;;; loadhist.el --- lisp functions for working with feature groups

;; Copyright (C) 1995, 1998, 2000-2020 Free Software Foundation, Inc.

;; Author: Eric S. Raymond <esr@snark.thyrsus.com>
;; Maintainer: emacs-devel@gnu.org
;; Keywords: internal

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; These functions exploit the load-history system variable.
;; Entry points include `unload-feature', `symbol-file', and
;; `feature-file', documented in the Emacs Lisp manual.

;;; Code:

(eval-when-compile (require 'cl-lib))

(defun feature-symbols (feature)
  "Return the file and list of definitions associated with FEATURE.
The value is actually the element of `load-history'
for the file that did (provide FEATURE)."
  (catch 'foundit
    (let ((element (cons 'provide feature)))
      (dolist (x load-history nil)
	(when (member element (cdr x))
	  (throw 'foundit x))))))

(defun feature-file (feature)
  "Return the file name from which a given FEATURE was loaded.
Actually, return the load argument, if any; this is sometimes the name of a
Lisp file without an extension.  If the feature came from an `eval-buffer' on
a buffer with no associated file, or an `eval-region', return nil."
  (if (not (featurep feature))
      (error "%S is not a currently loaded feature" feature)
    (car (feature-symbols feature))))

(defun file-loadhist-lookup (file)
  "Return the `load-history' element for FILE.
FILE can be a file name, or a library name.
A library name is equivalent to the file name that `load-library' would load."
  ;; First look for FILE as given.
  (let ((symbols (assoc file load-history)))
    ;; Try converting a library name to an absolute file name.
    (and (null symbols)
	 (let ((absname
		(locate-file file load-path (get-load-suffixes))))
	   (and absname (not (equal absname file))
		(setq symbols (cdr (assoc absname load-history))))))
    symbols))

(defun file-provides (file)
  "Return the list of features provided by FILE as it was loaded.
FILE can be a file name, or a library name.
A library name is equivalent to the file name that `load-library' would load."
  (let (provides)
    (dolist (x (file-loadhist-lookup file) provides)
      (when (eq (car-safe x) 'provide)
	(push (cdr x) provides)))))

(defun file-requires (file)
  "Return the list of features required by FILE as it was loaded.
FILE can be a file name, or a library name.
A library name is equivalent to the file name that `load-library' would load."
  (let (requires)
    (dolist (x (file-loadhist-lookup file) requires)
      (when (eq (car-safe x) 'require)
	(push (cdr x) requires)))))

(defsubst file-set-intersect (p q)
  "Return the set intersection of two lists."
  (let (ret)
    (dolist (x p ret)
      (when (memq x q) (push x ret)))))

(defun file-dependents (file)
  "Return the list of loaded libraries that depend on FILE.
This can include FILE itself.
FILE can be a file name, or a library name.
A library name is equivalent to the file name that `load-library' would load."
  (let ((provides (file-provides file))
	(dependents nil))
    (dolist (x load-history dependents)
      (when (and (stringp (car x))
                 (file-set-intersect provides (file-requires (car x))))
	(push (car x) dependents)))))

(defun read-feature (prompt &optional loaded-p)
  "Read feature name from the minibuffer, prompting with string PROMPT.
If optional second arg LOADED-P is non-nil, the feature must be loaded
from a file."
  (intern (completing-read
           prompt
           (mapcar #'symbol-name
                   (if loaded-p
                       (delq nil
                             (mapcar
                              (lambda (x) (and (feature-file x) x))
                              features))
                     features)))))

(defvaralias 'loadhist-hook-functions 'unload-feature-special-hooks)
(defvar unload-feature-special-hooks
  '(after-change-functions after-insert-file-functions
    after-make-frame-functions auto-coding-functions
    auto-fill-function before-change-functions
    blink-paren-function buffer-access-fontify-functions
    choose-completion-string-functions
    comint-output-filter-functions command-line-functions
    comment-indent-function compilation-finish-functions
    delete-frame-functions disabled-command-function
    fill-nobreak-predicate find-directory-functions
    find-file-not-found-functions
    font-lock-fontify-buffer-function
    font-lock-fontify-region-function
    font-lock-mark-block-function
    font-lock-syntactic-face-function
    font-lock-unfontify-buffer-function
    font-lock-unfontify-region-function
    kill-buffer-query-functions kill-emacs-query-functions
    lisp-indent-function mouse-position-function
    redisplay-end-trigger-functions suspend-tty-functions
    temp-buffer-show-function window-scroll-functions
    window-size-change-functions write-contents-functions
    write-file-functions write-region-annotate-functions)
  "A list of special hooks from Info node `(elisp)Standard Hooks'.

These are symbols with hooklike values whose names don't end in
`-hook' or `-hooks', from which `unload-feature' should try to remove
pertinent symbols.")

