Subject: [PATCH] Support displaying function name in the header line

From: Spencer Baugh <[email-masked]>
Date: Sat, 08 Jul 2023 13:56:23 -0400

Tags: patch

In some languages, the function name as displayed in the mode-line by
which-func-mode can be quite long.  It's useful to be able to display
it in the header-line instead.  Let's support that.

This was my original motivation for Bug#63825, so that the header line
was not displayed when which-func-mode wasn't enabled, but just teaching
which-function-mode to handle this is much easier.

* lisp/progmodes/which-func.el (which-func-use-header-line)
(which-func-use-mode-line): Add.
(which-func-try-to-enable): Support which-func-use-header-line.
(which-func--disable): Add, to support which-func-use-header-line.
(which-func-ff-hook, which-func-update-1): Use which-func--disable.

In GNU Emacs 29.0.92 (build 3, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.15.12, Xaw scroll bars) of 2023-07-05 built on
 igm-qws-u22796a
Repository revision: 4127aa427fc7e2cb5b3dbae9264c2ee628474db4
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: CentOS Linux 7 (Core)

Configured using:
 'configure --config-cache --with-x-toolkit=lucid
 --with-gif=ifavailable'

>From a3f3e73dfcce1ae92da42e95f57740448327332f Mon Sep 17 00:00:00 2001
From: Spencer Baugh <[email-masked]>
Date: Sat, 8 Jul 2023 13:54:01 -0400
Subject: [PATCH] Support displaying function name in the header line

In some languages, the function name as displayed in the mode-line by
which-func-mode can be quite long.  It's useful to be able to display
it in the header-line instead.  Let's support that.

* lisp/progmodes/which-func.el (which-func-use-header-line)
(which-func-use-mode-line): Add.
(which-func-try-to-enable): Support which-func-use-header-line.
(which-func--disable): Add, to support which-func-use-header-line.
(which-func-ff-hook, which-func-update-1): Use which-func--disable.
---
 lisp/progmodes/which-func.el | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/lisp/progmodes/which-func.el b/lisp/progmodes/which-func.el
index 09937a60988..846f28bddbd 100644
--- a/lisp/progmodes/which-func.el
+++ b/lisp/progmodes/which-func.el
@@ -86,6 +86,16 @@ which-func-non-auto-modes
 activation of Which Function until Imenu is used for the first time."
   :type '(repeat (symbol :tag "Major mode")))
 
+(defcustom which-func-use-header-line nil
+  "If non-nil, display the function name in the header line."
+  :type '(choice (const :tag "Display in header line" t)
+                 (const :tag "Don't display in header line" nil)))
+
+(defcustom which-func-use-mode-line t
+  "If non-nil, display the function name in the mode line."
+  :type '(choice (const :tag "Display in mode line" t)
+                 (const :tag "Don't display in mode line" nil)))
+
 (defcustom which-func-maxout 500000
   "Don't automatically compute the Imenu menu if buffer is this big or bigger.
 Zero means compute the Imenu menu regardless of size.
@@ -184,7 +194,7 @@ which-func-current
 ;;;###autoload (put 'which-func-current 'risky-local-variable t)
 
 (defvar-local which-func-mode nil
-  "Non-nil means display current function name in mode line.
+  "Non-nil means display current function name in mode or header line.
 This makes a difference only if variable `which-function-mode' is
 non-nil.")
 
@@ -194,7 +204,15 @@ which-func-try-to-enable
   (unless (or (not which-function-mode)
               (local-variable-p 'which-func-mode))
     (setq which-func-mode (or (eq which-func-modes t)
-                              (member major-mode which-func-modes)))))
+                              (member major-mode which-func-modes)))
+    (when (and which-func-mode which-func-use-header-line)
+      (add-to-list 'header-line-format '("" which-func-format " ")))))
+
+(defun which-func--disable ()
+  (when (and which-func-mode which-func-use-header-line)
+    (setq header-line-format
+          (delete '("" which-func-format " ") header-line-format)))
+  (setq which-func-mode nil))
 
 (defun which-func-ff-hook ()
   "`after-change-major-mode-hook' for Which Function mode.
@@ -210,10 +228,10 @@ which-func-ff-hook
 	  (setq imenu--index-alist
                 (save-excursion (funcall imenu-create-index-function))))
     (imenu-unavailable
-     (setq which-func-mode nil))
+     (which-func--disable))
     (error
      (message "which-func-ff-hook error: %S" err)
-     (setq which-func-mode nil))))
+     (which-func--disable))))
 
 (defun which-func-update ()
   "Update the Which-Function mode display in the current window."
@@ -231,7 +249,7 @@ which-func-update-1
 	      (puthash window current which-func-table)
 	      (force-mode-line-update)))
 	(error
-	 (setq which-func-mode nil)
+	 (which-func--disable)
 	 (error "Error in which-func-update: %S" info))))))
 
 (defvar which-func-update-timer nil)
@@ -241,7 +259,8 @@ which-func-update-timer
   (add-to-list 'mode-line-misc-info
                '(which-function-mode    ;Only display if mode is enabled.
                  (which-func-mode       ;Only display if buffer supports it.
-                  ("" which-func-format " ")))))
+                  (which-func-use-mode-line
+                   ("" which-func-format " "))))))
 
 ;; This is the name people would normally expect.
 ;;;###autoload
-- 
2.39.3