https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87582
Bug ID: 87582
Summary: Returning a reference to a data member via structured
bindings incorrectly reports dangling
Product: gcc
Version: 8.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: cfretz at icloud dot com
Target Milestone: ---
My apologies if I've misunderstood something, or if I've duplicated an issue
someone else already posted, but I ran into this late last night:
struct custom {
int one, two;
};
custom thing {1, 2};
auto& bad() {
auto& [one, two] = thing;
return one;
}
int main() {
[[maybe_unused]] auto& one = bad();
}
All versions of gcc I was able to test on godbolt reported returning a
reference to a local variable in the function "bad", while no versions of clang
reported the same.
For reference: https://godbolt.org/z/fcNZDb
To my knowledge, this code should have the end result of binding the reference
"one" in main to the first data member of the global "thing"; not returning a
reference to a local in the function "bad".
The warning is also not issued if "thing" is a std::tuple<int, int>, or if the
type "custom" is made to be a "tuple-like type" by specializing
std::tuple_size, std::tuple_element, etc.
I was originally expecting that this was an error somewhere in static analysis,
but if you go on to actually try to use the reference you get a segfault as in
this program: https://godbolt.org/z/lb1afO. Address-sanitizer reports a
null-pointer dereference.
Let me know if any clarifications are required, and I hope I haven't wasted
anyone's time!
