https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103960
Bug ID: 103960
Summary: Clang's -Wunknown-attributes is more useful than
-Wattributes
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: enhancement
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
(This is really c-family not c)
GCC's -Wattributes is used for both completely unknown attributes (e.g. the
user has a typo, or they use a new attribute on an old GCC) and for misplaced
attributes (e.g. a function attribute on a variable). This leaves users
wondering what they've done wrong.
For example, GCC 9 prints this because 'access' was added in GCC 10:
f.c:5:1: warning: ‘access’ attribute directive ignored [-Wattributes]
5 | __attribute__ ((access (read_only, 1))) bool my_func (const MyStruct *
const self);
| ^~~~~~~~~~~~~
This doesn't tell the user *why* it was ignored. Did they just use the wrong
grammar? You have to be quite familiar with GCC to know that using it in the
wrong place would give a different diagnostic:
f.c:5:1: warning: ‘access’ attribute only applies to function types
[-Wattributes]
5 | bool my_func (const MyStruct * const __attribute__ ((access (read_only,
1))) self);
| ^~~~
Apart from the caret being in the wrong place, this is pretty good. But for
unknown attributes our diagnostic is vague about what the problem is.
Clang's -Wunknown-attributes is more explicit:
f.c:5:17: warning: unknown attribute 'access' ignored [-Wunknown-attributes]
__attribute__ ((access (read_only, 1))) bool my_func (const MyStruct * const
self);
^~~~~~~~~~~~~~~~~~~~~
This tells you clearly that clang simply doesn't recognize the 'access'
attribute.
Could we just add the word "unknown" to the diagnostic for unrecognised
attributes?
