diff options
Diffstat (limited to 'lib/warn-on-use.h')
| -rw-r--r-- | lib/warn-on-use.h | 64 |
1 files changed, 43 insertions, 21 deletions
diff --git a/lib/warn-on-use.h b/lib/warn-on-use.h index 9f17e5bfd4b..7d11a156911 100644 --- a/lib/warn-on-use.h +++ b/lib/warn-on-use.h @@ -20,23 +20,32 @@ supported by the compiler. If the compiler does not support this feature, the macro expands to an unused extern declaration. - This macro is useful for marking a function as a potential + _GL_WARN_ON_USE_ATTRIBUTE ("literal string") expands to the + attribute used in _GL_WARN_ON_USE. If the compiler does not support + this feature, it expands to empty. + + These macros are useful for marking a function as a potential portability trap, with the intent that "literal string" include instructions on the replacement function that should be used - instead. However, one of the reasons that a function is a - portability trap is if it has the wrong signature. Declaring - FUNCTION with a different signature in C is a compilation error, so - this macro must use the same type as any existing declaration so - that programs that avoid the problematic FUNCTION do not fail to - compile merely because they included a header that poisoned the - function. But this implies that _GL_WARN_ON_USE is only safe to - use if FUNCTION is known to already have a declaration. Use of - this macro implies that there must not be any other macro hiding - the declaration of FUNCTION; but undefining FUNCTION first is part - of the poisoning process anyway (although for symbols that are - provided only via a macro, the result is a compilation error rather - than a warning containing "literal string"). Also note that in - C++, it is only safe to use if FUNCTION has no overloads. + instead. + _GL_WARN_ON_USE is for functions with 'extern' linkage. + _GL_WARN_ON_USE_ATTRIBUTE is for functions with 'static' or 'inline' + linkage. + + However, one of the reasons that a function is a portability trap is + if it has the wrong signature. Declaring FUNCTION with a different + signature in C is a compilation error, so this macro must use the + same type as any existing declaration so that programs that avoid + the problematic FUNCTION do not fail to compile merely because they + included a header that poisoned the function. But this implies that + _GL_WARN_ON_USE is only safe to use if FUNCTION is known to already + have a declaration. Use of this macro implies that there must not + be any other macro hiding the declaration of FUNCTION; but + undefining FUNCTION first is part of the poisoning process anyway + (although for symbols that are provided only via a macro, the result + is a compilation error rather than a warning containing + "literal string"). Also note that in C++, it is only safe to use if + FUNCTION has no overloads. For an example, it is possible to poison 'getline' by: - adding a call to gl_WARN_ON_USE_PREPARE([[#include <stdio.h>]], @@ -54,12 +63,21 @@ (less common usage, like &environ, will cause a compilation error rather than issue the nice warning, but the end result of informing the developer about their portability problem is still achieved): - #if HAVE_RAW_DECL_ENVIRON - static char ***rpl_environ (void) { return &environ; } - _GL_WARN_ON_USE (rpl_environ, "environ is not always properly declared"); - # undef environ - # define environ (*rpl_environ ()) - #endif + #if HAVE_RAW_DECL_ENVIRON + static char *** + rpl_environ (void) { return &environ; } + _GL_WARN_ON_USE (rpl_environ, "environ is not always properly declared"); + # undef environ + # define environ (*rpl_environ ()) + #endif + or better (avoiding contradictory use of 'static' and 'extern'): + #if HAVE_RAW_DECL_ENVIRON + static char *** + _GL_WARN_ON_USE_ATTRIBUTE ("environ is not always properly declared") + rpl_environ (void) { return &environ; } + # undef environ + # define environ (*rpl_environ ()) + #endif */ #ifndef _GL_WARN_ON_USE @@ -67,13 +85,17 @@ /* A compiler attribute is available in gcc versions 4.3.0 and later. */ # define _GL_WARN_ON_USE(function, message) \ extern __typeof__ (function) function __attribute__ ((__warning__ (message))) +# define _GL_WARN_ON_USE_ATTRIBUTE(message) \ + __attribute__ ((__warning__ (message))) # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING /* Verify the existence of the function. */ # define _GL_WARN_ON_USE(function, message) \ extern __typeof__ (function) function +# define _GL_WARN_ON_USE_ATTRIBUTE(message) # else /* Unsupported. */ # define _GL_WARN_ON_USE(function, message) \ _GL_WARN_EXTERN_C int _gl_warn_on_use +# define _GL_WARN_ON_USE_ATTRIBUTE(message) # endif #endif |