tree_entry_interesting(): give meaningful names to return values

It is a basic code hygiene to avoid magic constants that are unnamed.
Besides, this helps extending the value later on for "interesting, but
cannot decide if the entry truely matches yet" (ie. prefix matches)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/tree-diff.c b/tree-diff.c
index 6782484..7a51d09 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -64,14 +64,14 @@
 static void show_tree(struct diff_options *opt, const char *prefix,
 		      struct tree_desc *desc, struct strbuf *base)
 {
-	int match = 0;
+	enum interesting match = entry_not_interesting;
 	for (; desc->size; update_tree_entry(desc)) {
-		if (match != 2) {
+		if (match != all_entries_interesting) {
 			match = tree_entry_interesting(&desc->entry, base, 0,
 						       &opt->pathspec);
-			if (match < 0)
+			if (match == all_entries_not_interesting)
 				break;
-			if (match == 0)
+			if (match == entry_not_interesting)
 				continue;
 		}
 		show_entry(opt, prefix, desc, base);
@@ -114,12 +114,13 @@
 }
 
 static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
-			       struct diff_options *opt, int *match)
+			       struct diff_options *opt,
+			       enum interesting *match)
 {
 	while (t->size) {
 		*match = tree_entry_interesting(&t->entry, base, 0, &opt->pathspec);
 		if (*match) {
-			if (*match < 0)
+			if (*match == all_entries_not_interesting)
 				t->size = 0;
 			break;
 		}
@@ -132,7 +133,8 @@
 {
 	struct strbuf base;
 	int baselen = strlen(base_str);
-	int t1_match = 0, t2_match = 0;
+	enum interesting t1_match = entry_not_interesting;
+	enum interesting t2_match = entry_not_interesting;
 
 	/* Enable recursion indefinitely */
 	opt->pathspec.recursive = DIFF_OPT_TST(opt, RECURSIVE);