[clang] [Clang] Clarify diagnostic notes for implicitly generated deduction guides (PR #96084)

[Haojian Wu via cfe-commits]

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@@ -12078,6 +12079,43 @@ static void DiagnoseFailedExplicitSpec(Sema &S, OverloadCandidate *Cand) {
       << (ES.getExpr() ? ES.getExpr()->getSourceRange() : SourceRange());
 }
 
+static void NoteImplicitDeductionGuide(Sema &S, CXXDeductionGuideDecl *DG) {
+  // We want to always print synthesized deduction guides for type aliases.
+  // They would retain the explicit bit of the corresponding constructor.
+  TemplateDecl *OriginTemplate =
+      DG->getDeclName().getCXXDeductionGuideTemplate();
+  if (!DG->isImplicit() && (!OriginTemplate || !OriginTemplate->isTypeAlias()))
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hokein wrote:

nit: it's easier to read if we write it as `if (... && !(OriginTemplate && OriginTemplate->isTypeAlias()))`.

https://github.com/llvm/llvm-project/pull/96084