http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60875
Bug ID: 60875
Summary: `_Pragma("message \"foo\")"` doesn't work in
expression contexts.
Product: gcc
Version: 4.8.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: preprocessor
Assignee: unassigned at gcc dot gnu.org
Reporter: thakis at chromium dot org
Actual:
$ cat test.cc
int main() {
return _Pragma("message \"hello\"") 1234;
}
$ ~/gcc482prefix/bin/gcc -c test.cc -Wall
test.cc: In function ‘int main()’:
test.cc:2:1: error: ‘#pragma’ is not allowed here
return _Pragma("message \"my warning\"") 1234;
^
test.cc:2:44: error: expected ‘;’ before numeric constant
return _Pragma("message \"my warning\"") 1234;
^
test.cc:2:49: warning: statement has no effect [-Wunused-value]
return _Pragma("message \"my warning\"") 1234;
^
Expected (which is what clang does, and what MSVS does with `
__pragma(message...`):
Display the message instead.
(clang's output:
$ ../../../chrome/src/third_party/llvm-build/Release+Asserts/
bin/clang -c test.cc -Wall
test.cc:2:10: warning: my warning [-W#pragma-messages]
return _Pragma("message \"my warning\"") 1234;
^
<scratch space>:2:2: note: expanded from here
message "my warning"
^
1 warning generated.
)
A silly workaround is to use _Pragma("message_workaround...), then gcc will
warn like so:
test.cc:2:10: warning: unknown pragma ignored [-Wunknown-pragmas]
return _Pragma("message_workaround \"my warning\"") 1234;
^
It'd be nice if _Pragma(message...) could be used directly, instead of having
to rely on -Wunknown-pragmas for this functionality.
(The usecase we have for this in Chromium is that we want to make the compiler
print a diagnostic every time some symbols are used, so we define the symbols
as
#define MY_SYMBOL _Pragma("message \"foo\"") SYMBOL
This works fine in clang and MSVC, but for gcc we have to use a dummy pragma
and rely on -Wunknown-pragmas.)