(defvar unload-function-defs-list nil
  "List of definitions in the Lisp library being unloaded.

This is meant to be used by `FEATURE-unload-function'; see the
documentation of `unload-feature' for details.")

(defun unload--set-major-mode ()
  (save-current-buffer
    (dolist (buffer (buffer-list))
      (set-buffer buffer)
      (let ((proposed major-mode))
        ;; Look for a predecessor mode not defined in the feature we're processing
        (while (and proposed (rassq proposed unload-function-defs-list))
          (setq proposed (get proposed 'derived-mode-parent)))
        (unless (eq proposed major-mode)
          ;; Two cases: either proposed is nil, and we want to switch to fundamental
          ;; 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 nil
  "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 ((_ (head require))) nil)
(cl-defmethod loadhist-unload-element ((_ (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)))

(cl-defmethod loadhist-unload-element ((x (head define-type)))
  (let* ((name (cdr x)))
    ;; Remove the struct.
    (setf (cl--find-class name) nil)))

(cl-defmethod loadhist-unload-element ((x (head define-symbol-props)))
  (pcase-dolist (`(,symbol . ,props) (cdr x))
    (dolist (prop props)
      (put symbol prop nil))))

;;;###autoload
(defun unload-feature (feature &optional force)
  "Unload the library that provided FEATURE.
If the feature is required by any other loaded code, and prefix arg FORCE
is nil, raise an error.

Standard unloading activities include restoring old autoloads for
functions defined by the library, undoing any additions that the
library has made to hook variables or to `auto-mode-alist', undoing
ELP profiling of functions in that library, unproviding any features
provided by the library, and canceling timers held in variables
defined by the library.

If a function `FEATURE-unload-function' is defined, this function
calls it with no arguments, before doing anything else.  That function
can do whatever is appropriate to undo the loading of the library.  If
`FEATURE-unload-function' returns non-nil, that suppresses the
standard unloading of the library.  Otherwise the standard unloading
proceeds.

`FEATURE-unload-function' has access to the package's list of
definitions in the variable `unload-function-defs-list' and could
remove symbols from it in the event that the package has done
something strange, such as redefining an Emacs function."
  (interactive
   (list
    (read-feature "Unload feature: " t)
    current-prefix-arg))
  (unless (featurep feature)
    (error "%s is not a currently loaded feature" (symbol-name feature)))
  (unless force
    (let* ((file (feature-file feature))
	   (dependents (delete file (copy-sequence (file-dependents file)))))
      (when dependents
	(error "Loaded libraries %s depend on %s"
	       (prin1-to-string dependents) file))))
  (let* ((unload-function-defs-list (feature-symbols feature))
         (file (pop unload-function-defs-list))
	 (name (symbol-name feature))
         (unload-hook (intern-soft (concat name "-unload-hook")))
	 (unload-func (intern-soft (concat name "-unload-function"))))
    ;; If FEATURE-unload-function is defined and returns non-nil,
    ;; don't try to do anything more; otherwise proceed normally.
    (unless (and (fboundp unload-func)
		 (funcall unload-func))
      ;; Try to avoid losing badly when hooks installed in critical
      ;; places go away.  (Some packages install things on
      ;; `kill-buffer-hook', `activate-menubar-hook' and the like.)
      (if unload-hook
	  ;; First off, provide a clean way for package FOO to arrange
	  ;; this by adding hooks on the variable `FOO-unload-hook'.
	  ;; This is obsolete; FEATURE-unload-function should be used now.
	  (run-hooks unload-hook)
	;; Otherwise, do our best.  Look through the obarray for symbols
	;; which seem to be hook variables or special hook functions and
	;; remove anything from them which matches the feature-symbols
	;; about to get zapped.  Obviously this won't get anonymous
	;; functions which the package might just have installed, and
	;; there might be other important state, but this tactic
	;; normally works.
	(mapatoms
	 (lambda (x)
	   (when (and (boundp x)
		      (or (and (consp (symbol-value x)) ; Random hooks.
			       (string-match "-hooks?\\'" (symbol-name x)))
			  (memq x unload-feature-special-hooks)))	; Known abnormal hooks etc.
	     (dolist (y unload-function-defs-list)
	       (when (and (eq (car-safe y) 'defun)
			  (not (get (cdr y) 'autoload)))
		 (remove-hook x (cdr y)))))))
	;; Remove any feature-symbols from auto-mode-alist as well.
	(dolist (y unload-function-defs-list)
	  (when (and (eq (car-safe y) 'defun)
		     (not (get (cdr y) 'autoload)))
	    (setq auto-mode-alist
		  (rassq-delete-all (cdr y) auto-mode-alist)))))

      ;; Change major mode in all buffers using one defined in the feature being unloaded.
      (unload--set-major-mode)

      (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.
  nil)

(provide 'loadhist)

;;; loadhist.el ends here