Given the following invalid code,
```cpp
template <class T>
struct S {
T *a;
};
S s = {1};
```
we produce such diagnostics currently:
```
<source>:2:8: note: candidate template ignored: could not match 'S<T>' against 'int'
2 | struct S {
| ^
<source>:2:8: note: candidate template ignored: could not match 'T *' against 'int'
```
Which I think is confusing because there's no `S<T>` nor `T *` at the
location it points to. This is because we're deducing the initializer
against implicitly generated deduction guides, and their source
locations just point to the corresponding `RecordDecl`. Hence the
misleading notes.
This patch alleviates the issue by adding extra notes demonstrating
which implicit deduction guide we're deducing against. In other words,
in addition to the note of `could not match 'T *' against 'int'`, we
would also say the implicit deduction guide we're trying to use:
`template <class T> S(T *) -> S<T>`, which looks clearer IMO.
---------
Co-authored-by: Sirraide <aeternalmail@gmail.com>
source location in `ConvertConstructorToDeductionGuideTransform`.
The commit fec471649fffaa3ec44e17801e5c9605825e58bb was reverted by accident in 7415524b45392651969374c067041daa82dc89e7.
Reland it with a testcase.
The most recent declaration of a template as a friend can introduce a
different template parameter depth compared to what we anticipate from a
CTAD guide.
Fixes https://github.com/llvm/llvm-project/issues/86769
