g_key_file_has_key_full: New function to fix g_key_file_has_key()'s GError semantics

See https://bugzilla.gnome.org/show_bug.cgi?id=649657 for discussion
of why it's bad for bindings for gerror return values to both signal
errors and carry meaning.

https://bugzilla.gnome.org/show_bug.cgi?id=650345

docs/reference/glib/glib-sections.txt

@@ -1746,6 +1746,7 @@ g_key_file_get_groups
 g_key_file_get_keys
 g_key_file_has_group
 g_key_file_has_key
+g_key_file_has_key_full
 
 <SUBSECTION>
 g_key_file_get_value

glib/gkeyfile.c

@@ -3130,14 +3130,22 @@ g_key_file_has_group (GKeyFile    *key_file,
 }
 
 /**
- * g_key_file_has_key:
+ * g_key_file_has_key: (skip)
  * @key_file: a #GKeyFile
  * @group_name: a group name
  * @key: a key name
  * @error: return location for a #GError
  *
  * Looks whether the key file has the key @key in the group
- * @group_name. 
+ * @group_name.
+ *
+ * <note>This function does not follow the rules for #GError strictly;
+ * the return value both carries meaning and signals an error.  To use
+ * this function, you must pass a #GError pointer in @error, and check
+ * whether it is not %NULL to see if an error occurred.</note>
+ *
+ * See g_key_file_has_key_full() for a replacement function which does
+ * follow the #GError rules.
  *
  * Return value: %TRUE if @key is a part of @group_name, %FALSE
  * otherwise.
@@ -3149,6 +3157,44 @@ g_key_file_has_key (GKeyFile     *key_file,
 		    const gchar  *group_name,
 		    const gchar  *key,
 		    GError      **error)
+{
+  GError *temp_error = NULL;
+  gboolean has_key;
+
+  if (g_key_file_has_key_full (key_file, group_name, key, &has_key, &temp_error))
+    {
+      return has_key;
+    }
+  else
+    {
+      g_propagate_error (error, temp_error);
+      return FALSE;
+    }
+}
+
+/**
+ * g_key_file_has_key_full:
+ * @key_file: a #GKeyFile
+ * @group_name: a group name
+ * @key: a key name
+ * @has_key: (out) (allow-none): Return location for whether or not key exists
+ * @error: return location for a #GError
+ *
+ * Looks whether the key file has the key @key in the group
+ * @group_name.
+ *
+ * Return value: %TRUE if a group with the name @group_name
+ * exists. Otherwise, @error is set and %FALSE is returned.
+ *
+ * Since: 2.30
+ * Rename to: g_key_file_has_key
+ **/
+gboolean
+g_key_file_has_key_full (GKeyFile     *key_file,
+			 const gchar  *group_name,
+			 const gchar  *key,
+			 gboolean     *has_key,
+			 GError      **error)
 {
   GKeyFileKeyValuePair *pair;
   GKeyFileGroup *group;
@@ -3171,7 +3217,9 @@ g_key_file_has_key (GKeyFile     *key_file,
 
   pair = g_key_file_lookup_key_value_pair (key_file, group, key);
 
-  return pair != NULL;
+  if (has_key)
+    *has_key = pair != NULL;
+  return TRUE;
 }
 
 static void

glib/gkeyfile.h

@@ -94,6 +94,11 @@ gboolean  g_key_file_has_key                (GKeyFile             *key_file,
 					     const gchar          *group_name,
 					     const gchar          *key,
 					     GError              **error);
+gboolean  g_key_file_has_key_full           (GKeyFile             *key_file,
+					     const gchar          *group_name,
+					     const gchar          *key,
+					     gboolean             *has_key,
+					     GError              **error);
 gchar    *g_key_file_get_value              (GKeyFile             *key_file,
 					     const gchar          *group_name,
 					     const gchar          *key,

glib/glib.symbols

@@ -611,6 +611,7 @@ g_key_file_get_string_list G_GNUC_MALLOC
 g_key_file_get_value G_GNUC_MALLOC
 g_key_file_has_group
 g_key_file_has_key
+g_key_file_has_key_full
 g_key_file_load_from_dirs
 g_key_file_load_from_data
 g_key_file_load_from_data_dirs

glib/tests/keyfile.c

@@ -444,6 +444,7 @@ test_listing (void)
   gsize len;
   gchar *start;
   GError *error = NULL;
+  gboolean has_key;
 
   const gchar *data =
     "[group1]\n"
@@ -496,6 +497,21 @@ test_listing (void)
   g_key_file_has_key (keyfile, "no-such-group", "key", &error);
   check_error (&error, G_KEY_FILE_ERROR, G_KEY_FILE_ERROR_GROUP_NOT_FOUND);
 
+  g_assert (g_key_file_has_key_full (keyfile, "group1", "key1", &has_key, &error));
+  check_no_error (&error);
+  g_assert (has_key);
+
+  g_assert (g_key_file_has_key_full (keyfile, "group2", "key3", &has_key, &error));
+  check_no_error (&error);
+  g_assert (has_key);
+
+  g_assert (g_key_file_has_key_full (keyfile, "group2", "no-such-key", &has_key, &error));
+  g_assert (!has_key);
+  check_no_error (&error);
+
+  g_assert (!g_key_file_has_key_full (keyfile, "no-such-group", "key", &has_key, &error));
+  check_error (&error, G_KEY_FILE_ERROR, G_KEY_FILE_ERROR_GROUP_NOT_FOUND);
+
   g_key_file_free (keyfile);
 }