status: add status serialization mechanism

Teach STATUS to optionally serialize the results of a
status computation to a file.

Teach STATUS to optionally read an existing serialization
file and simply print the results, rather than actually
scanning.

This is intended for immediate status results on extremely
large repos and assumes the use of a service/daemon to
maintain a fresh current status snapshot.

2021-10-30: packet_read() changed its prototype in ec9a37d (pkt-line.[ch]:
remove unused packet_read_line_buf(), 2021-10-14).

2021-10-30: sscanf() now does an extra check that "%d" goes into an "int"
and complains about "uint32_t". Replacing with "%u" fixes the compile-time
error.

2021-10-30: string_list_init() was removed by abf897b (string-list.[ch]:
remove string_list_init() compatibility function, 2021-09-28), so we need to
initialize manually.

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

Documentation/config/status.txt

@@ -75,3 +75,9 @@ status.submoduleSummary::
 	the --ignore-submodules=dirty command-line option or the 'git
 	submodule summary' command, which shows a similar output but does
 	not honor these settings.
+
+status.deserializePath::
+	EXPERIMENTAL, Pathname to a file containing cached status results
+	generated by `--serialize`.  This will be overridden by
+	`--deserialize=<path>` on the command line.  If the cache file is
+	invalid or stale, git will fall-back and compute status normally.

Documentation/git-status.txt

@@ -149,6 +149,19 @@ ignored, then the directory is not shown, but all contents are shown.
 	threshold.
 	See also linkgit:git-diff[1] `--find-renames`.
 
+--serialize[=<version>]::
+	(EXPERIMENTAL) Serialize raw status results to stdout in a
+	format suitable for use by `--deserialize`.  Valid values for
+	`<version>` are "1" and "v1".
+
+--deserialize[=<path>]::
+	(EXPERIMENTAL) Deserialize raw status results from a file or
+	stdin rather than scanning the worktree.  If `<path>` is omitted
+	and `status.deserializePath` is unset, input is read from stdin.
+--no-deserialize::
+	(EXPERIMENTAL) Disable implicit deserialization of status results
+	from the value of `status.deserializePath`.
+
 <pathspec>...::
 	See the 'pathspec' entry in linkgit:gitglossary[7].
 
@@ -421,6 +434,26 @@ quoted as explained for the configuration variable `core.quotePath`
 (see linkgit:git-config[1]).
 
 
+SERIALIZATION and DESERIALIZATION (EXPERIMENTAL)
+------------------------------------------------
+
+The `--serialize` option allows git to cache the result of a
+possibly time-consuming status scan to a binary file.  A local
+service/daemon watching file system events could use this to
+periodically pre-compute a fresh status result.
+
+Interactive users could then use `--deserialize` to simply
+(and immediately) print the last-known-good result without
+waiting for the status scan.
+
+The binary serialization file format includes some worktree state
+information allowing `--deserialize` to reject the cached data
+and force a normal status scan if, for example, the commit, branch,
+or status modes/options change.  The format cannot, however, indicate
+when the cached data is otherwise stale -- that coordination belongs
+to the task driving the serializations.
+
+
 CONFIGURATION
 -------------
 

