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>

Author: peff

attr.c

@@ -490,6 +490,8 @@ static int git_attr_system(void)
 	return !git_env_bool("GIT_ATTR_NOSYSTEM", 0);
 }
 
+static GIT_PATH_FUNC(git_path_info_attributes, INFOATTRIBUTES_FILE)
+
 static void bootstrap_attr_stack(void)
 {
 	struct attr_stack *elem;
@@ -531,7 +533,7 @@ static void bootstrap_attr_stack(void)
 		debug_push(elem);
 	}
 
-	elem = read_attr_from_file(git_path(INFOATTRIBUTES_FILE), 1);
+	elem = read_attr_from_file(git_path_info_attributes(), 1);
 	if (!elem)
 		elem = xcalloc(1, sizeof(*elem));
 	elem->origin = NULL;

bisect.c

@@ -420,10 +420,13 @@ static int read_bisect_refs(void)
 	return for_each_ref_in("refs/bisect/", register_ref, NULL);
 }
 
+static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
+static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")
+
 static void read_bisect_paths(struct argv_array *array)
 {
 	struct strbuf str = STRBUF_INIT;
-	const char *filename = git_path("BISECT_NAMES");
+	const char *filename = git_path_bisect_names();
 	FILE *fp = fopen(filename, "r");
 
 	if (!fp)
@@ -644,7 +647,7 @@ static void exit_if_skipped_commits(struct commit_list *tried,
 
 static int is_expected_rev(const struct object_id *oid)
 {
-	const char *filename = git_path("BISECT_EXPECTED_REV");
+	const char *filename = git_path_bisect_expected_rev();
 	struct stat st;
 	struct strbuf str = STRBUF_INIT;
 	FILE *fp;

branch.c

@@ -302,11 +302,11 @@ void create_branch(const char *head,
 
 void remove_branch_state(void)
 {
-	unlink(git_path("CHERRY_PICK_HEAD"));
-	unlink(git_path("REVERT_HEAD"));
-	unlink(git_path("MERGE_HEAD"));
-	unlink(git_path("MERGE_RR"));
-	unlink(git_path("MERGE_MSG"));
-	unlink(git_path("MERGE_MODE"));
-	unlink(git_path("SQUASH_MSG"));
+	unlink(git_path_cherry_pick_head());
+	unlink(git_path_revert_head());
+	unlink(git_path_merge_head());
+	unlink(git_path_merge_rr());
+	unlink(git_path_merge_msg());
+	unlink(git_path_merge_mode());
+	unlink(git_path_squash_msg());
 }

builtin/blame.c

@@ -2227,20 +2227,19 @@ static struct commit_list **append_parent(struct commit_list **tail, const unsig
 static void append_merge_parents(struct commit_list **tail)
 {
 	int merge_head;
-	const char *merge_head_file = git_path("MERGE_HEAD");
 	struct strbuf line = STRBUF_INIT;
 
-	merge_head = open(merge_head_file, O_RDONLY);
+	merge_head = open(git_path_merge_head(), O_RDONLY);
 	if (merge_head < 0) {
 		if (errno == ENOENT)
 			return;
-		die("cannot open '%s' for reading", merge_head_file);
+		die("cannot open '%s' for reading", git_path_merge_head());
 	}
 
 	while (!strbuf_getwholeline_fd(&line, merge_head, '\n')) {
 		unsigned char sha1[20];
 		if (line.len < 40 || get_sha1_hex(line.buf, sha1))
-			die("unknown line in '%s': %s", merge_head_file, line.buf);
+			die("unknown line in '%s': %s", git_path_merge_head(), line.buf);
 		tail = append_parent(tail, sha1);
 	}
 	close(merge_head);

builtin/commit.c

@@ -166,9 +166,9 @@ static int opt_parse_m(const struct option *opt, const char *arg, int unset)
 
