Subject: RE: bug#8667: 24.0.50; `bounds-of-thing-at-point' returns (N . N) for `comment'

From: "Drew Adams" <[email-masked]>
Date: Sat, 21 May 2011 07:52:58 -0700

> > No, I don't think you did.  I just downloaded the latest 
> > thingatpt.el.  There is no fix AFAICT.
> 
> From which branch?

>From here:
http://repo.or.cz/w/emacs.git/tree/HEAD:/lisp

In the past that has always given the trunk AFAIK.  And in the past it has been
the _only_ HTTP access that has been reliable (works).  But apparently it is no
longer kept up-to-date.

I just now tried
http://bazaar.launchpad.net/~vcs-imports/emacs/trunk/files/head%3A/lisp/
and got this, which is typically the case:

 Please try again
 Sorry, there was a problem connecting to the Launchpad server. 

 Try reloading this page in a minute or two. If the problem persists,
 let us know in the #launchpad IRC channel on Freenode. 

 Thanks for your patience.

It used to be easy to access Emacs source code via HTTP (back when you used CVS,
IIRC).  Now it is difficult, even if occasionally still possible.  After
repeatedly trying that second URL, I was finally able to get your fixed file.

The first part of this bug report does seem to be fixed: no empty thing
returned.

The second part is not fixed.  `bounds-of-thing-at-point' can still return a
cons when it should return nil.  It can easily return a cons that represents a
purely whitespace, non-comment for thing-type `comment'.  This in turn means
that `thing-at-point' returns a whitespace, non-comment for thing-type
`comment'.

This is a bug in `thingatpt.el'.  It is either a bug in
`bounds-of-thing-at-point', if we expect that general function to DTRT in this
case, or it is a bug in that there is a missing function
`bounds-of-comment-at-point' and consequent (put 'comment
'bounds-of-thing-at-point 'bounds-of-comment-at-point).  Or some such fix.

I already gave the recipe to reproduce the bug.  I can repeat it if necessary.

`b-o-t-a-p' depends for its generic effect on functions such as `forward-THING'.
Sometimes that is enough to make `b-o-t-a-p' DTRT; sometimes it is not enough.
When it is not, as in this case, other measures need to be taken, such as
defining a THING-specific `bounds-of-THING-at-point' function and putting that
on the THING symbol as property `bounds-of-thing-at-point'.

One way or the other, and there are several alternatives, this needs to be
fixed.  It is a bug for `b-o-t-a-p' to return non-nil when there is no comment
at point, and thus for `thing-at-point' to return a non-nil, non-comment value.