Documentation/technical/status-serialization-format.txt

@@ -0,0 +1,107 @@
+Git status serialization format
+===============================
+
+Git status serialization enables git to dump the results of a status scan
+to a binary file.  This file can then be loaded by later status invocations
+to print the cached status results.
+
+The file contains the essential fields from:
+() the index
+() the "struct wt_status" for the overall results
+() the contents of "struct wt_status_change_data" for tracked changed files
+() the list of untracked and ignored files
+
+Version 1 Format:
+=================
+
+The V1 file begins with a required header section followed by optional
+sections for each type of item (changed, untracked, ignored).  Individual
+item sections are only present if necessary.  Each item section begins
+with an item-type header with the number of items in the section.
+
+Each "line" in the format is encoded using pkt-line with a final LF.
+Flush packets are used to terminate sections.
+
+-----------------
+PKT-LINE("version" SP "1")
+<v1-header-section>
+[<v1-changed-item-section>]
+[<v1-untracked-item-section>]
+[<v1-ignored-item-section>]
+-----------------
+
+
+V1 Header
+---------
+
+The v1-header-section fields are taken directly from "struct wt_status".
+Each field is printed on a separate pkt-line.  Lines for NULL string
+values are omitted.  All integers are printed with "%d".  OIDs are
+printed in hex.
+
+v1-header-section    = <v1-index-headers>
+		       <v1-wt-status-headers>
+		       PKT-LINE(<flush>)
+
+v1-index-headers     = PKT-LINE("index_mtime" SP <sec> SP <nsec> LF)
+
+v1-wt-status-headers = PKT-LINE("is_initial" SP <integer> LF)
+		       [ PKT-LINE("branch" SP <branch-name> LF) ]
+		       [ PKT-LINE("reference" SP <reference-name> LF) ]
+		       PKT-LINE("show_ignored_files" SP <integer> LF)
+		       PKT-LINE("show_untracked_files" SP <integer> LF)
+		       PKT-LINE("show_ignored_directory" SP <integer> LF)
+		       [ PKT-LINE("ignore_submodule_arg" SP <string> LF) ]
+		       PKT-LINE("detect_rename" SP <integer> LF)
+		       PKT-LINE("rename_score" SP <integer> LF)
+		       PKT-LINE("rename_limit" SP <integer> LF)
+		       PKT-LINE("detect_break" SP <integer> LF)
+		       PKT-LINE("sha1_commit" SP <oid> LF)
+		       PKT-LINE("committable" SP <integer> LF)
+		       PKT-LINE("workdir_dirty" SP <integer> LF)
+
+
+V1 Changed Items
+----------------
+
+The v1-changed-item-section lists all of the changed items with one
+item per pkt-line.  Each pkt-line contains:  a binary block of data
+from "struct wt_status_serialize_data_fixed" in a fixed header where
+integers are in network byte order and OIDs are in raw (non-hex) form.
+This is followed by one or two raw pathnames (not c-quoted) with NUL
+terminators (both NULs are always present even if there is no rename).
+
+v1-changed-item-section = PKT-LINE("changed" SP <count> LF)
+			  [ PKT-LINE(<changed_item> LF) ]+
+			  PKT-LINE(<flush>)
+
+changed_item = <byte[4] worktree_status>
+	       <byte[4] index_status>
+	       <byte[4] stagemask>
+	       <byte[4] score>
+	       <byte[4] mode_head>
+	       <byte[4] mode_index>
+	       <byte[4] mode_worktree>
+	       <byte[4] dirty_submodule>
+	       <byte[4] new_submodule_commits>
+	       <byte[20] oid_head>
+	       <byte[20] oid_index>
+	       <byte[*] path>
+	       NUL
+	       [ <byte[*] src_path> ]
+	       NUL
+
+
+V1 Untracked and Ignored Items
+------------------------------
+
+These sections are simple lists of pathnames.  They ARE NOT
+c-quoted.
+
+v1-untracked-item-section = PKT-LINE("untracked" SP <count> LF)
+			    [ PKT-LINE(<pathname> LF) ]+
+			    PKT-LINE(<flush>)
+
+v1-ignored-item-section = PKT-LINE("ignored" SP <count> LF)
+			  [ PKT-LINE(<pathname> LF) ]+
+			  PKT-LINE(<flush>)

Makefile

@@ -1201,6 +1201,8 @@ LIB_OBJS += wrapper.o
 LIB_OBJS += write-or-die.o
 LIB_OBJS += ws.o
 LIB_OBJS += wt-status.o
+LIB_OBJS += wt-status-deserialize.o
+LIB_OBJS += wt-status-serialize.o
 LIB_OBJS += xdiff-interface.o
 
 BUILTIN_OBJS += builtin/add.o

builtin/commit.c

@@ -175,6 +175,70 @@ static int opt_parse_porcelain(const struct option *opt, const char *arg, int un
 	return 0;
 }
 
