| Issue |
136624
|
| Summary |
Incorrect name qualification in AST / diagnostics for alias CTAD
|
| Labels |
clang:frontend
|
| Assignees |
mizvekov
|
| Reporter |
mizvekov
|
Consider this example: https://compiler-explorer.com/z/bGqdsa3qc
```C++
template<typename U> struct A {
U t;
};
template<typename V> A(V) -> A<V>;
namespace foo {
template<class Y> using Alias = A<Y>;
}
foo::Alias t = 0;
```
Produces:
```
error: no viable conversion from 'int' to 'foo::A<int>' (aka 'A<int>')
```
Note that the `foo::` qualification is applied to Alias in the source code, which is in that namespace, but
on the AST (and consequently in the diagnostic) it gets applied to `A` , where it cannot be found.
The problem here is many fold:
1) We have an elaborated type including `foo::` over the deduced template specialization (DTST), which names `foo::Alias`.
2) However, when printing a DTST which has already been deduced, we choose to print it as the deduced type instead, probably for diagnostics reasons (although this is wrong for -ast-print, and we don't control this with a policy).
3) For alias CTAD, we don't build a guide which actually contains the alias template specialization `Alias<int>`, instead the guide contains `A<int>`.
I see a couple of solutions:
* If we fix 3, then this would print as intended: `'foo::Alias<int>' (aka 'A<int>')`
* We could stop doing 2, then this would print as `'foo::Alias' (aka 'A<int>')`.
The first type does not include much information, as 2) probably intended to avoid, but it is correctly qualified, and then the 'aka' gives the missing information.
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