Change app-id rules again, now only allow dashes in last element

It turns out that live apps were exporting files with dashes
other than "-symbolic". For instance "org.libreoffice.LibreOffice" was
exporting "org.libreoffice.LibreOffice-writer.desktop".

Allowing any dashes in the last segment like this is really no diffent
than allowing org.libreoffice.LibreOffice.writer.desktop which we
already do. Any conflicts here are under the control of the owner
of the org.libreoffice prefix.

However, allowing dashes in the earlier segments is more problematic.
For instance, any file exported by "org.my-foo.App" could conflict with
an app called "org.my" if this was allowed.

So, as a middle ground, we're allowing dashes in the last segment of
the App id only.

common/flatpak-utils.c

@@ -361,19 +361,19 @@ flatpak_migrate_from_xdg_app (void)
 }
 
 static gboolean
-is_valid_initial_name_character (gint c)
+is_valid_initial_name_character (gint c, gboolean allow_dash)
 {
   return
     (c >= 'A' && c <= 'Z') ||
     (c >= 'a' && c <= 'z') ||
-    (c == '_') || (c == '-');
+    (c == '_') || (allow_dash && c == '-');
 }
 
 static gboolean
-is_valid_name_character (gint c)
+is_valid_name_character (gint c, gboolean allow_dash)
 {
   return
-    is_valid_initial_name_character (c) ||
+    is_valid_initial_name_character (c, allow_dash) ||
     (c >= '0' && c <= '9');
 }
 
@@ -388,16 +388,15 @@ is_valid_name_character (gint c)
  *
  * Each element must only contain the ASCII characters
  * "[A-Z][a-z][0-9]_-". Elements may not begin with a digit.
+ * Additionally "-" is only allowed in the last element.
  *
  * App names must not begin with a '.' (period) character.
  *
- * App names must not end with "-symbolic".
- *
  * App names must not exceed 255 characters in length.
  *
  * The above means that any app name is also a valid DBus well known
  * bus name, but not all DBus names are valid app names. The difference are:
- * 1) DBus name elements may contain '-'
+ * 1) DBus name elements may contain '-' in the non-last element.
  * 2) DBus names require only two elements
  *
  * Returns: %TRUE if valid, %FALSE otherwise.
@@ -412,7 +411,9 @@ flatpak_is_valid_name (const char *string,
   gboolean ret;
   const gchar *s;
   const gchar *end;
+  const gchar *last_dot;
   int dot_count;
+  gboolean last_element;
 
   g_return_val_if_fail (string != NULL, FALSE);
 
@@ -433,26 +434,19 @@ flatpak_is_valid_name (const char *string,
       goto out;
     }
 
-  /* To special case symbolic icons we allow org.foo.Bar to export
-     files named "org.foo.Bar-symbolic.*". To avoid conflicts for
-     we then forbid app names ending with "-symbolic". */
-  if (G_UNLIKELY (g_str_has_suffix (string, "-symbolic")))
-    {
-      g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
-                           "Name are not allowed to end with '-symbolic'");
-      goto out;
-    }
-
   end = string + len;
 
+  last_dot = strrchr (string, '.');
+  last_element = FALSE;
+
   s = string;
   if (G_UNLIKELY (*s == '.'))
     {
       g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
                            "Name can't start with a period");
       goto out;
     }
-  else if (G_UNLIKELY (!is_valid_initial_name_character (*s)))
+  else if (G_UNLIKELY (!is_valid_initial_name_character (*s, last_element)))
     {
       g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
                    "Name can't start with %c", *s);
@@ -465,25 +459,35 @@ flatpak_is_valid_name (const char *string,
     {
       if (*s == '.')
         {
+          if (s == last_dot)
+            last_element = TRUE;
           s += 1;
           if (G_UNLIKELY (s == end))
             {
               g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
                                    "Name can't end with a period");
               goto out;
             }
-          if (!is_valid_initial_name_character (*s))
+          if (!is_valid_initial_name_character (*s, last_element))
             {
-              g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
-                           "Name segment can't start with %c", *s);
+              if (*s == '-')
+                g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                             "Only last name segment can contain -");
+              else
+                g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                             "Name segment can't start with %c", *s);
               goto out;
             }
           dot_count++;
         }
-      else if (G_UNLIKELY (!is_valid_name_character (*s)))
+      else if (G_UNLIKELY (!is_valid_name_character (*s, last_element)))
         {
-          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
-                       "Name can't contain %c", *s);
+          if (*s == '-')
+            g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                         "Only last name segment can contain -");
+          else
+            g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                         "Name can't contain %c", *s);
           goto out;
         }
       s += 1;
@@ -515,9 +519,7 @@ flatpak_has_name_prefix (const char *string,
   return
     *rest == 0 ||
     *rest == '.' ||
-    !is_valid_name_character (*rest) ||
-    /* Special case -symbolic icon names */
-    g_str_has_prefix (rest, "-symbolic.");
+    !is_valid_name_character (*rest, FALSE);
 }
 
 static gboolean