https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95127
Bug ID: 95127
Summary: Self-calling lambda with auto return type gives
misleading error message
Product: gcc
Version: 9.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: xzlsmc at gmail dot com
Target Milestone: ---
$ cat bug.cc
int main() {
auto f = [](const auto &g, auto x) { return g(g, x); };
f(f, 0);
}
$ gcc -std=c++14 bug.cc
bug.cc: In instantiation of ‘main()::<lambda(const auto:1&, auto:2)> [with
auto:1 = main()::<lambda(const auto:1&, auto:2)>; auto:2 = int]’:
bug.cc:3:9: required from here
bug.cc:2:48: error: use of ‘main()::<lambda(const auto:1&, auto:2)> [with
auto:1 = main()::<lambda(const auto:1&, auto:2)>; auto:2 = int]’ before
deduction of ‘auto’
2 | auto f = [](const auto &g, auto x) { return g(g, x); };
| ~^~~~~~
This error message is technically correct, but the `auto' it refers to is very
misleading here: it's the implicit `auto' return type of the lambda expression,
rather than either `auto' argument type. The message can become clearer if
changed to "use of ... before deduction of _return type_".
GCC version: 9.3.1
