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.

1 files changed, 12 insertions, 1 deletions

diff --git a/test/lisp/emacs-lisp/rx-tests.el b/test/lisp/emacs-lisp/rx-tests.el
index 2e34d65a9aa..4888e1d9d1e 100644
--- a/test/lisp/emacs-lisp/rx-tests.el
+++ b/test/lisp/emacs-lisp/rx-tests.el
@@ -42,13 +42,24 @@
 (ert-deftest rx-or ()
   (should (equal (rx (or "ab" (| "c" nonl) "de"))
                  "ab\\|c\\|.\\|de"))
-  (should (equal (rx (or "ab" "abc" "a"))
+  (should (equal (rx (or "ab" "abc" ?a))
                  "\\(?:a\\(?:bc?\\)?\\)"))
+  (should (equal (rx (or "ab" (| (or "abcd" "abcde")) (or "a" "abc")))
+                 "\\(?:a\\(?:b\\(?:c\\(?:de?\\)?\\)?\\)?\\)"))
+  (should (equal (rx (or "a" (eval (string ?a ?b))))
+                 "\\(?:ab?\\)"))
   (should (equal (rx (| nonl "a") (| "b" blank))
                  "\\(?:.\\|a\\)\\(?:b\\|[[:blank:]]\\)"))
   (should (equal (rx (|))
                  "\\`a\\`")))
 
+(ert-deftest rx-def-in-or ()
+  (rx-let ((a b)
+           (b (or "abc" c))
+           (c ?a))
+    (should (equal (rx (or a (| "ab" "abcde") "abcd"))
+                   "\\(?:a\\(?:b\\(?:c\\(?:de?\\)?\\)?\\)?\\)"))))
+
 (ert-deftest rx-char-any ()
   "Test character alternatives with `]' and `-' (Bug#25123)."
   (should (equal