On Sat, Dec 15, 2012 at 11:49:25AM +0100, Johannes Sixt wrote:
> Am 14.12.2012 23:09, schrieb Jeff King:
> > Can anybody think of a clever way to expose the constant return value of
> > error() to the compiler? We could do it with a macro, but that is also
> > out for error(), as we do not assume the compiler has variadic macros. I
> > guess we could hide it behind "#ifdef __GNUC__", since it is after all
> > only there to give gcc's analyzer more information. But I'm not sure
> > there is a way to make a macro that is syntactically identical. I.e.,
> > you cannot just replace "error(...)" in "return error(...);" with a
> > function call plus a value for the return statement. You'd need
> > something more like:
> >
> > #define RETURN_ERROR(fmt, ...) \
> > do { \
> > error(fmt, __VA_ARGS__); \
> > return -1; \
> > } while(0) \
> >
> > which is awfully ugly.
>
> Does
>
> #define error(fmt, ...) (error_impl(fmt, __VA_ARGS__), -1)
>
> cause problems when not used in a return statement?
Thanks, that was the cleverness I was missing. The only problem is that
in standard C, doing this:
error("no other arguments");
generates:
(error_impl(fmt, ), 1);
which is bogus. This is a common problem with variadic macros, and
fortunately gcc has a solution (and since we are already inside a
gcc-only #ifdef, we should be OK).
So doing this works for me:
diff --git a/git-compat-util.h b/git-compat-util.h
index 2e79b8a..a036323 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -285,9 +285,18 @@ extern void warning(const char *err, ...) __attribute__((format (printf, 1, 2)))
extern NORETURN void usagef(const char *err, ...) __attribute__((format (printf, 1, 2)));
extern NORETURN void die(const char *err, ...) __attribute__((format (printf, 1, 2)));
extern NORETURN void die_errno(const char *err, ...) __attribute__((format (printf, 1, 2)));
-extern int error(const char *err, ...) __attribute__((format (printf, 1, 2)));
extern void warning(const char *err, ...) __attribute__((format (printf, 1, 2)));
+#ifdef __GNUC__
+#define ERROR_FUNC_NAME error_impl
+#define error(fmt, ...) (error_impl((fmt), ##__VA_ARGS__), -1)
+#else
+#define ERROR_FUNC_NAME error
+#endif
+
+extern int ERROR_FUNC_NAME(const char *err, ...)
+__attribute__((format (printf, 1, 2)));
+
extern void set_die_routine(NORETURN_PTR void (*routine)(const char *err, va_list params));
extern void set_error_routine(void (*routine)(const char *err, va_list params));
diff --git a/usage.c b/usage.c
index 8eab281..d1a58fa 100644
--- a/usage.c
+++ b/usage.c
@@ -130,7 +130,7 @@ void NORETURN die_errno(const char *fmt, ...)
va_end(params);
}
-int error(const char *err, ...)
+int ERROR_FUNC_NAME(const char *err, ...)
{
va_list params;
I think we could even get rid of the ERROR_FUNC_NAME ugliness by just
calling it "error", and doing an "#undef error" right before we define
it in usage.c.
-Peff
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