Merge branch 'nd/per-worktree-ref-iteration'

The code to traverse objects for reachability, used to decide what
objects are unreferenced and expendable, have been taught to also
consider per-worktree refs of other worktrees as starting points to
prevent data loss.

* nd/per-worktree-ref-iteration:
  git-worktree.txt: correct linkgit command name
  reflog expire: cover reflog from all worktrees
  fsck: check HEAD and reflog from other worktrees
  fsck: move fsck_head_link() to get_default_heads() to avoid some globals
  revision.c: better error reporting on ref from different worktrees
  revision.c: correct a parameter name
  refs: new ref types to make per-worktree refs visible to all worktrees
  Add a place for (not) sharing stuff between worktrees
  refs.c: indent with tabs, not spaces

Documentation/git-reflog.txt

@@ -20,7 +20,7 @@ depending on the subcommand:
 'git reflog' ['show'] [log-options] [<ref>]
 'git reflog expire' [--expire=<time>] [--expire-unreachable=<time>]
 	[--rewrite] [--updateref] [--stale-fix]
-	[--dry-run | -n] [--verbose] [--all | <refs>...]
+	[--dry-run | -n] [--verbose] [--all [--single-worktree] | <refs>...]
 'git reflog delete' [--rewrite] [--updateref]
 	[--dry-run | -n] [--verbose] ref@\{specifier\}...
 'git reflog exists' <ref>
@@ -72,6 +72,11 @@ Options for `expire`
 --all::
 	Process the reflogs of all references.
 
+--single-worktree::
+	By default when `--all` is specified, reflogs from all working
+	trees are processed. This option limits the processing to reflogs
+	from the current working tree only.
+
 --expire=<time>::
 	Prune entries older than the specified time. If this option is
 	not specified, the expiration time is taken from the

Documentation/git-worktree.txt

@@ -204,6 +204,35 @@ working trees, it can be used to identify worktrees. For example if
 you only have two working trees, at "/abc/def/ghi" and "/abc/def/ggg",
 then "ghi" or "def/ghi" is enough to point to the former working tree.
 
+REFS
+----
+In multiple working trees, some refs may be shared between all working
+trees, some refs are local. One example is HEAD is different for all
+working trees. This section is about the sharing rules and how to access
+refs of one working tree from another.
+
+In general, all pseudo refs are per working tree and all refs starting
+with "refs/" are shared. Pseudo refs are ones like HEAD which are
+directly under GIT_DIR instead of inside GIT_DIR/refs. There are one
+exception to this: refs inside refs/bisect and refs/worktree is not
+shared.
+
+Refs that are per working tree can still be accessed from another
+working tree via two special paths, main-worktree and worktrees. The
+former gives access to per-worktree refs of the main working tree,
+while the latter to all linked working trees.
+
+For example, main-worktree/HEAD or main-worktree/refs/bisect/good
+resolve to the same value as the main working tree's HEAD and
+refs/bisect/good respectively. Similarly, worktrees/foo/HEAD or
+worktrees/bar/refs/bisect/bad are the same as
+GIT_COMMON_DIR/worktrees/foo/HEAD and
+GIT_COMMON_DIR/worktrees/bar/refs/bisect/bad.
+
+To access refs, it's best not to look inside GIT_DIR directly. Instead
+use commands such as linkgit:git-rev-parse[1] or linkgit:git-update-ref[1]
+which will handle refs correctly.
+
 CONFIGURATION FILE
 ------------------
 By default, the repository "config" file is shared across all working
@@ -258,7 +287,8 @@ linked working tree `git rev-parse --git-path HEAD` returns
 `/path/other/test-next/.git/HEAD` or `/path/main/.git/HEAD`) while `git
 rev-parse --git-path refs/heads/master` uses
 $GIT_COMMON_DIR and returns `/path/main/.git/refs/heads/master`,
-since refs are shared across all working trees.
+since refs are shared across all working trees, except refs/bisect and
+refs/worktree.
 
 See linkgit:gitrepository-layout[5] for more information. The rule of
 thumb is do not make any assumption about whether a path belongs to

Documentation/gitrepository-layout.txt

@@ -95,8 +95,10 @@ refs::
 	References are stored in subdirectories of this
 	directory.  The 'git prune' command knows to preserve
 	objects reachable from refs found in this directory and
-	its subdirectories. This directory is ignored if $GIT_COMMON_DIR
-	is set and "$GIT_COMMON_DIR/refs" will be used instead.
+	its subdirectories.
+	This directory is ignored (except refs/bisect and
+	refs/worktree) if $GIT_COMMON_DIR is set and
+	"$GIT_COMMON_DIR/refs" will be used instead.
 
 refs/heads/`name`::
 	records tip-of-the-tree commit objects of branch `name`
@@ -170,6 +172,11 @@ hooks::
 	each hook. This directory is ignored if $GIT_COMMON_DIR is set
 	and "$GIT_COMMON_DIR/hooks" will be used instead.
 
