memoize common git-path "constant" files

One of the most common uses of git_path() is to pass a
constant, like git_path("MERGE_MSG"). This has two
drawbacks:

  1. The return value is a static buffer, and the lifetime
     is dependent on other calls to git_path, etc.

  2. There's no compile-time checking of the pathname. This
     is OK for a one-off (after all, we have to spell it
     correctly at least once), but many of these constant
     strings appear throughout the code.

This patch introduces a series of functions to "memoize"
these strings, which are essentially globals for the
lifetime of the program. We compute the value once, take
ownership of the buffer, and return the cached value for
subsequent calls.  cache.h provides a helper macro for
defining these functions as one-liners, and defines a few
common ones for global use.

Using a macro is a little bit gross, but it does nicely
document the purpose of the functions. If we need to touch
them all later (e.g., because we learned how to change the
git_dir variable at runtime, and need to invalidate all of
the stored values), it will be much easier to have the
complete list.

Note that the shared-global functions have separate, manual
declarations. We could do something clever with the macros
(e.g., expand it to a declaration in some places, and a
declaration _and_ a definition in path.c). But there aren't
that many, and it's probably better to stay away from
too-magical macros.

Likewise, if we abandon the C preprocessor in favor of
generating these with a script, we could get much fancier.
E.g., normalizing "FOO/BAR-BAZ" into "git_path_foo_bar_baz".
But the small amount of saved typing is probably not worth
the resulting confusion to readers who want to grep for the
function's definition.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 40 insertions, 47 deletions

diff --git a/sequencer.c b/sequencer.c
index c4f4b7d..147adfa 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -21,6 +21,11 @@
 const char sign_off_header[] = "Signed-off-by: ";
 static const char cherry_picked_prefix[] = "(cherry picked from commit ";
 
+static GIT_PATH_FUNC(git_path_todo_file, SEQ_TODO_FILE)
+static GIT_PATH_FUNC(git_path_opts_file, SEQ_OPTS_FILE)
+static GIT_PATH_FUNC(git_path_seq_dir, SEQ_DIR)
+static GIT_PATH_FUNC(git_path_head_file, SEQ_HEAD_FILE)
+
 static int is_rfc2822_line(const char *buf, int len)
 {
 	int i;
@@ -186,7 +191,7 @@ static void print_advice(int show_hint, struct replay_opts *opts)
 		 * (typically rebase --interactive) wants to take care
 		 * of the commit itself so remove CHERRY_PICK_HEAD
 		 */
-		unlink(git_path("CHERRY_PICK_HEAD"));
+		unlink(git_path_cherry_pick_head());
 		return;
 	}
 
@@ -467,7 +472,6 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 	struct commit *base, *next, *parent;
 	const char *base_label, *next_label;
 	struct commit_message msg = { NULL, NULL, NULL, NULL };
-	char *defmsg = NULL;
 	struct strbuf msgbuf = STRBUF_INIT;
 	int res, unborn = 0, allow;
 
@@ -537,8 +541,6 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 	 * reverse of it if we are revert.
 	 */
 
-	defmsg = git_pathdup("MERGE_MSG");
-
 	if (opts->action == REPLAY_REVERT) {
 		base = commit;
 		base_label = msg.label;
@@ -585,12 +587,12 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 	if (!opts->strategy || !strcmp(opts->strategy, "recursive") || opts->action == REPLAY_REVERT) {
 		res = do_recursive_merge(base, next, base_label, next_label,
 					 head, &msgbuf, opts);
-		write_message(&msgbuf, defmsg);
+		write_message(&msgbuf, git_path_merge_msg());
 	} else {
 		struct commit_list *common = NULL;
 		struct commit_list *remotes = NULL;
 
-		write_message(&msgbuf, defmsg);
+		write_message(&msgbuf, git_path_merge_msg());
 
 		commit_list_insert(base, &common);
 		commit_list_insert(next, &remotes);
@@ -628,11 +630,10 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 		goto leave;
 	}
 	if (!opts->no_commit)
-		res = run_git_commit(defmsg, opts, allow);
+		res = run_git_commit(git_path_merge_msg(), opts, allow);
 
 leave:
 	free_message(commit, &msg);
-	free(defmsg);
 
 	return res;
 }
@@ -756,24 +757,23 @@ static int parse_insn_buffer(char *buf, struct commit_list **todo_list,
 static void read_populate_todo(struct commit_list **todo_list,
 			struct replay_opts *opts)
 {
-	const char *todo_file = git_path(SEQ_TODO_FILE);
 	struct strbuf buf = STRBUF_INIT;
 	int fd, res;
 
