1 ;;;; unsafep.el -- Determine whether a Lisp form is safe to evaluate
3 ;; Copyright (C) 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
5 ;; Author: Jonathan Yavner <jyavner@member.fsf.org>
6 ;; Maintainer: Jonathan Yavner <jyavner@member.fsf.org>
7 ;; Keywords: safety lisp utility
9 ;; This file is part of GNU Emacs.
11 ;; GNU Emacs is free software; you can redistribute it and/or modify
12 ;; it under the terms of the GNU General Public License as published by
13 ;; the Free Software Foundation; either version 2, or (at your option)
16 ;; GNU Emacs is distributed in the hope that it will be useful,
17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 ;; GNU General Public License for more details.
21 ;; You should have received a copy of the GNU General Public License
22 ;; along with GNU Emacs; see the file COPYING. If not, write to the
23 ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
24 ;; Boston, MA 02110-1301, USA.
28 ;; This is a simplistic implementation that does not allow any modification of
29 ;; buffers or global variables. It does no dataflow analysis, so functions
30 ;; like `funcall' and `setcar' are completely disallowed. It is designed
31 ;; for "pure Lisp" formulas, like those in spreadsheets, that don't make any
32 ;; use of the text editing capabilities of Emacs.
34 ;; A formula is safe if:
36 ;; 2. It's a function call to a safe function and all arguments are safe
38 ;; 3. It's a special form whose arguments are like a function's (and,
39 ;; catch, if, or, prog1, prog2, progn, while, unwind-protect).
40 ;; 4. It's a special form or macro that creates safe temporary bindings
41 ;; (condition-case, dolist, dotimes, lambda, let, let*).
42 ;; 4. It's one of (cond, quote) that have special parsing.
43 ;; 5. It's one of (add-to-list, setq, push, pop) and the assignment variable
45 ;; 6. It's one of (apply, mapc, mapcar, mapconcat) and its first arg is a
46 ;; quoted safe function.
48 ;; A function is safe if:
49 ;; 1. It's a lambda containing safe formulas.
50 ;; 2. It's a member of list `safe-functions', so the user says it's safe.
51 ;; 3. It's a symbol with the `side-effect-free' property, defined by the
52 ;; byte compiler or function author.
53 ;; 4. It's a symbol with the `safe-function' property, defined here or by
54 ;; the function author. Value t indicates a function that is safe but
55 ;; has innocuous side effects. Other values will someday indicate
56 ;; functions with side effects that are not always safe.
57 ;; The `side-effect-free' and `safe-function' properties are provided for
58 ;; built-in functions and for functions and macros defined in subr.el.
60 ;; A temporary binding is unsafe if its symbol:
61 ;; 1. Has the `risky-local-variable' property.
62 ;; 2. Has a name that ends with -command, font-lock-keywords(-[0-9]+)?,
63 ;; font-lock-syntactic-keywords, -form, -forms, -frame-alist, -function,
64 ;; -functions, -history, -hook, -hooks, -map, -map-alist, -mode-alist,
65 ;; -predicate, or -program.
67 ;; An assignment variable is unsafe if:
68 ;; 1. It would be unsafe as a temporary binding.
69 ;; 2. It doesn't already have a temporary or buffer-local binding.
71 ;; There are unsafe forms that `unsafep' cannot detect. Beware of these:
72 ;; 1. The form's result is a string with a display property containing a
73 ;; form to be evaluated later, and you insert this result into a
74 ;; buffer. Always remove display properties before inserting!
75 ;; 2. The form alters a risky variable that was recently added to Emacs and
76 ;; is not yet marked with the `risky-local-variable' property.
77 ;; 3. The form uses undocumented features of built-in functions that have
78 ;; the `side-effect-free' property. For example, in Emacs-20 if you
79 ;; passed a circular list to `assoc', Emacs would crash. Historically,
80 ;; problems of this kind have been few and short-lived.
85 (require 'byte-opt) ;Set up the `side-effect-free' properties
87 (defcustom safe-functions nil
88 "A list of assumed-safe functions, or t to disable `unsafep'."
90 :type '(choice (const :tag "No" nil) (const :tag "Yes" t) hook))
92 (defvar unsafep-vars nil
93 "Dynamically-bound list of variables with lexical bindings at this point
95 (put 'unsafep-vars 'risky-local-variable t)
97 ;;Side-effect-free functions from subr.el
98 (dolist (x '(assoc-default assoc-ignore-case butlast last match-string
99 match-string-no-properties member-ignore-case remove remq))
100 (put x 'side-effect-free t))
102 ;;Other safe functions
103 (dolist (x '(;;Special forms
104 and catch if or prog1 prog2 progn while unwind-protect
105 ;;Safe subrs that have some side-effects
106 ding error message minibuffer-message random read-minibuffer
107 signal sleep-for string-match throw y-or-n-p yes-or-no-p
108 ;;Defsubst functions from subr.el
110 ;;Macros from subr.el
111 save-match-data unless when with-temp-message
112 ;;Functions from subr.el that have side effects
113 read-passwd split-string replace-regexp-in-string
115 (put x 'safe-function t))
118 (defun unsafep (form &optional unsafep-vars)
119 "Return nil if evaluating FORM couldn't possibly do any harm;
120 otherwise result is a reason why FORM is unsafe. UNSAFEP-VARS is a list
121 of symbols with local bindings."