+common::
+	When multiple working trees are used, most of files in
+	$GIT_DIR are per-worktree with a few known exceptions. All
+	files under 'common' however will be shared between all
+	working trees.
 
 index::
 	The current index file for the repository.  It is

builtin/fsck.c

@@ -19,6 +19,7 @@
 #include "packfile.h"
 #include "object-store.h"
 #include "run-command.h"
+#include "worktree.h"
 
 #define REACHABLE 0x0001
 #define SEEN      0x0002
@@ -36,8 +37,6 @@ static int check_strict;
 static int keep_cache_objects;
 static struct fsck_options fsck_walk_options = FSCK_OPTIONS_DEFAULT;
 static struct fsck_options fsck_obj_options = FSCK_OPTIONS_DEFAULT;
-static struct object_id head_oid;
-static const char *head_points_at;
 static int errors_found;
 static int write_lost_and_found;
 static int verbose;
@@ -446,7 +445,11 @@ static int fsck_handle_reflog_ent(struct object_id *ooid, struct object_id *noid
 static int fsck_handle_reflog(const char *logname, const struct object_id *oid,
 			      int flag, void *cb_data)
 {
-	for_each_reflog_ent(logname, fsck_handle_reflog_ent, (void *)logname);
+	struct strbuf refname = STRBUF_INIT;
+
+	strbuf_worktree_ref(cb_data, &refname, logname);
+	for_each_reflog_ent(refname.buf, fsck_handle_reflog_ent, refname.buf);
+	strbuf_release(&refname);
 	return 0;
 }
 
@@ -484,13 +487,34 @@ static int fsck_handle_ref(const char *refname, const struct object_id *oid,
 	return 0;
 }
 
+static int fsck_head_link(const char *head_ref_name,
+			  const char **head_points_at,
+			  struct object_id *head_oid);
+
 static void get_default_heads(void)
 {
-	if (head_points_at && !is_null_oid(&head_oid))
-		fsck_handle_ref("HEAD", &head_oid, 0, NULL);
+	struct worktree **worktrees, **p;
+	const char *head_points_at;
+	struct object_id head_oid;
+
 	for_each_rawref(fsck_handle_ref, NULL);
-	if (include_reflogs)
-		for_each_reflog(fsck_handle_reflog, NULL);
+
+	worktrees = get_worktrees(0);
+	for (p = worktrees; *p; p++) {
+		struct worktree *wt = *p;
+		struct strbuf ref = STRBUF_INIT;
+
+		strbuf_worktree_ref(wt, &ref, "HEAD");
+		fsck_head_link(ref.buf, &head_points_at, &head_oid);
+		if (head_points_at && !is_null_oid(&head_oid))
+			fsck_handle_ref(ref.buf, &head_oid, 0, NULL);
+		strbuf_release(&ref);
+
+		if (include_reflogs)
+			refs_for_each_reflog(get_worktree_ref_store(wt),
+					     fsck_handle_reflog, wt);
+	}
+	free_worktrees(worktrees);
 
 	/*
 	 * Not having any default heads isn't really fatal, but
@@ -579,33 +603,36 @@ static void fsck_object_dir(const char *path)
 	stop_progress(&progress);
 }
 
-static int fsck_head_link(void)
+static int fsck_head_link(const char *head_ref_name,
+			  const char **head_points_at,
+			  struct object_id *head_oid)
 {
 	int null_is_error = 0;
 
 	if (verbose)
-		fprintf(stderr, "Checking HEAD link\n");
+		fprintf(stderr, "Checking %s link\n", head_ref_name);
 
