Merge branch 'ds/disable-replace-refs' into jch

Introduce a mechanism to disable replace refs globally and per
repository.

* ds/disable-replace-refs:
  repository: create read_replace_refs setting
  replace-objects: create wrapper around setting
  repository: create disable_replace_refs()
  pack-bitmap.c: use commit boundary during bitmap traversal
  pack-bitmap.c: extract `fill_in_bitmap()`
  object: add object_array initializer helper function

Documentation/config/feature.txt

@@ -14,6 +14,9 @@ feature.experimental::
 +
 * `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by
 skipping more commits at a time, reducing the number of round trips.
++
+* `pack.useBitmapBoundaryTraversal=true` may improve bitmap traversal times by
+walking fewer objects.
 
 feature.manyFiles::
 	Enable config options that optimize for repos with many files in the

Documentation/config/pack.txt

@@ -123,6 +123,23 @@ pack.useBitmaps::
 	true. You should not generally need to turn this off unless
 	you are debugging pack bitmaps.
 
+pack.useBitmapBoundaryTraversal::
+	When true, Git will use an experimental algorithm for computing
+	reachability queries with bitmaps. Instead of building up
+	complete bitmaps for all of the negated tips and then OR-ing
+	them together, consider negated tips with existing bitmaps as
+	additive (i.e. OR-ing them into the result if they exist,
+	ignoring them otherwise), and build up a bitmap at the boundary
+	instead.
++
+When using this algorithm, Git may include too many objects as a result
+of not opening up trees belonging to certain UNINTERESTING commits. This
+inexactness matches the non-bitmap traversal algorithm.
++
+In many cases, this can provide a speed-up over the exact algorithm,
+particularly when there is poor bitmap coverage of the negated side of
+the query.
+
 pack.useSparse::
 	When true, git will default to using the '--sparse' option in
 	'git pack-objects' when the '--revs' option is present. This

builtin/cat-file.c

@@ -804,7 +804,7 @@ static int batch_objects(struct batch_options *opt)
 		if (repo_has_promisor_remote(the_repository))
 			warning("This repository uses promisor remotes. Some objects may not be loaded.");
 
-		read_replace_refs = 0;
+		disable_replace_refs();
 
 		cb.opt = opt;
 		cb.expand = &data;

builtin/commit-graph.c

@@ -325,7 +325,7 @@ int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 
 	git_config(git_default_config, NULL);
 
-	read_replace_refs = 0;
+	disable_replace_refs();
 	save_commit_buffer = 0;
 
 	argc = parse_options(argc, argv, prefix, options,

builtin/fsck.c

@@ -931,7 +931,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 	fetch_if_missing = 0;
 
 	errors_found = 0;
-	read_replace_refs = 0;
+	disable_replace_refs();
 	save_commit_buffer = 0;
 
 	argc = parse_options(argc, argv, prefix, fsck_opts, fsck_usage, 0);

builtin/index-pack.c

@@ -1753,7 +1753,7 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage(index_pack_usage);
 
-	read_replace_refs = 0;
+	disable_replace_refs();
 	fsck_options.walk = mark_link;
 
 	reset_pack_idx_option(&opts);

builtin/pack-objects.c

@@ -4284,7 +4284,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	if (DFS_NUM_STATES > (1 << OE_DFS_STATE_BITS))
 		BUG("too many dfs states, increase OE_DFS_STATE_BITS");
 
-	read_replace_refs = 0;
+	disable_replace_refs();
 
 	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", -1);
 	if (the_repository->gitdir) {

builtin/prune.c

@@ -165,7 +165,7 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 
 	expire = TIME_MAX;
 	save_commit_buffer = 0;
-	read_replace_refs = 0;
+	disable_replace_refs();
 	repo_init_revisions(the_repository, &revs, prefix);
 
 	argc = parse_options(argc, argv, prefix, options, prune_usage, 0);

builtin/replace.c

@@ -567,7 +567,7 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 
-	read_replace_refs = 0;
+	disable_replace_refs();
 	git_config(git_default_config, NULL);
 
 	argc = parse_options(argc, argv, prefix, options, git_replace_usage, 0);

builtin/unpack-objects.c

@@ -608,7 +608,7 @@ int cmd_unpack_objects(int argc, const char **argv, const char *prefix UNUSED)
 	int i;
 	struct object_id oid;
 
