re PR c/15052 (gcc frontend accepts mismatched function declaration/defintion)

PR c/15052
	* c-decl.c (grokdeclarator): Only pedwarn for qualified void
	return type on function definitions.  Move other warnings for
	qualified return type to -Wreturn-type.  Do not condition any such
	warnings on -pedantic.  Update comments.
	(start_function): Only copy function type from previous prototype
	declaration if return types are compatible.
	* c-typeck.c (function_types_compatible_p): Don't condition
	warning for incompatibility of volatile qualifiers on the return
	type on -pedantic.  Update comment.
	* doc/invoke.texi (-Wreturn-type, -Wextra): Update.

testsuite:
	* gcc.dg/noreturn-5.c: Test qualifiers on function type instead of
	on return type.
	* gcc.dg/qual-return-1.c: Use -Wreturn-type.  Update expected
	messages.
	* gcc.dg/qual-return-2.c: Update expected messages.
	* gcc.dg/qual-return-3.c, gcc.dg/qual-return-4.c: New tests.

From-SVN: r85024

gcc/ChangeLog

@@ -1,3 +1,17 @@
+2004-07-22  Joseph S. Myers  <jsm@polyomino.org.uk>
+
+	PR c/15052
+	* c-decl.c (grokdeclarator): Only pedwarn for qualified void
+	return type on function definitions.  Move other warnings for
+	qualified return type to -Wreturn-type.  Do not condition any such
+	warnings on -pedantic.  Update comments.
+	(start_function): Only copy function type from previous prototype
+	declaration if return types are compatible.
+	* c-typeck.c (function_types_compatible_p): Don't condition
+	warning for incompatibility of volatile qualifiers on the return
+	type on -pedantic.  Update comment.
+	* doc/invoke.texi (-Wreturn-type, -Wextra): Update.
+
 2004-07-22  Joseph S. Myers  <jsm@polyomino.org.uk>
 
 	* c-typeck.c (set_init_index): Require designator to be of integer

gcc/c-decl.c

@@ -4165,21 +4165,15 @@ grokdeclarator (tree declarator, tree declspecs,
 	     qualify the return type, not the function type.  */
 	  if (type_quals)
 	    {
-	      /* Type qualifiers on a function return type are normally
-		 permitted by the standard but have no effect, so give a
-		 warning at -Wextra.  Qualifiers on a void return type have
-		 meaning as a GNU extension, and are banned on function
-		 definitions in ISO C.  FIXME: strictly we shouldn't
-		 pedwarn for qualified void return types except on function
-		 definitions, but not doing so could lead to the undesirable
-		 state of a "volatile void" function return type not being
-		 warned about, and a use of the function being compiled
-		 with GNU semantics, with no diagnostics under -pedantic.  */
-	      if (VOID_TYPE_P (type) && pedantic && !in_system_header)
-		pedwarn ("ISO C forbids qualified void function return type");
-	      else if (extra_warnings
-		       && !(VOID_TYPE_P (type)
-			    && type_quals == TYPE_QUAL_VOLATILE))
+	      /* Type qualifiers on a function return type are
+		 normally permitted by the standard but have no
+		 effect, so give a warning at -Wreturn-type.
+		 Qualifiers on a void return type are banned on
+		 function definitions in ISO C; GCC used to used them
+		 for noreturn functions.  */
+	      if (VOID_TYPE_P (type) && really_funcdef)
+		pedwarn ("function definition has qualified void return type");
+	      else if (warn_return_type)
 		warning ("type qualifiers ignored on function return type");
 
 	      type = c_build_qualified_type (type, type_quals);
@@ -4499,7 +4493,7 @@ grokdeclarator (tree declarator, tree declspecs,
 	if (pedantic && type_quals && ! DECL_IN_SYSTEM_HEADER (decl))
 	  pedwarn ("ISO C forbids qualified function types");
 
