Merge branch 'gstring-free-warning' into 'main'

Make g_string_free (_, FALSE) warn on unused result

See merge request GNOME/glib!3226

gio/glib-compile-schemas.c

@@ -709,8 +709,8 @@ key_state_serialise (KeyState *state)
               gsize size;
               gsize i;
 
-              data = state->strinfo->str;
               size = state->strinfo->len;
+              data = g_string_free_and_steal (g_steal_pointer (&state->strinfo));
 
               words = data;
               for (i = 0; i < size / sizeof (guint32); i++)
@@ -720,9 +720,6 @@ key_state_serialise (KeyState *state)
                                                data, size, TRUE,
                                                g_free, data);
 
-              g_string_free (state->strinfo, FALSE);
-              state->strinfo = NULL;
-
               g_variant_builder_add (&builder, "(y@au)",
                                      state->is_flags ? 'f' :
                                      state->is_enum ? 'e' : 'c',

gio/tests/pollable.c

@@ -263,14 +263,12 @@ test_pollable_unix_file (void)
 static void
 test_pollable_unix_nulldev (void)
 {
-  int fd;
-
   g_test_summary ("Test that /dev/null is not considered pollable, but only if "
                   "on a system where we are able to tell it apart from devices "
                   "that actually implement poll");
 
 #if defined (HAVE_EPOLL_CREATE) || defined (HAVE_KQUEUE)
-  fd = g_open ("/dev/null", O_RDWR, 0);
+  int fd = g_open ("/dev/null", O_RDWR, 0);
   g_assert_cmpint (fd, !=, -1);
 
   g_assert_not_pollable (fd);

glib/gkeyfile.c

@@ -3546,10 +3546,7 @@ g_key_file_get_key_comment (GKeyFile     *key_file,
     }
 
   if (string != NULL)
-    {
-      comment = string->str;
-      g_string_free (string, FALSE);
-    }
+    comment = g_string_free_and_steal (g_steal_pointer (&string));
   else
     comment = NULL;
 

glib/gstring.c

@@ -206,8 +206,8 @@ g_string_new_len (const gchar *init,
  *          (i.e. %NULL if @free_segment is %TRUE)
  */
 gchar *
-g_string_free (GString  *string,
-               gboolean  free_segment)
+(g_string_free) (GString  *string,
+                 gboolean  free_segment)
 {
   gchar *segment;
 
@@ -242,7 +242,7 @@ g_string_free (GString  *string,
 gchar *
 g_string_free_and_steal (GString *string)
 {
-  return g_string_free (string, FALSE);
+  return (g_string_free) (string, FALSE);
 }
 
 /**

glib/gstring.h

@@ -57,10 +57,23 @@ GString*     g_string_new_len           (const gchar     *init,
 GLIB_AVAILABLE_IN_ALL
 GString*     g_string_sized_new         (gsize            dfl_size);
 GLIB_AVAILABLE_IN_ALL
-gchar*       g_string_free              (GString         *string,
+gchar*      (g_string_free)             (GString         *string,
                                          gboolean         free_segment);
 GLIB_AVAILABLE_IN_2_76
 gchar*       g_string_free_and_steal    (GString         *string) G_GNUC_WARN_UNUSED_RESULT;
+
+#if G_GNUC_CHECK_VERSION (2, 0) && (GLIB_VERSION_MIN_REQUIRED >= GLIB_VERSION_2_76)
+
+#define g_string_free(str, free_segment)        \
+  (__builtin_constant_p (free_segment) ?        \
+    ((free_segment) ?                           \
+      (g_string_free) ((str), (free_segment)) : \
+      g_string_free_and_steal (str))            \
+    :                                           \
+    (g_string_free) ((str), (free_segment)))
+
+#endif /* G_GNUC_CHECK_VERSION (2, 0) && (GLIB_VERSION_MIN_REQUIRED >= GLIB_VERSION_2_76) */
+
 GLIB_AVAILABLE_IN_2_34
 GBytes*      g_string_free_to_bytes     (GString         *string);
 GLIB_AVAILABLE_IN_ALL

glib/gwakeup.c

@@ -21,6 +21,7 @@
 
 #include "config.h"
 
+#include <stdint.h>
 
 /* gwakeup.c is special -- GIO and some test cases include it.  As such,
  * it cannot include other glib headers without triggering the single

glib/tests/cxx.cpp

@@ -472,6 +472,35 @@ test_string_append (void)
   g_string_free (string, TRUE);
 }
 
+static void
+test_string_free (void)
+{
+  GString *str;
+  gchar *data;
+
+  g_test_message ("Test that g_string_free() macro compiles and doesn’t "
+                  "cause any compiler warnings in C++ mode");
+
+  /* Test that g_string_free (_, TRUE) does not cause a warning if
+   * its return value is unused. */
+  str = g_string_new ("test");
+  g_string_free (str, TRUE);
+
+  /* Test that g_string_free (_, FALSE) does not emit a warning if
+   * its return value is used. */
+  str = g_string_new ("test");
+  data = g_string_free (str, FALSE);
+  g_free (data);
+
+  /* Test that g_string_free () with an expression that is always FALSE
+   * at runtime, but the compiler can't know it, does not cause any
+   * warnings if its return value is unused. */
+  str = g_string_new ("test");
+  data = str->str;
+  g_string_free (str, g_test_get_path ()[0] == 0);
+  g_free (data);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -502,6 +531,7 @@ main (int argc, char *argv[])
   g_test_add_func ("/C++/str-has-suffix", test_str_has_suffix);
   g_test_add_func ("/C++/str-has-suffix/macro", test_str_has_suffix_macro);
   g_test_add_func ("/C++/string-append", test_string_append);
+  g_test_add_func ("/C++/string-free", test_string_free);
 
   return g_test_run ();
 }

glib/tests/markup-subparser.c

@@ -83,9 +83,7 @@ subparser_end (GMarkupParseContext  *ctx,
   char *result;
 
   string = g_markup_parse_context_pop (ctx);
-  result = string->str;
-
-  g_string_free (string, FALSE);
+  result = g_string_free_and_steal (g_steal_pointer (&string));
   strings_allocated--;
 
   if (result == NULL || result[0] == '\0')
@@ -156,9 +154,7 @@ replay_parser_end (GMarkupParseContext  *ctx,
       return NULL;
     }
 
-  result = string->str;
-
-  g_string_free (string, FALSE);
+  result = g_string_free_and_steal (g_steal_pointer (&string));
   strings_allocated--;
 
   if (result == NULL || result[0] == '\0')