| Issue |
134519
|
| Summary |
[Clang] Spurious error when template template parameter substituted using a class template with an NTTP whose type is its first template parameter
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
ednolan
|
Given the following code:
```cpp
template <typename Foo, template <typename, Foo> typename>
class Bar {};
template <typename Foo, Foo>
class Quux : public Bar<Foo, Quux> {};
static_assert(sizeof(Quux<int, 0>));
```
Clang 20.1.2 and trunk produce the following error:
```
foo.cpp:4:20: error: conflicting deduction 'type-parameter-0-0' against 'int' for parameter
4 | template <typename Foo, Foo>
| ^
foo.cpp:5:30: note: template template argument has different template parameters than its corresponding template template parameter
5 | class Quux : public Bar<Foo, Quux> {};
| ^
foo.cpp:1:58: note: previous template template parameter is here
1 | template <typename Foo, template <typename, Foo> typename>
| ~~~~~~~~~~~~~~~~~~~~~~~~ ^
foo.cpp:7:15: note: in instantiation of template class 'Quux<int, 0>' requested here
7 | static_assert(sizeof(Quux<int, 0>));
| ^
1 error generated.
```
Compiler explorer link: https://godbolt.org/z/5Mar9h7zE
The code is accepted by Clang 19, GCC, MSVC, and EDG.
Bisecting shows that this started with 28ad8978ee2054298d4198bf10c8cb68730af037.
CC @mizvekov
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