https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83591
Bug ID: 83591
Summary: -Wduplicated-branches fires in system headers in
template instantiation
Product: gcc
Version: 7.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: TonyELewis at hotmail dot com
Target Milestone: ---
Compiling with:
g++ -Werror -Wduplicated-branches -c -isystem sysheaddir b.cpp
where b.cpp is :
#include "a.hpp"
...and sysheaddir/a.hpp is:
template <class...>
void f() {
int b;
( b ? b : b );
}
void g() {
f<>();
}
...gives:
sysheaddir/a.hpp:8:6: required from here
cc1plus: error: this condition has identical branches
[-Werror=duplicated-branches]
cc1plus: all warnings being treated as errors
Thought the code *does* have duplicate branches, I see two problems with this:
* the warning is firing even though all the code relevant to the warning is in
a system header
* the warning doesn't provide the line number on which the identical branches
appear
I suspect that it's already the intended design that this warning shouldn't
fire in system headers. Indeed, if I add a simple `void h() { int b; b ? b : b;
}` into b.cpp, it triggers the warning but if I add it to the system header
sysheaddir/a.hpp, it doesn't.
I'm using g++ (Ubuntu 7.2.0-8ubuntu3) 7.2.0. It looks to me from using
godbolt.org, that the same problems persist in trunk (8.0.0 20171225).
I suspect this is related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82541
but it has differences:
* I'm highlighting a true positive warning in a *system* header (rather than a
false positive in the .cpp file)
* I'm highlighting the lack of line number in the warning message
