add lisp packages

lisp/persist/persist.el

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+;;; persist.el --- Persist Variables between Emacs Sessions -*- lexical-binding: t -*-
+
+;; Copyright (C) 2019 Free Software Foundation, Inc.
+
+;; Author: Phillip Lord <phillip.lord@russet.org.uk>
+;; Maintainer: Phillip Lord <phillip.lord@russet.org.uk>
+;; Package-Type: multi
+;; Version: 0.4
+
+;; The contents of this file are subject to the GPL License, Version 3.0.
+
+;; This file is not part of Emacs
+
+;; This program 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.
+
+;; This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This package provides variables which persist across sessions.
+
+;; The main entry point is `persist-defvar' which behaves like
+;; `defvar' but which persists the variables between session.  Variables
+;; are automatically saved when Emacs exits.
+
+;; Other useful functions are `persist-save' which saves the variable
+;; immediately, `persist-load' which loads the saved value,
+;; `persist-reset' which resets to the default value.
+
+;; Values are stored in a directory in `user-emacs-directory', using
+;; one file per value.  This makes it easy to delete or remove unused
+;; variables.
+
+;;; Code:
+(defvar persist--directory-location
+  (locate-user-emacs-file "persist")
+  "The location of persist directory.")
+
+(defvar persist--symbols nil
+  "List of symbols to persist.")
+
+(defvar persist-load-hook nil
+  "Special hook run on loading a variable.
+
+Hook functions are called with two values: the symbol and the
+value it will be set to.  If any function returns nil, the
+variable is not set to the value.")
+
+(defun persist--file-location (symbol)
+  "Return the file name at which SYMBOL does or will persist."
+  (expand-file-name
+   (symbol-name symbol)
+   (or (get symbol 'persist-location)
+       persist--directory-location)))
+
+(defun persist--defvar-1 (symbol location)
+  "Set symbol up for persistance."
+  (when location
+    (persist-location symbol location))
+  (persist-symbol symbol (symbol-value symbol))
+  (persist-load symbol))
+
+(defmacro persist-defvar (symbol initvalue docstring &optional location)
+  "Define SYMBOL as a persistant variable and return SYMBOL.
+
+This form is nearly equivalent to `defvar', except that the
+variable persists between Emacs sessions.
+
+It does not support the optional parameters.  Both INITVALUE and
+DOCSTRING need to be given."
+  ;; We cannot distinguish between calls with initvalue of nil and a
+  ;; single parameter call. Unfortunately, these two calls have
+  ;; different semantics -- the single arity shuts up the byte
+  ;; compiler, but does not define the symbol. So, don't support a
+  ;; single arity persist-defvar.
+
+  ;; Don't support 2-arity calls either because we are lazy and
+  ;; because if you want to persist it, you want to doc it.
+  (declare (debug (symbolp form stringp &optional form)) (doc-string 3))
+  ;; Define inside progn so the byte compiler sees defvar
+  `(progn
+     (defvar ,symbol ,initvalue ,docstring)
+     ;; Access initvalue through its symbol because the defvar form
+     ;; has to stay at first level within a progn
+     (persist--defvar-1 ',symbol ,location)
+     ',symbol))
+
+(defun persist-location (symbol directory)
+  "Set the directory for persisting the value of symbol.
+
+This does not force the loading of value from this directory, so
+to persist a variable, you will normally need to call
+`persist-load' to load a previously saved location."
+  (put symbol 'persist-location (expand-file-name directory)))
+
+(defun persist-symbol (symbol &optional initvalue)
+  "Make SYMBOL a persistant variable.
+
+If non-nil, INITVALUE is the value to which SYMBOL will be set if
+`persist-reset' is called.  Otherwise, the INITVALUE will be the
+current `symbol-value' of SYMBOL.
+
+INITVALUE is set for the session and will itself not persist
+across sessions.
+
+This does force the loading of value from this directory, so to
+persist a variable, you will normally need to call `persist-load'
+to load a previously saved location."
+  (let ((initvalue (or initvalue (symbol-value symbol))))
+    (add-to-list 'persist--symbols symbol)
+    (put symbol 'persist t)
+    (put symbol 'persist-default initvalue)))
+
+(defun persist--persistant-p (symbol)
+  "Return non-nil if SYMBOL is a persistant variable."
+  (get symbol 'persist))
+
+(defun persist-save (symbol)
+  "Save SYMBOL now.
+
+Normally, it should not be necessary to call this explicitly, as
+variables persist automatically when Emacs exits."
+  (unless (persist--persistant-p symbol)
+    (error (format
+            "Symbol %s is not persistant" symbol)))
+  (unless (equal (symbol-value symbol)
+                 (persist-default symbol))
+    (let ((dir-loc
+           (file-name-directory
+            (persist--file-location symbol))))
+      (unless (file-exists-p dir-loc)
+        (mkdir dir-loc)))
+    (with-temp-buffer
+      (print (symbol-value symbol) (current-buffer))
+      (write-region (point-min) (point-max)
+                    (persist--file-location symbol)
+                    nil 'quiet))))
+
+(defun persist-default (symbol)
+  "Return the default value for SYMBOL."
+  (get symbol 'persist-default))
+
+(defun persist-reset (symbol)
+  "Reset the value of SYMBOL to the default."
+  (set symbol (persist-default symbol)))
+
+(defun persist-load (symbol)
+  "Load the saved value of SYMBOL."
+  (when (file-exists-p (persist--file-location symbol))
+    (with-temp-buffer
+      (insert-file-contents (persist--file-location symbol))
+      (let ((val (read (current-buffer))))
+        (when (run-hook-with-args-until-failure 'persist-load-hook
+                                                symbol val)
+          (set symbol val))))))
+
+(defun persist-unpersist (symbol)
+  "Stop the value in SYMBOL from persisting.
+
+This does not remove any saved value of SYMBOL."
+  (put symbol 'persist nil)
+  (setq persist--symbols
+        (remove symbol persist--symbols)))
+
+(defun persist--save-all ()
+  "Save all persistant symbols."
+  (mapc 'persist-save persist--symbols))
+
+;; Save on kill-emacs-hook anyway
+(add-hook 'kill-emacs-hook
+          'persist--save-all)
+
+(provide 'persist)
+;;; persist.el ends here