<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/141732>141732</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang] Failed to compile simple and legal code while gcc is ok
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          yaoxinliu
      </td>
    </tr>
</table>

<pre>
    See: [https://godbolt.org/z/GqbzYfa78](https://godbolt.org/z/GqbzYfa78)

```
template<typename T>
concept IsOK =
    []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();

static_assert(IsOK<int>);

int main() {
}
```
**gcc is ok, but clang gives errors as follows:**

> <source>:3:67: error: substitution into constraint expression resulted in a non-constant expression
>     3 |     []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();
>       | ^~~~~~~~~~~~~
> <source>:3:67: note: while checking the satisfaction of nested requirement requested here
>     3 |     []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();
>       | ^~~~~~~~~~~~~
> <source>:3:67: note: in instantiation of requirement here
> 3 |     []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();
>       | ^~~~~~~~~~~~~
> <source>:3:67: note: while checking the satisfaction of nested requirement requested here
> 3 |     []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();
>       | ^~~~~~~~~~~~~
> <source>:3:38: note: while substituting into a lambda expression here
>     3 | []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();
>       | ^
> <source>:3:5: note: while substituting template arguments into constraint expression here
>     3 |     []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> <source>:5:15: note: while checking the satisfaction of concept 'IsOK<int>' requested here
>     5 | static_assert(IsOK<int>);
>       | ^~~~~~~~~
> <source>:3:67: note: subexpression not valid in a constant expression
>     3 |     []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();
>       | ^
> <source>:5:15: error: static assertion failed
>     5 | static_assert(IsOK<int>);
> |               ^~~~~~~~~
> <source>:5:15: note: because 'int' does not satisfy 'IsOK'
> <source>:3:5: note: because '[]<typename U>() -> bool {
> return requires { requires <<error-expression>>; };
> }.template operator()<int>()' evaluated to false
>     3 |     []<typename U> consteval -> bool { return requires { requires sizeof(U) > 1; }; }.template operator()<T>();
>       |     ^
> 2 errors generated.
> Compiler returned: 1
> 
</pre>
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