lambda call
+ // construction until after we have sufficient template arguments. For
+ // example, template <class> struct S {
+ // template <class U>
+ // using Type = decltype([](U){}(42.0));
+ // };
+ // void foo() {
+ // using T = S<int>::Type<float>;
+ // ^~~~~~
+ // }
+ // We would end up here from instantiating the S<int> as we're ensuring the
+ // completeness. That would make us transform the lambda call expression
+ // despite the fact that we don't see the argument for U yet. We have a
+ // mechanism that circumvents the semantic checking if the CallExpr is
+ // dependent. We can harness that by recomputing the lambda dependency from
+ // the instantiation arguments. I'm putting it here rather than the above
+ // since we can see transformed lambda parameters in case that they're
+ // useful for calculation.
+ DependencyKind = getDerived().ComputeLambdaDependency(&LSICopy);
+ Class->setLambdaDependencyKind(DependencyKind);
+ // Clean up the type cache created previously. Then, we re-create a type for
+ // such Decl with the new DependencyKind.
+ Class->setTypeForDecl(nullptr);
+ getSema().Context.getTypeDeclType(Class);
+
return getSema().BuildLambdaExpr(E->getBeginLoc(), Body.get()->getEndLoc(),
&LSICopy);
}
diff --git a/clang/test/SemaTemplate/alias-template-with-lambdas.cpp b/clang/test/SemaTemplate/alias-template-with-lambdas.cpp
new file mode 100644
index 00000000000000..c3931287cb6404
--- /dev/null
+++ b/clang/test/SemaTemplate/alias-template-with-lambdas.cpp
@@ -0,0 +1,82 @@
+// RUN: %clang_cc1 -std=c++2c -fsyntax-only -verify %s
+namespace lambda_calls {
+
+template <class>
+concept True = true;
+
+template <class>
+concept False = false; // #False
+
+template <class T> struct S {
+ template <class... U> using type = decltype([](U...) {}(U()...));
+ template <class U> using type2 = decltype([](auto) {}(1));
+ template <class U> using type3 = decltype([](True auto) {}(1));
+ template <class>
+ using type4 = decltype([](auto... pack) { return sizeof...(pack); }(1, 2));
+
+ template <class U> using type5 = decltype([](False auto...) {}(1)); // #Type5
+
+ template <class U>
+ using type6 = decltype([]<True> {}.template operator()<char>());
+ template <class U>
+ using type7 = decltype([]<False> {}.template operator()<char>()); // #Type7
+
+ template <class U>
+ using type8 = decltype([]() // #Type8
+ requires(sizeof(U) == 32) // #Type8-requirement
+ {}());
+
+ template <class... U>
+ using type9 = decltype([]<True>(U...) {}.template operator()<char>(U()...));
+ // https://github.com/llvm/llvm-project/issues/76674
+ template <class U>
+ using type10 = decltype([]<class V> { return V(); }.template operator()<U>());
+
+ template <class U> using type11 = decltype([] { return U{}; });
+};
+
+template <class> using Meow = decltype([]<True> {}.template operator()<int>());
+
+template <class... U>
+using MeowMeow = decltype([]<True>(U...) {}.template operator()<char>(U()...));
+
+// https://github.com/llvm/llvm-project/issues/70601
+template <class> using U = decltype([]<True> {}.template operator()<int>());
+
+U<int> foo();
+
+void bar() {
+ using T = S<int>::type<int, int, int>;
+ using T2 = S<int>::type2<int>;
+ using T3 = S<int>::type3<char>;
+ using T4 = S<int>::type4<void>;
+ using T5 = S<int>::type5<void>; // #T5
+ // expected-error@#Type5 {{no matching function for call}}
+ // expected-note@#T5 {{type alias 'type5' requested here}}
+ // expected-note@#Type5 {{constraints not satisfied [with auto:1 = <int>]}}
+ // expected-note@#Type5 {{because 'int' does not satisfy 'False'}}
+ // expected-note@#False {{because 'false' evaluated to false}}
+
+ using T6 = S<int>::type6<void>;
+ using T7 = S<int>::type7<void>; // #T7
+ // expected-error@#Type7 {{no matching member function for call}}
+ // expected-note@#T7 {{type alias 'type7' requested here}}
+ // expected-note@#Type7 {{constraints not satisfied [with $0 = char]}}
+ // expected-note@#Type7 {{because 'char' does not satisfy 'False'}}
+ // expected-note@#False {{because 'false' evaluated to false}}
+
+ using T8 = S<int>::type8<char>; // #T8
+ // expected-error@#Type8 {{no matching function for call}}
+ // expected-note@#T8 {{type alias 'type8' requested here}}
+ // expected-note@#Type8 {{constraints not satisfied}}
+ // expected-note@#Type8-requirement {{because 'sizeof(char) == 32' (1 == 32) evaluated to false}}
+
+ using T9 = S<int>::type9<long, long, char>;
+ using T10 = S<int>::type10<int>;
+ using T11 = S<int>::type11<int>;
+ int x = T11()();
+ using T12 = Meow<int>;
+ using T13 = MeowMeow<char, int, long, unsigned>;
+}
+
+} // namespace lambda_calls
``````````
</details>
https://github.com/llvm/llvm-project/pull/82310
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