cast: fix cast of void * when we don't have GCC features.

I thought using sizeof() comparison to compare the types was clever,
but it doesn't work on void pointers, as sizeof(void) is illegal.

ccan/cast/cast.h

@@ -122,11 +122,8 @@
 #else
 #define cast_sign_compatible(type, expr)		\
 	(sizeof(*(type)0) == 1 && sizeof(*(expr)) == 1)
-#define cast_const_compat1(expr, type)		\
-	(sizeof(*(expr)) == sizeof(*(type)0))
-#define cast_const_compat2(expr, type)		\
-	(sizeof(**(expr)) == sizeof(**(type)0))
-#define cast_const_compat3(expr, type)			\
-	(sizeof(***(expr)) == sizeof(***(type)0))
+#define cast_const_compat1(expr, type)		(1)
+#define cast_const_compat2(expr, type)		(1)
+#define cast_const_compat3(expr, type)		(1)
 #endif
 #endif /* CCAN_CAST_H */

ccan/cast/test/compile_fail-cast_const-sizesame.c

-#include <ccan/cast/cast.h>
-#include <stdlib.h>
-
-/* Note: this *isn't* sizeof(char) on all platforms. */
-struct char_struct {
-	char c;
-};
-
-int main(int argc, char *argv[])
-{
-	char *uc;
-	const
-#ifdef FAIL
-		struct char_struct
-#else
-		char
-#endif
-		*p = NULL;
-
-	uc = cast_const(char *, p);
-	return 0;
-}
-
-#ifdef FAIL
-#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
-#error "Unfortunately we don't fail if cast_const can only use size"
-#endif
-#endif

ccan/cast/test/compile_fail-cast_const.c

 #include <ccan/cast/cast.h>
 #include <stdlib.h>
 
+/* Note: this *isn't* sizeof(char) on all platforms. */
+struct char_struct {
+	char c;
+};
+
 int main(int argc, char *argv[])
 {
 	char *uc;
-	const 
+	const
 #ifdef FAIL
-		int
+		struct char_struct
 #else
 		char
 #endif
@@ -15,3 +20,9 @@ int main(int argc, char *argv[])
 	uc = cast_const(char *, p);
 	return 0;
 }
+
+#ifdef FAIL
+#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
+#error "Unfortunately we don't fail if cast_const can only use size"
+#endif
+#endif

ccan/cast/test/compile_fail-cast_const2-sizesame.c

-#include <ccan/cast/cast.h>
-#include <stdlib.h>
-
-/* Note: this *isn't* sizeof(char) on all platforms. */
-struct char_struct {
-	char c;
-};
-
-int main(int argc, char *argv[])
-{
-	char **uc;
-	const
-#ifdef FAIL
-		struct char_struct
-#else
-		char
-#endif
-		**p = NULL;
-
-	uc = cast_const2(char **, p);
-	return 0;
-}
-
-#ifdef FAIL
-#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
-#error "Unfortunately we don't fail if cast_const can only use size"
-#endif
-#endif

ccan/cast/test/compile_fail-cast_const2.c

 #include <ccan/cast/cast.h>
 #include <stdlib.h>
 
+/* Note: this *isn't* sizeof(char) on all platforms. */
+struct char_struct {
+	char c;
+};
+
 int main(int argc, char *argv[])
 {
 	char **uc;
-	const 
+	const
 #ifdef FAIL
-		int
+		struct char_struct
 #else
 		char
 #endif
@@ -15,3 +20,9 @@ int main(int argc, char *argv[])
 	uc = cast_const2(char **, p);
 	return 0;
 }
+
+#ifdef FAIL
+#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
+#error "Unfortunately we don't fail if cast_const can only use size"
+#endif
+#endif

ccan/cast/test/compile_fail-cast_const3-sizesame.c

-#include <ccan/cast/cast.h>
-#include <stdlib.h>
-
-/* Note: this *isn't* sizeof(char) on all platforms. */
-struct char_struct {
-	char c;
-};
-
-int main(int argc, char *argv[])
-{
-	char ***uc;
-	const
-#ifdef FAIL
-		struct char_struct
-#else
-		char
-#endif
-		***p = NULL;
-
-	uc = cast_const3(char ***, p);
-	return 0;
-}
-
-#ifdef FAIL
-#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
-#error "Unfortunately we don't fail if cast_const can only use size"
-#endif
-#endif

ccan/cast/test/compile_fail-cast_const3.c

 #include <ccan/cast/cast.h>
 #include <stdlib.h>
 
+/* Note: this *isn't* sizeof(char) on all platforms. */
+struct char_struct {
+	char c;
+};
+
 int main(int argc, char *argv[])
 {
 	char ***uc;
-	const 
+	const
 #ifdef FAIL
-		int
+		struct char_struct
 #else
 		char
 #endif
@@ -15,3 +20,9 @@ int main(int argc, char *argv[])
 	uc = cast_const3(char ***, p);
 	return 0;
 }
+
+#ifdef FAIL
+#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
+#error "Unfortunately we don't fail if cast_const can only use size"
+#endif
+#endif

ccan/cast/test/compile_fail-cast_signed-const.c

@@ -13,3 +13,9 @@ int main(int argc, char *argv[])
 	uc = cast_signed(unsigned char *, p);
 	return 0;
 }
+
+#ifdef FAIL
+#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
+#error "Unfortunately we don't fail if cast_const can only use size"
+#endif
+#endif

ccan/cast/test/compile_ok-cast_void.c

+#include <ccan/cast/cast.h>
+
+static void *remove_void(const void *p)
+{
+	return cast_const(void *, p);
+}
+
+int main(void)
+{
+	void *p = remove_void("foo");
+	return !p;
+}