Merge branch 'tg/worktree-create-tracking'

The way "git worktree add" determines what branch to create from
where and checkout in the new worktree has been updated a bit.

* tg/worktree-create-tracking:
  add worktree.guessRemote config option
  worktree: add --guess-remote flag to add subcommand
  worktree: make add <path> <branch> dwim
  worktree: add --[no-]track option to the add subcommand
  worktree: add can be created from any commit-ish
  checkout: factor out functions to new lib file

8 files changed, 277 insertions, 51 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index c1598ee703..9fac2f2b88 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -3468,3 +3468,13 @@ web.browser::
 	Specify a web browser that may be used by some commands.
 	Currently only linkgit:git-instaweb[1] and linkgit:git-help[1]
 	may use it.
+
+worktree.guessRemote::
+	With `add`, if no branch argument, and neither of `-b` nor
+	`-B` nor `--detach` are given, the command defaults to
+	creating a new branch from HEAD.  If `worktree.guessRemote` is
+	set to true, `worktree add` tries to find a remote-tracking
+	branch whose name uniquely matches the new branch name.  If
+	such a branch exists, it is checked out and set as "upstream"
+	for the new branch.  If no such match can be found, it falls
+	back to creating a new branch from the current HEAD.
diff --git a/Documentation/git-worktree.txt b/Documentation/git-worktree.txt
index b472acc356..f850e8ffb6 100644
--- a/Documentation/git-worktree.txt
+++ b/Documentation/git-worktree.txt
@@ -9,7 +9,7 @@ git-worktree - Manage multiple working trees
 SYNOPSIS
 --------
 [verse]
-'git worktree add' [-f] [--detach] [--checkout] [--lock] [-b <new-branch>] <path> [<branch>]
+'git worktree add' [-f] [--detach] [--checkout] [--lock] [-b <new-branch>] <path> [<commit-ish>]
 'git worktree list' [--porcelain]
 'git worktree lock' [--reason <string>] <worktree>
 'git worktree prune' [-n] [-v] [--expire <expire>]
@@ -45,14 +45,22 @@ specifying `--reason` to explain why the working tree is locked.
 
 COMMANDS
 --------
-add <path> [<branch>]::
+add <path> [<commit-ish>]::
 
-Create `<path>` and checkout `<branch>` into it. The new working directory
+Create `<path>` and checkout `<commit-ish>` into it. The new working directory
 is linked to the current repository, sharing everything except working
 directory specific files such as HEAD, index, etc. `-` may also be
-specified as `<branch>`; it is synonymous with `@{-1}`.
+specified as `<commit-ish>`; it is synonymous with `@{-1}`.
 +
-If `<branch>` is omitted and neither `-b` nor `-B` nor `--detach` used,
+If <commit-ish> is a branch name (call it `<branch>` and is not found,
+and neither `-b` nor `-B` nor `--detach` are used, but there does
+exist a tracking branch in exactly one remote (call it `<remote>`)
+with a matching name, treat as equivalent to
+------------
+$ git worktree add --track -b <branch> <path> <remote>/<branch>
+------------
++
+If `<commit-ish>` is omitted and neither `-b` nor `-B` nor `--detach` used,
 then, as a convenience, a new branch based at HEAD is created automatically,
 as if `-b $(basename <path>)` was specified.
 
@@ -84,29 +92,45 @@ OPTIONS
 
 -f::
 --force::
-	By default, `add` refuses to create a new working tree when `<branch>`
+	By default, `add` refuses to create a new working tree when `<commit-ish>` is a branch name and
 	is already checked out by another working tree. This option overrides
 	that safeguard.
 
 -b <new-branch>::
 -B <new-branch>::
 	With `add`, create a new branch named `<new-branch>` starting at
-	`<branch>`, and check out `<new-branch>` into the new working tree.
-	If `<branch>` is omitted, it defaults to HEAD.
+	`<commit-ish>`, and check out `<new-branch>` into the new working tree.
+	If `<commit-ish>` is omitted, it defaults to HEAD.
 	By default, `-b` refuses to create a new branch if it already
 	exists. `-B` overrides this safeguard, resetting `<new-branch>` to
-	`<branch>`.
+	`<commit-ish>`.
 
 --detach::
 	With `add`, detach HEAD in the new working tree. See "DETACHED HEAD"
 	in linkgit:git-checkout[1].
 
