status: reject deserialize in V2 and conflicts

Teach status deserialize code to reject status cache
when printing in porcelain V2 and there are unresolved
conflicts in the cache file.  A follow-on task might
extend the cache format to include this additiona data.

See code for longer explanation.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

t/t7522-serialized-status.sh

@@ -51,8 +51,14 @@ test_expect_success 'setup' '
 
 	test_oid_cache <<-EOF
 	branch_oid sha1:68d4a437ea4c2de65800f48c053d4d543b55c410
+	x_base sha1:587be6b4c3f93f93c489c0111bba5596147a26cb
+	x_ours sha1:b68025345d5301abad4d9ec9166f455243a0d746
+	x_theirs sha1:975fbec8256d3e8a3797e7a3611380f27c49f4ac
 
 	branch_oid sha256:6b95e4b1ea911dad213f2020840f5e92d3066cf9e38cf35f79412ec58d409ce4
+	x_base sha256:14f5162e2fe3d240d0d37aaab0f90e4af9a7cfa79639f3bab005b5bfb4174d9f
+	x_ours sha256:3a404ba030a4afa912155c476a48a253d4b3a43d0098431b6d6ca6e554bd78fb
+	x_theirs sha256:44dc634218adec09e34f37839b3840bad8c6103693e9216626b32d00e093fa35
 	EOF
 '
 
@@ -171,7 +177,7 @@ test_expect_success 'verify no-ahead-behind and serialized status integration' '
 '
 
 test_expect_success 'verify new --serialize=path mode' '
-	#test_when_finished "rm serialized_status.dat expect new_change.txt output.1 output.2" &&
+	test_when_finished "rm serialized_status.dat expect new_change.txt output.1 output.2" &&
 	cat >expect <<-\EOF &&
 	? expect
 	? output.1
@@ -193,4 +199,86 @@ test_expect_success 'verify new --serialize=path mode' '
 	test_cmp expect output.2
 '
 
+test_expect_success 'merge conflicts' '
+
+	# create a merge conflict.
+
+	git init -b main conflicts &&
+	echo x >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m x &&
+	git -C conflicts branch a &&
+	git -C conflicts branch b &&
+	git -C conflicts checkout a &&
+	echo y >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m a &&
+	git -C conflicts checkout b &&
+	echo z >conflicts/x.txt &&
+	git -C conflicts add x.txt &&
+	git -C conflicts commit -m b &&
+	test_must_fail git -C conflicts merge --no-commit a &&
+
+	# verify that regular status correctly identifies it
+	# in each format.
+
+	cat >expect.v2 <<EOF &&
+u UU N... 100644 100644 100644 100644 $(test_oid x_base) $(test_oid x_ours) $(test_oid x_theirs) x.txt
+EOF
+	git -C conflicts status --porcelain=v2 >observed.v2 &&
+	test_cmp expect.v2 observed.v2 &&
+
+	cat >expect.long <<EOF &&
+On branch b
+You have unmerged paths.
+  (fix conflicts and run "git commit")
+  (use "git merge --abort" to abort the merge)
+
+Unmerged paths:
+  (use "git add <file>..." to mark resolution)
+	both modified:   x.txt
+
+no changes added to commit (use "git add" and/or "git commit -a")
+EOF
+	git -C conflicts status --long >observed.long &&
+	test_cmp expect.long observed.long &&
+
+	cat >expect.short <<EOF &&
+UU x.txt
+EOF
+	git -C conflicts status --short >observed.short &&
+	test_cmp expect.short observed.short &&
+
+	# save status data in serialized cache.
+
+	git -C conflicts status --serialize >serialized &&
+
+	# make some dirt in the worktree so we can tell whether subsequent
+	# status commands used the cached data or did a fresh status.
+
+	echo dirt >conflicts/dirt.txt &&
+
+	# run status using the cached data.
+
+	git -C conflicts status --long --deserialize=../serialized >observed.long &&
+	test_cmp expect.long observed.long &&
+
+	git -C conflicts status --short --deserialize=../serialized >observed.short &&
+	test_cmp expect.short observed.short &&
+
+	# currently, the cached data does not have enough information about
+	# merge conflicts for porcelain V2 format.  (And V2 format looks at
+	# the index to get that data, but the whole point of the serialization
+	# is to avoid reading the index unnecessarily.)  So V2 always rejects
+	# the cached data when there is an unresolved conflict.
+
+	cat >expect.v2.dirty <<EOF &&
+u UU N... 100644 100644 100644 100644 $(test_oid x_base) $(test_oid x_ours) $(test_oid x_theirs) x.txt
+? dirt.txt
+EOF
+	git -C conflicts status --porcelain=v2 --deserialize=../serialized >observed.v2 &&
+	test_cmp expect.v2.dirty observed.v2
+
+'
+
 test_done

wt-status-deserialize.c

@@ -180,7 +180,8 @@ static int wt_deserialize_v1_header(struct wt_status *s, int fd)
 /*
  * Build a string-list of (count) <changed-item> lines from the input.
  */
-static int wt_deserialize_v1_changed_items(struct wt_status *s, int fd, int count)
+static int wt_deserialize_v1_changed_items(const struct wt_status *cmd_s,
+					   struct wt_status *s, int fd, int count)
 {
 	struct wt_status_serialize_data *sd;
 	char *p;
@@ -236,6 +237,29 @@ static int wt_deserialize_v1_changed_items(struct wt_status *s, int fd, int coun
 			oid_to_hex(&d->oid_index),
 			item->string,
 			(d->rename_source ? d->rename_source : ""));
+
+		if (d->stagemask &&
+		    cmd_s->status_format == STATUS_FORMAT_PORCELAIN_V2) {
+			/*
+			 * We have an unresolved conflict and the user wants
+			 * to see porcelain V2 output.  The cached status data
+			 * does not contain enough information for V2 (because
+			 * the main status computation does not capture it).
+			 * We only get a single change record for the file with
+			 * a single SHA -- we don't get the stage [123] mode
+			 * and SHA data.  The V2 detail-line print code looks
+			 * up this information directly from the index.  The
+			 * whole point of this serialization cache is to avoid
+			 * reading the index, so the V2 print code gets zeros.
+			 * So we reject the status cache and let the fallback
+			 * code run.
+			 */
+			trace_printf_key(
+				&trace_deserialize,
+				"reject: V2 format and umerged file: %s",
+				item->string);
+			return DESERIALIZE_ERR;
+		}
 	}
 
 	return DESERIALIZE_OK;
@@ -388,7 +412,7 @@ static int wt_deserialize_v1(const struct wt_status *cmd_s, struct wt_status *s,
 	while ((line = my_packet_read_line(fd, &line_len))) {
 		if (skip_prefix(line, "changed ", &arg)) {
 			nr_changed = (int)strtol(arg, NULL, 10);
-			if (wt_deserialize_v1_changed_items(s, fd, nr_changed)
+			if (wt_deserialize_v1_changed_items(cmd_s, s, fd, nr_changed)
 			    == DESERIALIZE_ERR)
 				return DESERIALIZE_ERR;
 			continue;