vasprintf, c-vasprintf: Remind users to consider the return value

[Bruno Haible]

Eric Blake wrote:
> >    The only reasonable change that should be done is to mark the
> >    declaration of asprintf and vasprintf with attribute
> >    __warn_unused_result__. This way, the compiler will warn about
> >    the crappy code.
> 
> Makes sense; I would be in favor of that change in gnulib

Done:


2024-07-29  Bruno Haible  <bruno@clisp.org>

        vasprintf, c-vasprintf: Remind users to consider the return value.
        * lib/stdio.in.h (aszprintf, vaszprintf, asprintf, vasprintf): Mark with
        _GL_ATTRIBUTE_NODISCARD.
        * lib/c-vasprintf.h (c_aszprintf, c_vaszprintf, c_asprintf,
        c_vasprintf): Likewise.

diff --git a/lib/c-vasprintf.h b/lib/c-vasprintf.h
index 048ecf0f62..628d04fa6f 100644
--- a/lib/c-vasprintf.h
+++ b/lib/c-vasprintf.h
@@ -17,7 +17,7 @@
 #ifndef _C_VASPRINTF_H
 #define _C_VASPRINTF_H
 
-/* This file uses _GL_ATTRIBUTE_FORMAT.  */
+/* This file uses _GL_ATTRIBUTE_FORMAT, _GL_ATTRIBUTE_NODISCARD.  */
 #if !_GL_CONFIG_H_INCLUDED
  #error "Please include config.h first."
 #endif
@@ -47,8 +47,10 @@ extern "C" {
 
    Formatting takes place in the C locale, that is, the decimal point
    used in floating-point formatting directives is always '.'. */
+_GL_ATTRIBUTE_NODISCARD
 ptrdiff_t c_aszprintf (char **resultp, const char *format, ...)
        _GL_ATTRIBUTE_FORMAT ((_GL_ATTRIBUTE_SPEC_PRINTF_STANDARD, 2, 3));
+_GL_ATTRIBUTE_NODISCARD
 ptrdiff_t c_vaszprintf (char **resultp, const char *format, va_list args)
        _GL_ATTRIBUTE_FORMAT ((_GL_ATTRIBUTE_SPEC_PRINTF_STANDARD, 2, 0));
 
@@ -59,8 +61,10 @@ ptrdiff_t c_vaszprintf (char **resultp, const char *format, 
va_list args)
 
    Formatting takes place in the C locale, that is, the decimal point
    used in floating-point formatting directives is always '.'. */
+_GL_ATTRIBUTE_NODISCARD
 int c_asprintf (char **resultp, const char *format, ...)
        _GL_ATTRIBUTE_FORMAT ((_GL_ATTRIBUTE_SPEC_PRINTF_STANDARD, 2, 3));
+_GL_ATTRIBUTE_NODISCARD
 int c_vasprintf (char **resultp, const char *format, va_list args)
        _GL_ATTRIBUTE_FORMAT ((_GL_ATTRIBUTE_SPEC_PRINTF_STANDARD, 2, 0));
 
diff --git a/lib/stdio.in.h b/lib/stdio.in.h
index 38572382d4..4ea4e3cc16 100644
--- a/lib/stdio.in.h
+++ b/lib/stdio.in.h
@@ -64,8 +64,8 @@
 #define _@GUARD_PREFIX@_STDIO_H
 
 /* This file uses _GL_ATTRIBUTE_DEALLOC, _GL_ATTRIBUTE_FORMAT,
-   _GL_ATTRIBUTE_MALLOC, _GL_ATTRIBUTE_NOTHROW, GNULIB_POSIXCHECK,
-   HAVE_RAW_DECL_*.  */
+   _GL_ATTRIBUTE_MALLOC, _GL_ATTRIBUTE_NODISCARD, _GL_ATTRIBUTE_NOTHROW,
+   GNULIB_POSIXCHECK, HAVE_RAW_DECL_*.  */
 #if !_GL_CONFIG_H_INCLUDED
  #error "Please include config.h first."
 #endif
@@ -1693,12 +1693,14 @@ _GL_WARN_ON_USE (tmpfile, "tmpfile is not usable on 
mingw - "
    Failure code EOVERFLOW can only occur when a width > INT_MAX is used.
    Therefore, if the format string is valid and does not use %ls/%lc
    directives nor widths, the only possible failure code is ENOMEM.  */
+_GL_ATTRIBUTE_NODISCARD
 _GL_FUNCDECL_SYS (aszprintf, ptrdiff_t,
                   (char **result, const char *format, ...)
                   _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD (2, 3)
                   _GL_ARG_NONNULL ((1, 2)));
 _GL_CXXALIAS_SYS (aszprintf, ptrdiff_t,
                   (char **result, const char *format, ...));
+_GL_ATTRIBUTE_NODISCARD
 _GL_FUNCDECL_SYS (vaszprintf, ptrdiff_t,
                   (char **result, const char *format, va_list args)
                   _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD (2, 0)
@@ -1717,6 +1719,7 @@ _GL_CXXALIAS_SYS (vaszprintf, ptrdiff_t,
 #   define asprintf rpl_asprintf
 #  endif
 #  define GNULIB_overrides_asprintf
+_GL_ATTRIBUTE_NODISCARD
 _GL_FUNCDECL_RPL (asprintf, int,
                   (char **result, const char *format, ...)
                   _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD (2, 3)
@@ -1725,6 +1728,7 @@ _GL_CXXALIAS_RPL (asprintf, int,
                   (char **result, const char *format, ...));
 # else
 #  if !@HAVE_VASPRINTF@
+_GL_ATTRIBUTE_NODISCARD
 _GL_FUNCDECL_SYS (asprintf, int,
                   (char **result, const char *format, ...)
                   _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD (2, 3)
@@ -1739,6 +1743,7 @@ _GL_CXXALIASWARN (asprintf);
 #   define vasprintf rpl_vasprintf
 #  endif
 #  define GNULIB_overrides_vasprintf 1
+_GL_ATTRIBUTE_NODISCARD
 _GL_FUNCDECL_RPL (vasprintf, int,
                   (char **result, const char *format, va_list args)
                   _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD (2, 0)
@@ -1747,6 +1752,7 @@ _GL_CXXALIAS_RPL (vasprintf, int,
                   (char **result, const char *format, va_list args));
 # else
 #  if !@HAVE_VASPRINTF@
+_GL_ATTRIBUTE_NODISCARD
 _GL_FUNCDECL_SYS (vasprintf, int,
                   (char **result, const char *format, va_list args)
                   _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD (2, 0)