which-function-mode: put hook function on after-change-major-mode-hook

, rather than find-file-hook.  This keeps which-function-mode active should
the major mode be reinitialized.  Also accept a null result from
add-log-current-defun as definitive, should that function have run.  This
fixes bug #40714.

* lisp/progmodes/which-func.el (which-func-ff-hook): Put on
after-change-major-mode-hook.
(which-function): Enhance the logic to accept a null result from
add-log-current-defun.

1 files changed, 50 insertions, 47 deletions

diff --git a/lisp/progmodes/which-func.el b/lisp/progmodes/which-func.el
index 1cee552b0c0..266f40abbae 100644
--- a/lisp/progmodes/which-func.el
+++ b/lisp/progmodes/which-func.el
@@ -186,7 +186,7 @@ and you want to simplify them for the mode line
   "Non-nil means display current function name in mode line.
 This makes a difference only if `which-function-mode' is non-nil.")
 
-(add-hook 'find-file-hook 'which-func-ff-hook t)
+(add-hook 'after-change-major-mode-hook 'which-func-ff-hook t)
 
 (defun which-func-try-to-enable ()
   (unless (or (not which-function-mode)
@@ -195,7 +195,7 @@ This makes a difference only if `which-function-mode' is non-nil.")
                               (member major-mode which-func-modes)))))
 
 (defun which-func-ff-hook ()
-  "File find hook for Which Function mode.
+  "`after-change-major-mode-hook' for Which Function mode.
 It creates the Imenu index for the buffer, if necessary."
   (which-func-try-to-enable)
 
@@ -282,52 +282,55 @@ If no function name is found, return nil."
     (when (null name)
       (setq name (add-log-current-defun)))
     ;; If Imenu is loaded, try to make an index alist with it.
+    ;; If `add-log-current-defun' ran and gave nil, accept that.
     (when (and (null name)
-               (boundp 'imenu--index-alist)
-               (or (null imenu--index-alist)
-                   ;; Update if outdated
-                   (/= (buffer-chars-modified-tick) imenu-menubar-modified-tick))
-               (null which-function-imenu-failed))
-      (ignore-errors (imenu--make-index-alist t))
-      (unless imenu--index-alist
-        (set (make-local-variable 'which-function-imenu-failed) t)))
-    ;; If we have an index alist, use it.
-    (when (and (null name)
-               (boundp 'imenu--index-alist) imenu--index-alist)
-      (let ((alist imenu--index-alist)
-            (minoffset (point-max))
-            offset pair mark imstack namestack)
-        ;; Elements of alist are either ("name" . marker), or
-        ;; ("submenu" ("name" . marker) ... ). The list can be
-        ;; arbitrarily nested.
-        (while (or alist imstack)
-          (if (null alist)
-              (setq alist     (car imstack)
-                    namestack (cdr namestack)
-                    imstack   (cdr imstack))
-
-            (setq pair (car-safe alist)
-                  alist (cdr-safe alist))
-
-            (cond
-             ((atom pair))              ; Skip anything not a cons.
-
-             ((imenu--subalist-p pair)
-              (setq imstack   (cons alist imstack)
-                    namestack (cons (car pair) namestack)
-                    alist     (cdr pair)))
-
-             ((or (number-or-marker-p (setq mark (cdr pair)))
-                  (and (overlayp mark)
-                       (setq mark (overlay-start mark))))
-              (when (and (>= (setq offset (- (point) mark)) 0)
-                         (< offset minoffset)) ; Find the closest item.
-                (setq minoffset offset
-                      name (if (null which-func-imenu-joiner-function)
-                               (car pair)
-                             (funcall
-                              which-func-imenu-joiner-function
-                              (reverse (cons (car pair) namestack))))))))))))
+               (null add-log-current-defun-function))
+      (when (and (null name)
+                 (boundp 'imenu--index-alist)
+                 (or (null imenu--index-alist)
+                     ;; Update if outdated
+                     (/= (buffer-chars-modified-tick) imenu-menubar-modified-tick))
+                 (null which-function-imenu-failed))
+        (ignore-errors (imenu--make-index-alist t))
+        (unless imenu--index-alist
+          (set (make-local-variable 'which-function-imenu-failed) t)))
+      ;; If we have an index alist, use it.
+      (when (and (null name)
+                 (boundp 'imenu--index-alist) imenu--index-alist)
+        (let ((alist imenu--index-alist)
+              (minoffset (point-max))
+              offset pair mark imstack namestack)
+          ;; Elements of alist are either ("name" . marker), or
+          ;; ("submenu" ("name" . marker) ... ). The list can be
+          ;; arbitrarily nested.
+          (while (or alist imstack)
+            (if (null alist)
+                (setq alist     (car imstack)
+                      namestack (cdr namestack)
+                      imstack   (cdr imstack))
+
+              (setq pair (car-safe alist)
+                    alist (cdr-safe alist))
+
+              (cond
+               ((atom pair))            ; Skip anything not a cons.
+
+               ((imenu--subalist-p pair)
+                (setq imstack   (cons alist imstack)
+                      namestack (cons (car pair) namestack)
+                      alist     (cdr pair)))
+
+               ((or (number-or-marker-p (setq mark (cdr pair)))
+                    (and (overlayp mark)
+                         (setq mark (overlay-start mark))))
+                (when (and (>= (setq offset (- (point) mark)) 0)
+                           (< offset minoffset)) ; Find the closest item.
+                  (setq minoffset offset
+                        name (if (null which-func-imenu-joiner-function)
+                                 (car pair)
+                               (funcall
+                                which-func-imenu-joiner-function
+                                (reverse (cons (car pair) namestack)))))))))))))
     ;; Filter the name if requested.
     (when name
       (if which-func-cleanup-function