 --[no-]checkout::
-	By default, `add` checks out `<branch>`, however, `--no-checkout` can
+	By default, `add` checks out `<commit-ish>`, however, `--no-checkout` can
 	be used to suppress checkout in order to make customizations,
 	such as configuring sparse-checkout. See "Sparse checkout"
 	in linkgit:git-read-tree[1].
 
+--[no-]guess-remote::
+	With `worktree add <path>`, without `<commit-ish>`, instead
+	of creating a new branch from HEAD, if there exists a tracking
+	branch in exactly one remote matching the basename of `<path>,
+	base the new branch on the remote-tracking branch, and mark
+	the remote-tracking branch as "upstream" from the new branch.
++
+This can also be set up as the default behaviour by using the
+`worktree.guessRemote` config option.
+
+--[no-]track::
+	When creating a new branch, if `<commit-ish>` is a branch,
+	mark it as "upstream" from the new branch.  This is the
+	default if `<commit-ish>` is a remote-tracking branch.  See
+	"--track" in linkgit:git-branch[1] for details.
+
 --lock::
 	Keep the working tree locked after creation. This is the
 	equivalent of `git worktree lock` after `git worktree add`,
diff --git a/Makefile b/Makefile
index fef9c8d272..9dc5a588e2 100644
--- a/Makefile
+++ b/Makefile
@@ -759,6 +759,7 @@ LIB_OBJS += branch.o
 LIB_OBJS += bulk-checkin.o
 LIB_OBJS += bundle.o
 LIB_OBJS += cache-tree.o
+LIB_OBJS += checkout.o
 LIB_OBJS += color.o
 LIB_OBJS += column.o
 LIB_OBJS += combine-diff.o
diff --git a/builtin/checkout.c b/builtin/checkout.c
index e1e157d205..9b886356bf 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1,5 +1,6 @@
 #include "builtin.h"
 #include "config.h"
+#include "checkout.h"
 #include "lockfile.h"
 #include "parse-options.h"
 #include "refs.h"
@@ -872,46 +873,6 @@ static int git_checkout_config(const char *var, const char *value, void *cb)
 	return git_xmerge_config(var, value, NULL);
 }
 
-struct tracking_name_data {
-	/* const */ char *src_ref;
-	char *dst_ref;
-	struct object_id *dst_oid;
-	int unique;
-};
-
-static int check_tracking_name(struct remote *remote, void *cb_data)
-{
-	struct tracking_name_data *cb = cb_data;
-	struct refspec query;
-	memset(&query, 0, sizeof(struct refspec));
-	query.src = cb->src_ref;
-	if (remote_find_tracking(remote, &query) ||
-	    get_oid(query.dst, cb->dst_oid)) {
-		free(query.dst);
-		return 0;
-	}
-	if (cb->dst_ref) {
-		free(query.dst);
-		cb->unique = 0;
-		return 0;
-	}
-	cb->dst_ref = query.dst;
-	return 0;
-}
-
-static const char *unique_tracking_name(const char *name, struct object_id *oid)
-{
-	struct tracking_name_data cb_data = { NULL, NULL, NULL, 1 };
-	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
-	cb_data.dst_oid = oid;
-	for_each_remote(check_tracking_name, &cb_data);
-	free(cb_data.src_ref);
-	if (cb_data.unique)
-		return cb_data.dst_ref;
-	free(cb_data.dst_ref);
-	return NULL;
-}
-
 static int parse_branchname_arg(int argc, const char **argv,
 				int dwim_new_local_branch_ok,
 				struct branch_info *new,
diff --git a/builtin/worktree.c b/builtin/worktree.c
index ed043d5f1c..002a569a11 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "checkout.h"
 #include "config.h"
 #include "builtin.h"
 #include "dir.h"
@@ -32,8 +33,19 @@ struct add_opts {
 
 static int show_only;
 static int verbose;
+static int guess_remote;
 static timestamp_t expire;
 
