https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105130
Bug ID: 105130
Summary: gcc does not warn about unused return value of last
expression of statement expr
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dani at danielbertalan dot dev
Target Milestone: ---
Created attachment 52739
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52739&action=edit
Proposed patch
The following code does not cause a warning about the return value of the foo()
function being ignored:
$ cat unused.cc
[[nodiscard]] int foo();
int main() {
({ foo(); });
}
$ g++ -Wunused-value -std=c++20 unused.cc
[no warnings]
The issue seems to be that CLEANUP_POINT_EXPR and STATEMENT_LIST -- which are
what statement expressions are turned into -- are not handled in
convert_to_void() (cp/cvt.cc).
The attached patch resolves the issue, but as a newbie to hacking on gcc, I
can't evaluate if it has any unintended consequences.