 static void determine_whence(struct wt_status *s)
 {
-	if (file_exists(git_path("MERGE_HEAD")))
+	if (file_exists(git_path_merge_head()))
 		whence = FROM_MERGE;
-	else if (file_exists(git_path("CHERRY_PICK_HEAD"))) {
+	else if (file_exists(git_path_cherry_pick_head())) {
 		whence = FROM_CHERRY_PICK;
 		if (file_exists(git_path(SEQ_DIR)))
 			sequencer_in_use = 1;
@@ -725,12 +725,12 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		format_commit_message(commit, "fixup! %s\n\n",
 				      &sb, &ctx);
 		hook_arg1 = "message";
-	} else if (!stat(git_path("MERGE_MSG"), &statbuf)) {
-		if (strbuf_read_file(&sb, git_path("MERGE_MSG"), 0) < 0)
+	} else if (!stat(git_path_merge_msg(), &statbuf)) {
+		if (strbuf_read_file(&sb, git_path_merge_msg(), 0) < 0)
 			die_errno(_("could not read MERGE_MSG"));
 		hook_arg1 = "merge";
-	} else if (!stat(git_path("SQUASH_MSG"), &statbuf)) {
-		if (strbuf_read_file(&sb, git_path("SQUASH_MSG"), 0) < 0)
+	} else if (!stat(git_path_squash_msg(), &statbuf)) {
+		if (strbuf_read_file(&sb, git_path_squash_msg(), 0) < 0)
 			die_errno(_("could not read SQUASH_MSG"));
 		hook_arg1 = "squash";
 	} else if (template_file) {
@@ -1684,10 +1684,10 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		if (!reflog_msg)
 			reflog_msg = "commit (merge)";
 		pptr = &commit_list_insert(current_head, pptr)->next;
-		fp = fopen(git_path("MERGE_HEAD"), "r");
+		fp = fopen(git_path_merge_head(), "r");
 		if (fp == NULL)
 			die_errno(_("could not open '%s' for reading"),
-				  git_path("MERGE_HEAD"));
+				  git_path_merge_head());
 		while (strbuf_getline(&m, fp, '\n') != EOF) {
 			struct commit *parent;
 
@@ -1698,8 +1698,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		}
 		fclose(fp);
 		strbuf_release(&m);
-		if (!stat(git_path("MERGE_MODE"), &statbuf)) {
-			if (strbuf_read_file(&sb, git_path("MERGE_MODE"), 0) < 0)
+		if (!stat(git_path_merge_mode(), &statbuf)) {
+			if (strbuf_read_file(&sb, git_path_merge_mode(), 0) < 0)
 				die_errno(_("could not read MERGE_MODE"));
 			if (!strcmp(sb.buf, "no-ff"))
 				allow_fast_forward = 0;
@@ -1775,12 +1775,12 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	}
 	ref_transaction_free(transaction);
 
-	unlink(git_path("CHERRY_PICK_HEAD"));
-	unlink(git_path("REVERT_HEAD"));
-	unlink(git_path("MERGE_HEAD"));
-	unlink(git_path("MERGE_MSG"));
-	unlink(git_path("MERGE_MODE"));
-	unlink(git_path("SQUASH_MSG"));
+	unlink(git_path_cherry_pick_head());
+	unlink(git_path_revert_head());
+	unlink(git_path_merge_head());
+	unlink(git_path_merge_msg());
+	unlink(git_path_merge_mode());
+	unlink(git_path_squash_msg());
 
 	if (commit_index_files())
 		die (_("Repository has been updated, but unable to write\n"

builtin/fetch.c

@@ -591,7 +591,7 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 	const char *what, *kind;
 	struct ref *rm;
 	char *url;
-	const char *filename = dry_run ? "/dev/null" : git_path("FETCH_HEAD");
+	const char *filename = dry_run ? "/dev/null" : git_path_fetch_head();
 	int want_status;
 
 	fp = fopen(filename, "a");
@@ -834,7 +834,7 @@ static void check_not_current_branch(struct ref *ref_map)
 
 static int truncate_fetch_head(void)
 {
-	const char *filename = git_path("FETCH_HEAD");
+	const char *filename = git_path_fetch_head();
 	FILE *fp = fopen(filename, "w");
 
 	if (!fp)

builtin/merge.c

@@ -231,9 +231,9 @@ static struct option builtin_merge_options[] = {
 /* Cleans up metadata that is uninteresting after a succeeded merge. */
 static void drop_save(void)
 {
-	unlink(git_path("MERGE_HEAD"));
-	unlink(git_path("MERGE_MSG"));
-	unlink(git_path("MERGE_MODE"));
+	unlink(git_path_merge_head());
+	unlink(git_path_merge_msg());
+	unlink(git_path_merge_mode());
 }
 
 static int save_state(unsigned char *stash)
@@ -338,7 +338,7 @@ static void squash_message(struct commit *commit, struct commit_list *remotehead
 	struct pretty_print_context ctx = {0};
 
 	printf(_("Squash commit -- not updating HEAD\n"));
-	filename = git_path("SQUASH_MSG");
+	filename = git_path_squash_msg();
 	fd = open(filename, O_WRONLY | O_CREAT, 0666);
 	if (fd < 0)
 		die_errno(_("Could not write to '%s'"), filename);
@@ -754,7 +754,7 @@ static void add_strategies(const char *string, unsigned attr)
 
