[clang] [Clang][RFC] Do not eat SFINAE diagnostics for explicit template arguments (PR #139066)

[via cfe-commits]

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@@ -12166,6 +12174,15 @@ static void DiagnoseBadDeduction(Sema &S, NamedDecl *Found, Decl *Templated,
              diag::note_ovl_candidate_explicit_arg_mismatch_unnamed)
           << (index + 1);
     }
+
+    if (PartialDiagnosticAt *PDiag = DeductionFailure.getSFINAEDiagnostic()) {
+      unsigned DiagID =
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Sirraide wrote:

> Maybe we should just emit them as errors and leave a TODO for @Sirraide to fix in once they get nested errors to work?

I’ll add this to my ‘list of places where we’d like to be able to nest diagnostics’; hopefully I’ll be able to open a pr for that next week.

https://github.com/llvm/llvm-project/pull/139066