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

> 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
>