Rework how ghostel buffers are created

- Until now `M-x ghostel` created a new unique buffers every time
- Other packages like eshell, eat and vterm switch to an existing
  buffer if it exits.
- Now ghostel behaves like these packages too.
- Pass `C-u` (universal argument) to `M-x ghostel` to create new,
  unique buffer (e.g. *ghostel*<2>).
- When provided with a numeric argument create a ghostel buffer with
  that name or switch to if it already exists (eg. `C-5 M-x ghostel`
  to switch to buffer *ghostel*<5>).

Author: affe-mit-waffel

README.md

@@ -322,8 +322,8 @@ individual faces with `M-x customize-face`.
 
 | Command                        | Description                                  |
 |--------------------------------|----------------------------------------------|
-| `M-x ghostel`                  | Open a new terminal                          |
-| `M-x ghostel-project`          | Open a terminal in the current project root  |
+| `M-x ghostel`                  | Open a new terminal (create new buffer with prefix arg) |
+| `M-x ghostel-project`          | Open a terminal in the current project root (create new buffer with prefix arg)  |
 | `M-x ghostel-other`            | Switch to next terminal or create one        |
 | `M-x ghostel-clear`            | Clear screen and scrollback                  |
 | `M-x ghostel-clear-scrollback` | Clear scrollback only                        |

ghostel.el

@@ -576,9 +576,6 @@ DIR is the module directory."
 (defvar-local ghostel--input-timer nil
   "Timer for flushing coalesced input.")
 
-
-
-
 (defvar-local ghostel--last-directory nil
   "Last known working directory from OSC 7, used for dedup.")
 
@@ -591,10 +588,6 @@ variable re-enables automatic renaming for the next title update.")
   "List of prompt positions as (buffer-line . exit-status) pairs.
 Used for prompt navigation and optional re-application after full redraws.")
 
-
-(defvar ghostel--buffer-counter 0
-  "Counter for generating unique terminal buffer names.")
-
 
 ;;; Keymap
 
@@ -1984,9 +1977,14 @@ wheel events reach ghostel's own scroll commands."
 ;;; Entry point
 
 ;;;###autoload
-(defun ghostel ()
-  "Create a new Ghostel terminal buffer."
-  (interactive)
+(defun ghostel (&optional arg)
+  "Start a new Ghostel terminal. If the buffer already exists, switch to it.
+With a non-numeric prefix arg, create a new buffer.
+With a numeric prefix ARG, switch to the buffer with that number or
+create it if it doesn't exist yet.
+The name of the buffer is determined by the value of `ghostel-buffer-name'."
+  (interactive "P")
+  (cl-assert ghostel-buffer-name)
   (unless (fboundp 'ghostel--new)
     (let ((dir (file-name-directory (locate-library "ghostel"))))
       (ghostel--ensure-module dir)
@@ -1995,33 +1993,41 @@ wheel events reach ghostel's own scroll commands."
         (if (file-exists-p mod)
             (module-load mod)
           (user-error "Ghostel native module not available")))))
-  (let* ((index (cl-incf ghostel--buffer-counter))
-         (buf-name (if (= index 1)
-                       ghostel-buffer-name
-                     (format "%s<%d>" ghostel-buffer-name index)))
-         (buffer (generate-new-buffer buf-name)))
+  (let ((buffer (cond ((numberp arg)
+		       (get-buffer-create (format "%s<%d>"
+						  ghostel-buffer-name
+						  arg)))
+		      (arg
+		       (generate-new-buffer ghostel-buffer-name))
+		      (t
+		       (get-buffer-create ghostel-buffer-name)))))
+    (cl-assert (and buffer (buffer-live-p buffer)))
     (with-current-buffer buffer
-      (ghostel-mode)
-      (setq ghostel--managed-buffer-name (buffer-name))
-      (let* ((height (window-body-height))
-             (width (window-max-chars-per-line)))
-        (setq ghostel--term
-              (ghostel--new height width ghostel-max-scrollback))
-        (ghostel--apply-palette ghostel--term))
-      (ghostel--start-process))
+      (unless (derived-mode-p 'ghostel-mode)
+        (ghostel-mode)
+        (setq ghostel--managed-buffer-name (buffer-name))
+        (let* ((height (window-body-height))
+               (width (window-max-chars-per-line)))
+          (setq ghostel--term
+                (ghostel--new height width ghostel-max-scrollback))
+          (ghostel--apply-palette ghostel--term))
+        (ghostel--start-process)))
     (switch-to-buffer buffer)))
 
 ;;;###autoload
 (defun ghostel-project ()
-  "Create a new Ghostel terminal in the current project's root.
+  "Start a new Ghostel terminal in the current project's root.
 The buffer name is prefixed with the project name.
+If a buffer already exists for this project switch to it.
+Otherwise create a new Ghostel buffer. This function accepts the same
+universal arguments that `ghostel' does.
 To add this to `project-switch-commands':
   (add-to-list \\='project-switch-commands \\='(ghostel-project \"Ghostel\") t)"
   (interactive)
   (let ((default-directory (project-root (project-current t)))
         (ghostel-buffer-name (project-prefixed-buffer-name
                               (string-trim ghostel-buffer-name "*" "*"))))
-    (ghostel)))
+    (ghostel current-prefix-arg)))
 
 (defun ghostel-other ()
   "Switch to the next ghostel terminal buffer, or create one."

test/ghostel-test.el

@@ -1199,7 +1199,7 @@ cell, so the visual line width must equal the terminal column count."
               ((symbol-function 'project-root)
                (lambda (proj) (cdr proj)))
               ((symbol-function 'ghostel)
-               (lambda ()
+               (lambda (&optional _)
                  (setq result (cons default-directory ghostel-buffer-name)))))
       (ghostel-project)
       ;; default-directory should be the project root
@@ -1208,6 +1208,28 @@ cell, so the visual line width must equal the terminal column count."
       (should (string-match-p "ghostel" (cdr result)))
       (should-not (string-match-p "\\*\\*" (cdr result))))))
 
+;; -----------------------------------------------------------------------
+;; Test: ghostel-project passes universal args to ghostel
+;; -----------------------------------------------------------------------
+
+(ert-deftest ghostel-test-project-universal-arg ()
+  "Test that `ghostel-project' passes the universal arg to `ghostel'."
+  (require 'project)
+  (let ((ghostel-buffer-name "*ghostel*")
+	(current-prefix-arg '4)
+        result)
+    ;; Stub project-current, project-root, and ghostel to capture args
+    (cl-letf (((symbol-function 'project-current)
+               (lambda (_maybe-prompt) '(transient . "/tmp/myproj/")))
+              ((symbol-function 'project-root)
+               (lambda (proj) (cdr proj)))
+              ((symbol-function 'ghostel)
+               (lambda (&optional arg)
+                 (setq result arg))))
+      (ghostel-project)
+      ;; Pass the prefix argument to `ghostel'
+      (should (equal '4 result)))))
+
 ;; -----------------------------------------------------------------------
 ;; Runner
 ;; -----------------------------------------------------------------------
@@ -1536,6 +1558,7 @@ cell, so the visual line width must equal the terminal column count."
     ghostel-test-copy-mode-cursor
     ghostel-test-copy-mode-hl-line
     ghostel-test-project-buffer-name
+    ghostel-test-project-universal-arg
     ghostel-test-package-version
     ghostel-test-module-version-match
     ghostel-test-module-version-mismatch