[2.26 COMMITTED] assert: Suppress pedantic warning caused by statement expression [BZ #21242]

[Florian Weimer]

(cherry picked from commit 8b2c63e4e2ad1fd161f80004ed30624f2a37b57b)

2017-08-11  Florian Weimer  <fweimer@redhat.com>

	[BZ #21242]
	* assert/assert.h [__GNUC__ && !__STRICT_ANSI__] (assert):
	Suppress pedantic warning resulting from statement expression.
	(__ASSERT_FUNCTION): Add missing __extension__.

diff --git a/NEWS b/NEWS
index ec6cf34122..d57c4052cf 100644
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,7 @@ Version 2.26.1
 
 The following bugs are resolved with this release:
 
+  [21242] assert: Suppress pedantic warning caused by statement expression
   [21885] getaddrinfo: Release resolver context on error in gethosts
   [21932] Unpaired __resolv_context_get in generic get*_r implementation
 
diff --git a/assert/assert.h b/assert/assert.h
index 22f019537c..6801cfeb10 100644
--- a/assert/assert.h
+++ b/assert/assert.h
@@ -91,13 +91,19 @@ __END_DECLS
      ? __ASSERT_VOID_CAST (0)						\
      : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
 # else
+/* The first occurrence of EXPR is not evaluated due to the sizeof,
+   but will trigger any pedantic warnings masked by the __extension__
+   for the second occurrence.  The explicit comparison against zero is
+   required to support function pointers and bit fields in this
+   context, and to suppress the evaluation of variable length
+   arrays.  */
 #  define assert(expr)							\
-    ({									\
+  ((void) sizeof ((expr) == 0), __extension__ ({			\
       if (expr)								\
         ; /* empty */							\
       else								\
         __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION);	\
-    })
+    }))
 # endif
 
 # ifdef	__USE_GNU
@@ -113,7 +119,7 @@ __END_DECLS
    C9x has a similar variable called __func__, but prefer the GCC one since
    it demangles C++ function names.  */
 # if defined __cplusplus ? __GNUC_PREREQ (2, 6) : __GNUC_PREREQ (2, 4)
-#   define __ASSERT_FUNCTION	__PRETTY_FUNCTION__
+#   define __ASSERT_FUNCTION	__extension__ __PRETTY_FUNCTION__
 # else
 #  if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
 #   define __ASSERT_FUNCTION	__func__