[PATCH v1 2/2] worktree: make add dwim

[Thomas Gummerer <t.gummerer@gmail.com>]

Currently git worktree add creates a new branch, that matches the HEAD
of whichever worktree we were on when calling "git worktree add".

Add a --guess flag to git worktree add, that makes it behave like the
dwim machinery in 'git checkout <new-branch>', i.e. check if the new
branch name uniquely matches the branch name of a remote tracking
branch, and if so check out that branch, and set the upstream to the
remote tracking branch.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
---

I'm a bit torn about hiding his behind an additional flag in git
worktree add or not.  I would like to have the feature without the
additional flag, but it might break some peoples expectations, so
dunno.

 builtin/worktree.c      | 14 +++++++++-
 t/t2025-worktree-add.sh | 70 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+), 1 deletion(-)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 7b9307aa58..5740d1f8a3 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"
@@ -341,6 +342,7 @@ static int add(int ac, const char **av, const char *prefix)
 	const char *new_branch_force = NULL;
 	char *path;
 	const char *branch;
+	int dwim_new_branch = 0;
 	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 +352,7 @@ 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_BOOL(0, "guess", &dwim_new_branch, N_("checkout upstream branch if there's a unique match")),
 		OPT_END()
 	};
 
@@ -363,6 +366,7 @@ static int add(int ac, const char **av, const char *prefix)
 
 	path = prefix_filename(prefix, av[0]);
 	branch = ac < 2 ? "HEAD" : av[1];
+	dwim_new_branch = ac < 2 ? dwim_new_branch : 0;
 
 	if (!strcmp(branch, "-"))
 		branch = "@{-1}";
@@ -387,13 +391,21 @@ static int add(int ac, const char **av, const char *prefix)
 	}
 
 	if (opts.new_branch) {
+		struct object_id oid;
+		const char *remote;
 		struct child_process cp = CHILD_PROCESS_INIT;
+
+		remote = unique_tracking_name(opts.new_branch, &oid);
+
 		cp.git_cmd = 1;
 		argv_array_push(&cp.args, "branch");
 		if (opts.force_new_branch)
 			argv_array_push(&cp.args, "--force");
 		argv_array_push(&cp.args, opts.new_branch);
-		argv_array_push(&cp.args, branch);
+		if (dwim_new_branch && remote)
+			argv_array_push(&cp.args, remote);
+		else
+			argv_array_push(&cp.args, branch);
 		if (run_command(&cp))
 			return -1;
 		branch = opts.new_branch;
diff --git a/t/t2025-worktree-add.sh b/t/t2025-worktree-add.sh
index b5c47ac602..b37c279787 100755
--- a/t/t2025-worktree-add.sh
+++ b/t/t2025-worktree-add.sh
@@ -6,6 +6,16 @@ test_description='test git worktree add'
 
 . "$TEST_DIRECTORY"/lib-rebase.sh
 
+# 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 'setup' '
 	test_commit init
 '
@@ -314,4 +324,64 @@ test_expect_success 'rename a branch under bisect not allowed' '
 	test_must_fail git branch -M under-bisect bisect-with-new-name
 '
 
+test_expect_success 'git worktree add does not dwim' '
+	test_when_finished rm -rf repo_a &&
+	test_when_finished rm -rf repo_b &&
+	test_when_finished rm -rf foo &&
+	git init repo_a &&
+	(
+		cd repo_a &&
+		test_commit a_master &&
+		git checkout -b foo &&
+		test_commit a_foo
+	) &&
+	git init repo_b &&
+	(
+		cd repo_b &&
+		test_commit b_master &&
+		git remote add repo_a ../repo_a &&
+		git config remote.repo_a.fetch \
+			"+refs/heads/*:refs/remotes/other_a/*" &&
+		git fetch --all &&
+		git worktree add ../foo
+	) &&
+	(
+		cd foo &&
+		! test_branch_upstream foo repo_a foo &&
+		git rev-parse other_a/foo >expect &&
+		git rev-parse foo >actual &&
+		! test_cmp expect actual
+	)
+'
+
+test_expect_success 'git worktree add --guess dwims' '
+	test_when_finished rm -rf repo_a &&
+	test_when_finished rm -rf repo_b &&
+	test_when_finished rm -rf foo &&
+	git init repo_a &&
+	(
+		cd repo_a &&
+		test_commit a_master &&
+		git checkout -b foo &&
+		test_commit a_foo
+	) &&
+	git init repo_b &&
+	(
+		cd repo_b &&
+		test_commit b_master &&
+		git remote add repo_a ../repo_a &&
+		git config remote.repo_a.fetch \
+			"+refs/heads/*:refs/remotes/other_a/*" &&
+		git fetch --all &&
+		git worktree add --guess ../foo
+	) &&
+	(
+		cd foo &&
+		test_branch_upstream foo repo_a foo &&
+		git rev-parse other_a/foo >expect &&
+		git rev-parse foo >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done
-- 
2.15.0.403.gc27cc4dac6