| Issue |
130362
|
| Summary |
Variadic template template parameter of another template template parameter causes spurious error upon instantiation
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
ednolan
|
Given the following code:
```cpp
template <template <template <typename...> typename> typename>
struct foo {};
template <template <typename> typename>
struct bar {};
using baz = foo<bar>;
```
Clang 20 produces the following error:
```
<source>:1:52: error: too few template parameters in template template parameter redeclaration
1 | template <template <template <typename...> typename> typename>
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
2 | struct foo {};
| ~~~~~~~~~~~~~~
3 |
4 | template <template <typename> typename>
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>:7:17: note: template template argument is incompatible with its corresponding template template parameter
7 | using baz = foo<bar>;
| ^
<source>:4:39: note: template parameter is declared here
4 | template <template <typename> typename>
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
<source>:7:17: note: template template argument is incompatible with its corresponding template template parameter
7 | using baz = foo<bar>;
| ^
<source>:1:62: note: template parameter is declared here
1 | template <template <template <typename...> typename> typename>
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
```
Compiler explorer link: https://godbolt.org/z/7q7n459E1
This code was accepted by Clang 19, and is accepted by GCC, MSVC, and EDG.
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