From 76938e1789ecf447507199b6f1b7c0d4f7924ea3 Mon Sep 17 00:00:00 2001
From: Juri Linkov <juri@linkov.net>
Date: Mon, 28 Aug 2023 19:57:16 +0300
Subject: [PATCH] * lisp/tab-bar.el: Add tab-bar-tab-name-format-functions
 (bug#65554)

(tab-bar-tab-name-format-truncated)
(tab-bar-tab-name-format-hints)
(tab-bar-tab-name-format-close-button)
(tab-bar-tab-name-format-face): New functions.
(tab-bar-tab-name-format-functions): New defcustom.
(tab-bar-tab-name-format-default): Rewrite to use
'tab-bar-tab-name-format-functions'.
---
 etc/NEWS        |  6 +++++
 lisp/tab-bar.el | 70 ++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 63 insertions(+), 13 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 9d356240f9c..0c9275f1e10 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -146,6 +146,12 @@ Anything following the symbol 'mode-line-format-right-align' in
 right-aligned to is controlled by the new user option
 'mode-line-right-align-edge'.
 
+** Tab Bars and Tab Lines
+
+*** New user option 'tab-bar-tab-name-format-functions'.
+It can be used to add, remove and reorder functions that change
+the appearance of every tab on the tab bar.
+
 
 * Editing Changes in Emacs 30.1
 
diff --git a/lisp/tab-bar.el b/lisp/tab-bar.el
index 9a59e480f06..6b286598a14 100644
--- a/lisp/tab-bar.el
+++ b/lisp/tab-bar.el
@@ -782,6 +782,31 @@ Return its existing value or a new value."
   (set-frame-parameter frame 'tabs tabs))
 
 
+(defun tab-bar-tab-name-format-truncated (name _tab _i)
+  "Truncate the tab name.
+The maximal length is specified by `tab-bar-tab-name-truncated-max'.
+Append ellipsis `tab-bar-tab-name-ellipsis' at the end."
+  (if (< (length name) tab-bar-tab-name-truncated-max)
+      name
+    (truncate-string-to-width
+     name tab-bar-tab-name-truncated-max nil nil
+     tab-bar-tab-name-ellipsis)))
+
+(defun tab-bar-tab-name-format-hints (name _tab i)
+  "Show absolute numbers on tabs in the tab bar before the tab name.
+It has effect when `tab-bar-tab-hints' is non-nil."
+  (if tab-bar-tab-hints (concat (format "%d " i) name) name))
+
+(defun tab-bar-tab-name-format-close-button (name tab _i)
+  "Show the tab close button.
+The variable `tab-bar-close-button-show' defines when to show it."
+  (if (and tab-bar-close-button-show
+           (not (eq tab-bar-close-button-show
+                    (if (eq (car tab) 'current-tab) 'non-selected 'selected)))
+           tab-bar-close-button)
+      (concat name tab-bar-close-button)
+    name))
+
 (defcustom tab-bar-tab-face-function #'tab-bar-tab-face-default
   "Function to define a tab face.
 Function gets one argument: a tab."
@@ -792,6 +817,38 @@ Function gets one argument: a tab."
 (defun tab-bar-tab-face-default (tab)
   (if (eq (car tab) 'current-tab) 'tab-bar-tab 'tab-bar-tab-inactive))
 
+(defun tab-bar-tab-name-format-face (name tab _i)
+  "Apply the face to the tab name.
+It uses the function `tab-bar-tab-face-function'."
+  (add-face-text-property
+   0 (length name) (funcall tab-bar-tab-face-function tab) t name)
+  name)
+
+(defcustom tab-bar-tab-name-format-functions
+  '(tab-bar-tab-name-format-hints
+    tab-bar-tab-name-format-close-button
+    tab-bar-tab-name-format-face)
+  "Functions called to modify the tab name.
+Each function is called with three arguments: the name returned
+by the previously called modifier, the tab and its number.
+It should return the formatted tab name to display in the tab bar."
+  :type '(repeat
+          (choice (function-item tab-bar-tab-name-format-truncated)
+                  (function-item tab-bar-tab-name-format-hints)
+                  (function-item tab-bar-tab-name-format-close-button)
+                  (function-item tab-bar-tab-name-format-face)
+                  (function :tag "Custom function")))
+  :group 'tab-bar
+  :version "30.1")
+
+(defun tab-bar-tab-name-format-default (tab i)
+  (let ((name (copy-sequence (alist-get 'name tab))))
+    (run-hook-wrapped 'tab-bar-tab-name-format-functions
+                      (lambda (fun)
+                        (setq name (funcall fun name tab i))
+                        nil))
+    name))
+
 (defcustom tab-bar-tab-name-format-function #'tab-bar-tab-name-format-default
   "Function to format a tab name.
 Function gets two arguments, the tab and its number, and should return
@@ -804,19 +861,6 @@ the formatted tab name to display in the tab bar."
   :group 'tab-bar
   :version "28.1")
 
-(defun tab-bar-tab-name-format-default (tab i)
-  (let* ((current-p (eq (car tab) 'current-tab))
-         (name (concat (if tab-bar-tab-hints (format "%d " i) "")
-                       (alist-get 'name tab)
-                       (or (and tab-bar-close-button-show
-                                (not (eq tab-bar-close-button-show
-                                         (if current-p 'non-selected 'selected)))
-                                tab-bar-close-button)
-                           ""))))
-    (add-face-text-property
-     0 (length name) (funcall tab-bar-tab-face-function tab) t name)
-    name))
-
 (defcustom tab-bar-format '(tab-bar-format-history
                             tab-bar-format-tabs
                             tab-bar-separator
-- 
2.39.2