Similar to Bug 96311, but not quite the same. This code is flags "is_zero" as being unused but set: template <typename Pred, typename Val> bool test(Pred p, Val v) { return p(v); } bool func(int* p) { static constexpr auto is_zero = [](auto v) { return v == 0;}; return test([](auto v){return is_zero(*v);}, p); } Output: <source>: In function 'bool func(int*)': <source>:9:27: warning: variable 'is_zero' set but not used [-Wunused-but-set-variable] 9 | static constexpr auto is_zero = [](auto v) { return v == 0;}; | ^~~~~~~ "is_zero" can correctly be used in the lambda without being captured, since it's static. The warning only appears when using the extra indirection "test()". Calling the anonymous lambda directly, without the indirection "test()", does not display the warning. Possibly "constexpr" is a red herring above. Godbolt link: https://godbolt.org/z/x4zb3s
Here is the most reduced C++20 testcase which produce the warning: void test(auto){} void func() { static auto is_zero = [](){ }; test([](auto v){return is_zero(*v);}); } Here is a C++17 testcase: template<typename t> void test(t){} void func() { static auto is_zero = [](){ }; test([](auto v){return is_zero(*v);}); }
*** Bug 105743 has been marked as a duplicate of this bug. ***
Changing "[](auto v)" to "[](int *v)" removes the warning. So this is a dup of bug 88804. *** This bug has been marked as a duplicate of bug 88804 ***