bug#15841: Display bugs with cache-long-lines non-nil

[Stephen Berman <stephen.berman@gmx.net>]

On Mon, 11 Nov 2013 15:12:15 +0100 Stephen Berman <stephen.berman@gmx.net> wrote:

> This change broke dired-maybe-insert-subdir.  Perhaps this should be a
> new bug number, but since part of the breakage is display-related, I
> decided to report it here.  To reproduce:
>
> 0. emacs -Q (built from trunk bzr 115033 or later)
> 1. Open a directory in Dired, e.g. the Emacs source tree root.
> 2. Put point on an entry listing a directory, e.g. admin.
> 3. Type `i'.
> => Emacs hangs.
>
> If I repeat the recipe but after step 1 type `M-: (setq cache-long-lines
> nil)', then at step 3, `i' works as expected.
>
> Here are more details of the breakage:
>
> Typing `C-g' releases the hang and shows the admin subdirectory, but its
> display is corrupted: (i) the "available" blocks information, which
> should appear at the end of the "total" line, instead appears to the
> right of the first entry `.' and is fontified with dired-directory face;
> (ii) while all the entries of admin are listed below the `..' entry, the
> entire line of each entry is fontified with dired-directory face, and
> these lines cannot be accessed by vertical motion commands like `C-n' or
> `C-p', though they can be with horizontal motion commands like `C-f' and
> `C-p'.  In fact, all of these entries appear to Dired to be part of the
> line of the `..' entry, and AFACT this is what causes the hang: Emacs
> infloops in dired-move-to-filename because, when point appears to be at
> eof, beginning-of-line moves it back to the start of the `..' entry.

I tracked the problematic fontification and motion behavior to
insert-directory in files.el: it happens during the loop when
decode-coding-region is called on the file names of the subdirectory
entries.  I stepped through the code with Edebug but could not tell why
it goes wrong here, and I'm too tired to pursue it further now.  Also,
when I step through this code, the "available" information is added at
the end of the entire subdirectory listing, unlike what I observed above
when just invoking `i' and then `C-g'.  I guess this is due to the
interaction of redisplay with stepping through the code; it's still
clear that the subdirectory listing is being treated as part of the line
containing the `..' entry.

Steve Berman