================
@@ -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
----------------
cor3ntin wrote:
```suggestion
// Then we assume the template arguments of the using alias
// declaration are necessary for constraint instantiation. We have to do
```
https://github.com/llvm/llvm-project/pull/82310
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