 static void write_merge_msg(struct strbuf *msg)
 {
-	const char *filename = git_path("MERGE_MSG");
+	const char *filename = git_path_merge_msg();
 	int fd = open(filename, O_WRONLY | O_CREAT, 0666);
 	if (fd < 0)
 		die_errno(_("Could not open '%s' for writing"),
@@ -766,7 +766,7 @@ static void write_merge_msg(struct strbuf *msg)
 
 static void read_merge_msg(struct strbuf *msg)
 {
-	const char *filename = git_path("MERGE_MSG");
+	const char *filename = git_path_merge_msg();
 	strbuf_reset(msg);
 	if (strbuf_read_file(msg, filename, 0) < 0)
 		die_errno(_("Could not read from '%s'"), filename);
@@ -799,10 +799,10 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 		strbuf_commented_addf(&msg, _(merge_editor_comment), comment_line_char);
 	write_merge_msg(&msg);
 	if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg",
-			    git_path("MERGE_MSG"), "merge", NULL))
+			    git_path_merge_msg(), "merge", NULL))
 		abort_commit(remoteheads, NULL);
 	if (0 < option_edit) {
-		if (launch_editor(git_path("MERGE_MSG"), NULL, NULL))
+		if (launch_editor(git_path_merge_msg(), NULL, NULL))
 			abort_commit(remoteheads, NULL);
 	}
 	read_merge_msg(&msg);
@@ -865,7 +865,7 @@ static int suggest_conflicts(void)
 	FILE *fp;
 	struct strbuf msgbuf = STRBUF_INIT;
 
-	filename = git_path("MERGE_MSG");
+	filename = git_path_merge_msg();
 	fp = fopen(filename, "a");
 	if (!fp)
 		die_errno(_("Could not open '%s' for writing"), filename);
@@ -967,7 +967,7 @@ static void write_merge_state(struct commit_list *remoteheads)
 		}
 		strbuf_addf(&buf, "%s\n", sha1_to_hex(sha1));
 	}
-	filename = git_path("MERGE_HEAD");
+	filename = git_path_merge_head();
 	fd = open(filename, O_WRONLY | O_CREAT, 0666);
 	if (fd < 0)
 		die_errno(_("Could not open '%s' for writing"), filename);
@@ -977,7 +977,7 @@ static void write_merge_state(struct commit_list *remoteheads)
 	strbuf_addch(&merge_msg, '\n');
 	write_merge_msg(&merge_msg);
 
-	filename = git_path("MERGE_MODE");
+	filename = git_path_merge_mode();
 	fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0666);
 	if (fd < 0)
 		die_errno(_("Could not open '%s' for writing"), filename);
@@ -1070,7 +1070,7 @@ static void handle_fetch_head(struct commit_list **remotes, struct strbuf *merge
 	if (!merge_names)
 		merge_names = &fetch_head_file;
 
-	filename = git_path("FETCH_HEAD");
+	filename = git_path_fetch_head();
 	fd = open(filename, O_RDONLY);
 	if (fd < 0)
 		die_errno(_("could not open '%s' for reading"), filename);
@@ -1204,7 +1204,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		int nargc = 2;
 		const char *nargv[] = {"reset", "--merge", NULL};
 
-		if (!file_exists(git_path("MERGE_HEAD")))
+		if (!file_exists(git_path_merge_head()))
 			die(_("There is no merge to abort (MERGE_HEAD missing)."));
 
 		/* Invoke 'git reset --merge' */
@@ -1215,7 +1215,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	if (read_cache_unmerged())
 		die_resolve_conflict("merge");
 
-	if (file_exists(git_path("MERGE_HEAD"))) {
+	if (file_exists(git_path_merge_head())) {
 		/*
 		 * There is no unmerged entry, don't advise 'git
 		 * add/rm <file>', just 'git commit'.
@@ -1226,7 +1226,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		else
 			die(_("You have not concluded your merge (MERGE_HEAD exists)."));
 	}
-	if (file_exists(git_path("CHERRY_PICK_HEAD"))) {
+	if (file_exists(git_path_cherry_pick_head())) {
 		if (advice_resolve_conflict)
 			die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists).\n"
 			    "Please, commit your changes before you merge."));

builtin/reset.c

@@ -36,7 +36,7 @@ static const char *reset_type_names[] = {
 
 static inline int is_merge(void)
 {
-	return !access(git_path("MERGE_HEAD"), F_OK);
+	return !access(git_path_merge_head(), F_OK);
 }
 
 static int reset_index(const unsigned char *sha1, int reset_type, int quiet)

cache.h

@@ -735,6 +735,32 @@ extern char *git_pathdup_submodule(const char *path, const char *fmt, ...)
 
