rerere: simplify check_one_conflict() helper function

The helper function is responsible for inspecting the index and
deciding if the path is merged, is conflicted in a way that we would
want to handle, or is conflicted in a way that we cannot handle.

Currently, only conflicts with both stage #2 and stage #3 are
handled, but eventually we would want to be able to deal with
delete-modify conflicts (i.e. only one of stages #2 and #3 exist).
Streamline the implementation of the function to make it easier to
extend.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

rerere.c

@@ -499,41 +499,37 @@ static int handle_file(struct index_state *istate,
 }
 
 /*
- * Look at a cache entry at "i" and see if it is not conflicting,
- * conflicting and we are willing to handle, or conflicting and
- * we are unable to handle, and return the determination in *type.
+ * Look at a cache entry at "i" and see if it is not conflicting
+ * (RESOLVED), conflicting and we are willing to handle (THREE_STAGED),
+ * or conflicting and we are unable to handle (PUNTED), and return the
+ * determination in *type.
+ *
  * Return the cache index to be looked at next, by skipping the
  * stages we have already looked at in this invocation of this
  * function.
  */
 static int check_one_conflict(struct index_state *istate, int i, int *type)
 {
 	const struct cache_entry *e = istate->cache[i];
+	unsigned int seen_stages = 0;
 
 	if (!ce_stage(e)) {
 		*type = RESOLVED;
 		return i + 1;
 	}
 
 	*type = PUNTED;
-	while (i < istate->cache_nr && ce_stage(istate->cache[i]) == 1)
-		i++;
-
-	/* Only handle regular files with both stages #2 and #3 */
-	if (i + 1 < istate->cache_nr) {
-		const struct cache_entry *e2 = istate->cache[i];
-		const struct cache_entry *e3 = istate->cache[i + 1];
-		if (ce_stage(e2) == 2 &&
-		    ce_stage(e3) == 3 &&
-		    ce_same_name(e, e3) &&
-		    S_ISREG(e2->ce_mode) &&
-		    S_ISREG(e3->ce_mode))
-			*type = THREE_STAGED;
+	for (; i < istate->cache_nr; i++) {
+		const struct cache_entry *n = istate->cache[i];
+		if (!ce_same_name(n, e))
+			break;
+		if (S_ISREG(n->ce_mode))
+			seen_stages |= 1u << (ce_stage(n) - 1);
 	}
 
-	/* Skip the entries with the same name */
-	while (i < istate->cache_nr && ce_same_name(e, istate->cache[i]))
-		i++;
+	if ((seen_stages & 6) == 6)
+		*type = THREE_STAGED; /* has both stages #2 and #3 */
+
 	return i;
 }