-	head_points_at = resolve_ref_unsafe("HEAD", 0, &head_oid, NULL);
-	if (!head_points_at) {
+	*head_points_at = resolve_ref_unsafe(head_ref_name, 0, head_oid, NULL);
+	if (!*head_points_at) {
 		errors_found |= ERROR_REFS;
-		return error("Invalid HEAD");
+		return error("Invalid %s", head_ref_name);
 	}
-	if (!strcmp(head_points_at, "HEAD"))
+	if (!strcmp(*head_points_at, head_ref_name))
 		/* detached HEAD */
 		null_is_error = 1;
-	else if (!starts_with(head_points_at, "refs/heads/")) {
+	else if (!starts_with(*head_points_at, "refs/heads/")) {
 		errors_found |= ERROR_REFS;
-		return error("HEAD points to something strange (%s)",
-			     head_points_at);
+		return error("%s points to something strange (%s)",
+			     head_ref_name, *head_points_at);
 	}
-	if (is_null_oid(&head_oid)) {
+	if (is_null_oid(head_oid)) {
 		if (null_is_error) {
 			errors_found |= ERROR_REFS;
-			return error("HEAD: detached HEAD points at nothing");
+			return error("%s: detached HEAD points at nothing",
+				     head_ref_name);
 		}
-		fprintf(stderr, "notice: HEAD points to an unborn branch (%s)\n",
-			head_points_at + 11);
+		fprintf(stderr, "notice: %s points to an unborn branch (%s)\n",
+			head_ref_name, *head_points_at + 11);
 	}
 	return 0;
 }
@@ -720,7 +747,6 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 
 	git_config(fsck_config, NULL);
 
-	fsck_head_link();
 	if (connectivity_only) {
 		for_each_loose_object(mark_loose_for_connectivity, NULL, 0);
 		for_each_packed_object(mark_packed_for_connectivity, NULL, 0);

builtin/reflog.c

@@ -10,6 +10,7 @@
 #include "diff.h"
 #include "revision.h"
 #include "reachable.h"
+#include "worktree.h"
 
 /* NEEDSWORK: switch to using parse_options */
 static const char reflog_expire_usage[] =
@@ -52,6 +53,7 @@ struct collect_reflog_cb {
 	struct collected_reflog **e;
 	int alloc;
 	int nr;
+	struct worktree *wt;
 };
 
 /* Remember to update object flag allocation in object.h */
@@ -330,13 +332,27 @@ static int push_tip_to_list(const char *refname, const struct object_id *oid,
 	return 0;
 }
 
+static int is_head(const char *refname)
+{
+	switch (ref_type(refname)) {
+	case REF_TYPE_OTHER_PSEUDOREF:
+	case REF_TYPE_MAIN_PSEUDOREF:
+		if (parse_worktree_ref(refname, NULL, NULL, &refname))
+			BUG("not a worktree ref: %s", refname);
+		break;
+	default:
+		break;
+	}
+	return !strcmp(refname, "HEAD");
+}
+
 static void reflog_expiry_prepare(const char *refname,
 				  const struct object_id *oid,
 				  void *cb_data)
 {
 	struct expire_reflog_policy_cb *cb = cb_data;
 
-	if (!cb->cmd.expire_unreachable || !strcmp(refname, "HEAD")) {
+	if (!cb->cmd.expire_unreachable || is_head(refname)) {
 		cb->tip_commit = NULL;
 		cb->unreachable_expire_kind = UE_HEAD;
 	} else {
@@ -388,8 +404,19 @@ static int collect_reflog(const char *ref, const struct object_id *oid, int unus
 {
 	struct collected_reflog *e;
 	struct collect_reflog_cb *cb = cb_data;
+	struct strbuf newref = STRBUF_INIT;
+
+	/*
+	 * Avoid collecting the same shared ref multiple times because
+	 * they are available via all worktrees.
+	 */
+	if (!cb->wt->is_current && ref_type(ref) == REF_TYPE_NORMAL)
+		return 0;
+
+	strbuf_worktree_ref(cb->wt, &newref, ref);
+	FLEX_ALLOC_STR(e, reflog, newref.buf);
+	strbuf_release(&newref);
 
-	FLEX_ALLOC_STR(e, reflog, ref);
 	oidcpy(&e->oid, oid);
 	ALLOC_GROW(cb->e, cb->nr + 1, cb->alloc);
 	cb->e[cb->nr++] = e;
@@ -512,7 +539,7 @@ static int cmd_reflog_expire(int argc, const char **argv, const char *prefix)
 {
 	struct expire_reflog_policy_cb cb;
 	timestamp_t now = time(NULL);
-	int i, status, do_all;
+	int i, status, do_all, all_worktrees = 1;
 	int explicit_expiry = 0;
 	unsigned int flags = 0;
 