123 (if (or (eq safe-functions t) ;User turned off safety-checking
124 (atom form)) ;Atoms are never unsafe
125 (throw 'unsafep nil))
126 (let* ((fun (car form))
127 (reason (unsafep-function fun))
131 ;;It's a normal function - unsafe if any arg is
132 (unsafep-progn (cdr form)))
136 ((memq fun '(apply mapc mapcar mapconcat))
137 ;;Unsafe if 1st arg isn't a quoted lambda
138 (setq arg (cadr form))
140 ((memq (car-safe arg) '(quote function))
141 (setq reason (unsafep-function (cadr arg))))
142 ((eq (car-safe arg) 'lambda)
143 ;;Self-quoting lambda
144 (setq reason (unsafep arg unsafep-vars)))
146 (setq reason `(unquoted ,arg))))
147 (or reason (unsafep-progn (cddr form))))
149 ;;First arg is temporary bindings
151 (let ((y (unsafep-variable x t)))
152 (if y (throw 'unsafep y)))
153 (or (memq x '(&optional &rest))
154 (push x unsafep-vars)))
156 (unsafep-progn (cddr form)))
158 ;;Creates temporary bindings in one step
159 (setq unsafep-vars (nconc (mapcar #'unsafep-let (cadr form))
161 (unsafep-progn (cddr form)))
163 ;;Creates temporary bindings iteratively
164 (dolist (x (cadr form))
165 (push (unsafep-let x) unsafep-vars))
166 (unsafep-progn (cddr form)))
168 ;;Safe if odd arguments are local-var syms, evens are safe exprs
169 (setq arg (cdr form))
171 (setq reason (or (unsafep-variable (car arg) nil)
172 (unsafep (cadr arg) unsafep-vars)))
173 (if reason (throw 'unsafep reason))
174 (setq arg (cddr arg))))
176 ;;safe if arg is local-var sym
177 (unsafep-variable (cadr form) nil))
179 ;;Safe if 2nd arg is a local-var sym
180 (or (unsafep (cadr form) unsafep-vars)
181 (unsafep-variable (nth 2 form) nil)))
182 ((eq fun 'add-to-list)
183 ;;Safe if first arg is a quoted local-var sym
184 (setq arg (cadr form))
185 (if (not (eq (car-safe arg) 'quote))
187 (or (unsafep-variable (cadr arg) nil)
188 (unsafep-progn (cddr form)))))
190 ;;Special form with unusual syntax - safe if all args are
191 (dolist (x (cdr form))
192 (setq reason (unsafep-progn x))
193 (if reason (throw 'unsafep reason))))
194 ((memq fun '(dolist dotimes))
195 ;;Safe if COUNT and RESULT are safe. VAR is bound while checking BODY.
196 (setq arg (cadr form))
197 (or (unsafep-progn (cdr arg))
198 (let ((unsafep-vars (cons (car arg) unsafep-vars)))
199 (unsafep-progn (cddr form)))))
200 ((eq fun 'condition-case)
201 ;;Special form with unusual syntax - safe if all args are
202 (or (unsafep-variable (cadr form) t)
203 (unsafep (nth 2 form) unsafep-vars)
204 (let ((unsafep-vars (cons (cadr form) unsafep-vars)))
205 ;;var is bound only during handlers
206 (dolist (x (nthcdr 3 form))
207 (setq reason (unsafep-progn (cdr x)))
208 (if reason (throw 'unsafep reason))))))
210 ;;First unsafep-function call above wasn't nil, no special case applies
214 (defun unsafep-function (fun)
215 "Return nil iff FUN is a safe function.
216 \(either a safe lambda or a symbol that names a safe function). Otherwise
217 result is a reason code."
219 ((eq (car-safe fun) 'lambda)
220 (unsafep fun unsafep-vars))
221 ((not (and (symbolp fun)
222 (or (get fun 'side-effect-free)
223 (eq (get fun 'safe-function) t)
224 (eq safe-functions t)
225 (memq fun safe-functions))))
228 (defun unsafep-progn (list)
229 "Return nil if all forms in LIST are safe, or the reason
230 for the first unsafe form."
231 (catch 'unsafep-progn
234 (setq reason (unsafep x unsafep-vars))
235 (if reason (throw 'unsafep-progn reason))))))
237 (defun unsafep-let (clause)
238 "Check the safety of a let binding.
239 CLAUSE is a let-binding, either SYM or (SYM) or (SYM VAL). Checks VAL
240 and throws a reason to `unsafep' if unsafe. Returns SYM."
244 (setq sym (car clause)
245 reason (unsafep (cadr clause) unsafep-vars)))
246 (setq reason (or (unsafep-variable sym t) reason))
247 (if reason (throw 'unsafep reason))
250 (defun unsafep-variable (sym global-okay)
251 "Return nil if SYM is safe as a let-binding sym
252 \(because it already has a temporary binding or is a non-risky buffer-local
253 variable), otherwise a reason why it is unsafe. Failing to be locally bound
254 is okay if GLOBAL-OKAY is non-nil."
258 ((risky-local-variable-p sym nil)
259 `(risky-local-variable ,sym))
260 ((not (or global-okay
261 (memq sym unsafep-vars)
262 (local-variable-p sym)))
263 `(global-variable ,sym))))
265 ;; arch-tag: 6216f98b-eb8f-467a-9c33-7a7644f50658
266 ;;; unsafep.el ends here