worktree: add utility to find worktree by pathname

find_worktree() employs heuristics to match user provided input -- which
may be a pathname or some sort of shorthand -- with an actual worktree.
Although this convenience allows a user to identify a worktree with
minimal typing, the black-box nature of these heuristics makes it
potentially difficult for callers which already know the exact path of a
worktree to be confident that the correct worktree will be returned for
any specific pathname (particularly a relative one), especially as the
heuristics are enhanced and updated.

Therefore, add a companion function, find_worktree_by_path(), which
deterministically identifies a worktree strictly by pathname with no
interpretation and no magic matching.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

worktree.c

@@ -215,7 +215,6 @@ struct worktree *find_worktree(struct worktree **list,
 			       const char *arg)
 {
 	struct worktree *wt;
-	char *path;
 	char *to_free = NULL;
 
 	if ((wt = find_worktree_by_suffix(list, arg)))
@@ -223,11 +222,17 @@ struct worktree *find_worktree(struct worktree **list,
 
 	if (prefix)
 		arg = to_free = prefix_filename(prefix, arg);
-	path = real_pathdup(arg, 0);
-	if (!path) {
+	wt = find_worktree_by_path(list, arg);
 	free(to_free);
+	return wt;
+}
+
+struct worktree *find_worktree_by_path(struct worktree **list, const char *p)
+{
+	char *path = real_pathdup(p, 0);
+
+	if (!path)
 		return NULL;
-	}
 	for (; *list; list++) {
 		const char *wt_path = real_path_if_valid((*list)->path);
 
@@ -235,7 +240,6 @@ struct worktree *find_worktree(struct worktree **list,
 			break;
 	}
 	free(path);
-	free(to_free);
 	return *list;
 }
 

worktree.h

@@ -61,6 +61,12 @@ struct worktree *find_worktree(struct worktree **list,
 			       const char *prefix,
 			       const char *arg);
 
+/*
+ * Return the worktree corresponding to `path`, or NULL if no such worktree
+ * exists.
+ */
+struct worktree *find_worktree_by_path(struct worktree **, const char *path);
+
 /*
  * Return true if the given worktree is the main one.
  */