<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/64373>64373</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Fail to compile a requires-clause for a class method, which checks invocation of another method of the same class.
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

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

<pre>
    Here is the SO post related to this issue: https://stackoverflow.com/questions/76820396/using-a-class-inside-the-requires-clause-for-the-method-of-this-class.

The issue occurs when compiling the following code:
```cpp
#include <type_traits>
#include <ranges>
#include <vector>

struct MyClass
{
    void g( int ) {}
    void g( char ) {}

 template <std::ranges::input_range Rng>
        requires requires ( MyClass cls, const std::ranges::range_value_t<Rng>& val )
        {
 { cls.g( val ) };
        }
    void f( Rng&& rng ) {}
};

int main()
{
    MyClass cls;
    cls.g( 10 );
 cls.g( 'a' );
    cls.f( std::vector<int>{ 10, 15 } );
}
```
Clang does not compile this program, although other compilers (MSVC and GCC) work as expected. Here is the error produced by Clang:
```
<source>:13:18: error: member access into incomplete type 'MyClass'
   13 |             { cls.g( val ) };
      | ^
<source>:5:8: note: definition of 'MyClass' is not complete until the closing '}'
    5 | struct MyClass
      |        ^
<source>:23:9: error: no matching member function for call to 'f'
   23 |     cls.f( std::vector<int>{ 10, 15 } );
      |     ~~~~^
<source>:15:10: note: candidate template ignored: constraints not satisfied [with Rng = std::vector<int>]
   15 |     void f( Rng&& rng ) {}
      | ^
<source>:11:18: note: because substituted constraint expression is ill-formed: constraint depends on a previously diagnosed expression
   11 |         requires requires ( MyClass cls, const std::ranges::range_value_t<Rng>& val )
      |                  ^
2 errors generated.
Compiler returned: 1
```

So basically, Clang demands a type in requires-clause to be complete. Moreover, if we change our example slightly, so that `MyClass::f` is never called:
```cpp
#include <type_traits>
#include <ranges>
#include <vector>

struct MyClass
{
    void g( int ) {}
    void g( char ) {}

 template <std::ranges::input_range Rng>
        requires requires ( MyClass cls, const std::ranges::range_value_t<Rng>& val )
        {
 { cls.g( val ) };
        }
    void f( Rng&& rng ) {}
};

int main()
{
    MyClass cls;
    cls.g( 10 );
 cls.g( 'a' );
    //cls.f( std::vector<int>{ 10, 15 } );
}
```
clang would anyway complain about incompleteness and fail compilation!
```
<source>:13:18: error: member access into incomplete type 'MyClass'
   13 |             { cls.g( val ) };
      | ^
<source>:5:8: note: definition of 'MyClass' is not complete until the closing '}'
    5 | struct MyClass
      |        ^
1 error generated.
Compiler returned: 1
```

The last code snippet is available in Godbolt for the ease of reproduction: https://godbolt.org/z/f7G5PxfKv.


**Expected behavior**: compilation is consistent with other compilers, both programs are accepted.
**Actual behavior**: clang fails to compile both programs.
</pre>
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