From 1fd9bb7b89397f7b13bff4dee6d3c5f033549370 Mon Sep 17 00:00:00 2001
From: David Turner <dturner@twopensource.com>
Date: Mon, 8 May 2017 11:41:42 +0200
Subject: [PATCH] unpack-trees: preserve index extensions

Make git checkout (and other unpack_tree operations) preserve the
untracked cache. This is valuable for two reasons:

1. Often, an unpack_tree operation will not touch large parts of the
working tree, and thus most of the untracked cache will continue to be
valid.

2. Even if the untracked cache were entirely invalidated by such an
operation, the user has signaled their intention to have such a cache,
and we don't want to throw it away.

[jes: backed out the watchman-specific parts]

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 cache.h                           |  1 +
 read-cache.c                      |  6 ++++++
 t/t7063-status-untracked-cache.sh | 22 ++++++++++++++++++++++
 unpack-trees.c                    |  1 +
 4 files changed, 30 insertions(+)

diff --git a/cache.h b/cache.h
index 2e7c6ca0dc2b07..3404119989cd59 100644
--- a/cache.h
+++ b/cache.h
@@ -600,6 +600,7 @@ extern int read_index_unmerged(struct index_state *);
 #define CLOSE_LOCK		(1 << 1)
 extern int write_locked_index(struct index_state *, struct lock_file *lock, unsigned flags);
 extern int discard_index(struct index_state *);
+extern void move_index_extensions(struct index_state *dst, struct index_state *src);
 extern int unmerged_index(const struct index_state *);
 extern int verify_path(const char *path);
 extern int strcmp_offset(const char *s1, const char *s2, size_t *first_change);
diff --git a/read-cache.c b/read-cache.c
index 6b046f7934bb45..854e097114ba2e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2701,3 +2701,9 @@ void stat_validity_update(struct stat_validity *sv, int fd)
 		fill_stat_data(sv->sd, &st);
 	}
 }
+
+void move_index_extensions(struct index_state *dst, struct index_state *src)
+{
+	dst->untracked = src->untracked;
+	src->untracked = NULL;
+}
diff --git a/t/t7063-status-untracked-cache.sh b/t/t7063-status-untracked-cache.sh
index 0667bd9dd3e8bc..e5fb892f9575fd 100755
--- a/t/t7063-status-untracked-cache.sh
+++ b/t/t7063-status-untracked-cache.sh
@@ -661,4 +661,26 @@ test_expect_success 'test ident field is working' '
 	test_i18ncmp ../expect ../err
 '
 
+test_expect_success 'untracked cache survives a checkout' '
+	git commit --allow-empty -m empty &&
+	test-dump-untracked-cache >../before &&
+	test_when_finished  "git checkout master" &&
+	git checkout -b other_branch &&
+	test-dump-untracked-cache >../after &&
+	test_cmp ../before ../after &&
+	test_commit test &&
+	test-dump-untracked-cache >../before &&
+	git checkout master &&
+	test-dump-untracked-cache >../after &&
+	test_cmp ../before ../after
+'
+
+test_expect_success 'untracked cache survives a commit' '
+	test-dump-untracked-cache >../before &&
+	git add done/two &&
+	git commit -m commit &&
+	test-dump-untracked-cache >../after &&
+	test_cmp ../before ../after
+'
+
 test_done
diff --git a/unpack-trees.c b/unpack-trees.c
index 71e9f237d03d8d..4b5187ca824f56 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1483,6 +1483,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 						  WRITE_TREE_SILENT |
 						  WRITE_TREE_REPAIR);
 		}
+		move_index_extensions(&o->result, o->dst_index);
 		discard_index(o->dst_index);
 		*o->dst_index = o->result;
 	} else {