Subject: 27.0.50; uncomment-region fails correctly to reverse the action of comment-region.

From: Alan Mackenzie <[email-masked]>
Date: Mon, 6 May 2019 10:11:00 +0000

Hello, Emacs.

In the master branch:

With indent-tabs-mode t, and tab-width (say) 8, start off with the
following two line of Emacs lisp:

    (if (null bs-state)
	(ignore)
    ^
  <tab>

(the first of these lines being indented by four spaces, the second by a
<tab>).

Mark the two lines, and execute M-x comment-region.  We get this:

    ;; (if (null bs-state)
    ;;  (ignore)
       ^
     <tab>

(where all the space is space characters except for the <tab> just
before "(ignore)").

Now execute M-x uncomment-region.  This should restore the region to
what it started as.  Instead one gets:

    (if (null bs-state)
    	(ignore)
^^^^  ^
SPCs <tab>

, there now being four spurious spaces before the <tab> preceding
"(ignore)".  This is a bug.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

In uncomment-region-default-1, the variable `spt' gets set to the result
of comment-search-forward, the ";" at the beginning of the comment on
the current line.  The function then narrows to between `spt' and BO
next line.

In this narrowed region, the function removes the comment starter.
Because of the narrowing, it cannot take any account of the spaces at
the start of the line.

Possibly, uncomment-region needs to be amended so that that narrowing
includes any space preceding the comment starter, and that space gets
properly handled.

-- 
Alan Mackenzie (Nuremberg, Germany).