c-typeck.c (process_init_element): For -Wtraditional, warn about initialization of unions.

	* c-typeck.c (process_init_element): For -Wtraditional, warn about
	initialization of unions.

	* invoke.texi (-Wtraditional): Document new behavior.

From-SVN: r35595

gcc/ChangeLog

+2000-08-09  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
+
+	* c-typeck.c (process_init_element): For -Wtraditional, warn about
+	initialization of unions.
+
+	* invoke.texi (-Wtraditional): Document new behavior.
+
 2000-08-09  Zack Weinberg  <zack@wolery.cumb.org>
 
 	* configure.in (--enable-c-cpplib): Uncomment.  Use AC_DEFINE

gcc/c-typeck.c

@@ -6400,6 +6400,15 @@ process_init_element (value)
 	    fieldtype = TYPE_MAIN_VARIANT (fieldtype);
 	  fieldcode = TREE_CODE (fieldtype);
 
+	  /* Warn that traditional C rejects initialization of unions.
+	     We skip the warning if the value is zero.  This is done
+	     under the assumption that the zero initializer in user
+	     code appears conditioned on e.g. __STDC__ to avoid
+	     "missing initializer" warnings and relies on default
+	     initialization to zero in the traditional C case.  */
+	  if (warn_traditional && !integer_zerop (value))
+	    warning ("traditional C rejects initialization of unions");
+
 	  /* Accept a string constant to initialize a subarray.  */
 	  if (value != 0
 	      && fieldcode == ARRAY_TYPE

gcc/invoke.texi

@@ -1831,6 +1831,13 @@ Initialization of automatic aggregates.
 @item
 Identifier conflicts with labels.  Traditional C lacks a separate
 namespace for labels.
+
+@item
+Initialization of unions.  If the initializer is zero, the warning is
+omitted.  This is done under the assumption that the zero initializer in
+user code appears conditioned on e.g. @code{__STDC__} to avoid missing
+initializer warnings and relies on default initialization to zero in the
+traditional C case.
 @end itemize
 
 @item -Wundef