Add new cache library (persistent-soft wrapper)

core/autoload/cache.el

@@ -0,0 +1,97 @@
+;;; ../core/autoload/cache.el -*- lexical-binding: t; -*-
+
+;; This little library thinly wraps around persistent-soft (which is a pcache
+;; wrapper, how about that). It has three purposes:
+;;
+;; + To encapsulate the cache backend (persistent-soft/pcache in this case), in
+;;   case it needs to change.
+;; + To provide `doom-cache-persist': a mechanism for easily persisting
+;;   variables across Emacs sessions.
+;; + To lazy-load persistent-soft until it is really needed.
+;;
+;; Like persistent-soft, caches assume a 2-tier structure, where all caches are
+;; namespaced by location.
+
+(require 'persistent-soft)
+
+(defvar doom-cache-alists ()
+  "An alist of alists, containing lists of variables for the doom cache library
+to persist across Emacs sessions.")
+
+(defvar doom-cache-location 'doom
+  "The default location for cache files. This symbol is translated into a file
+name under `pcache-directory' (by default a subdirectory under
+`doom-cache-dir'). One file may contain multiple cache entries.")
+
+(defun doom|save-persistent-cache ()
+  "Hook to run when an Emacs session is killed. Saves all persisted variables
+listed in `doom-cache-alists' to files."
+  (dolist (alist doom-cache-alists)
+    (cl-loop with key = (car alist)
+             for var in (cdr alist)
+             if (symbol-value var)
+             do (doom-cache-set var it nil key))))
+(add-hook 'kill-emacs-hook #'doom|save-persistent-cache)
+
+
+;;
+;; Library
+;;
+
+;;;###autoload
+(defmacro with-cache! (location &rest body)
+  "Runs BODY with a different default `doom-cache-location'."
+  (declare (indent defun))
+  `(let ((doom-cache-location ',location))
+     ,@body))
+
+;;;###autoload
+(defun doom-cache-persist (location variables)
+  "Persist VARIABLES (list of symbols) in LOCATION (symbol).
+
+This populates these variables with cached values, if one exists, and saves them
+to file when Emacs quits.
+
+Warning: this is incompatible with buffer-local variables."
+  (dolist (var variables)
+    (when (doom-cache-exists var location)
+      (set var (doom-cache-get var location))))
+  (map-put doom-cache-alists location
+           (append variables (cdr (assq location doom-cache-alists)))))
+
+;;;###autoload
+(defun doom-cache-desist (location &optional variables)
+  "Unregisters VARIABLES (list of symbols) in LOCATION (symbol) from
+`doom-cache-alists', thus preventing them from being saved between sessions.
+Does not affect the actual variables themselves or their values."
+  (if variables
+      (map-put doom-cache-alists location
+               (cl-set-difference (cdr (assq location doom-cache-alists))
+                                  variables))
+    (map-delete doom-cache-alists location)))
+
+;;;###autoload
+(defun doom-cache-get (key &optional location)
+  "Retrieve KEY from LOCATION (defaults to `doom-cache-location'), if it exists
+and hasn't expired."
+  (persistent-soft-fetch
+   key (symbol-name (or location doom-cache-location))))
+
+;;;###autoload
+(defun doom-cache-set (key value &optional ttl location)
+  "Set KEY to VALUE in the cache. TTL is the time (in seconds) until this cache
+entry expires. LOCATION is the super-key to store this cache item under; the
+default is `doom-cache-location'. "
+  (persistent-soft-store
+   key value
+   (symbol-name (or location doom-cache-location)) ttl))
+
+;;;###autoload
+(defun doom-cache-exists (key &optional location)
+  "Returns t if KEY exists at LOCATION (defaults to `doom-cache-location')."
+  (persistent-soft-exists-p key (or location doom-cache-location)))
+
+;;;###autoload
+(defun doom-cache-clear (&optional location)
+  "Clear a cache LOCATION (defaults to `doom-cache-location')."
+  (persistent-soft-flush (or location doom-cache-location)))