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

[Haojian Wu via cfe-commits]

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@@ -12114,6 +12115,35 @@ static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
     return;
   }
 
+  // If this is an implicit deduction guide against an implicitly defined
+  // constructor, add a note for it. Neither these deduction guides nor their
+  // corresponding constructors are explicitly spelled in the source code,
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hokein wrote:

Any reason to filter out the "explicit constructor" case? We still synthesize a deduction guide from a constructor, and they are not identical, e.g. its template parameters is a combination of template parameters of the class and template parameters of the corresponding constructor. I think it is useful to print them as well.

I think a simple model here would be that we always print synthesized deduction guides (this covers the using-alias case.)

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