[clang] [clang] Implement P2582R1: CTAD from inherited constructors (PR #98788)

[via cfe-commits]

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@@ -936,19 +940,21 @@ Expr *buildIsDeducibleConstraint(Sema &SemaRef,
         Context.DeclarationNames.getCXXDeductionGuideName(AliasTemplate));
   };
 
+  TemplateDecl *TD = DeducingTemplate ? DeducingTemplate : AliasTemplate;
+
   SmallVector<TypeSourceInfo *> IsDeducibleTypeTraitArgs = {
       Context.getTrivialTypeSourceInfo(
           Context.getDeducedTemplateSpecializationType(
-              TemplateName(AliasTemplate), /*DeducedType=*/QualType(),
+              TemplateName(TD), /*DeducedType=*/QualType(),
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antangelo wrote:

Based on the current writing of the standard I think we should be copying all of the constraints over, including the deducible constraint. However, it's probably not the intent to break existing code as in the above example.

I have filed https://github.com/cplusplus/CWG/issues/607 . Is the best course of action in the meantime to update the implementation in this PR to accept that above code, or leave it as breaking until CWG responds?

https://github.com/llvm/llvm-project/pull/98788