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

2 files changed, 44 insertions, 10 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`,