-	/* GNU C interprets a `volatile void' return type to indicate
+	/* GNU C interprets a volatile-qualified function type to indicate
 	   that the function does not return.  */
 	if ((type_quals & TYPE_QUAL_VOLATILE)
 	    && !VOID_TYPE_P (TREE_TYPE (TREE_TYPE (decl))))
@@ -5714,8 +5708,8 @@ start_function (tree declspecs, tree declarator, tree attributes)
   old_decl = lookup_name_in_scope (DECL_NAME (decl1), current_scope);
   if (old_decl != 0 && TREE_CODE (TREE_TYPE (old_decl)) == FUNCTION_TYPE
       && !DECL_BUILT_IN (old_decl)
-      && (TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (decl1)))
-	  == TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (old_decl))))
+      && comptypes (TREE_TYPE (TREE_TYPE (decl1)),
+		    TREE_TYPE (TREE_TYPE (old_decl)))
       && TYPE_ARG_TYPES (TREE_TYPE (decl1)) == 0)
     {
       TREE_TYPE (decl1) = TREE_TYPE (old_decl);

gcc/c-typeck.c

@@ -958,9 +958,9 @@ function_types_compatible_p (tree f1, tree f2)
   ret1 = TREE_TYPE (f1);
   ret2 = TREE_TYPE (f2);
 
-  /* 'volatile' qualifiers on a function's return type mean the function
-     is noreturn.  */
-  if (pedantic && TYPE_VOLATILE (ret1) != TYPE_VOLATILE (ret2))
+  /* 'volatile' qualifiers on a function's return type used to mean
+     the function is noreturn.  */
+  if (TYPE_VOLATILE (ret1) != TYPE_VOLATILE (ret2))
     pedwarn ("function return types not compatible due to `volatile'");
   if (TYPE_VOLATILE (ret1))
     ret1 = build_qualified_type (TYPE_MAIN_VARIANT (ret1),

gcc/doc/invoke.texi

@@ -2349,6 +2349,12 @@ Warn whenever a function is defined with a return-type that defaults to
 @code{int}.  Also warn about any @code{return} statement with no
 return-value in a function whose return-type is not @code{void}.
 
+For C, also warn if the return type of a function has a type qualifier
+such as @code{const}.  Such a type qualifier has no effect, since the
+value returned by a function is not an lvalue.  ISO C prohibits
+qualified @code{void} return types on function definitions, so such
+return types always receive a warning even without this option.
+
 For C++, a function without return type always produces a diagnostic
 message, even when @option{-Wno-return-type} is specified.  The only
 exceptions are @samp{main} and functions defined in system headers.
@@ -2578,13 +2584,6 @@ An unsigned value is compared against zero with @samp{<} or @samp{>=}.
 Storage-class specifiers like @code{static} are not the first things in
 a declaration.  According to the C Standard, this usage is obsolescent.
 
-@item
-The return type of a function has a type qualifier such as @code{const}.
-Such a type qualifier has no effect, since the value returned by a
-function is not an lvalue.  (But don't warn about the GNU extension of
-@code{volatile void} return types.  That extension will be warned about
-if @option{-pedantic} is specified.)
-
 @item
 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
 arguments.

gcc/testsuite/ChangeLog

@@ -1,3 +1,13 @@
+2004-07-22  Joseph S. Myers  <jsm@polyomino.org.uk>
+
+	PR c/15052
+	* gcc.dg/noreturn-5.c: Test qualifiers on function type instead of
+	on return type.
+	* gcc.dg/qual-return-1.c: Use -Wreturn-type.  Update expected
+	messages.
+	* gcc.dg/qual-return-2.c: Update expected messages.
+	* gcc.dg/qual-return-3.c, gcc.dg/qual-return-4.c: New tests.
+
 2004-07-22  Joseph S. Myers  <jsm@polyomino.org.uk>
 
 	* gcc.dg/c99-init-3.c, gcc.dg/gnu99-init-2.c: New tests.

