bug#10856: 24.0.93; hs-hide-block changes cursor column when collapsing a comment

[John Yates <john@yates-sheets.org>]

When hs-show-block reveals a collapsed comment block it preserves the
position of the cursor.  This honors the "principle of least
astonishment".  By contrast when hs-hide-block collapses a comment
block it moves the cursor to the comment's left boundary.  This is
unexpected and a jarring asymmetry w.r.t. hs-show-block.

The following patch maintain the cursor column whenever possible:

--- cur/hideshow.el
+++ fix/hideshow.el
@@ -552,11 +552,13 @@
 (defun hs-hide-comment-region (beg end &optional repos-end)
  "Hide a region from BEG to END, marking it as a comment.
 Optional arg REPOS-END means reposition at end."
-  (let ((beg-eol (progn (goto-char beg) (line-end-position)))
+  (let ((goal-col (current-column))
+        (beg-bol (progn (goto-char beg) (line-beginning-position)))
+        (beg-eol (line-end-position))
        (end-eol (progn (goto-char end) (line-end-position))))
    (hs-discard-overlays beg-eol end-eol)
-    (hs-make-overlay beg-eol end-eol 'comment beg end))
-  (goto-char (if repos-end end beg)))
+    (hs-make-overlay beg-eol end-eol 'comment beg end)
+    (goto-char (if repos-end end (min end (+ beg-bol goal-col))))))