tree-diff: rename compare_tree_entry -> tree_entry_pathcmp

Since previous commit, this function does not compare entry hashes, and
mode are compared fully outside of it. So what it does is compare entry
names and DIR bit in modes. Reflect this in its name.

Add documentation stating the semantics, and move the note about
files/dirs comparison to it.

Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

tree-diff.c

@@ -9,7 +9,14 @@
 static void show_path(struct strbuf *base, struct diff_options *opt,
 		      struct tree_desc *t1, struct tree_desc *t2);
 
-static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2)
+/*
+ * Compare two tree entries, taking into account only path/S_ISDIR(mode),
+ * but not their sha1's.
+ *
+ * NOTE files and directories *always* compare differently, even when having
+ *      the same name - thanks to base_name_compare().
+ */
+static int tree_entry_pathcmp(struct tree_desc *t1, struct tree_desc *t2)
 {
 	unsigned mode1, mode2;
 	const char *path1, *path2;
@@ -22,10 +29,6 @@ static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2)
 	pathlen1 = tree_entry_len(&t1->entry);
 	pathlen2 = tree_entry_len(&t2->entry);
 
-	/*
-	 * NOTE files and directories *always* compare differently,
-	 * even when having the same name.
-	 */
 	cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
 	return cmp;
 }
@@ -168,7 +171,7 @@ int diff_tree(struct tree_desc *t1, struct tree_desc *t2,
 			continue;
 		}
 
-		cmp = compare_tree_entry(t1, t2);
+		cmp = tree_entry_pathcmp(t1, t2);
 
 		/* t1 = t2 */
 		if (cmp == 0) {