environment: add global variable to disable replacement

This new "read_replace_refs" global variable is set to 1 by
default, so that replace refs are used by default. But
reachability traversal and packing commands ("cmd_fsck",
"cmd_prune", "cmd_pack_objects", "upload_pack",
"cmd_unpack_objects") set it to 0, as they must work with the
original DAG.
Signed-off-by: NChristian Couder <chriscool@tuxfamily.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-fsck.c

@@ -589,6 +589,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 	struct alternate_object_database *alt;
 
 	errors_found = 0;
+	read_replace_refs = 0;
 
 	argc = parse_options(argc, argv, prefix, fsck_opts, fsck_usage, 0);
 	if (write_lost_and_found) {

builtin-pack-objects.c

@@ -2103,6 +2103,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	int rp_ac_alloc = 64;
 	int rp_ac;
 
+	read_replace_refs = 0;
+
 	rp_av = xcalloc(rp_ac_alloc, sizeof(*rp_av));
 
 	rp_av[0] = "pack-objects";

builtin-prune.c

@@ -140,6 +140,7 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 	char *s;
 
 	save_commit_buffer = 0;
+	read_replace_refs = 0;
 	init_revisions(&revs, prefix);
 
 	argc = parse_options(argc, argv, prefix, options, prune_usage, 0);

builtin-unpack-objects.c

@@ -495,6 +495,8 @@ int cmd_unpack_objects(int argc, const char **argv, const char *prefix)
 	int i;
 	unsigned char sha1[20];
 
+	read_replace_refs = 0;
+
 	git_config(git_default_config, NULL);
 
 	quiet = !isatty(2);

cache.h

@@ -516,6 +516,7 @@ extern size_t packed_git_window_size;
 extern size_t packed_git_limit;
 extern size_t delta_base_cache_limit;
 extern int auto_crlf;
+extern int read_replace_refs;
 extern int fsync_object_files;
 extern int core_preload_index;
 

environment.c

@@ -38,6 +38,7 @@ int pager_use_color = 1;
 const char *editor_program;
 const char *excludes_file;
 int auto_crlf = 0;	/* 1: both ways, -1: only when adding git objects */
+int read_replace_refs = 1;
 enum safe_crlf safe_crlf = SAFE_CRLF_WARN;
 unsigned whitespace_rule_cfg = WS_DEFAULT_RULE;
 enum branch_track git_branch_track = BRANCH_TRACK_REMOTE;

replace_object.c

@@ -94,6 +94,9 @@ const unsigned char *lookup_replace_object(const unsigned char *sha1)
 	int pos, depth = MAXREPLACEDEPTH;
 	const unsigned char *cur = sha1;
 
+	if (!read_replace_refs)
+		return sha1;
+
 	prepare_replace_object();
 
 	/* Try to recursively replace the object */

t/t6050-replace.sh

@@ -82,6 +82,29 @@ test_expect_success 'tag replaced commit' '
      git mktag <tag.sig >.git/refs/tags/mytag 2>message
 '
 
+test_expect_success '"git fsck" works' '
+     git fsck master > fsck_master.out &&
+     grep "dangling commit $R" fsck_master.out &&
+     grep "dangling tag $(cat .git/refs/tags/mytag)" fsck_master.out &&
+     test -z "$(git fsck)"
+'
+
+test_expect_success 'repack, clone and fetch work' '
+     git repack -a -d &&
+     git clone --no-hardlinks . clone_dir &&
+     cd clone_dir &&
+     git show HEAD~5 | grep "A U Thor" &&
+     git show $HASH2 | grep "A U Thor" &&
+     git cat-file commit $R &&
+     git repack -a -d &&
+     test_must_fail git cat-file commit $R &&
+     git fetch ../ "refs/replace/*:refs/replace/*" &&
+     git show HEAD~5 | grep "O Thor" &&
+     git show $HASH2 | grep "O Thor" &&
+     git cat-file commit $R &&
+     cd ..
+'
+
 #
 #
 test_done

upload-pack.c

@@ -618,6 +618,7 @@ int main(int argc, char **argv)
 	int strict = 0;
 
 	git_extract_argv0_path(argv[0]);
+	read_replace_refs = 0;
 
 	for (i = 1; i < argc; i++) {
 		char *arg = argv[i];