Subject: 24.5; align-region assumes that match does not contain newline

From: Josh <[email-masked]>
Date: Thu, 21 Apr 2016 23:20:19 -0700

The align-region function assumes that a matching regexp does not
contain a newline.  This causes unexpected behavior in cases where the
first "column" being aligned contains only whitespace.  The following
script exhibits the unexpected behavior:

emacs -Q --eval '(progn
 (switch-to-buffer "*test*")
 (text-mode)
 (setq indent-tabs-mode nil)
 (insert "lorem ipsum, dolor sit amet,\n ,,\n")
 (let ((table (make-syntax-table (syntax-table))))
   ;; (modify-syntax-entry ?\n ">" table) ; <= UNCOMMENT THIS LINE TO FIX
   (with-syntax-table table
   (align-regexp (point-min) (point-max) "\\(\\s-*\\)," 1 1 t))))'

Uncommenting the seventh line and running again will show the expected
behavior.  The fix works around the problem by using a syntax map in
which the newline character does not belong to the whitespace syntax
class, thus preventing \s-* from matching the newline.

In GNU Emacs 24.5.1 (x86_64-apple-darwin13.4.0, NS apple-appkit-1265.21)
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