From 8f4be27dca714b168414171bde3eeee9fefc44e9 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.

(isearch-fold-groups group-fold-table): New variables.

When `isearch-fold-groups' is non-nil `group-fold-table' is used as the
case table.
---
 lisp/isearch.el | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/lisp/isearch.el b/lisp/isearch.el
index 99ca73f..7d568dd 100644
--- a/lisp/isearch.el
+++ b/lisp/isearch.el
@@ -272,6 +272,38 @@ 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 group-fold-table
+  (eval-when-compile
+    (let ((table (make-char-table 'case-table))
+          (eq (make-char-table 'equiv)))
+      (require 'subr-x)
+      ;; Build the group table.
+      (dotimes (i (length eq))
+        (when-let ((d (get-char-code-property i 'decomposition))
+                   (k (car-safe d)))
+          (unless (eq i k)
+            (aset eq i (if (characterp k) k (cadr d))))))
+      ;; Put it in the right place.
+      (set-char-table-extra-slot table 1 eq)
+      table))
+  "Used for folding characters of the same group during search.")
+
+(defmacro with-group-folding (&rest body)
+  "Execute BODY with character-group folding turned on.
+This sets `group-fold-table' as the case-table during the
+execution of BODY."
+  `(let ((case-fold-search t))
+     (with-case-table group-fold-table
+       ,@body)))
+
 (defcustom isearch-lazy-highlight t
   "Controls the lazy-highlighting during incremental search.
 When non-nil, all text in the buffer matching the current search
@@ -2568,6 +2600,12 @@ Can be changed via `isearch-search-fun-function' for special needs."
 (defun isearch-search-fun-default ()
   "Return default functions to use for the search."
   (cond
+   (isearch-fold-groups
+    (lambda (&rest args)
+      (let* ((isearch-fold-groups nil)
+             (function (isearch-search-fun-default)))
+        (with-group-folding
+         (apply function args)))))
    (isearch-word
     (lambda (string &optional bound noerror count)
       ;; Use lax versions to not fail at the end of the word while
-- 
2.2.2