-	fd = open(todo_file, O_RDONLY);
+	fd = open(git_path_todo_file(), O_RDONLY);
 	if (fd < 0)
-		die_errno(_("Could not open %s"), todo_file);
+		die_errno(_("Could not open %s"), git_path_todo_file());
 	if (strbuf_read(&buf, fd, 0) < 0) {
 		close(fd);
 		strbuf_release(&buf);
-		die(_("Could not read %s."), todo_file);
+		die(_("Could not read %s."), git_path_todo_file());
 	}
 	close(fd);
 
 	res = parse_insn_buffer(buf.buf, todo_list, opts);
 	strbuf_release(&buf);
 	if (res)
-		die(_("Unusable instruction sheet: %s"), todo_file);
+		die(_("Unusable instruction sheet: %s"), git_path_todo_file());
 }
 
 static int populate_opts_cb(const char *key, const char *value, void *data)
@@ -813,12 +813,10 @@ static int populate_opts_cb(const char *key, const char *value, void *data)
 
 static void read_populate_opts(struct replay_opts **opts_ptr)
 {
-	const char *opts_file = git_path(SEQ_OPTS_FILE);
-
-	if (!file_exists(opts_file))
+	if (!file_exists(git_path_opts_file()))
 		return;
-	if (git_config_from_file(populate_opts_cb, opts_file, *opts_ptr) < 0)
-		die(_("Malformed options sheet: %s"), opts_file);
+	if (git_config_from_file(populate_opts_cb, git_path_opts_file(), *opts_ptr) < 0)
+		die(_("Malformed options sheet: %s"), git_path_opts_file());
 }
 
 static void walk_revs_populate_todo(struct commit_list **todo_list,
@@ -836,31 +834,29 @@ static void walk_revs_populate_todo(struct commit_list **todo_list,
 
 static int create_seq_dir(void)
 {
-	const char *seq_dir = git_path(SEQ_DIR);
-
-	if (file_exists(seq_dir)) {
+	if (file_exists(git_path_seq_dir())) {
 		error(_("a cherry-pick or revert is already in progress"));
 		advise(_("try \"git cherry-pick (--continue | --quit | --abort)\""));
 		return -1;
 	}
-	else if (mkdir(seq_dir, 0777) < 0)
-		die_errno(_("Could not create sequencer directory %s"), seq_dir);
+	else if (mkdir(git_path_seq_dir(), 0777) < 0)
+		die_errno(_("Could not create sequencer directory %s"),
+			  git_path_seq_dir());
 	return 0;
 }
 
 static void save_head(const char *head)
 {
-	const char *head_file = git_path(SEQ_HEAD_FILE);
 	static struct lock_file head_lock;
 	struct strbuf buf = STRBUF_INIT;
 	int fd;
 
-	fd = hold_lock_file_for_update(&head_lock, head_file, LOCK_DIE_ON_ERROR);
+	fd = hold_lock_file_for_update(&head_lock, git_path_head_file(), LOCK_DIE_ON_ERROR);
 	strbuf_addf(&buf, "%s\n", head);
 	if (write_in_full(fd, buf.buf, buf.len) < 0)
-		die_errno(_("Could not write to %s"), head_file);
+		die_errno(_("Could not write to %s"), git_path_head_file());
 	if (commit_lock_file(&head_lock) < 0)
-		die(_("Error wrapping up %s."), head_file);
+		die(_("Error wrapping up %s."), git_path_head_file());
 }
 
 static int reset_for_rollback(const unsigned char *sha1)
@@ -877,8 +873,8 @@ static int rollback_single_pick(void)
 {
 	unsigned char head_sha1[20];
 
-	if (!file_exists(git_path("CHERRY_PICK_HEAD")) &&
-	    !file_exists(git_path("REVERT_HEAD")))
+	if (!file_exists(git_path_cherry_pick_head()) &&
+	    !file_exists(git_path_revert_head()))
 		return error(_("no cherry-pick or revert in progress"));
 	if (read_ref_full("HEAD", 0, head_sha1, NULL))
 		return error(_("cannot resolve HEAD"));
@@ -889,13 +885,11 @@ static int rollback_single_pick(void)
 
 static int sequencer_rollback(struct replay_opts *opts)
 {
-	const char *filename;
 	FILE *f;
 	unsigned char sha1[20];
 	struct strbuf buf = STRBUF_INIT;
 
