<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/119046>119046</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Clang] Linker error after immediate escalation
        </td>
    </tr>

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

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

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

<pre>
    Found this while investigating #118560. This (started from libc++ `std::visit`, now reduced beyond recognition)
```c++
struct S {
    consteval void operator()() {}
};

template <class Fn>
constexpr void dispatch(Fn fn) {
    fn();
}

template <class Visitor>
struct value_visitor {
 constexpr void operator()() { visitor(); }
    Visitor&& visitor;
};

template <class Visitor>
constexpr auto make_dispatch() {
 return dispatch<value_visitor<S>>;
}

template <class Visitor>
constexpr void visit(Visitor&&) {
 make_dispatch<Visitor>();
}

int main() { visit(S{}); }
```
results in a linker error:
```
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/15.0.0/../../../../x86_64-linux-gnu/bin/ld: /tmp/example-02182a.o: in function `auto make_dispatch<S>()':
<source>:19:(.text._Z13make_dispatchI1SEDav[_Z13make_dispatchI1SEDav]+0x7): undefined reference to `void dispatch<value_visitor<S> >(value_visitor<S>)'
```
GCC accepts it without issue. [Compiler Explorer link](https://godbolt.org/z/hMjj67j8b).

Issue seems related to immediate escalation, as making `make_dispatch` or `visit` `consteval` solves the issue.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJyUVUGPqzYQ_jXOZRRk7EDIgUNCHu2TXk9b9dDLyphJ8D5jI9uwef31lSG7m2yzh0qIxHj8zcz3zYyF9-psEEuSHUh2XIkxdNaVP37_IUanjFo1tv1V1nY0LYROeXjtlEZQZkIf1FkEZc5AGE_TIstpAn9GG8IKH4QL2MLJ2R60aiRhB8IOQHLqQ0v4nvD9pLwKJKeEVWDsKzhsR4ktNPjLmhYcSns2KihrCNsRuo-m83MFI3TvgxtlgCcg27gEAJDW-ICT0DBZ1YId0IlgHWFFRJnfs_X2GCG3R8LjSUL3AftBi4BAeCW18B5qQ_g3QvcL5GVwC2Sr_CCC7AgragMn84a4-I_r2dWCu7h5hP5XTN-6xcU1kUnoEZ-nZecN9JP7rzKC67F397A4j0G9-WI5Yfm74XuEX1NwF-RHIGIMFnrxE59vyLjhwWEYnflgild3mRFePUXI-Pwflj4xsRQQK-6yu4niPkBe3WA9kkiZAL1Q5jOlhBVP14q55fW9HAndO_SjDh6UAQFamZ_oAJ2LvvafTAmr7RAIq6XtB6XRrfEyaOvQEVafpVx7Iwbf2WiiVbN8JKy-FPlzvllrZcbL-mxGwuo0S2hCCauT5L-vB_ZNzK3Wsf2AsDr0A2E1XkQ_aFxTlhZMJDZuKgOn0cjYerFjH6h9FfBagttrmrzydnQSZ2H36S5-ZkUS8BKS579TfofxPX36dhQTyQ5fbx0JO9DLduZ9D6Np8aQMxtlwQodGIgQbI7zvy8fVBkvADwtxSeJeqN-qCoSUOERdA7yq0NkxgPJ-xARIdqiuAsK3q4Cz8nPQRRfC4Of066igbRurQ2LdmbD6H8Lq7o-Xl3z7UjSE7ZKl_L5HYPCIvQeHsQvamJ3qe2xV7An0UmixzMMKhI-SzOM3p_fi5BTi9Mjp24SN_9_nYlx7qyf0EDq85rNqS97u-E6ssEy3nGec7bJ81ZXppmhOfCMyLrc0x7bgdMc5k7ihnDfYrlTJKNukjG4pzbIsT7JN0zbs1G63_IQoM7Kh2AulE62nPlKwml2Wabqjm3ylRYPaz_cPY1ILcyaMxavIlfHAuhnPnmyoVj74D4iggp4vrWo-kR3hx03XgTgFdA-pW41Ol5_UUaEbm0TaPnaHnt5-1oOzLyhjI84R-9hyS9BTyf4NAAD__08rPFQ">