@@ -549,6 +576,8 @@ static int cmd_reflog_expire(int argc, const char **argv, const char *prefix)
 			flags |= EXPIRE_REFLOGS_UPDATE_REF;
 		else if (!strcmp(arg, "--all"))
 			do_all = 1;
+		else if (!strcmp(arg, "--single-worktree"))
+			all_worktrees = 0;
 		else if (!strcmp(arg, "--verbose"))
 			flags |= EXPIRE_REFLOGS_VERBOSE;
 		else if (!strcmp(arg, "--")) {
@@ -577,10 +606,19 @@ static int cmd_reflog_expire(int argc, const char **argv, const char *prefix)
 
 	if (do_all) {
 		struct collect_reflog_cb collected;
+		struct worktree **worktrees, **p;
 		int i;
 
 		memset(&collected, 0, sizeof(collected));
-		for_each_reflog(collect_reflog, &collected);
+		worktrees = get_worktrees(0);
+		for (p = worktrees; *p; p++) {
+			if (!all_worktrees && !(*p)->is_current)
+				continue;
+			collected.wt = *p;
+			refs_for_each_reflog(get_worktree_ref_store(*p),
+					     collect_reflog, &collected);
+		}
+		free_worktrees(worktrees);
 		for (i = 0; i < collected.nr; i++) {
 			struct collected_reflog *e = collected.e[i];
 			set_reflog_expiry_param(&cb.cmd, explicit_expiry, e->reflog);

path.c

@@ -108,6 +108,7 @@ struct common_dir {
 
 static struct common_dir common_list[] = {
 	{ 0, 1, 0, "branches" },
+	{ 0, 1, 0, "common" },
 	{ 0, 1, 0, "hooks" },
 	{ 0, 1, 0, "info" },
 	{ 0, 0, 1, "info/sparse-checkout" },
@@ -118,6 +119,7 @@ static struct common_dir common_list[] = {
 	{ 0, 1, 0, "objects" },
 	{ 0, 1, 0, "refs" },
 	{ 0, 1, 1, "refs/bisect" },
+	{ 0, 1, 1, "refs/worktree" },
 	{ 0, 1, 0, "remotes" },
 	{ 0, 1, 0, "worktrees" },
 	{ 0, 1, 0, "rr-cache" },

refs.c

@@ -624,6 +624,7 @@ int dwim_log(const char *str, int len, struct object_id *oid, char **log)
 static int is_per_worktree_ref(const char *refname)
 {
 	return !strcmp(refname, "HEAD") ||
+		starts_with(refname, "refs/worktree/") ||
 		starts_with(refname, "refs/bisect/") ||
 		starts_with(refname, "refs/rewritten/");
 }
@@ -640,13 +641,34 @@ static int is_pseudoref_syntax(const char *refname)
 	return 1;
 }
 
+static int is_main_pseudoref_syntax(const char *refname)
+{
+	return skip_prefix(refname, "main-worktree/", &refname) &&
+		*refname &&
+		is_pseudoref_syntax(refname);
+}
+
+static int is_other_pseudoref_syntax(const char *refname)
+{
+	if (!skip_prefix(refname, "worktrees/", &refname))
+		return 0;
+	refname = strchr(refname, '/');
+	if (!refname || !refname[1])
+		return 0;
+	return is_pseudoref_syntax(refname + 1);
+}
+
 enum ref_type ref_type(const char *refname)
 {
 	if (is_per_worktree_ref(refname))
 		return REF_TYPE_PER_WORKTREE;
 	if (is_pseudoref_syntax(refname))
 		return REF_TYPE_PSEUDOREF;
-       return REF_TYPE_NORMAL;
+	if (is_main_pseudoref_syntax(refname))
+		return REF_TYPE_MAIN_PSEUDOREF;
+	if (is_other_pseudoref_syntax(refname))
+		return REF_TYPE_OTHER_PSEUDOREF;
+	return REF_TYPE_NORMAL;
 }
 
 long get_files_ref_lock_timeout_ms(void)

refs.h

@@ -714,9 +714,11 @@ int parse_hide_refs_config(const char *var, const char *value, const char *);
 int ref_is_hidden(const char *, const char *);
 
 enum ref_type {
-	REF_TYPE_PER_WORKTREE,
-	REF_TYPE_PSEUDOREF,
-	REF_TYPE_NORMAL,
+	REF_TYPE_PER_WORKTREE,	  /* refs inside refs/ but not shared       */
+	REF_TYPE_PSEUDOREF,	  /* refs outside refs/ in current worktree */
+	REF_TYPE_MAIN_PSEUDOREF,  /* pseudo refs from the main worktree     */
+	REF_TYPE_OTHER_PSEUDOREF, /* pseudo refs from other worktrees       */
+	REF_TYPE_NORMAL,	  /* normal/shared refs inside refs/        */
 };
 
 enum ref_type ref_type(const char *refname);