+static int git_worktree_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "worktree.guessremote")) {
+		guess_remote = git_config_bool(var, value);
+		return 0;
+	}
+
+	return git_default_config(var, value, cb);
+}
+
 static int prune_worktree(const char *id, struct strbuf *reason)
 {
 	struct stat st;
@@ -341,6 +353,7 @@ static int add(int ac, const char **av, const char *prefix)
 	const char *new_branch_force = NULL;
 	char *path;
 	const char *branch;
+	const char *opt_track = NULL;
 	struct option options[] = {
 		OPT__FORCE(&opts.force, N_("checkout <branch> even if already checked out in other worktree")),
 		OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
@@ -350,6 +363,11 @@ static int add(int ac, const char **av, const char *prefix)
 		OPT_BOOL(0, "detach", &opts.detach, N_("detach HEAD at named commit")),
 		OPT_BOOL(0, "checkout", &opts.checkout, N_("populate the new working tree")),
 		OPT_BOOL(0, "lock", &opts.keep_locked, N_("keep the new working tree locked")),
+		OPT_PASSTHRU(0, "track", &opt_track, NULL,
+			     N_("set up tracking mode (see git-branch(1))"),
+			     PARSE_OPT_NOARG | PARSE_OPT_OPTARG),
+		OPT_BOOL(0, "guess-remote", &guess_remote,
+			 N_("try to match the new branch name with a remote-tracking branch")),
 		OPT_END()
 	};
 
@@ -384,6 +402,28 @@ static int add(int ac, const char **av, const char *prefix)
 		int n;
 		const char *s = worktree_basename(path, &n);
 		opts.new_branch = xstrndup(s, n);
+		if (guess_remote) {
+			struct object_id oid;
+			const char *remote =
+				unique_tracking_name(opts.new_branch, &oid);
+			if (remote)
+				branch = remote;
+		}
+	}
+
+	if (ac == 2 && !opts.new_branch && !opts.detach) {
+		struct object_id oid;
+		struct commit *commit;
+		const char *remote;
+
+		commit = lookup_commit_reference_by_name(branch);
+		if (!commit) {
+			remote = unique_tracking_name(branch, &oid);
+			if (remote) {
+				opts.new_branch = branch;
+				branch = remote;
+			}
+		}
 	}
 
 	if (opts.new_branch) {
@@ -394,9 +434,13 @@ static int add(int ac, const char **av, const char *prefix)
 			argv_array_push(&cp.args, "--force");
 		argv_array_push(&cp.args, opts.new_branch);
 		argv_array_push(&cp.args, branch);
+		if (opt_track)
+			argv_array_push(&cp.args, opt_track);
 		if (run_command(&cp))
 			return -1;
 		branch = opts.new_branch;
+	} else if (opt_track) {
+		die(_("--[no-]track can only be used if a new branch is created"));
 	}
 
 	UNLEAK(path);
@@ -557,7 +601,7 @@ int cmd_worktree(int ac, const char **av, const char *prefix)
 		OPT_END()
 	};
 
-	git_config(git_default_config, NULL);
+	git_config(git_worktree_config, NULL);
 
