Commit 49d3cd90 authored by Mattias Engdegård's avatar Mattias Engdegård

rx: Improve 'or' compositionality (bug#37659)

Perform 'regexp-opt' on nested 'or' forms, and after expansion of
user-defined and 'eval' forms.  Characters are now turned into strings
for wider 'regexp-opt' scope.  This preserves the longest-match
semantics for string in 'or' forms over composition.

* doc/lispref/searching.texi (Rx Constructs): Document.
* lisp/emacs-lisp/rx.el (rx--normalise-or-arg)
(rx--all-string-or-args): New.
(rx--translate-or): Normalise arguments first, and check for strings
in subforms.
(rx--expand-eval): Extracted from rx--translate-eval.
(rx--translate-eval): Call rx--expand-eval.
* test/lisp/emacs-lisp/rx-tests.el (rx-or, rx-def-in-or): Add tests.
* etc/NEWS: Announce.
parent 6b48aedb
Pipeline #4903 failed with stage
in 54 minutes and 9 seconds
......@@ -1086,8 +1086,9 @@ Corresponding string regexp: @samp{@var{A}@var{B}@dots{}}
@itemx @code{(| @var{rx}@dots{})}
@cindex @code{|} in rx
Match exactly one of the @var{rx}s.
If all arguments are string literals, the longest possible match
will always be used. Otherwise, either the longest match or the
If all arguments are strings, characters, or @code{or} forms
so constrained, the longest possible match will always be used.
Otherwise, either the longest match or the
first (in left-to-right order) will be used.
Without arguments, the expression will not match anything at all.@*
Corresponding string regexp: @samp{@var{A}\|@var{B}\|@dots{}}.
......@@ -2325,6 +2325,12 @@ expressions from simpler parts.
*** 'not' argument can now be a character or single-char string.
*** Nested 'or' forms of strings guarantee a longest match.
For example, (or (or "IN" "OUT") (or "INPUT" "OUTPUT")) now matches
the whole string "INPUT" if present, not just "IN". Previously, this
was only guaranteed inside a single 'or' form of string literals.
** Frames
......@@ -254,22 +254,39 @@ Left-fold the list L, starting with X, by the binary function F."
(setq l (cdr l)))
(defun rx--normalise-or-arg (form)
"Normalise the `or' argument FORM.
Characters become strings, user-definitions and `eval' forms are expanded,
and `or' forms are normalised recursively."
(cond ((characterp form)
(char-to-string form))
((and (consp form) (memq (car form) '(or |)))
(cons (car form) (mapcar #'rx--normalise-or-arg (cdr form))))
((and (consp form) (eq (car form) 'eval))
(rx--normalise-or-arg (rx--expand-eval (cdr form))))
(let ((expanded (rx--expand-def form)))
(if expanded
(rx--normalise-or-arg expanded)
(defun rx--all-string-or-args (body)
"If BODY only consists of strings or such `or' forms, return all the strings.
Otherwise throw `rx--nonstring'."
(mapcan (lambda (form)
(cond ((stringp form) (list form))
((and (consp form) (memq (car form) '(or |)))
(rx--all-string-or-args (cdr form)))
(t (throw 'rx--nonstring nil))))
(defun rx--translate-or (body)
"Translate an or-pattern of zero or more rx items.
;; FIXME: Possible improvements:
;; - Turn single characters to strings: (or ?a ?b) -> (or "a" "b"),
;; so that they can be candidates for regexp-opt.
;; - Translate compile-time strings (`eval' forms), again for regexp-opt.
;; - Flatten sub-patterns first: (or (or A B) (or C D)) -> (or A B C D)
;; in order to improve effectiveness of regexp-opt.
;; This would also help composability.
;; - Use associativity to run regexp-opt on contiguous subsets of arguments
;; if not all of them are strings. Example:
;; Then call regexp-opt on runs of string arguments. Example:
;; (or (+ digit) "CHARLIE" "CHAN" (+ blank))
;; -> (or (+ digit) (or "CHARLIE" "CHAN") (+ blank))
......@@ -279,27 +296,26 @@ Return (REGEXP . PRECEDENCE)."
;; so that (or "@" "%" digit (any "A-Z" space) (syntax word))
;; -> (any "@" "%" digit "A-Z" space word)
;; -> "[A-Z@%[:digit:][:space:][:word:]]"
;; Problem: If a subpattern is carefully written to be
;; optimizable by regexp-opt, how do we prevent the transforms
;; above from destroying that property?
;; Example: (or "a" (or "abc" "abd" "abe"))
((null body) ; No items: a never-matching regexp.
((null (cdr body)) ; Single item.
(rx--translate (car body)))
((rx--every #'stringp body) ; All strings.
(cons (list (regexp-opt body nil))
((rx--every #'rx--charset-p body) ; All charsets.
(rx--translate-union nil body))
(cons (append (car (rx--translate (car body)))
(mapcan (lambda (item)
(cons "\\|" (car (rx--translate item))))
(cdr body)))
(let* ((args (mapcar #'rx--normalise-or-arg body))
(all-strings (catch 'rx--nonstring (rx--all-string-or-args args))))
(all-strings ; Only strings.
(cons (list (regexp-opt all-strings nil))
((rx--every #'rx--charset-p args) ; All charsets.
(rx--translate-union nil args))
(cons (append (car (rx--translate (car args)))
(mapcan (lambda (item)
(cons "\\|" (car (rx--translate item))))
(cdr args)))
(defun rx--charset-p (form)
"Whether FORM looks like a charset, only consisting of character intervals
......@@ -840,11 +856,15 @@ Return (REGEXP . PRECEDENCE)."
(cons (list (list 'regexp-quote arg)) 'seq))
(t (error "rx `literal' form with non-string argument")))))
(defun rx--translate-eval (body)
"Translate the `eval' form. Return (REGEXP . PRECEDENCE)."
(defun rx--expand-eval (body)
"Expand `eval' arguments. Return a new rx form."
(unless (and body (null (cdr body)))
(error "rx `eval' form takes exactly one argument"))
(rx--translate (eval (car body))))
(eval (car body)))
(defun rx--translate-eval (body)
"Translate the `eval' form. Return (REGEXP . PRECEDENCE)."
(rx--translate (rx--expand-eval body)))
(defvar rx--regexp-atomic-regexp nil)
......@@ -42,13 +42,24 @@
(ert-deftest rx-or ()
(should (equal (rx (or "ab" (| "c" nonl) "de"))
(should (equal (rx (or "ab" "abc" "a"))
(should (equal (rx (or "ab" "abc" ?a))
(should (equal (rx (or "ab" (| (or "abcd" "abcde")) (or "a" "abc")))
(should (equal (rx (or "a" (eval (string ?a ?b))))
(should (equal (rx (| nonl "a") (| "b" blank))
(should (equal (rx (|))
(ert-deftest rx-def-in-or ()
(rx-let ((a b)
(b (or "abc" c))
(c ?a))
(should (equal (rx (or a (| "ab" "abcde") "abcd"))
(ert-deftest rx-char-any ()
"Test character alternatives with `]' and `-' (Bug#25123)."
(should (equal
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