print circle, and escape file names for `fs' backend

store.el

@@ -51,6 +51,7 @@
 
 (require 'cl-lib)
 (require 'cl-generic)
+(require 'url)
 
 ;;; Customs
 (defgroup persistence nil "Persistence facility."
@@ -153,7 +154,9 @@ Return the new list with VALUE removed."
 
 ;;; General Utilities
 (defsubst store--print (form)
-  (let ((print-length nil) (print-level nil))
+  (let ((print-length nil)
+        (print-level nil)
+        (print-circle t))
     (prin1 form (current-buffer)))
   (insert "\n"))
 
@@ -318,9 +321,14 @@ Arrange for compacting if log count exceeds (compact-ratio * size-of-table)."
   ;; We normalize PATH right away, saving future hassles.
   (store-fs--make :path (file-name-as-directory path)))
 
+;;We allow some more chars that is usually safe, and makes printed Lisp objects more readable
+(defvar store-fs--path-allowed-chars (cl-list* ?\ ?\( ?\) ?\[ ?\] ?\# url-unreserved-chars))
 (defsubst store-fs--key-to-path (key store)
-  ;; TODO: escape illegal characters
-  (concat (store-fs--path store) (prin1-to-string key)))
+  (concat (store-fs--path store)
+          (let ((print-length nil)
+                (print-level nil))
+            (url-hexify-string (prin1-to-string key) store-fs--path-allowed-chars))))
+
 (cl-defmethod store-put (key value (store store-fs))
   (with-temp-buffer
     (store--print value)