assert.h: allow gcc to detect assert(a = 1) errors

* assert/assert.h (assert): Rewrite assert's definition so that
a s/==/=/ typo, e.g., assert(errno = ENOENT) is not hidden from
gcc's -Wparentheses by assert-added parentheses.  The new definition
uses "if (expr) /* empty */; else __assert_fail...", so
gcc -Wall will now detect that type of error in an assert, too.
The __STRICT_ANSI__ disjunct is to make this work also with both
-ansi and  -pedantic, which would reject the use of ({...}).
I would have preferred to use __extension__ to mark that, but
doing so would mistakenly suppress warnings about any extension
in the user-supplied "expr".
E.g., "assert ( ({1;}) )" must continue to evoke a warning.

1 files changed, 17 insertions, 4 deletions

diff --git a/assert/assert.h b/assert/assert.h
index 729edeb949..0f25131ae4 100644
--- a/assert/assert.h
+++ b/assert/assert.h
@@ -82,10 +82,23 @@ extern void __assert (const char *__assertion, const char *__file, int __line)
 
 __END_DECLS
 
-# define assert(expr)							\
-  ((expr)								\
-   ? __ASSERT_VOID_CAST (0)						\
-   : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
+/* When possible, define assert so that it does not add extra
+   parentheses around EXPR.  Otherwise, those added parentheses would
+   suppress warnings we'd expect to be detected by gcc's -Wparentheses.  */
+# if !defined __GNUC__ || defined __STRICT_ANSI__
+#  define assert(expr)							\
+    ((expr)								\
+     ? __ASSERT_VOID_CAST (0)						\
+     : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
+# else
+#  define assert(expr)							\
+    ({									\
+      if (expr)								\
+        ; /* empty */							\
+      else								\
+        __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION);	\
+    })
+# endif
 
 # ifdef	__USE_GNU
 #  define assert_perror(errnum)						\