bug#10457: (Broken?) programmable completion in shell buffers

[Stefan Monnier]

> First, I'm unable to complete options to commands.  Take, for example,
> "ssh".  If I'm in my home directory, type "ssh -", and hit TAB, the
> command line changes to "ssh .-", and when I hit TAB again, a
> completions buffer pops up showing only the file and directory names
> starting with a dot and containing a dash.  I assume that instead of
> offering the options available for ssh, Emacs performs some sort of
> "fuzzy" matching against file and directory names.

It's partial-completion at work: "a-b" matches "a*-b*" and "-" just
matches "*-*".  Apparently all your file names that contained "-"
started with ".", hence the ".-".

> Is this the intended behavior, and if so, how can I disable this
> fuzzy matching?

You can remove partial-completion from completion-styles.

> TAB.  When I am in a directory that doesn't contain files with a dash
> in the name, typing "ssh -" and hitting TAB produces only "No match"
> message in the minibuffer.

Indeed, pcomplete doesn't seem to provide any completion for ssh's "-"
options, currently, even though the code does do something for it:

(defun pcomplete/ssh ()
  "Completion rules for the `ssh' command."
  (pcomplete-opt "1246AaCfgKkMNnqsTtVvXxYbcDeFiLlmOopRSw")
  (pcomplete-here (pcmpl-ssh-hosts)))

I don't think completion of "-" is very useful for ssh since there's no
long options, and most ascii letters are valid options, but still it
seems we have a bug that prevents pcomplete-opt from doing its job.

> Second, more disturbingly, trying to complete options to "tar" locks Emacs.
> Here is how to reproduce it:

> emacs -Q
> M-x shell
> cd <some directory without dashes in file and directory names>
> tar - TAB SPC

I believe I've fixed this bug "recently".  If you can try the code in
the trunk to confirm that it's fixed, it would be wonderful.

> I've had high hopes for `pcomplete', but I am put off by its
> weirdness.

There's a lot more to it than "turning it on", so yes, it's been
a source of many bug reports.  Thank you for trying it out to help track
down the various problems.

> I have just checked: the issues I've described happen only in shell,
> not in eshell (in eshell everything seems to work as expected).

For ssh, eshell actually overwrites pcomplete/ssh with an alias for
pcomplete/rsh so it doesn't use the same code (I suspect that using
eshell and then doing M-x shell will similarly "work as expected").


        Stefan