-	filename = git_path(SEQ_HEAD_FILE);
-	f = fopen(filename, "r");
+	f = fopen(git_path_head_file(), "r");
 	if (!f && errno == ENOENT) {
 		/*
 		 * There is no multiple-cherry-pick in progress.
@@ -905,18 +899,18 @@ static int sequencer_rollback(struct replay_opts *opts)
 		return rollback_single_pick();
 	}
 	if (!f)
-		return error(_("cannot open %s: %s"), filename,
+		return error(_("cannot open %s: %s"), git_path_head_file(),
 						strerror(errno));
 	if (strbuf_getline(&buf, f, '\n')) {
-		error(_("cannot read %s: %s"), filename, ferror(f) ?
-			strerror(errno) : _("unexpected end of file"));
+		error(_("cannot read %s: %s"), git_path_head_file(),
+		      ferror(f) ?  strerror(errno) : _("unexpected end of file"));
 		fclose(f);
 		goto fail;
 	}
 	fclose(f);
 	if (get_sha1_hex(buf.buf, sha1) || buf.buf[40] != '\0') {
 		error(_("stored pre-cherry-pick HEAD file '%s' is corrupt"),
-			filename);
+			git_path_head_file());
 		goto fail;
 	}
 	if (reset_for_rollback(sha1))
@@ -931,28 +925,27 @@ fail:
 
 static void save_todo(struct commit_list *todo_list, struct replay_opts *opts)
 {
-	const char *todo_file = git_path(SEQ_TODO_FILE);
 	static struct lock_file todo_lock;
 	struct strbuf buf = STRBUF_INIT;
 	int fd;
 
-	fd = hold_lock_file_for_update(&todo_lock, todo_file, LOCK_DIE_ON_ERROR);
+	fd = hold_lock_file_for_update(&todo_lock, git_path_todo_file(), LOCK_DIE_ON_ERROR);
 	if (format_todo(&buf, todo_list, opts) < 0)
-		die(_("Could not format %s."), todo_file);
+		die(_("Could not format %s."), git_path_todo_file());
 	if (write_in_full(fd, buf.buf, buf.len) < 0) {
 		strbuf_release(&buf);
-		die_errno(_("Could not write to %s"), todo_file);
+		die_errno(_("Could not write to %s"), git_path_todo_file());
 	}
 	if (commit_lock_file(&todo_lock) < 0) {
 		strbuf_release(&buf);
-		die(_("Error wrapping up %s."), todo_file);
+		die(_("Error wrapping up %s."), git_path_todo_file());
 	}
 	strbuf_release(&buf);
 }
 
 static void save_opts(struct replay_opts *opts)
 {
-	const char *opts_file = git_path(SEQ_OPTS_FILE);
+	const char *opts_file = git_path_opts_file();
 
 	if (opts->no_commit)
 		git_config_set_in_file(opts_file, "options.no-commit", "true");
@@ -1013,8 +1006,8 @@ static int continue_single_pick(void)
 {
 	const char *argv[] = { "commit", NULL };
 
-	if (!file_exists(git_path("CHERRY_PICK_HEAD")) &&
-	    !file_exists(git_path("REVERT_HEAD")))
+	if (!file_exists(git_path_cherry_pick_head()) &&
+	    !file_exists(git_path_revert_head()))
 		return error(_("no cherry-pick or revert in progress"));
 	return run_command_v_opt(argv, RUN_GIT_CMD);
 }
@@ -1023,14 +1016,14 @@ static int sequencer_continue(struct replay_opts *opts)
 {
 	struct commit_list *todo_list = NULL;
 
-	if (!file_exists(git_path(SEQ_TODO_FILE)))
+	if (!file_exists(git_path_todo_file()))
 		return continue_single_pick();
 	read_populate_opts(&opts);
 	read_populate_todo(&todo_list, opts);
 
 	/* Verify that the conflict has been resolved */
-	if (file_exists(git_path("CHERRY_PICK_HEAD")) ||
-	    file_exists(git_path("REVERT_HEAD"))) {
+	if (file_exists(git_path_cherry_pick_head()) ||
+	    file_exists(git_path_revert_head())) {
 		int ret = continue_single_pick();
 		if (ret)
 			return ret;