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Byte-compiler warning about mutation of constant values

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When we can easily detect mutation of constants (quoted lists, strings
and vectors), warn.  For example,

  (setcdr '(1 . 2) 3)
  (nreverse [1 2 3])
  (put-text-property 0 3 'face 'highlight "moo")

Such code can result in surprising behaviour and problems that
are difficult to debug.

* lisp/emacs-lisp/bytecomp.el (byte-compile-form, mutating-fns):
Add the warning and a list of functions to warn about.
* etc/NEWS: Announce.
* test/lisp/emacs-lisp/bytecomp-tests.el
(bytecomp-test--with-suppressed-warnings): Add test cases.
This commit is contained in:
Mattias Engdegård 2023-05-11 19:24:51 +02:00
parent fa598571ad
commit bfc07100d2
3 changed files with 103 additions and 0 deletions
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53
lisp/emacs-lisp/bytecomp.el
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@ -3488,6 +3488,22 @@ lambda-expression."
(format-message "; use `%s' instead."
interactive-only))
(t "."))))
(let ((mutargs (function-get (car form) 'mutates-arguments)))
(when mutargs
(dolist (idx (if (eq mutargs 'all-but-last)
(number-sequence 1 (- (length form) 2))
mutargs))
(let ((arg (nth idx form)))
(when (and (or (and (eq (car-safe arg) 'quote)
(consp (nth 1 arg)))
(arrayp arg))
(byte-compile-warning-enabled-p
'suspicious (car form)))
(byte-compile-warn-x form "`%s' on constant %s (arg %d)"
(car form)
(if (consp arg) "list" (type-of arg))
idx))))))
(if (eq (car-safe (symbol-function (car form))) 'macro)
(byte-compile-report-error
(format-message "`%s' defined after use in %S (missing `require' of a library file?)"
@ -3557,6 +3573,43 @@ lambda-expression."
(dolist (fn important-return-value-fns)
(put fn 'important-return-value t)))
(let ((mutating-fns
;; FIXME: Should there be a function declaration for this?
;;
;; (FUNC . ARGS) means that FUNC mutates arguments whose indices are
;; in the list ARGS, starting at 1, or all but the last argument if
;; ARGS is `all-but-last'.
'(
(setcar 1) (setcdr 1) (aset 1)
(nreverse 1)
(nconc . all-but-last)
(nbutlast 1) (ntake 2)
(sort 1)
(delq 2) (delete 2)
(delete-dups 1) (delete-consecutive-dups 1)
(plist-put 1)
(fillarray 1)
(store-substring 1)
(clear-string 1)
(add-text-properties 4) (put-text-property 5) (set-text-properties 4)
(remove-text-properties 4) (remove-list-of-text-properties 4)
(alter-text-property 5)
(add-face-text-property 5) (add-display-text-property 5)
(cl-delete 2) (cl-delete-if 2) (cl-delete-if-not 2)
(cl-delete-duplicates 1)
(cl-nsubst 3) (cl-nsubst-if 3) (cl-nsubst-if-not 3)
(cl-nsubstitute 3) (cl-nsubstitute-if 3) (cl-nsubstitute-if-not 3)
(cl-nsublis 2)
(cl-nunion 1 2) (cl-nintersection 1 2) (cl-nset-difference 1 2)
(cl-nset-exclusive-or 1 2)
(cl-nreconc 1)
(cl-sort 1) (cl-stable-sort 1) (cl-merge 2 3)
)))
(dolist (entry mutating-fns)
(put (car entry) 'mutates-arguments (cdr entry))))
(defun byte-compile-normal-call (form)
(when (and (symbolp (car form))