| Issue |
159663
|
| Summary |
[Clang] Lambda in a `decltype()` in template parameters causing incorrect type mismatches
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
Metadorius
|
The following code (minimal repro. example)
```cpp
template <typename T>
struct X {};
template <typename>
using DistinctCollector = X<decltype([]{})>;
DistinctCollector<int*> getCellSpreadItems()
{
DistinctCollector<int*> set;
return set;
}
int main() { getCellSpreadItems(); }
```
https://godbolt.org/z/obMWeKjKr
fails with
`error: no viable conversion from returned value of type 'DistinctCollector<...>' to function return type 'DistinctCollector<...>'`
The same error is not observed on GCC or MSVC (in conformance mode, iow `/permissive-`) compilers.
If you use
```cpp
auto getCellSpreadItems()
{
DistinctCollector<int*> set;
return set;
}
```
https://godbolt.org/z/4fnocEr13
it works.
Per @Sirraide on Discord:
> Looking at the AST, it seems like we’re instantiating that template twice; so it seems what it’s complaining about is that the two instances of `DistinctCollector<T>` are ... not the same type, which er, is not quite right
> There are some things we try to diagnose even if the function is still dependent, but usually you need to instantiate it yes, and this also looks like a problem specifically w/ instantiation
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