From 7f344ed1590b81323e24cdedf77477ae57cb49f9 Mon Sep 17 00:00:00 2001
From: Jared Finder <jared@finder.org>
Date: Fri, 26 Jan 2024 09:49:03 -0800
Subject: [PATCH 1/3] Enable multiple modes to appear in tab line

This adds space for window-tool-bar-mode, which will be added in an
upcoming commit.

* lisp/tab-line.el (tab-line-format-template): Add separator space.
(tab-line-display-order): New user variable to control display order.
(tab-line--runtime-display-order, tab-line--cookie): New internal
variables.
(tab-line-set-display): New function for modes to call to enable only
their content.
(tab-line-mode): Call `tab-line-set-display'.
---
 lisp/tab-line.el | 89 +++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 80 insertions(+), 9 deletions(-)

diff --git a/lisp/tab-line.el b/lisp/tab-line.el
index cc60f94c9c5..c7283641cbd 100644
--- a/lisp/tab-line.el
+++ b/lisp/tab-line.el
@@ -573,7 +573,8 @@ tab-line-format-template
      (when (and (eq tab-line-tabs-function #'tab-line-tabs-window-buffers)
                 tab-line-new-button-show
                 tab-line-new-button)
-       (list tab-line-new-button)))))
+       (list tab-line-new-button))
+     (list " "))))
 
 (defun tab-line-tab-face-inactive-alternating (tab tabs face _buffer-p selected-p)
   "Return FACE for TAB in TABS with alternation.
@@ -997,18 +998,88 @@ tab-line-event-start
       (event-start event)))
 
 
+;;; Tab line display ordering
+(defcustom tab-line-display-order
+  (copy-tree '(tab-line-mode window-tool-bar-mode))
+  "The order to display content in the tab-line.
+
+This is a list of symbols.  By convention, the symbols correspond
+to the mode name that enables / disables content.  Any symbol not
+listed here will automatically be put at the end of the tab line.
+
+See `tab-line-set-display' for the Lisp interface to add and
+remove content."
+  :type '(repeat symbol)
+  :group 'tab-line
+  :version "30.1")
+
+(defvar tab-line--runtime-display-order
+  nil
+  "Symbols that contain content but are not in `tab-line-display-order'.
+This list ensures that content stays in a stable position in the
+tab line.")
+
+(defconst tab-line--cookie
+  '(tab-line-set-display nil)
+  "Cookie used by `tab-line-set-display'.
+This is used to tell if the tab line is being set based on
+`tab-line-display-order' or was overridden by the user.")
+
+(defun tab-line-set-display (sym value)
+  "Lisp interface to add or remove content from the tab line.
+
+After calling this, if there is no content in the tab line, it
+will be automatically hidden.
+
+SYM is a symbol, usually the symbol corresponding to the mode
+showing content such as `tab-line-mode'.
+
+VALUE is the content to display and will be added to
+`tab-line-format' at an appropriate index based on
+`tab-line-display-order'.  If you want to remove content because
+the mode is being disabled, set this to nil."
+  ;; Preserve tab-line-format if altered outside of this function.
+  (when (or (null tab-line-format)
+            ;; Assume that user modifications will not use this
+            ;; cookie.
+            (equal (car tab-line-format) tab-line--cookie))
+    (let (pos)
+      (setf pos (seq-position tab-line-display-order sym))
+      (unless pos
+        (when-let ((append-pos (seq-position tab-line--runtime-display-order sym)))
+          (setf pos (+ (length tab-line-display-order)
+                       append-pos))))
+      (unless pos
+        (warn "Symbol %S not found in `tab-line-display-order'.  Putting at end."
+              sym)
+        (setf pos (+ (length tab-line-display-order)
+                     (length tab-line--runtime-display-order))
+              tab-line--runtime-display-order
+              (append tab-line--runtime-display-order
+                      (list sym))))
+
+      (let ((desired-length (+ pos 2))  ;Plus 1 additional for the cookie,
+            (current-length (length tab-line-format)))
+        (when (> desired-length current-length)
+          (setf tab-line-format
+                (append tab-line-format
+                        (make-list (- desired-length current-length) nil))
+                ;; If tab-line-format was nil, then the cookie needs to be set.
+                (car tab-line-format) tab-line--cookie)))
+
+      (setf (nth (1+ pos) tab-line-format) value))
+
+    ;; If the entire display has been disabled, tab line would display
+    ;; as empty.  Explicitly hide the tab line in this case.
+    (when (seq-every-p #'null (cdr tab-line-format))
+      (setf tab-line-format nil))))
+
 ;;;###autoload
 (define-minor-mode tab-line-mode
   "Toggle display of tab line in the windows displaying the current buffer."
   :lighter nil
-  (let ((default-value '(:eval (tab-line-format))))
-    (if tab-line-mode
-        ;; Preserve the existing tab-line set outside of this mode
-        (unless tab-line-format
-          (setq tab-line-format default-value))
-      ;; Reset only values set by this mode
-      (when (equal tab-line-format default-value)
-        (setq tab-line-format nil)))))
+  (tab-line-set-display 'tab-line-mode
+                        (if tab-line-mode '(:eval (tab-line-format)) nil)))
 
 (defcustom tab-line-exclude-modes
   '(completion-list-mode)
-- 
2.39.2