-	read_replace_refs = 0;
+	disable_replace_refs();
 
 	git_config(git_default_config, NULL);
 

builtin/upload-pack.c

@@ -36,7 +36,7 @@ int cmd_upload_pack(int argc, const char **argv, const char *prefix)
 	};
 
 	packet_trace_identity("upload-pack");
-	read_replace_refs = 0;
+	disable_replace_refs();
 
 	argc = parse_options(argc, argv, prefix, options, upload_pack_usage, 0);
 

ci/run-build-and-tests.sh

@@ -29,6 +29,7 @@ linux-TEST-vars)
 	export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master
 	export GIT_TEST_NO_WRITE_REV_INDEX=1
 	export GIT_TEST_CHECKOUT_WORKERS=2
+	export GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL=1
 	;;
 linux-clang)
 	export GIT_TEST_DEFAULT_HASH=sha1

commit-graph.c

@@ -205,14 +205,12 @@ static struct commit_graph *alloc_commit_graph(void)
 	return g;
 }
 
-extern int read_replace_refs;
-
 static int commit_graph_compatible(struct repository *r)
 {
 	if (!r->gitdir)
 		return 0;
 
-	if (read_replace_refs) {
+	if (replace_refs_enabled(r)) {
 		prepare_replace_object(r);
 		if (hashmap_get_size(&r->objects->replace_map->map))
 			return 0;

config.c

@@ -1844,11 +1844,6 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
-	if (!strcmp(var, "core.usereplacerefs")) {
-		read_replace_refs = git_config_bool(var, value);
-		return 0;
-	}
-
 	/* Add other config variables here and to Documentation/config.txt. */
 	return platform_core_config(var, value, cb);
 }

environment.c

@@ -63,7 +63,6 @@ const char *editor_program;
 const char *askpass_program;
 const char *excludes_file;
 enum auto_crlf auto_crlf = AUTO_CRLF_FALSE;
-int read_replace_refs = 1;
 enum eol core_eol = EOL_UNSET;
 int global_conv_flags_eol = CONV_EOL_RNDTRP_WARN;
 char *check_roundtrip_encoding = "SHIFT-JIS";
@@ -184,7 +183,7 @@ void setup_git_env(const char *git_dir)
 	strvec_clear(&to_free);
 
 	if (getenv(NO_REPLACE_OBJECTS_ENVIRONMENT))
-		read_replace_refs = 0;
+		disable_replace_refs();
 	replace_ref_base = getenv(GIT_REPLACE_REF_BASE_ENVIRONMENT);
 	git_replace_ref_base = xstrdup(replace_ref_base ? replace_ref_base
 							  : "refs/replace/");

git.c

@@ -187,7 +187,7 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			if (envchanged)
 				*envchanged = 1;
 		} else if (!strcmp(cmd, "--no-replace-objects")) {
-			read_replace_refs = 0;
+			disable_replace_refs();
 			setenv(NO_REPLACE_OBJECTS_ENVIRONMENT, "1", 1);
 			if (envchanged)
 				*envchanged = 1;

log-tree.c

@@ -158,7 +158,7 @@ static int add_ref_decoration(const char *refname, const struct object_id *oid,
 
 	if (starts_with(refname, git_replace_ref_base)) {
 		struct object_id original_oid;
-		if (!read_replace_refs)
+		if (!replace_refs_enabled(the_repository))
 			return 0;
 		if (get_oid_hex(refname + strlen(git_replace_ref_base),
 				&original_oid)) {

object.c

@@ -357,6 +357,12 @@ void object_list_free(struct object_list **list)
  */
 static char object_array_slopbuf[1];
 
+void object_array_init(struct object_array *array)
+{
+	struct object_array blank = OBJECT_ARRAY_INIT;
+	memcpy(array, &blank, sizeof(*array));
+}
+
 void add_object_array_with_path(struct object *obj, const char *name,
 				struct object_array *array,
 				unsigned mode, const char *path)

object.h

@@ -58,6 +58,8 @@ struct object_array {
 
 #define OBJECT_ARRAY_INIT { 0 }
 
+void object_array_init(struct object_array *array);
+
 /*
  * object flag allocation:
  * revision.h:               0---------10         15             23------27