[PATCH v2 2/3] worktree: make add <path> <branch> dwim

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

Currently 'git worktree add <path> <branch>', errors out when 'branch'
is not a local branch.   It has no additional dwim'ing features that one
might expect.

Make it behave more like 'git checkout <branch>' when the branch doesn't
exist locally, but a remote tracking branch uniquely matches the desired
branch name, i.e. create a new branch from the remote tracking branch
and set the upstream to the remote tracking branch.

As 'git worktree add' currently just dies in this situation, there are
no backwards compatibility worries when introducing this feature.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
---
 Documentation/git-worktree.txt |  7 +++++++
 builtin/worktree.c             | 15 ++++++++++++++
 t/t2025-worktree-add.sh        | 44 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+)

diff --git a/Documentation/git-worktree.txt b/Documentation/git-worktree.txt
index b472acc356..3c7c8c3cee 100644
--- a/Documentation/git-worktree.txt
+++ b/Documentation/git-worktree.txt
@@ -52,6 +52,13 @@ 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}`.
 +
+If <branch> is not found 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 -b <branch> <path> <remote>/<branch>
+------------
++
 If `<branch>` 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.
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 7b9307aa58..92b583ae39 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"
@@ -386,6 +387,20 @@ static int add(int ac, const char **av, const char *prefix)
 		opts.new_branch = xstrndup(s, n);
 	}
 
+	if (ac == 2) {
+		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 (!commit && remote) {
+			opts.new_branch = branch;
+			branch = remote;
+		}
+	}
+
 	if (opts.new_branch) {
 		struct child_process cp = CHILD_PROCESS_INIT;
 		cp.git_cmd = 1;
diff --git a/t/t2025-worktree-add.sh b/t/t2025-worktree-add.sh
index b5c47ac602..e5959800c0 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 +324,38 @@ 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 '"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 &&
+	test_when_finished rm -rf repo_dwim &&
+	test_when_finished rm -rf foo &&
+	git init repo_upstream &&
+	(
+		cd repo_upstream &&
+		test_commit upstream_master &&
+		git checkout -b foo &&
+		test_commit a_foo
+	) &&
+	git init repo_dwim &&
+	(
+		cd repo_dwim &&
+		test_commit dwim_master &&
+		git remote add repo_upstream ../repo_upstream &&
+		git config remote.repo_upstream.fetch \
+			  "refs/heads/*:refs/remotes/repo_upstream/*" &&
+		git fetch --all &&
+		git worktree add ../foo foo
+	) &&
+	(
+		cd foo &&
+		test_branch_upstream foo repo_upstream foo &&
+		git rev-parse repo_upstream/foo >expect &&
+		git rev-parse foo >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done
-- 
2.15.0.345.gf926f18f3d