+static int do_serialize = 0;
+static int do_implicit_deserialize = 0;
+static int do_explicit_deserialize = 0;
+static char *deserialize_path = NULL;
+
+/*
+ * --serialize | --serialize=1 | --serialize=v1
+ *
+ * Request that we serialize our output rather than printing in
+ * any of the established formats.  Optionally specify serialization
+ * version.
+ */
+static int opt_parse_serialize(const struct option *opt, const char *arg, int unset)
+{
+	enum wt_status_format *value = (enum wt_status_format *)opt->value;
+	if (unset || !arg)
+		*value = STATUS_FORMAT_SERIALIZE_V1;
+	else if (!strcmp(arg, "v1") || !strcmp(arg, "1"))
+		*value = STATUS_FORMAT_SERIALIZE_V1;
+	else
+		die("unsupported serialize version '%s'", arg);
+
+	if (do_explicit_deserialize)
+		die("cannot mix --serialize and --deserialize");
+	do_implicit_deserialize = 0;
+
+	do_serialize = 1;
+	return 0;
+}
+
+/*
+ * --deserialize | --deserialize=<path> |
+ * --no-deserialize
+ *
+ * Request that we deserialize status data from some existing resource
+ * rather than performing a status scan.
+ *
+ * The input source can come from stdin or a path given here -- or be
+ * inherited from the config settings.
+ */
+static int opt_parse_deserialize(const struct option *opt, const char *arg, int unset)
+{
+	if (unset) {
+		do_implicit_deserialize = 0;
+		do_explicit_deserialize = 0;
+	} else {
+		if (do_serialize)
+			die("cannot mix --serialize and --deserialize");
+		if (arg) {
+			/* override config or stdin */
+			free(deserialize_path);
+			deserialize_path = xstrdup(arg);
+		}
+		if (deserialize_path && *deserialize_path
+		    && (access(deserialize_path, R_OK) != 0))
+			die("cannot find serialization file '%s'",
+			    deserialize_path);
+
+		do_explicit_deserialize = 1;
+	}
+
+	return 0;
+}
+
 static int opt_parse_m(const struct option *opt, const char *arg, int unset)
 {
 	struct strbuf *buf = opt->value;
@@ -1176,6 +1240,8 @@ static void handle_untracked_files_arg(struct wt_status *s)
 		s->show_untracked_files = SHOW_NORMAL_UNTRACKED_FILES;
 	else if (!strcmp(untracked_files_arg, "all"))
 		s->show_untracked_files = SHOW_ALL_UNTRACKED_FILES;
+	else if (!strcmp(untracked_files_arg,"complete"))
+		s->show_untracked_files = SHOW_COMPLETE_UNTRACKED_FILES;
 	/*
 	 * Please update $__git_untracked_file_modes in
 	 * git-completion.bash when you add new options
@@ -1463,6 +1529,19 @@ static int git_status_config(const char *k, const char *v,
 		s->relative_paths = git_config_bool(k, v);
 		return 0;
 	}
+	if (!strcmp(k, "status.deserializepath")) {
+		/*
+		 * Automatically assume deserialization if this is
+		 * set in the config and the file exists.  Do not
+		 * complain if the file does not exist, because we
+		 * silently fall back to normal mode.
+		 */
+		if (v && *v && access(v, R_OK) == 0) {
+			do_implicit_deserialize = 1;
+			deserialize_path = xstrdup(v);
+		}
+		return 0;
+	}
 	if (!strcmp(k, "status.showuntrackedfiles")) {
 		if (!v)
 			return config_error_nonbool(k);
@@ -1503,7 +1582,8 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	static const char *rename_score_arg = (const char *)-1;
 	static struct wt_status s;
 	unsigned int progress_flag = 0;
-	int fd;
+	int try_deserialize;
+	int fd = -1;
 	struct object_id oid;
 	static struct option builtin_status_options[] = {
 		OPT__VERBOSE(&verbose, N_("be verbose")),
@@ -1518,6 +1598,12 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 		OPT_CALLBACK_F(0, "porcelain", &status_format,
 		  N_("version"), N_("machine-readable output"),
 		  PARSE_OPT_OPTARG, opt_parse_porcelain),
+		{ OPTION_CALLBACK, 0, "serialize", &status_format,
+		  N_("version"), N_("serialize raw status data to stdout"),
+		  PARSE_OPT_OPTARG | PARSE_OPT_NONEG, opt_parse_serialize },
+		{ OPTION_CALLBACK, 0, "deserialize", NULL,
+		  N_("path"), N_("deserialize raw status data from file"),
+		  PARSE_OPT_OPTARG, opt_parse_deserialize },
 		OPT_SET_INT(0, "long", &status_format,
 			    N_("show status in long format (default)"),
 			    STATUS_FORMAT_LONG),
@@ -1562,10 +1648,26 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	    s.show_untracked_files == SHOW_NO_UNTRACKED_FILES)
 		die(_("Unsupported combination of ignored and untracked-files arguments"));
 
