<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/91650>91650</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Identical return type considered different in redeclaration with trailing return type and enough templates
        </td>
    </tr>

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

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

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

<pre>
    The following valid code:

```c++
template<bool>
struct enable_if {
        using type = void;
};

template<typename>
struct trait {
        static constexpr bool value = false;
};

template<typename T>
struct s {
 typename enable_if<trait<T>::value>::type assign();
};

template<typename T>
auto s<T>::assign() -> typename enable_if<trait<T>::value>::type {
}
```

is rejected by clang with

```console
<source>:17:12: error: return type of out-of-line definition of 's::assign' differs from that in the declaration
   17 | auto s<T>::assign() -> typename enable_if<trait<T>::value>::type {
      |            ^
<source>:13:45: note: previous declaration is here
   13 |   typename enable_if<trait<T>::value>::type assign();
      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
1 error generated.
Compiler returned: 1
```

This occurred on clang trunk very recently, so it's not yet showing up on Godbolt: https://godbolt.org/z/KTE7dvcjd

@sdkrystian: It was introduced by 62b5b61f436add042d8729dc9837d055613180d9.
</pre>
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