* lisp/character-fold.el: Remove special case-folding support

(character-fold-to-regexp): Remove special code for
case-folding.  Char-fold search still respects the
`case-fold-search' variable (i.e., f matches F).  This only
removes the code that was added to ensure that f also matched
all chars that F matched.  For instance, after this commit, f
no longer matches 𝔽.

This was necessary because the logic created a regexp with
2^(length of the string) redundant paths.  So, when a very
long string "almost" matched, Emacs took a very long time to
figure out that it didn't.  This became particularly relevant
because isearch's lazy-highlight does a search bounded by (1-
match-end) (which, in most circumstances, is a search that
almost matches).  A recipe for this can be found in bug#22090.

1 files changed, 21 insertions, 0 deletions

diff --git a/test/automated/character-fold-tests.el b/test/automated/character-fold-tests.el
index 40735e5df7f..4e8761e6f7b 100644
--- a/test/automated/character-fold-tests.el
+++ b/test/automated/character-fold-tests.el
@@ -98,6 +98,27 @@
     ;; (character-fold--test-match-exactly "a12" "xxyy")
     ))
 
+(ert-deftest character-fold--speed-test ()
+  (dolist (string (append '("tty-set-up-initial-frame-face"
+                            "tty-set-up-initial-frame-face-frame-faceframe-faceframe-faceframe-face")
+                          (mapcar #'character-fold--random-word '(10 50 100
+                                                                     50 100))))
+    (message "Testing %s" string)
+    ;; Make sure we didn't just fallback on the trivial search.
+    (should-not (string= (regexp-quote string)
+                         (character-fold-to-regexp string)))
+    (with-temp-buffer
+      (save-excursion (insert string))
+      (let ((time (time-to-seconds (current-time))))
+        ;; Our initial implementation of case-folding in char-folding
+        ;; created a lot of redundant paths in the regexp. Because of
+        ;; that, if a really long string "almost" matches, the regexp
+        ;; engine took a long time to realise that it doesn't match.
+        (should-not (character-fold-search-forward (concat string "c") nil 'noerror))
+        ;; Ensure it took less than a second.
+        (should (< (- (time-to-seconds (current-time))
+                      time)
+                   1))))))
 
 (provide 'character-fold-tests)
 ;;; character-fold-tests.el ends here