Merge branch 'en/rerere-multi-stage-1-fix' into maint

A corner case bugfix in "git rerere" code.

* en/rerere-multi-stage-1-fix:
  rerere: avoid buffer overrun
  t4200: demonstrate rerere segfault on specially crafted merge

rerere.c

@@ -533,7 +533,7 @@ static int check_one_conflict(int i, int *type)
 	}
 
 	*type = PUNTED;
-	while (ce_stage(active_cache[i]) == 1)
+	while (i < active_nr && ce_stage(active_cache[i]) == 1)
 		i++;
 
 	/* Only handle regular files with both stages #2 and #3 */

t/t4200-rerere.sh

@@ -577,4 +577,33 @@ test_expect_success 'multiple identical conflicts' '
 	count_pre_post 0 0
 '
 
+test_expect_success 'setup simple stage 1 handling' '
+	test_create_repo stage_1_handling &&
+	(
+		cd stage_1_handling &&
+
+		test_seq 1 10 >original &&
+		git add original &&
+		git commit -m original &&
+
+		git checkout -b A master &&
+		git mv original A &&
+		git commit -m "rename to A" &&
+
+		git checkout -b B master &&
+		git mv original B &&
+		git commit -m "rename to B"
+	)
+'
+
+test_expect_success 'test simple stage 1 handling' '
+	(
+		cd stage_1_handling &&
+
+		git config rerere.enabled true &&
+		git checkout A^0 &&
+		test_must_fail git merge B^0
+	)
+'
+
 test_done