[clang] [clang][Sema] Improve template argument deduction diagnostic (PR #122754)

[Vlad Serebrennikov via cfe-commits]

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@@ -649,15 +649,15 @@ namespace cwg241 { // cwg241: 9
     A::g<3>(b);
     C::f<3>(b);
     // expected-error at -1 {{no matching function for call to 'f'}}
-    //   expected-note@#cwg241-C-f {{candidate template ignored: invalid explicitly-specified argument for template parameter 'T'}}
+    //   expected-note@#cwg241-C-f {{candidate template ignored: invalid explicitly-specified argument for template parameter 'T': could not convert '3' from 'int' to class 'T' (expected a class, but got '3')}}
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Endilll wrote:

The newly added diagnostic wording seems confusing to me, but the text in parentheses might be salvageable:
```suggestion
    //   expected-note@#cwg241-C-f {{candidate template ignored: invalid explicitly-specified argument for template parameter 'T': expected a type, but got value '3' (of type 'int'))}}
```

https://github.com/llvm/llvm-project/pull/122754