-Wall gives spurious "is not used" warning when expanding variadic capture and other pack

[Aster89]

(Maybe related to #40556.)

(Complete repro steps.)

auto foo(auto ...x) {
    return [...x = x](auto ...f) {
        (f(x), ...);
    };
}

int main() {
    foo(0)([](auto x){ return x; });
}

Compiling the code above via

clang++ -std=c++20 -Wall file.cpp

produces this spurious warning:

file.cpp:2:16: warning: lambda capture 'x' is not used [-Wunused-lambda-capture]
    2 |     return [...x = x](auto ...f) {
      |                ^
file.cpp:8:5: note: in instantiation of function template specialization 'foo<int>' requested here
    8 |     foo(0)([](auto x){ return x; });
      |     ^
1 warning generated.

---

$ clang++ --version
clang version 18.1.8
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

[EugeneZelenko]

Could you please try 19 or main branch? https://godbolt.org should be helpful.

[Aster89]

Isn't this Clang 19.1.0?

[EugeneZelenko]

Original description tells about 18.1.8.