+	if (s.show_untracked_files == SHOW_COMPLETE_UNTRACKED_FILES &&
+	    s.show_ignored_mode == SHOW_NO_IGNORED)
+		die(_("Complete Untracked only supported with ignored files"));
+
 	parse_pathspec(&s.pathspec, 0,
 		       PATHSPEC_PREFER_FULL,
 		       prefix, argv);
 
+	/*
+	 * If we want to try to deserialize status data from a cache file,
+	 * we need to re-order the initialization code.  The problem is that
+	 * this makes for a very nasty diff and causes merge conflicts as we
+	 * carry it forward.  And it easy to mess up the merge, so we
+	 * duplicate some code here to hopefully reduce conflicts.
+	 */
+	try_deserialize = (!do_serialize &&
+			   (do_implicit_deserialize || do_explicit_deserialize));
+	if (try_deserialize)
+		goto skip_init;
+
 	enable_fscache(0);
 	if (status_format != STATUS_FORMAT_PORCELAIN &&
 	    status_format != STATUS_FORMAT_PORCELAIN_V2)
@@ -1580,6 +1682,7 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	else
 		fd = -1;
 
+skip_init:
 	s.is_initial = repo_get_oid(the_repository, s.reference, &oid) ? 1 : 0;
 	if (!s.is_initial)
 		oidcpy(&s.oid_commit, &oid);
@@ -1596,6 +1699,24 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 			s.rename_score = parse_rename_score(&rename_score_arg);
 	}
 
+	if (try_deserialize) {
+		if (s.relative_paths)
+			s.prefix = prefix;
+
+		if (wt_status_deserialize(&s, deserialize_path) == DESERIALIZE_OK)
+			return 0;
+
+		/* deserialize failed, so force the initialization we skipped above. */
+		enable_fscache(1);
+		repo_read_index_preload(the_repository, &s.pathspec, 0);
+		refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED, &s.pathspec, NULL, NULL);
+
+		if (use_optional_locks())
+			fd = repo_hold_locked_index(the_repository, &index_lock, 0);
+		else
+			fd = -1;
+	}
+
 	wt_status_collect(&s);
 
 	if (0 <= fd)

contrib/completion/git-completion.bash

@@ -1675,7 +1675,7 @@ _git_clone ()
 	esac
 }
 
-__git_untracked_file_modes="all no normal"
+__git_untracked_file_modes="all no normal complete"
 
 _git_commit ()
 {

pkt-line.c

@@ -230,7 +230,7 @@ static int do_packet_write(const int fd_out, const char *buf, size_t size,
 	return 0;
 }
 
-static int packet_write_gently(const int fd_out, const char *buf, size_t size)
+int packet_write_gently(const int fd_out, const char *buf, size_t size)
 {
 	struct strbuf err = STRBUF_INIT;
 	if (do_packet_write(fd_out, buf, size, &err)) {

pkt-line.h

@@ -30,6 +30,7 @@ void packet_write(int fd_out, const char *buf, size_t size);
 void packet_buf_write(struct strbuf *buf, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
 int packet_flush_gently(int fd);
 int packet_write_fmt_gently(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
+int packet_write_gently(const int fd_out, const char *buf, size_t size);
 int write_packetized_from_fd_no_flush(int fd_in, int fd_out);
 int write_packetized_from_buf_no_flush_count(const char *src_in, size_t len,
 					     int fd_out, int *packet_counter);