rerere: record resolution even if file is not in merge base

Two-file merges were rare enough that they were dropped outside of the
radar.  This fix is a trivial change to builtin-rerere.c::find_conflict().
It is still sane to insist that we do not do rerere for symlinks, and
require to have stages #2 and #3, but we can drop the requirement to have
stage #1. rerere does not use information from there anyway.

This fix is from Junio, together with two tests to verify that it works
as expected.
Acked-by: NUwe Kleine-König <ukleinek@informatik.uni-freiburg.de>
Signed-off-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-rerere.c

@@ -168,19 +168,16 @@ static int find_conflict(struct path_list *conflict)
 	int i;
 	if (read_cache() < 0)
 		return error("Could not read index");
-	for (i = 0; i + 2 < active_nr; i++) {
-		struct cache_entry *e1 = active_cache[i];
-		struct cache_entry *e2 = active_cache[i+1];
-		struct cache_entry *e3 = active_cache[i+2];
-		if (ce_stage(e1) == 1 &&
-		    ce_stage(e2) == 2 &&
+	for (i = 0; i+1 < active_nr; i++) {
+		struct cache_entry *e2 = active_cache[i];
+		struct cache_entry *e3 = active_cache[i+1];
+		if (ce_stage(e2) == 2 &&
 		    ce_stage(e3) == 3 &&
-		    ce_same_name(e1, e2) && ce_same_name(e1, e3) &&
-		    S_ISREG(ntohl(e1->ce_mode)) &&
+		    ce_same_name(e2, e3) &&
 		    S_ISREG(ntohl(e2->ce_mode)) &&
 		    S_ISREG(ntohl(e3->ce_mode))) {
-			path_list_insert((const char *)e1->name, conflict);
-			i += 2;
+			path_list_insert((const char *)e2->name, conflict);
+			i++; /* skip over both #2 and #3 */
 		}
 	}
 	return 0;

t/t4200-rerere.sh

@@ -116,11 +116,12 @@ test_expect_success 'commit succeeds' \
 
 test_expect_success 'recorded postimage' "test -f $rr/postimage"
 
-git checkout -b third master
-git show second^:a1 | sed 's/To die: t/To die! T/' > a1
-git commit -q -a -m third
-
-test_expect_failure 'another conflicting merge' 'git pull . first'
+test_expect_success 'another conflicting merge' '
+	git checkout -b third master &&
+	git show second^:a1 | sed "s/To die: t/To die! T/" > a1 &&
+	git commit -q -a -m third &&
+	! git pull . first
+'
 
 git show first:a1 | sed 's/To die: t/To die! T/' > expect
 test_expect_success 'rerere kicked in' "! grep ======= a1"
@@ -164,4 +165,37 @@ test_expect_success 'garbage collection (part2)' 'git rerere gc'
 test_expect_success 'old records rest in peace' \
 	"test ! -f $rr/preimage && test ! -f $rr2/preimage"
 
+test_expect_success 'file2 added differently in two branches' '
+	git reset --hard &&
+	git checkout -b fourth &&
+	echo Hallo > file2 &&
+	git add file2 &&
+	git commit -m version1 &&
+	git checkout third &&
+	echo Bello > file2 &&
+	git add file2 &&
+	git commit -m version2 &&
+	! git merge fourth &&
+	sha1=$(sed -e "s/	.*//" .git/rr-cache/MERGE_RR) &&
+	rr=.git/rr-cache/$sha1 &&
+	echo Cello > file2 &&
+	git add file2 &&
+	git commit -m resolution
+'
+
+test_expect_success 'resolution was recorded properly' '
+	git reset --hard HEAD~2 &&
+	git checkout -b fifth &&
+	echo Hallo > file3 &&
+	git add file3 &&
+	git commit -m version1 &&
+	git checkout third &&
+	echo Bello > file3 &&
+	git add file3 &&
+	git commit -m version2 &&
+	! git merge fifth &&
+	git diff-files -q &&
+	test Cello = "$(cat file3)"
+'
+
 test_done