 	if (ac < 2)
 		usage_with_options(worktree_usage, options);
diff --git a/checkout.c b/checkout.c
new file mode 100644
index 0000000000..ac42630f74
--- /dev/null
+++ b/checkout.c
@@ -0,0 +1,43 @@
+#include "cache.h"
+#include "remote.h"
+#include "checkout.h"
+
+struct tracking_name_data {
+	/* const */ char *src_ref;
+	char *dst_ref;
+	struct object_id *dst_oid;
+	int unique;
+};
+
+static int check_tracking_name(struct remote *remote, void *cb_data)
+{
+	struct tracking_name_data *cb = cb_data;
+	struct refspec query;
+	memset(&query, 0, sizeof(struct refspec));
+	query.src = cb->src_ref;
+	if (remote_find_tracking(remote, &query) ||
+	    get_oid(query.dst, cb->dst_oid)) {
+		free(query.dst);
+		return 0;
+	}
+	if (cb->dst_ref) {
+		free(query.dst);
+		cb->unique = 0;
+		return 0;
+	}
+	cb->dst_ref = query.dst;
+	return 0;
+}
+
+const char *unique_tracking_name(const char *name, struct object_id *oid)
+{
+	struct tracking_name_data cb_data = { NULL, NULL, NULL, 1 };
+	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
+	cb_data.dst_oid = oid;
+	for_each_remote(check_tracking_name, &cb_data);
+	free(cb_data.src_ref);
+	if (cb_data.unique)
+		return cb_data.dst_ref;
+	free(cb_data.dst_ref);
+	return NULL;
+}
diff --git a/checkout.h b/checkout.h
new file mode 100644
index 0000000000..9980711179
--- /dev/null
+++ b/checkout.h
@@ -0,0 +1,13 @@
+#ifndef CHECKOUT_H
+#define CHECKOUT_H
+
+#include "cache.h"
+
+/*
+ * Check if the branch name uniquely matches a branch name on a remote
+ * tracking branch.  Return the name of the remote if such a branch
+ * exists, NULL otherwise.
+ */
+extern const char *unique_tracking_name(const char *name, struct object_id *oid);
+
+#endif /* CHECKOUT_H */
diff --git a/t/t2025-worktree-add.sh b/t/t2025-worktree-add.sh
index b5c47ac602..6ce9b9c070 100755
--- a/t/t2025-worktree-add.sh
+++ b/t/t2025-worktree-add.sh
@@ -313,5 +313,135 @@ test_expect_success 'checkout a branch under bisect' '
 test_expect_success 'rename a branch under bisect not allowed' '
 	test_must_fail git branch -M under-bisect bisect-with-new-name
 '
+# Is branch "refs/heads/$1" set to pull from "$2/$3"?
+test_branch_upstream () {
+	printf "%s\n" "$2" "refs/heads/$3" >expect.upstream &&
+	{
+		git config "branch.$1.remote" &&
+		git config "branch.$1.merge"
+	} >actual.upstream &&
+	test_cmp expect.upstream actual.upstream
+}
+
+test_expect_success '--track sets up tracking' '
+	test_when_finished rm -rf track &&
+	git worktree add --track -b track track master &&
+	test_branch_upstream track . master
+'
+
+# setup remote repository $1 and repository $2 with $1 set up as
+# remote.  The remote has two branches, master and foo.
+setup_remote_repo () {
+	git init $1 &&
+	(
+		cd $1 &&
+		test_commit $1_master &&
+		git checkout -b foo &&
+		test_commit upstream_foo
+	) &&
+	git init $2 &&
+	(
+		cd $2 &&
+		test_commit $2_master &&
+		git remote add $1 ../$1 &&
+		git config remote.$1.fetch \
+			"refs/heads/*:refs/remotes/$1/*" &&
+		git fetch --all
+	)
+}
+
+test_expect_success '--no-track avoids setting up tracking' '
+	test_when_finished rm -rf repo_upstream repo_local foo &&
+	setup_remote_repo repo_upstream repo_local &&
+	(
+		cd repo_local &&
+		git worktree add --no-track -b foo ../foo repo_upstream/foo
+	) &&
+	(
+		cd foo &&
+		test_must_fail git config "branch.foo.remote" &&
+		test_must_fail git config "branch.foo.merge" &&
+		test_cmp_rev refs/remotes/repo_upstream/foo refs/heads/foo
+	)
+'
+
+test_expect_success '"add" <path> <non-existent-branch> fails' '
+	test_must_fail git worktree add foo non-existent
+'
+
+test_expect_success '"add" <path> <branch> dwims' '
+	test_when_finished rm -rf repo_upstream repo_dwim foo &&
+	setup_remote_repo repo_upstream repo_dwim &&
+	git init repo_dwim &&
+	(
+		cd repo_dwim &&
+		git worktree add ../foo foo
+	) &&
+	(
+		cd foo &&
+		test_branch_upstream foo repo_upstream foo &&
+		test_cmp_rev refs/remotes/repo_upstream/foo refs/heads/foo
+	)
+'
+
+test_expect_success 'git worktree add does not match remote' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git worktree add ../foo
+	) &&
+	(
+		cd foo &&
+		test_must_fail git config "branch.foo.remote" &&
+		test_must_fail git config "branch.foo.merge" &&
+		! test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
+	)
+'
+
+test_expect_success 'git worktree add --guess-remote sets up tracking' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git worktree add --guess-remote ../foo
+	) &&
+	(
+		cd foo &&
+		test_branch_upstream foo repo_a foo &&
+		test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
+	)
+'
+
+test_expect_success 'git worktree add with worktree.guessRemote sets up tracking' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git config worktree.guessRemote true &&
+		git worktree add ../foo
+	) &&
+	(
+		cd foo &&
+		test_branch_upstream foo repo_a foo &&
+		test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
+	)
+'
+
+test_expect_success 'git worktree --no-guess-remote option overrides config' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git config worktree.guessRemote true &&
+		git worktree add --no-guess-remote ../foo
+	) &&
+	(
+		cd foo &&
+		test_must_fail git config "branch.foo.remote" &&
+		test_must_fail git config "branch.foo.merge" &&
+		! test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
+	)
+'
 
 test_done