[PATCH 5/6] am: Allow flipping worktree creation with prefix argument

[Kyle Meyer <kyle@kyleam.com>]

I tend to use a few dedicated worktrees for projects and am not
interested in creating a worktree for each patch series I apply.
However, I can imagine wanting to create one every now and then.  Make
it possible by adding a prefix argument to piem-am and
piem-b4-am-from-mid that flips the meaning of piem-am-create-worktree.
---
 piem-b4.el | 15 +++++++++++----
 piem.el    | 18 ++++++++++++------
 2 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/piem-b4.el b/piem-b4.el
index 27ecf19..172236f 100644
--- a/piem-b4.el
+++ b/piem-b4.el
@@ -130,15 +130,21 @@ (defun piem-b4-am-ready-from-mid (mid &optional args)
          (append args (list mid))))
 
 ;;;###autoload
-(defun piem-b4-am-from-mid (mid &optional args)
+(defun piem-b4-am-from-mid (mid &optional args toggle-worktree)
   "Get the thread for MID, extract an am-ready mbox, and apply it.
+
 Try to get a thread for the Message-Id MID with
 `piem-mid-to-thread-functions', falling back to letting b4
 download it.  After calling `b4 am' with ARGS to prepare an
-am-ready mbox, feed the result to `git am'."
+am-ready mbox, feed the result to `git am'.
+
+When prefix argument TOGGLE-WORKTREE is non-nil, invert the
+meaning of `piem-am-create-worktree'.  With the default value,
+this triggers the creation of a new worktree."
   (interactive (list (or (piem-mid)
                          (read-string "Message ID: "))
-                     (transient-args 'piem-b4-am)))
+                     (transient-args 'piem-b4-am)
+                     current-prefix-arg))
   (when-let ((badopt (cl-some
                       (lambda (arg)
                         (and (string-match
@@ -158,7 +164,8 @@ (defun piem-b4-am-from-mid (mid &optional args)
                  (with-temp-buffer
                    (insert-file-contents (or cover mbox-file))
                    (piem-extract-mbox-info))
-                 coderepo)
+                 coderepo
+                 toggle-worktree)
       (when clean-fn
         (funcall clean-fn)))))
 
diff --git a/piem.el b/piem.el
index ac9812c..0cb1093 100644
--- a/piem.el
+++ b/piem.el
@@ -663,7 +663,7 @@ (defun piem-am-read-worktree (coderepo branch)
                   (replace-regexp-in-string "/" "-" branch))))))
 
 ;;;###autoload
-(defun piem-am (mbox &optional format info coderepo)
+(defun piem-am (mbox &optional format info coderepo toggle-worktree)
   "Feed an am-ready mbox to `git am'.
 
 MBOX is a buffer whose contents are an am-ready mbox (obtained
@@ -677,7 +677,11 @@ (defun piem-am (mbox &optional format info coderepo)
 for a list of possible properties).
 
 CODEREPO, if given, indicates the code repository to operate
-within.  If not specified, the default directory is used."
+within.  If not specified, the default directory is used.
+
+When prefix argument TOGGLE-WORKTREE is non-nil, invert the
+meaning of `piem-am-create-worktree'.  With the default value,
+this triggers the creation of a new worktree."
   (interactive
    (pcase-let ((`(,mbox . ,format)
                 (or (piem-am-ready-mbox)
@@ -689,10 +693,12 @@ (defun piem-am (mbox &optional format info coderepo)
      (list (cons :interactive mbox)
            format
            (piem-extract-mbox-info mbox)
-           (piem-inbox-coderepo-maybe-read))))
+           (piem-inbox-coderepo-maybe-read)
+           current-prefix-arg)))
   (setq format (or format "mboxrd"))
   (let* ((default-directory (or coderepo default-directory))
          (am-directory default-directory)
+         (use-worktree (xor piem-am-create-worktree toggle-worktree))
          (interactivep (eq (car-safe mbox) :interactive)))
     (when interactivep
       (setq mbox (cdr mbox)))
@@ -707,7 +713,7 @@ (defun piem-am (mbox &optional format info coderepo)
                                    (magit-list-local-branch-names)))
                        (base (plist-get info :base-commit)))
                    (if base (cons base cands) cands)))))
-      (when piem-am-create-worktree
+      (when use-worktree
         (setq am-directory
               (expand-file-name
                (funcall piem-am-read-worktree-function
@@ -715,11 +721,11 @@ (defun piem-am (mbox &optional format info coderepo)
         (when (file-exists-p am-directory)
           (user-error "Worktree directory already exists")))
       (apply #'piem-process-call nil piem-git-executable
-             (append (if piem-am-create-worktree
+             (append (if use-worktree
                          (list "worktree" "add")
                        (list "checkout"))
                      (if new-branch (list "-b" new-branch) (list "--detach"))
-                     (and piem-am-create-worktree (list am-directory))
+                     (and use-worktree (list am-directory))
                      (and (not (string-blank-p base))
                           (list base)))))
     (let ((args (cons (concat "--patch-format=" format)
-- 
2.29.2