gcc/testsuite/gcc.dg/noreturn-5.c

@@ -4,4 +4,5 @@
    The testsuite uses -ansi -pedantic-errors by default, so this has
    to override.  */
 extern void xxx (int) __attribute__((noreturn));
-__volatile extern void xxx (int);
+typedef void voidfn (int);
+__volatile extern voidfn xxx;

gcc/testsuite/gcc.dg/qual-return-1.c

@@ -1,7 +1,7 @@
 /* Test for warnings for qualified function return types.  */
 /* Origin: Joseph Myers <jsm28@cam.ac.uk> */
 /* { dg-do compile } */
-/* { dg-options "-std=gnu99 -W" } */
+/* { dg-options "-std=gnu99 -Wreturn-type" } */
 
 /* Qualifying a function return type makes no sense.  */
 
@@ -11,13 +11,11 @@ const int int_fn2 (void) { return 0; } /* { dg-warning "qualifiers" "int defn" }
 
 const void void_fn (void); /* { dg-warning "qualifiers" "void decl" } */
 const void (*void_ptr) (void); /* { dg-warning "qualifiers" "void ptr" } */
-const void void_fn2 (void) { } /* { dg-warning "qualifiers" "void defn" } */
+const void void_fn2 (void) { } /* { dg-warning "qualified" "void defn" } */
 
-/* "volatile void" is a GNU extension, so only warn at -pedantic.  */
-
-volatile void vvoid_fn (void);
-volatile void (*vvoid_ptr) (void);
-volatile void vvoid_fn2 (void) { }
+volatile void vvoid_fn (void); /* { dg-warning "qualifiers" "void decl" } */
+volatile void (*vvoid_ptr) (void); /* { dg-warning "qualifiers" "void ptr" } */
+volatile void vvoid_fn2 (void) { } /* { dg-warning "qualified" "void defn" } */
 
 int *restrict ip_fn (void); /* { dg-warning "qualifiers" "restrict decl" } */
 int *restrict (*ip_ptr) (void); /* { dg-warning "qualifiers" "restrict ptr" } */

gcc/testsuite/gcc.dg/qual-return-2.c

@@ -5,10 +5,9 @@
 
 /* Qualifying a function return type makes no sense.  */
 
-/* "volatile void" is a GNU extension, so only warn at -pedantic.
-   Strictly, the first two of these should warn only if the function is
-   somewhere used or defined.  */
+/* The first two of these shouldn't warn (with just -pedantic) as long
+   as the function is not defined.  */
 
-volatile void vvoid_fn (void); /* { dg-warning "qualified" "volatile decl" } */
-volatile void (*vvoid_ptr) (void); /* { dg-warning "qualified" "volatile ptr" } */
+volatile void vvoid_fn (void);
+volatile void (*vvoid_ptr) (void);
 volatile void vvoid_fn2 (void) { } /* { dg-warning "qualified" "volatile defn" } */

gcc/testsuite/gcc.dg/qual-return-3.c

@@ -0,0 +1,16 @@
+/* Test for warnings for qualified function return types.  Bug 15052
+   from Olatunji Ruwase (tjruwase at stanfordalumni.org): qualifiers
+   should not be lost when merging declarations.  */
+
+/* Origin: Joseph Myers <jsm@polyomino.org.uk> */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+int foo (); /* { dg-error "previous declaration" "different qualifiers" } */
+const int foo () { return 0; } /* { dg-error "conflicting types" "different qualifiers" } */
+
+void bar (void);
+volatile void bar () { } /* { dg-warning "qualified|volatile" "different qualifiers" } */
+
+volatile void baz (void);
+void baz () { } /* { dg-warning "not compatible" "different qualifiers" } */

gcc/testsuite/gcc.dg/qual-return-4.c

@@ -0,0 +1,10 @@
+/* Test for warnings for qualified function return types.  -pedantic
+   test.  Only the definition gets a warning for qualified void return
+   types, not other such types within the definition.  */
+/* Origin: Joseph Myers <jsm@polyomino.org.uk> */
+/* { dg-do compile } */
+/* { dg-options "-pedantic" } */
+
+volatile void (*y)(int);
+
+volatile void (*vvf(int x))(int) { return y; }