bug#64533: [PATCH] Support displaying function name in the header line

[Spencer Baugh]

Eli Zaretskii <eliz@gnu.org> writes:
>> From: Spencer Baugh <sbaugh@janestreet.com>
>> Date: Sat, 8 Jul 2023 14:14:30 -0400
>> Cc: 64533@debbugs.gnu.org
>> 
>> Although I could make these current defcustoms into internal variables and 
>> just set them based on a
>> single defcustom, would that be good?
>
> Yes, why not?

Fixed, along with your previous comments.

>From 3086671e447a188b2cdceda779b447d095b3b118 Mon Sep 17 00:00:00 2001
From: Spencer Baugh <sbaugh@janestreet.com>
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-display)
(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.
---
 doc/emacs/programs.texi      | 10 +++++++--
 etc/NEWS                     |  9 +++++++++
 lisp/progmodes/which-func.el | 39 ++++++++++++++++++++++++++++++------
 3 files changed, 50 insertions(+), 8 deletions(-)

diff --git a/doc/emacs/programs.texi b/doc/emacs/programs.texi
index 953de2e4786..c01503ab9f0 100644
--- a/doc/emacs/programs.texi
+++ b/doc/emacs/programs.texi
@@ -396,8 +396,8 @@ Which Function
 @cindex current function name in mode line
 
   Which Function mode is a global minor mode (@pxref{Minor Modes})
-which displays the current function name in the mode line, updating it
-as you move around in a buffer.
+which displays the current function name in the mode line or header
+line, updating it as you move around in a buffer.
 
 @findex which-function-mode
 @vindex which-func-modes
@@ -410,6 +410,12 @@ Which Function
 @code{t} (which means to support all available major modes) to a list
 of major mode names.
 
+@vindex which-func-display
+  By default, Which Function mode displays the current function name
+using the mode line.  Customize @code{which-func-display} to
+@code{header}, @code{mode}, or @code{both} to use the header line,
+mode line, or both, respectively.
+
 @node Program Indent
 @section Indentation for Programs
 @cindex indentation for programs
diff --git a/etc/NEWS b/etc/NEWS
index 0556e8be585..9f100d93281 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -243,6 +243,15 @@ docstring, or a comment, or (re)indents the surrounding 
defun if
 point is not in a comment or a string.  It is by default bound to
 'M-q' in 'prog-mode' and all its descendants.
 
+** Which Function Mode
+
++++
+*** Displaying the function name in the header line is now supported.
+The new user option 'which-func-display' allows choosing where the
+function name is displayed.  The default is 'mode' to display in the
+mode line.  'header' will display in the header line.  'both' displays
+in both the header line and mode line.
+
 ** Tramp
 
 +++
diff --git a/lisp/progmodes/which-func.el b/lisp/progmodes/which-func.el
index 09937a60988..0152670bc98 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-display 'mode
+  "Where to display the function name.
+
+If 'mode, display in the mode line.  If 'header, display in the
+header line.  If 'both, display in both."
+  :type '(choice (const :tag "Display in mode line" mode)
+                 (const :tag "Display in header line" header)
+                 (const :tag "Display in both header and mode line" both))
+  :version "30.1")
+
 (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.
@@ -184,17 +194,33 @@ 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.")
 
+(defvar-local which-func--use-header-line nil
+  "If non-nil, display the function name in the header line.")
+
+(defvar-local which-func--use-mode-line nil
+  "If non-nil, display the function name in the mode line.")
+
 (add-hook 'after-change-major-mode-hook #'which-func-ff-hook t)
 
 (defun 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)))
+    (setq which-func--use-mode-line (member which-func-display '(mode both)))
+    (setq which-func--use-header-line (member which-func-display '(header 
both)))
+    (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 +236,10 @@ 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 +257,7 @@ 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 +267,8 @@ 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