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

[Haojian Wu via cfe-commits]

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@@ -108,8 +108,11 @@ struct Foo {
   Foo(T const (&)[N]);
 };
 
+// FIXME: Prefer non-canonical template arguments in the deduction guide?
 template <typename X, int Y>
 using Bar = Foo<X, sizeof(X)>; // expected-note {{candidate template ignored: couldn't infer template argument 'X'}} \
+                               // expected-note {{implicit deduction guide declared as 'template <typename X> Bar(Foo<type-parameter-0-0, sizeof(type-parameter-0-0)>) -> Foo<type-parameter-0-0, sizeof(type-parameter-0-0)>'}} \
+                               // expected-note {{implicit deduction guide declared as 'template <typename X> Bar(const type-parameter-0-0 (&)[sizeof(type-parameter-0-0)]) -> Foo<type-parameter-0-0, sizeof(type-parameter-0-0)>'}} \
                                // expected-note {{candidate template ignored: constraints not satisfied [with X = int]}} \
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hokein wrote:

Right, it is not great for constraints not written in the source code. 

If we print constraints (see my another comment), it will improve the situation.

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