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[clang-tidy] bugprone-macro-repeated-side-effects false positive with assert() in glibc 2.44 #233597
Description
In glibc 2.44, the definition of the assert() macro changed to accommodate the C++26 feature that allows non-parenthesised commas within assertions. The relevant part is this:
# define assert(...) \
((__VA_ARGS__) \
? void (1 ? 1 : bool (__VA_ARGS__)) \
: __assert_fail (#__VA_ARGS__, __ASSERT_FILE, __ASSERT_LINE, \
__ASSERT_FUNCTION))Note that __VA_ARGS__ is only evaluated once, even though it appears twice. Unfortunately, this makes clang-tidy produce the bugprone-macro-repeated-side-effects warning in code like this, even if bugprone-assert-side-effect is not enabled:
#include <cassert>
int main() {
int x = 0;
assert(++x == 1);
assert(++x == 1);
}The result:
warning: side effects in the 1st macro argument '__VA_ARGS__' are repeated in macro expansion [bugprone-macro-repeated-side-effects]
4 | assert( ++x == 1 );
| ^
/usr/include/assert.h:137:13: note: macro 'assert' defined here
137 | # define assert(...) \
| ^
warning: side effects in the 1st macro argument '__VA_ARGS__' are repeated in macro expansion [bugprone-macro-repeated-side-effects]
5 | assert( ++x == 2 );
| ^
/usr/include/assert.h:137:13: note: macro 'assert' defined here
137 | # define assert(...) \
| ^
Perhaps the bugprone-macro-repeated-side-effects could specifically ignore the assert() macro; or, even better, it could be configurable with an option to ignore specific macros.
Activity
llvmorg-github-actions commentedon Oct 19, 2026
@llvm/issue-subscribers-clang-tidy
Author: Nikola Beneš (nikola-benes)
Details
In glibc 2.44, the definition of the `assert()` macro changed to accommodate the C++26 feature that allows non-parenthesised commas within assertions. The relevant part is this:(source: https://sourceware.org/git/?p=glibc.git;a=blob;f=assert/assert.h;hb=ea37298b65bd67f94c3c2640e91ec5865a5019ad#l137)
Note that
__VA_ARGS__is only evaluated once, even though it appears twice. Unfortunately, this makes clang-tidy produce the bugprone-macro-repeated-side-effects warning in code like this, even if bugprone-assert-side-effect is not enabled:The result:
Perhaps the bugprone-macro-repeated-side-effects could specifically ignore the assert macro; or, even better, it could be configurable with an option to ignore specific macros.
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