bug#27371: 26.0.50; Unexpected element (define-type . tramp-file-name) in load-history

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

>>> However, it just skips the entry. Wouldn't it be better to remove the
>>> defstruct itself, and all inherited symbols? And where could I find
>>> information how to destroy a defstruct?
>> Better would be to add some hook so cl-lib can add support for
>> define-type.
> Likely yes. But I'm not familiar with cl*; I have no idea how such a
> hook should look like. And how it shall be implemented.

The hook shouldn't be specific to cl.  Maybe something like the patch
below would make sense?
Then we can add support for define-type, ert-deftest, cl-defmethod, ...


        Stefan


diff --git a/lisp/loadhist.el b/lisp/loadhist.el
index 28d0b18c81..bf15399c11 100644
--- a/lisp/loadhist.el
+++ b/lisp/loadhist.el
@@ -162,6 +162,60 @@ unload--set-major-mode
           ;; mode, or proposed is not nil and not major-mode, and so we use it.
           (funcall (or proposed 'fundamental-mode)))))))
 
+(cl-defgeneric loadhist-unload-element (x)
+  "Unload an element from the `load-history'."
+  (message "Unexpected element %S in load-history" x))
+
+;; In `load-history', the definition of a previously autoloaded
+;; function is represented by 2 entries: (t . SYMBOL) comes before
+;; (defun . SYMBOL) and says we should restore SYMBOL's autoload when
+;; we undefine it.
+;; So we use this auxiliary variable to keep track of the last (t . SYMBOL)
+;; that occurred.
+(defvar loadhist--restore-autoload
+  "If non-nil, this is a symbol for which we should
+restore a previous autoload if possible.")
+
+(cl-defmethod loadhist-unload-element ((x (head t)))
+  (setq loadhist--restore-autoload (cdr x)))
+
+(defun loadhist--unload-function (x)
+  (let ((fun (cdr x)))
+    (when (fboundp fun)
+      (when (fboundp 'ad-unadvise)
+	(ad-unadvise fun))
+      (let ((aload (get fun 'autoload)))
+	(defalias fun
+          (if (and aload (eq fun loadhist--restore-autoload))
+	      (cons 'autoload aload)
+            nil))))))
+  (setq loadhist--restore-autoload nil))
+
+(cl-defmethod loadhist-unload-element ((x (head defun)))
+  (loadhist--unload-function x))
+(cl-defmethod loadhist-unload-element ((x (head autoload)))
+  (loadhist--unload-function x))
+
+(cl-defmethod loadhist-unload-element ((x (head require))) nil)
+(cl-defmethod loadhist-unload-element ((x (head defface))) nil)
+
+(cl-defmethod loadhist-unload-element ((x (head provide)))
+  ;; Remove any feature names that this file provided.
+  (setq features (delq (cdr x) features)))
+
+(cl-defmethod loadhist-unload-element ((x symbol))
+  ;; Kill local values as much as possible.
+  (dolist (buf (buffer-list))
+    (with-current-buffer buf
+      (if (and (boundp x) (timerp (symbol-value x)))
+	  (cancel-timer (symbol-value x)))
+      (kill-local-variable x)))
+  (if (and (boundp x) (timerp (symbol-value x)))
+      (cancel-timer (symbol-value x)))
+  ;; Get rid of the default binding if we can.
+  (unless (local-variable-if-set-p x)
+    (makunbound x)))
+
 ;;;###autoload
 (defun unload-feature (feature &optional force)
   "Unload the library that provided FEATURE.
@@ -200,9 +254,6 @@ unload-feature
 	       (prin1-to-string dependents) file))))
   (let* ((unload-function-defs-list (feature-symbols feature))
          (file (pop unload-function-defs-list))
-	 ;; If non-nil, this is a symbol for which we should
-	 ;; restore a previous autoload if possible.
-	 restore-autoload
 	 (name (symbol-name feature))
          (unload-hook (intern-soft (concat name "-unload-hook")))
 	 (unload-func (intern-soft (concat name "-unload-function"))))
@@ -250,38 +301,7 @@ unload-feature
 	  (when (symbolp elt)
 	    (elp-restore-function elt))))
 
-      (dolist (x unload-function-defs-list)
-	(if (consp x)
-	    (pcase (car x)
-	      ;; Remove any feature names that this file provided.
-	      (`provide
-	       (setq features (delq (cdr x) features)))
-	      ((or `defun `autoload)
-	       (let ((fun (cdr x)))
-		 (when (fboundp fun)
-		   (when (fboundp 'ad-unadvise)
-		     (ad-unadvise fun))
-		   (let ((aload (get fun 'autoload)))
-		     (if (and aload (eq fun restore-autoload))
-			 (fset fun (cons 'autoload aload))
-		       (fmakunbound fun))))))
-	      ;; (t . SYMBOL) comes before (defun . SYMBOL)
-	      ;; and says we should restore SYMBOL's autoload
-	      ;; when we undefine it.
-	      (`t (setq restore-autoload (cdr x)))
-	      ((or `require `defface) nil)
-	      (_ (message "Unexpected element %s in load-history" x)))
-	  ;; Kill local values as much as possible.
-	  (dolist (buf (buffer-list))
-	    (with-current-buffer buf
-	      (if (and (boundp x) (timerp (symbol-value x)))
-		  (cancel-timer (symbol-value x)))
-	      (kill-local-variable x)))
-	  (if (and (boundp x) (timerp (symbol-value x)))
-	      (cancel-timer (symbol-value x)))
-	  ;; Get rid of the default binding if we can.
-	  (unless (local-variable-if-set-p x)
-	    (makunbound x))))
+      (mapc #'loadhist-unload-element unload-function-defs-list)
       ;; Delete the load-history element for this file.
       (setq load-history (delq (assoc file load-history) load-history))))
   ;; Don't return load-history, it is not useful.