* lisp/character-fold.el (character-fold-to-regexp)

Warn about using long strings.

* test/automated/character-fold-tests.el
(character-fold--test-lax-whitespace)
(character-fold--test-consistency): Reduce string size for tests.

lisp/character-fold.el

@@ -150,6 +150,10 @@ Any character in STRING that has an entry in
 `character-fold-table' is replaced with that entry (which is a
 regexp) and other characters are `regexp-quote'd.
 
+Note that this function can potentially return regexps too long
+for Emacs to handle.  If STRING is longer than 30 characters,
+consider not using this function.
+
 FROM is for internal use.  It specifies an index in the STRING
 from which to start."
   (let* ((spaces 0)

test/automated/character-fold-tests.el

@@ -37,13 +37,13 @@
 
 
 (ert-deftest character-fold--test-consistency ()
-  (dotimes (n 50)
+  (dotimes (n 30)
     (let ((w (character-fold--random-word n)))
       ;; A folded string should always match the original string.
       (character-fold--test-search-with-contents w w))))
 
 (ert-deftest character-fold--test-lax-whitespace ()
-  (dotimes (n 50)
+  (dotimes (n 40)
     (let ((w1 (character-fold--random-word n))
           (w2 (character-fold--random-word n))
           (search-spaces-regexp "\\s-+"))