<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/157103>157103</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang] Valid constexpr noexcept expression with explicit lambda return type is rejected
        </td>
    </tr>

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

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

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

<pre>
    [Godbolt Demo](https://godbolt.org/z/4x4KEGxeP)

Clang version: 22.0.0git

#### Reproducer:
`clang test.cpp`

`test.cpp`:
```cpp
template<typename>
constexpr void bar() noexcept([]<typename...>() -> bool { return true; }()) {}

int main() {
 bar<void>();
}
```
#### Clang output:
```
test.cpp:2:31: error: noexcept specifier argument is not a constant expression
    2 | constexpr void bar() noexcept([]<typename...>() -> bool { return true; }()) {}
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:2:16: note: in instantiation of exception specification for 'bar<void>' requested here
 2 | constexpr void bar() noexcept([]<typename...>() -> bool { return true; }()) {}
      |                ^
test.cpp:5:5: note: in instantiation of function template specialization 'bar<void>' requested here
    5 | bar<void>();
      |     ^
test.cpp:2:31: note: undefined function 'operator()<>' cannot be used in a constant expression
    2 | constexpr void bar() noexcept([]<typename...>() -> bool { return true; }()) {}
      | ^
test.cpp:2:31: note: declared here
```
#### Expected behavior:
Successfully produces essentially empty executable.
#### Environment:
```
clang version 22.0.0git (https://github.com/llvm/llvm-project.git 779868de6975f6fd0ea17bb9a8e929037d3752d7)
Target: x86_64-w64-windows-gnu
Thread model: posix
```
#### Notes:
Removing `-> bool` results in successful compilation:
```cpp
template<typename>
constexpr void bar() noexcept([]<typename...>() /*-> bool*/ { return true; }()) {}

int main() {
    bar<void>();
}
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzUlt-P46YTwP8a8jJai-Bg4oc8eHeTe_hKX1XXU18rDJOEKwYXcDZ7D_3bK2wn2dvVXbdS1R-WrQSYgZkPwwwyRnNwiBvC7wl_XMghHX3YfDpiY43Cexl_wXAy1uKi9fo5i33wuvU2wSN2nvBHwtbHlPpIyoawHWG7wzRe-HAgbPeFsN3qvPrf9sMZfyCsJrQhtHmw0h3ghCEa70jZAGMFLejBpGmcsPL6wkfsg9eDwpDXoA2pqBr1E8ZUqL4nFZ3VKvqy7yI9vbmTNgm73sqEpHxIzz062SEpt4Q2yruY8NwHOHmjoZWBsDVhNTiPZ4V9ys0R0gvVoiiy9iR4R8ottN5bIOIeAqYhOEhhQFLeAxGPk1iWJOI-t0ebjUvQSePmSfIQbcbly4dsyXV-UuaRWe_i1GtWE1g_pH5Ir_wfnZ_hlA0jZVMuM3oMwWeyV0ch9qjM3mAAGQ5Dhy6BieB8AgkjJukSZFQYx_2jDQAAAyIe4B_BCOOTlyd8-9v7n7dIltVEIgdIA8aBmdw1MhnvwO9h8iI3ZkxqGtr7AISJVxsnIOCvA8aEGo4YMBv7rwD16iF8-zUMPn_fZbEfnBr_X07VxERa82WSeR8QAOCjUd-M-q_tfmPsLZgv1g5O49441DcbCRO-xyCTD5epH2aTlHQ5uluEIaLOrv4XAv2PGGhUVoYb528mje25R5U3pMWjPBk_59kfB6Uwxv1g7TPMKTgCxog5BnIndn16BjyjGpJsLRZvZnYnE7zLKeRtNlIvi8CtAsDbimLScWgL5TvCdtaeLj93ffCfUaUiawlRr6u1xqoWfF_tNUW5FG1byzXWrKal0KXgTIupBn2S4YDZJjivq5-r1d1T_ozT_ineHdyQRY4BpYbOa7RZsPfRnL-H8f8-YZzc_IidPxl3AFLR6zaTikLAONgUc4jFK15QvuuNHY_M3120RsLNzUaWmf8FBQzg3TVsoTelrstaLnCzFFxQsa5qvjhumKwroZe4ZrTat6xFulrXXFV73bYlr-uF2TDKOK0pX5ZsxXnBFdWralULTYXm9ZqsKHbS2CKHS76RLEyMA26WXCxpubCyRRvHuw9jYzgSxvI1KGzG-GqHQyQrak1M8TZFMsmOF6ZJgz_CT9Ia_SIjXCvpLXfAk0nH3LZGmQRWdq2WV8bPPeYSG_DzeBAXQ7CbP3cGCNuNrkXCdrN3pw37PQAA__8LdvTK">