bug#24997: 26.0.50; ibuffer-decompose-filter has side effects on error

[Tino Calancha]

M-x ibuffer RET
/ m lisp-interaction-mode RET
/ > 10 RET
;; here `ibuffer-filtering-qualifiers' has value:
;; ((size-gt . 10) (used-mode . lisp-interaction-mode))
/ d
;; Signals error:
ibuffer-decompose-filter: Filter type size-gt is not compound

Note that previous command has side effects on `ibuffer-filtering-qualifiers'
even when there is an error; after this command the var has value:
((used-mode . lisp-interaction-mode))

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>From 4540c12df119e247b5eb0a33c216375a43421e62 Mon Sep 17 00:00:00 2001
From: Tino Calancha <tino.calancha@gmail.com>
Date: Wed, 23 Nov 2016 16:28:49 +0900
Subject: [PATCH] ibuffer-decompose-filter: Avoid side effects on error

* lisp/ibuf-ext.el (ibuffer-decompose-filter):
Update 'ibuffer-filtering-qualifiers' only if there is no error (Bug#24997).
---
 lisp/ibuf-ext.el | 39 +++++++++++++++++----------------------
 1 file changed, 17 insertions(+), 22 deletions(-)

diff --git a/lisp/ibuf-ext.el b/lisp/ibuf-ext.el
index 5ef0746..3d11972 100644
--- a/lisp/ibuf-ext.el
+++ b/lisp/ibuf-ext.el
@@ -840,29 +840,24 @@ ibuffer-decompose-filter
 be a complex filter like (OR [name: foo] [mode: bar-mode]), will be
 turned into two separate filters [name: foo] and [mode: bar-mode]."
   (interactive)
-  (when (null ibuffer-filtering-qualifiers)
+  (unless ibuffer-filtering-qualifiers
     (error "No filters in effect"))
-  (let ((lim (pop ibuffer-filtering-qualifiers)))
-    (pcase (car lim)
-      (`or
-       (setq ibuffer-filtering-qualifiers (append
-                                         (cdr lim)
-                                         ibuffer-filtering-qualifiers)))
-      (`saved
-       (let ((data
-             (assoc (cdr lim)
-                    ibuffer-saved-filters)))
-        (unless data
-          (ibuffer-filter-disable)
-          (error "Unknown saved filter %s" (cdr lim)))
-        (setq ibuffer-filtering-qualifiers (append
-                                           (cadr data)
-                                           ibuffer-filtering-qualifiers))))
-      (`not
-       (push (cdr lim)
-            ibuffer-filtering-qualifiers))
-      (_
-       (error "Filter type %s is not compound" (car lim)))))
+  (let* ((filters ibuffer-filtering-qualifiers)
+         (head (cdar filters))
+         (tail (cdr filters))
+         (value
+          (pcase (caar filters)
+            (`or (nconc head tail))
+            (`saved
+             (let ((data (assoc head ibuffer-saved-filters)))
+               (unless data
+                 (ibuffer-filter-disable)
+                 (error "Unknown saved filter %s" head))
+               (nconc (cadr data) tail)))
+            (`not (cons head tail))
+            (_
+             (error "Filter type %s is not compound" (caar filters))))))
+    (setq ibuffer-filtering-qualifiers value))
   (ibuffer-update nil t))
 
 ;;;###autoload
-- 
2.10.2

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In GNU Emacs 26.0.50.5 (x86_64-pc-linux-gnu, GTK+ Version 3.22.3)
 of 2016-11-23 built on calancha-pc
Repository revision: c542fab20f53374dd0c71dce949ef370fc76fa48