https://github.com/Dash198 created https://github.com/llvm/llvm-project/pull/235456
This PR builds on the approach explored in #142278 to address incorrect error recovery when a class definition appears within an alias template. Fixes #91564 Initial attempt to change the underlying type of the invalid `TemplateTypeParmDecl` to `int` triggered an assertion as template type parameter declarations are expected to retain their `TemplateTypeParmType` representation. Instead, the declarations in the template-parameter scope are invalidated when the invalid class definition parsing begins and then any subsequent references to the invalid template type parameters are recovered as `int` explicitly in `Sema::getTypeName`. Note on AI assistance: An LLM was used to help diagnose the crash encountered during the initial approach, understand the relevant Clang codebase, and trace the source files and code paths involved in the issue. >From b47f903709c2f400ee09bdaf505d349b638cce2b Mon Sep 17 00:00:00 2001 From: Dash198 <[email protected]> Date: Sun, 25 Oct 2026 19:33:41 +0530 Subject: [PATCH] [Clang] Improve error recovery for invalid alias templates --- clang/lib/Sema/SemaDecl.cpp | 19 ++++++++++++++++++- .../SemaCXX/concept-crash-on-diagnostic.cpp | 15 +++++++++++++++ 2 files changed, 33 insertions(+), 1 deletion(-) diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp index 6aae0b57df0f99..037a74af032755 100644 --- a/clang/lib/Sema/SemaDecl.cpp +++ b/clang/lib/Sema/SemaDecl.cpp @@ -544,11 +544,18 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc, SS ? SS->getWithLocInContext(Context) : NestedNameSpecifierLoc(), NameLoc); } else { - T = Context.getTypeDeclType(TD); + // For invalid TTP mark them as integers to avoid incorrect error recovery + if(auto *TTP = dyn_cast<TemplateTypeParmDecl>(TD); + TTP && TTP->isInvalidDecl()) + T = Context.IntTy; + else + T = Context.getTypeDeclType(TD); if (!WantNontrivialTypeSourceInfo) return ParsedType::make(T); if (isa<ObjCTypeParamType>(T)) TLB.push<ObjCTypeParamTypeLoc>(T).setNameLoc(NameLoc); + else if (T->isBuiltinType()) + TLB.pushTrivial(Context, T, NameLoc); else TLB.pushTypeSpec(T).setNameLoc(NameLoc); } @@ -19324,6 +19331,16 @@ void Sema::ActOnTagStartDefinition(Scope *S, Decl *TagD) { AdjustDeclIfTemplate(TagD); TagDecl *Tag = cast<TagDecl>(TagD); + // If class is defined within the alias template then mark the parameters of + // the template as invalid first to avoid incorrect error recovery. + if (Scope *Parent = S->getParent(); + Parent && Parent->isTypeAliasScope() && + Parent->isTemplateParamScope()){ + for (Decl *D : Parent->decls()){ + D->setInvalidDecl(); + } + } + // Enter the tag context. PushDeclContext(S, Tag); diff --git a/clang/test/SemaCXX/concept-crash-on-diagnostic.cpp b/clang/test/SemaCXX/concept-crash-on-diagnostic.cpp index a021267b45d2fe..1083adaf1ca480 100644 --- a/clang/test/SemaCXX/concept-crash-on-diagnostic.cpp +++ b/clang/test/SemaCXX/concept-crash-on-diagnostic.cpp @@ -86,3 +86,18 @@ static_assert(requires { requires bar<int>; }); // expected-note@-5 {{because 'bar<int>' would be invalid}} } + +namespace GH91564 { + +template <class T> using A = struct B { // expected-error {{'GH91564::B' cannot be defined in a type alias template}} + template <class> void f() requires (T()); // expected-error {{atomic constraint must be of type 'bool' (found 'int')}} expected-note {{explicit instantiation refers here}} +}; +template void B::f<void>(); // expected-error {{explicit instantiation of undefined function template 'f'}} + +template <class T> using C = struct D { // expected-error {{'GH91564::D' cannot be defined in a type alias template}} + using E = T; +}; +template <class> void g() requires (D::E()); // expected-error {{atomic constraint must be of type 'bool' (found 'D::E' (aka 'int'))}} expected-note {{explicit instantiation refers here}} +template void g<void>(); // expected-error {{explicit instantiation of undefined function template 'g'}} + +} // namespace GH91564 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
