--- /dev/null
+;;; validate.el --- Schema validation for Emacs-lisp -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2016 Free Software Foundation, Inc.
+
+;; Author: Artur Malabarba <emacs@endlessparentheses.com>
+;; Keywords: lisp
+;; Package-Requires: ((emacs "24.1") (cl-lib "0.5"))
+;; Version: 0.2
+
+;;; Commentary:
+;;
+;; This library offers two functions that perform schema validation.
+;; Use this is your Elisp packages to provide very informative error
+;; messages when your users accidentally misconfigure a variable.
+;; For instance, if everything is fine, these do the same thing:
+;;
+;; 1. (validate-variable 'cider-known-endpoints)
+;; 2. cider-known-endpoints
+;;
+;; However, if the user has misconfigured this variable, option
+;; 1. will immediately give them an informative error message, while
+;; option 2. won't say anything and will lead to confusing errors down
+;; the line.
+;;
+;; The format and language of the schemas is the same one used in the
+;; `:type' property of a `defcustom'.
+;;
+;; See: (info "(elisp) Customization Types")
+;;
+;; Both functions throw a `user-error' if the value in question
+;; doesn't match the schema, and return the value itself if it
+;; matches. The function `validate-variable' verifies whether the value of a
+;; custom variable matches its custom-type, while `validate-value' checks an
+;; arbitrary value against an arbitrary schema.
+;;
+;; Missing features: `:inline', `plist', `coding-system', `color',
+;; `hook', `restricted-sexp'.
+
+;;; License:
+;;
+;; 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 <http://www.gnu.org/licenses/>.
+
+;;; Code:
+(require 'cl-lib)
+(require 'seq)
+(require 'cus-edit)
+
+(defun validate--check-list-contents (values schemas)
+ "Check that all VALUES match all SCHEMAS."
+ (if (not (= (length values) (length schemas)))
+ "wrong number of elements"
+ (seq-find #'identity (seq-mapn #'validate--check values schemas))))
+
+(defun validate--check (value schema)
+ "Return nil if VALUE matches SCHEMA.
+If they don't match, return an explanation."
+ (let ((args (cdr-safe schema))
+ (expected-type (or (car-safe schema) schema))
+ (props nil))
+ (while (and (keywordp (car args)) (cdr args))
+ (setq props `(,(pop args) ,(pop args) ,@props)))
+ (setq args (or (plist-get props :args)
+ args))
+ (let ((r
+ (cl-labels ((wtype ;wrong-type
+ (tt) (unless (funcall (intern (format "%sp" tt)) value)
+ (format "not a %s" tt))))
+ ;; TODO: hook (top-level only).
+ (cl-case expected-type
+ ((sexp other) nil)
+ (variable (cond ((wtype 'symbol))
+ ((not (boundp value)) "this symbol has no variable binding")))
+ ((integer number float string character symbol function boolean face)
+ (wtype expected-type))
+ (regexp (cond ((ignore-errors (string-match value "") t) nil)
+ ((wtype 'string))
+ (t "not a valid regexp")))
+ (repeat (cond
+ ((or (not args) (cdr args)) (error "`repeat' needs exactly one argument"))
+ ((wtype 'list))
+ (t (let ((subschema (car args)))
+ (seq-some (lambda (v) (validate--check v subschema)) value)))))
+ ((const function-item variable-item) (unless (eq value (car args))
+ "not the expected value"))
+ (file (cond ((wtype 'string))
+ ((file-exists-p value) nil)
+ ((plist-get props :must-match) "file does not exist")
+ ((not (file-writable-p value)) "file is not accessible")))
+ (directory (cond ((wtype 'string))
+ ((file-directory-p value) nil)
+ ((file-exists-p value) "path is not a directory")
+ ((not (file-writable-p value)) "directory is not accessible")))
+ (key-sequence (and (wtype 'string)
+ (wtype 'vector)))
+ ;; TODO: `coding-system', `color'
+ (coding-system (wtype 'symbol))
+ (color (wtype 'string))
+ (cons (or (wtype 'cons)
+ (validate--check (car value) (car args))
+ (validate--check (cdr value) (cadr args))))
+ ((list group) (or (wtype 'list)
+ (validate--check-list-contents value args)))
+ (vector (or (wtype 'vector)
+ (validate--check-list-contents value args)))
+ (alist (let ((value-type (plist-get props :value-type))
+ (key-type (plist-get props :key-type)))
+ (cond ((not value-type) (error "`alist' needs a :value-type"))
+ ((not key-type) (error "`alist' needs a :key-type"))
+ ((wtype 'list))
+ (t (validate--check value
+ `(repeat (cons ,key-type ,value-type)))))))
+ ;; TODO: `plist'
+ ((choice radio) (if (not (cdr args))
+ (error "`choice' needs at least one argument")
+ (let ((gather (mapcar (lambda (x) (validate--check value x)) args)))
+ (when (seq-every-p #'identity gather)
+ (concat "all of the options failed\n "
+ (mapconcat #'identity gather "\n "))))))
+ ;; TODO: `restricted-sexp'
+ (set (or (wtype 'list)
+ (let ((failed (list t)))
+ (dolist (schema args)
+ (let ((elem (seq-find (lambda (x) (not (validate--check x schema)))
+ value
+ failed)))
+ (unless (eq elem failed)
+ (setq value (remove elem value)))))
+ (when value
+ (concat "the following values don't match any of the options:\n "
+ (mapconcat (lambda (x) (format "%s" x)) value "\n "))))))))))
+ (when r
+ (let ((print-length 4)
+ (print-level 2))
+ (format "Looking for `%S' in `%S' failed because:\n%s"
+ schema value r))))))
+
+\f
+;;; Exposed API
+;;;###autoload
+(defun validate-value (value schema &optional noerror)
+ "Check that VALUE matches SCHEMA.
+If it matches return VALUE, otherwise signal a `user-error'.
+
+If NOERROR is non-nil, return t to indicate a match and nil to
+indicate a failure."
+ (let ((report (validate--check value schema)))
+ (if report
+ (unless noerror
+ (user-error report))
+ value)))
+
+;;;###autoload
+(defun validate-variable (symbol &optional noerror)
+ "Check that SYMBOL's value matches its schema.
+SYMBOL must be the name of a custom option with a defined
+`custom-type'. If SYMBOL has a value and a type, they are checked
+with `validate-value'. NOERROR is passed to `validate-value'."
+ (let* ((val (symbol-value symbol))
+ (type (custom-variable-type symbol)))
+ (if type
+ (validate-value val type)
+ (if noerror val
+ (error "Variable `%s' has no custom-type." symbol)))))
+
+;;;###autoload
+(defun validate-mark-safe-local (symbol)
+ "Mark SYMBOL as a safe local if its custom type is obeyed."
+ (put symbol 'safe-local-variable
+ (lambda (val)
+ (validate-value val (custom-variable-type symbol) 'noerror))))
+
+(provide 'validate)
+;;; validate.el ends here