Re: [PATCH] emacs: Fix point motion in `beginning-of-visual-line'

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+Date: Thu, 10 Jan 2013 17:39:13 -0500\r
+From: Austin Clements <amdragon@MIT.EDU>\r
+To: notmuch@notmuchmail.org\r
+Subject: Re: [PATCH] emacs: Fix point motion in `beginning-of-visual-line'\r
+Message-ID: <20130110223836.GV17581@mit.edu>\r
+References: <1357852215-16788-1-git-send-email-markwalters1009@gmail.com>\r
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+\r
+After some IRC discussion, Mark and I have found that my patch doesn't\r
+fix everything related to w3m that Mark's patch does (though my patch\r
+does fix other things not related to w3m).\r
+\r
+Quoth myself on Jan 10 at  4:59 pm:\r
+> `beginning-of-visual-line' interacts poorly with our use of invisible\r
+> overlays and often moves point into the previous message or part even\r
+> though it looks like it's in the next message or part (e.g., if you\r
+> press C-a on a header line and the previous message is invisible,\r
+> point will move into the previous message, even though it appears to\r
+> still be on the header line).  This advises `beginning-of-visual-line'\r
+> to address this behavior.\r
+> ---\r
+> \r
+> This is a completely different approach that should fix the HTML\r
+> problem, as well as other problems.  I also have an alternate approach\r
+> to this that sets 'field properties on the header line and part\r
+> buttons, which has the same effect, but seems to have more\r
+> side-effects (e.g., if point is at the end of a part button, C-a won't\r
+> go to the beginning).  This patch, OTOH, strikes directly at the\r
+> strange (maybe even buggy) behavior of beginning-of-visual-line.  The\r
+> downside is that it's advice, and advice always feels a little\r
+> sketchy.\r
+> \r
+>  emacs/notmuch-show.el |   22 ++++++++++++++++++++++\r
+>  1 file changed, 22 insertions(+)\r
+> \r
+> diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el\r
+> index 5751d98..6f5c53a 100644\r
+> --- a/emacs/notmuch-show.el\r
+> +++ b/emacs/notmuch-show.el\r
+> @@ -1120,6 +1120,28 @@ function is used."\r
+>      (notmuch-show-goto-first-wanted-message)\r
+>      (current-buffer)))\r
+>  \r
+> +(defadvice beginning-of-visual-line (around constrain-invisible activate)\r
+> +  "Fix point motion around invisible overlays.\r
+> +\r
+> +In `notmuch-show-mode', we often hide overlays that end with a\r
+> +newline (e.g., messages, parts, etc).  This has the effect of\r
+> +collapsing the overlayed text into the beginning of the next\r
+> +line.  Unfortunately, this causes `visual-motion' and hence\r
+> +`beginning-of-visual-line' to move to the first character of the\r
+> +invisible overlay rather than the more obvious first character of\r
+> +the visible line.  Visually, these two points are\r
+> +indistinguishable, but this tends to make actions mysteriously\r
+> +apply to the previous message when it looks like they should\r
+> +apply to the next message.\r
+> +\r
+> +This advice fixes this behavior in `notmuch-show-mode' by\r
+> +restricting the motion of `beginning-of-visual-line'."\r
+> +  (if (eq major-mode 'notmuch-show-mode)\r
+> +      (save-restriction\r
+> +    (narrow-to-region (line-beginning-position) (point-max))\r
+> +    ad-do-it)\r
+> +    ad-do-it))\r
+> +\r
+>  (defun notmuch-show-build-buffer ()\r
+>    (let ((inhibit-read-only t))\r
+>  \r