path_utils: new mp_stripext shorthand

This functionality has at least two users, screenshot template expansion
of %F and the filename/no-ext property getter. Generalize what the
latter does, so it can be reused by the former, which currently relies
on a private stripext function.

Also the check in mp_splitext, if there is a leading dot in the path
did not work on paths that were not basenames already. It would've also
split a partial path, in case there were more than one. And the check
for / in the split portion, was ignoring the possibility of windows
paths which use \ as separator.
Thus only work with the basename of the provided path.

Author: WhitePeter

misc/path_utils.c

@@ -92,15 +92,27 @@ void mp_path_strip_trailing_separator(char *path)
 char *mp_splitext(const char *path, bstr *root)
 {
     mp_assert(path);
-    int skip = (*path == '.'); // skip leading dot for "hidden" unix files
-    const char *split = strrchr(path + skip, '.');
-    if (!split || !split[1] || strchr(split, '/'))
+    char *bn = mp_basename(path);
+
+    // Skip all leading dots, not just for "hidden" unix files, otherwise we
+    // end up splitting a part of the filename sans leading dot.
+    while (*bn == '.')
+        bn++ ;
+
+    const char *split = strrchr(bn, '.');
+    if (!split || !split[1])
         return NULL;
     if (root)
         *root = (bstr){(char *)path, split - path};
     return (char *)split + 1;
 }
 
+char *mp_stripext(void *talloc_ctx, const char *s)
+{
+    bstr root;
+    return mp_splitext(s, &root) ? bstrto0(talloc_ctx, root) : (char *)s;
+}
+
 bool mp_path_is_absolute(struct bstr path)
 {
     if (path.len && strchr(mp_path_separators, path.start[0]))

misc/path_utils.h

@@ -37,6 +37,9 @@ char *mp_basename(const char *path);
  */
 char *mp_splitext(const char *path, bstr *root);
 
+// This is a shorthand to remove the extension
+char *mp_stripext(void *talloc_ctx, const char *s);
+
 /* Return struct bstr referencing directory part of path, or if that
  * would be empty, ".".
  */