================
@@ -1604,3 +1604,59 @@ void Sema::DeclareImplicitDeductionGuides(TemplateDecl
*Template,
SavedContext.pop();
}
+
+TypeAliasTemplateDecl *Sema::BuildAliasForCTADFromTypeTemplateParameter(
+ TemplateTemplateParmDecl *D, TemplateName Replacement, SourceLocation Loc)
{
+
+ // [C++26] [over.match.class.deduct]p3
+ // When resolving a placeholder for a deduced class type where the
+ // template-name designates a type template template parameter P, let A be an
+ // alias template whose template parameter list is that of P and whose
+ // defining-type-id designates the type template template argument with a
+ // simpletemplate-id in which the template-argument-list consists of a list
of
+ // identifiers naming each template-parameter of P, with the argument being a
+ // pack expansion if the template-parameter is a pack. A is then used instead
+ // of the original template-name to resolve the placeholder
+
+ LocalInstantiationScope Scope(SemaRef);
+
+ auto &AST = SemaRef.getASTContext();
+ auto *Func = cast<NamedDecl>(CurContext);
+ auto *Ctx = CurContext->getParent();
+
+ MultiLevelTemplateArgumentList MTAL =
+ SemaRef.getTemplateInstantiationArgs(Func);
+ llvm::SmallVector<NamedDecl *> Parameters;
+ llvm::SmallVector<TemplateArgument> Args;
+ for (NamedDecl *P : D->getTemplateParameters()->asArray()) {
+ auto [Depth, Index] = getDepthAndIndex(P);
+ NamedDecl *NewParam =
+ transformTemplateParameter(*this, Ctx, P, MTAL, Index, Depth - 1);
+ if (!NewParam)
+ return nullptr;
+ Parameters.push_back(NewParam);
+ Args.push_back(SemaRef.Context.getInjectedTemplateArg(NewParam));
+ }
+
+ auto *ParamList =
+ TemplateParameterList::Create(AST, SourceLocation(), SourceLocation(),
+ Parameters, SourceLocation(), nullptr);
+
+ QualType Type = AST.getCanonicalType(AST.getTemplateSpecializationType(
+ ElaboratedTypeKeyword::Class, Replacement, Args, {}));
+
+ auto *Alias = TypeAliasDecl::Create(AST, Ctx, Loc, SourceLocation(), nullptr,
+ AST.getTrivialTypeSourceInfo(Type));
+ Alias->setImplicit(true);
+
+ auto *Template = TypeAliasTemplateDecl::Create(
+ AST, Ctx, Loc, Alias->getDeclName(), ParamList, Alias);
+
+ Alias->setDescribedAliasTemplate(Template);
+
+ Template->setImplicit(true);
+ Template->setLexicalDeclContext(Alias->getDeclContext());
+ Ctx->addDecl(Template);
+
+ return Template;
----------------
mizvekov wrote:
I'd expect the quoted paragraph to just be a wording artifact, it would be
inefficient as an implementation strategy if we had to synthesize two
declarations for each of these uses. But then again I am not sure what it fixes.
https://github.com/llvm/llvm-project/pull/191409
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