Support (rx (and (regexp EXPR) (literal EXPR))) (Bug#36237)

* lisp/emacs-lisp/rx.el (rx-regexp): Allow non-string forms.
(rx-constituents): Add literal constituent, which is like a plain
STRING form, but allows arbitrary lisp expressions.
(rx-literal): New function.
(rx-compile-to-lisp): New variable.
(rx--subforms): New helper function for handling subforms, including
non-constant case.
(rx-group-if, rx-and, rx-or, rx-=, rx->=, rx-repeat, rx-submatch)
(rx-submatch-n, rx-kleene, rx-atomic-p): Use it to handle non-constant
subforms.
(rx): Document new form, wrap non-constant forms with concat call.
* test/lisp/emacs-lisp/rx-tests.el (rx-tests--match): New macro.
(rx-nonstring-expr, rx-nonstring-expr-non-greedy): New tests.
* etc/NEWS: Announce changes.

1 files changed, 6 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 7de94a7b11d..29b74ee682b 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1441,12 +1441,18 @@ when given in a string.  Previously, '(any "\x80-\xff")' would match
 characters U+0080...U+00FF.  Now the expression matches raw bytes in
 the 128...255 range, as expected.
 
+---
 *** The rx 'or' and 'seq' forms no longer require any arguments.
 (or) produces a regexp that never matches anything, while (seq)
 matches the empty string, each being an identity for the operation.
 This also works for their aliases: '|' for 'or'; ':', 'and' and
 'sequence' for 'seq'.
 
+---
+*** 'regexp' and new 'literal' accept arbitrary lisp as arguments.
+In this case, 'rx' will generate code which produces a regexp string
+at run time, instead of a constant string.
+
 ** Frames
 
 +++