 extern void report_linked_checkout_garbage(void);
 
+/*
+ * You can define a static memoized git path like:
+ *
+ *    static GIT_PATH_FUNC(git_path_foo, "FOO");
+ *
+ * or use one of the global ones below.
+ */
+#define GIT_PATH_FUNC(func, filename) \
+	const char *func(void) \
+	{ \
+		static char *ret; \
+		if (!ret) \
+			ret = git_pathdup(filename); \
+		return ret; \
+	}
+
+const char *git_path_cherry_pick_head(void);
+const char *git_path_revert_head(void);
+const char *git_path_squash_msg(void);
+const char *git_path_merge_msg(void);
+const char *git_path_merge_rr(void);
+const char *git_path_merge_mode(void);
+const char *git_path_merge_head(void);
+const char *git_path_fetch_head(void);
+const char *git_path_shallow(void);
+
 /*
  * Return the name of the file in the local object database that would
  * be used to store a loose object with the specified sha1.  The

contrib/examples/builtin-fetch--tool.c

@@ -516,7 +516,7 @@ int cmd_fetch__tool(int argc, const char **argv, const char *prefix)
 
 		if (argc != 8)
 			return error("append-fetch-head takes 6 args");
-		filename = git_path("FETCH_HEAD");
+		filename = git_path_fetch_head();
 		fp = fopen(filename, "a");
 		if (!fp)
 			return error("cannot open %s: %s", filename, strerror(errno));
@@ -534,7 +534,7 @@ int cmd_fetch__tool(int argc, const char **argv, const char *prefix)
 
 		if (argc != 5)
 			return error("fetch-native-store takes 3 args");
-		filename = git_path("FETCH_HEAD");
+		filename = git_path_fetch_head();
 		fp = fopen(filename, "a");
 		if (!fp)
 			return error("cannot open %s: %s", filename, strerror(errno));

dir.c

@@ -2185,6 +2185,8 @@ int remove_dir_recursively(struct strbuf *path, int flag)
 	return remove_dir_recurse(path, flag, NULL);
 }
 
+static GIT_PATH_FUNC(git_path_info_exclude, "info/exclude")
+
 void setup_standard_excludes(struct dir_struct *dir)
 {
 	const char *path;
@@ -2199,7 +2201,7 @@ void setup_standard_excludes(struct dir_struct *dir)
 					 dir->untracked ? &dir->ss_excludes_file : NULL);
 
 	/* per repository user preference */
-	path = git_path("info/exclude");
+	path = git_path_info_exclude();
 	if (!access_or_warn(path, R_OK, 0))
 		add_excludes_from_file_1(dir, path,
 					 dir->untracked ? &dir->ss_info_exclude : NULL);

fetch-pack.c

@@ -948,7 +948,7 @@ static void update_shallow(struct fetch_pack_args *args,
 
 	if (args->depth > 0 && alternate_shallow_file) {
 		if (*alternate_shallow_file == '\0') { /* --unshallow */
-			unlink_or_warn(git_path("shallow"));
+			unlink_or_warn(git_path_shallow());
 			rollback_lock_file(&shallow_lock);
 		} else
 			commit_lock_file(&shallow_lock);

path.c

@@ -933,3 +933,13 @@ char *xdg_config_home(const char *filename)
 		return mkpathdup("%s/.config/git/%s", home, filename);
 	return NULL;
 }
+
+GIT_PATH_FUNC(git_path_cherry_pick_head, "CHERRY_PICK_HEAD")
+GIT_PATH_FUNC(git_path_revert_head, "REVERT_HEAD")
+GIT_PATH_FUNC(git_path_squash_msg, "SQUASH_MSG")
+GIT_PATH_FUNC(git_path_merge_msg, "MERGE_MSG")
+GIT_PATH_FUNC(git_path_merge_rr, "MERGE_RR")
+GIT_PATH_FUNC(git_path_merge_mode, "MERGE_MODE")
+GIT_PATH_FUNC(git_path_merge_head, "MERGE_HEAD")
+GIT_PATH_FUNC(git_path_fetch_head, "FETCH_HEAD")
+GIT_PATH_FUNC(git_path_shallow, "shallow")