From 3ffd3e4bdb9208bbfa16a4029680f6f42f6bd703 Mon Sep 17 00:00:00 2001 From: Matheus Izvekov Date: Sat, 4 Oct 2025 21:51:38 -0300 Subject: [PATCH] [clang] don't print redundant context notes when instantiating alias templates The redundant notes were introduced with the workaround for finding the template instantiationa args for lambdas inside template type aliases. This removes the notes for the cases where we are simply instantiating an outer template, and when diagnosing uses of the alias template. Also adds comments calling the workaround explicitly. --- clang/lib/Sema/SemaTemplate.cpp | 13 +++++++++---- clang/lib/Sema/SemaTemplateInstantiate.cpp | 6 ++++++ clang/lib/Sema/SemaTemplateInstantiateDecl.cpp | 18 ++++++++++-------- .../SemaTemplate/alias-template-deprecated.cpp | 17 ++++++----------- clang/test/SemaTemplate/alias-templates.cpp | 8 ++++++++ 5 files changed, 39 insertions(+), 23 deletions(-) diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp index dcf2876af81fc..419f3e1ad30ed 100644 --- a/clang/lib/Sema/SemaTemplate.cpp +++ b/clang/lib/Sema/SemaTemplate.cpp @@ -3822,14 +3822,19 @@ QualType Sema::CheckTemplateIdType(ElaboratedTypeKeyword Keyword, AliasTemplate->getTemplateParameters()->getDepth()); LocalInstantiationScope Scope(*this); - InstantiatingTemplate Inst( - *this, /*PointOfInstantiation=*/TemplateLoc, - /*Entity=*/AliasTemplate, - /*TemplateArgs=*/TemplateArgLists.getInnermost()); // Diagnose uses of this alias. (void)DiagnoseUseOfDecl(AliasTemplate, TemplateLoc); + // FIXME: The TemplateArgs passed here are not used for the context note, + // nor they should, because this note will be pointing to the specialization + // anyway. These arguments are needed for a hack for instantiating lambdas + // in the pattern of the alias. In getTemplateInstantiationArgs, these + // arguments will be used for collating the template arguments needed to + // instantiate the lambda. + InstantiatingTemplate Inst(*this, /*PointOfInstantiation=*/TemplateLoc, + /*Entity=*/AliasTemplate, + /*TemplateArgs=*/CTAI.SugaredConverted); if (Inst.isInvalid()) return QualType(); diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp index 1f762ca64c05f..7b05e4cf1385f 100644 --- a/clang/lib/Sema/SemaTemplateInstantiate.cpp +++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp @@ -1271,6 +1271,12 @@ void Sema::PrintInstantiationStack(InstantiationContextDiagFuncRef DiagFunc) { PDiag(diag::note_building_deduction_guide_here)); break; case CodeSynthesisContext::TypeAliasTemplateInstantiation: + // Workaround for a workaround: don't produce a note if we are merely + // instantiating some other template which contains this alias template. + // This would be redundant either with the error itself, or some other + // context note attached to it. + if (Active->NumTemplateArgs == 0) + break; DiagFunc(Active->PointOfInstantiation, PDiag(diag::note_template_type_alias_instantiation_here) << cast(Active->Entity) diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp index e2dc70360506e..3819f775811e5 100644 --- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp +++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp @@ -1580,17 +1580,19 @@ Decl *TemplateDeclInstantiator::InstantiateTypeAliasTemplateDecl( if (!InstParams) return nullptr; - TypeAliasDecl *Pattern = D->getTemplatedDecl(); - Sema::InstantiatingTemplate InstTemplate( - SemaRef, D->getBeginLoc(), D, - D->getTemplateDepth() >= TemplateArgs.getNumLevels() - ? ArrayRef() - : (TemplateArgs.begin() + TemplateArgs.getNumLevels() - 1 - - D->getTemplateDepth()) - ->Args); + // FIXME: This is a hack for instantiating lambdas in the pattern of the + // alias. We are not really instantiating the alias at its template level, + // that only happens in CheckTemplateId, this is only for outer templates + // which contain it. In getTemplateInstantiationArgs, the template arguments + // used here would be used for collating the template arguments needed to + // instantiate the lambda. Pass an empty argument list, so this workaround + // doesn't get confused if there is an outer alias being instantiated. + Sema::InstantiatingTemplate InstTemplate(SemaRef, D->getBeginLoc(), D, + ArrayRef()); if (InstTemplate.isInvalid()) return nullptr; + TypeAliasDecl *Pattern = D->getTemplatedDecl(); TypeAliasTemplateDecl *PrevAliasTemplate = nullptr; if (getPreviousDeclForInstantiation(Pattern)) { DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName()); diff --git a/clang/test/SemaTemplate/alias-template-deprecated.cpp b/clang/test/SemaTemplate/alias-template-deprecated.cpp index 7418e222bcfc5..6dffd37d14909 100644 --- a/clang/test/SemaTemplate/alias-template-deprecated.cpp +++ b/clang/test/SemaTemplate/alias-template-deprecated.cpp @@ -46,23 +46,19 @@ using UsingInstWithCPPAttr [[deprecated("Do not use this")]] = NoAttr; void bar() { NoAttr obj; // Okay - // expected-warning@+2 {{'UsingWithAttr' is deprecated}} - // expected-note@+1 {{in instantiation of template type alias 'UsingWithAttr' requested here}} + // expected-warning@+1 {{'UsingWithAttr' is deprecated}} UsingWithAttr objUsingWA; - // expected-warning@+2 {{'UsingWithAttr' is deprecated}} - // expected-note@+1 {{in instantiation of template type alias 'UsingWithAttr' requested here}} + // expected-warning@+1 {{'UsingWithAttr' is deprecated}} NoAttr> s; // expected-note@+1 {{'DepInt' has been explicitly marked deprecated here}} using DepInt [[deprecated]] = int; - // expected-warning@+3 {{'UsingWithAttr' is deprecated}} - // expected-warning@+2 {{'DepInt' is deprecated}} - // expected-note@+1 {{in instantiation of template type alias 'UsingWithAttr' requested here}} + // expected-warning@+2 {{'UsingWithAttr' is deprecated}} + // expected-warning@+1 {{'DepInt' is deprecated}} using X = UsingWithAttr; - // expected-warning@+2 {{'UsingWithAttr' is deprecated}} - // expected-note@+1 {{in instantiation of template type alias 'UsingWithAttr' requested here}} + // expected-warning@+1 {{'UsingWithAttr' is deprecated}} UsingWithAttr().foo(); // expected-warning@+1 {{'UsingInstWithAttr' is deprecated}} @@ -74,8 +70,7 @@ void bar() { // expected-warning@+1 {{'UsingTDWithAttr' is deprecated}} UsingTDWithAttr objUTDWA; - // expected-warning@+2 {{'UsingWithCPPAttr' is deprecated}} - // expected-note@+1 {{in instantiation of template type alias 'UsingWithCPPAttr' requested here}} + // expected-warning@+1 {{'UsingWithCPPAttr' is deprecated}} UsingWithCPPAttr objUsingWCPPA; // expected-warning@+1 {{'UsingInstWithCPPAttr' is deprecated: Do not use this}} diff --git a/clang/test/SemaTemplate/alias-templates.cpp b/clang/test/SemaTemplate/alias-templates.cpp index ab5cad72faf1b..09fe72e9c7db0 100644 --- a/clang/test/SemaTemplate/alias-templates.cpp +++ b/clang/test/SemaTemplate/alias-templates.cpp @@ -312,3 +312,11 @@ namespace resolved_nttp { using TC2 = decltype(C::p); // expected-note {{instantiation of}} } + +namespace OuterSubstFailure { + template struct A { + template using B = T&; + // expected-error@-1 {{cannot form a reference to 'void'}} + }; + template struct A; // expected-note {{requested here}} +} // namespace OuterSubstFailure