cache-tree: create/update cache-tree on checkout

When git checkout checks out a branch, create or update the
cache-tree so that subsequent operations are faster.

update_main_cache_tree learned a new flag, WRITE_TREE_REPAIR.  When
WRITE_TREE_REPAIR is set, portions of the cache-tree which do not
correspond to existing tree objects are invalidated (and portions which
do are marked as valid).  No new tree objects are created.

Signed-off-by: David Turner <dturner@twitter.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -553,6 +553,14 @@ static int merge_working_tree(const struct checkout_opts *opts,
 		}
 	}
 
+	if (!active_cache_tree)
+		active_cache_tree = cache_tree();
+
+	if (!cache_tree_fully_valid(active_cache_tree))
+		cache_tree_update(active_cache_tree,
+				  (const struct cache_entry * const *)active_cache,
+				  active_nr, WRITE_TREE_SILENT | WRITE_TREE_REPAIR);
+
 	if (write_cache(newfd, active_cache, active_nr) ||
 	    commit_locked_index(lock_file))
 		die(_("unable to write new index file"));

cache-tree.c

@@ -239,9 +239,12 @@ static int update_one(struct cache_tree *it,
 	struct strbuf buffer;
 	int missing_ok = flags & WRITE_TREE_MISSING_OK;
 	int dryrun = flags & WRITE_TREE_DRY_RUN;
+	int repair = flags & WRITE_TREE_REPAIR;
 	int to_invalidate = 0;
 	int i;
 
+	assert(!(dryrun && repair));
+
 	*skip_count = 0;
 
 	if (0 <= it->entry_count && has_sha1_file(it->sha1))
@@ -374,7 +377,14 @@ static int update_one(struct cache_tree *it,
 #endif
 	}
 
-	if (dryrun)
+	if (repair) {
+		unsigned char sha1[20];
+		hash_sha1_file(buffer.buf, buffer.len, tree_type, sha1);
+		if (has_sha1_file(sha1))
+			hashcpy(it->sha1, sha1);
+		else
+			to_invalidate = 1;
+	} else if (dryrun)
 		hash_sha1_file(buffer.buf, buffer.len, tree_type, it->sha1);
 	else if (write_sha1_file(buffer.buf, buffer.len, tree_type, it->sha1)) {
 		strbuf_release(&buffer);

cache-tree.h

@@ -39,6 +39,7 @@ int update_main_cache_tree(int);
 #define WRITE_TREE_IGNORE_CACHE_TREE 2
 #define WRITE_TREE_DRY_RUN 4
 #define WRITE_TREE_SILENT 8
+#define WRITE_TREE_REPAIR 16
 
 /* error return codes */
 #define WRITE_TREE_UNREADABLE_INDEX (-1)

t/t0090-cache-tree.sh

@@ -44,14 +44,14 @@ test_expect_success 'read-tree HEAD establishes cache-tree' '
 
 test_expect_success 'git-add invalidates cache-tree' '
 	test_when_finished "git reset --hard; git read-tree HEAD" &&
-	echo "I changed this file" > foo &&
+	echo "I changed this file" >foo &&
 	git add foo &&
 	test_invalid_cache_tree
 '
 
 test_expect_success 'update-index invalidates cache-tree' '
 	test_when_finished "git reset --hard; git read-tree HEAD" &&
-	echo "I changed this file" > foo &&
+	echo "I changed this file" >foo &&
 	git update-index --add foo &&
 	test_invalid_cache_tree
 '
@@ -85,9 +85,22 @@ test_expect_success 'reset --hard without index gives cache-tree' '
 	test_shallow_cache_tree
 '
 
-test_expect_failure 'checkout gives cache-tree' '
+test_expect_success 'checkout gives cache-tree' '
+	git tag current &&
 	git checkout HEAD^ &&
 	test_shallow_cache_tree
 '
 
+test_expect_success 'checkout -b gives cache-tree' '
+	git checkout current &&
+	git checkout -b prev HEAD^ &&
+	test_shallow_cache_tree
+'
+
+test_expect_success 'checkout -B gives cache-tree' '
+	git checkout current &&
+	git checkout -B prev HEAD^ &&
+	test_shallow_cache_tree
+'
+
 test_done