From f67ae7ed53e6a90cf4f97ac1bba9498b5d58e6dc Mon Sep 17 00:00:00 2001
From: Artur Malabarba <address@hidden>
Date: Tue, 27 Jan 2015 14:08:01 -0200
Subject: [PATCH] (isearch-search-fun-default): Implement group folding in
 isearch.

Use `isearch-fold-groups', `isearch-groups-alist', and
`isearch--replace-groups-in-string'.
---
 lisp/isearch.el | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/lisp/isearch.el b/lisp/isearch.el
index 99ca73f..accfb72 100644
--- a/lisp/isearch.el
+++ b/lisp/isearch.el
@@ -58,6 +58,7 @@
 ;;; Code:
 
 (eval-when-compile (require 'cl-lib))
+(eval-when-compile (require 'subr-x))
 
 ;; Some additional options and constants.
 
@@ -272,6 +273,23 @@ Default value, nil, means edit the string instead."
   :version "23.1"
   :group 'isearch)
 
+(defcustom isearch-fold-groups t
+  "Whether regular isearch should do group folding.
+This means some characters will match entire groups of charactes,
+such as \" matching ”, for instance."
+  :type 'boolean
+  :group 'isearch
+  :version "25.1")
+
+(defvar isearch-groups-alist
+  ;; FIXME: Add all the latin accented letters like Ã.
+  '((?\" . "[\"＂“””„⹂〞‟‟❞❝❠“„〝〟🙷🙶🙸❮❯«»‹›󠀢]")
+    (?' . "[`'❟❛❜‘’’‚‛‛‚‘󠀢❮❯«»‹›]")
+    ;; `isearch-fold-groups' doesn't interact with
+    ;; `isearch-lax-whitespace' yet.  So we need to add this here.
+    (?\s . "[ 	\r\n]+"))
+  "Alist of groups to use when `isearch-fold-groups' is non-nil.")
+
 (defcustom isearch-lazy-highlight t
   "Controls the lazy-highlighting during incremental search.
 When non-nil, all text in the buffer matching the current search
@@ -2565,6 +2583,18 @@ search for the first occurrence of STRING or its translation.")
 Can be changed via `isearch-search-fun-function' for special needs."
   (funcall (or isearch-search-fun-function 'isearch-search-fun-default)))
 
+(defun isearch--replace-groups-in-string (string)
+  "Return a group-folded regexp version of STRING.
+Any character that has an entry in `isearch-groups-alist' is
+replaced with the cdr of that entry (which should be a regexp).
+Other characters are `regexp-quote'd."
+  (apply #'concat
+    (mapcar (lambda (c)
+              (if-let ((entry (assq c isearch-groups-alist)))
+                  (cdr entry)
+                (regexp-quote (string c))))
+      string)))
+
 (defun isearch-search-fun-default ()
   "Return default functions to use for the search."
   (cond
@@ -2591,6 +2621,13 @@ Can be changed via `isearch-search-fun-function' for special needs."
       're-search-backward-lax-whitespace))
    (isearch-regexp
     (if isearch-forward 're-search-forward 're-search-backward))
+   ;; `isearch-regexp' is essentially a superset of
+   ;; `isearch-fold-groups'.  So fold-groups comes after it.
+   (isearch-fold-groups
+    (lambda (string &optional bound noerror count)
+      (funcall (if isearch-forward #'re-search-forward #'re-search-backward)
+        (isearch--replace-groups-in-string string)
+        bound noerror count)))
    ((and isearch-lax-whitespace search-whitespace-regexp)
     (if isearch-forward
 	'search-forward-lax-whitespace
-- 
2.2.2