bug#28096: 25.2; c-a-p/shell/ielm: Broken directory completion for directories that contain spaces

[Basil L. Contovounesios]

Noam Postavsky <npostavs@gmail.com> writes:

> One minor question, what does the "C-a-k" mean
> in your original report?

I think Xristos meant C-a C-k.

The only thing needed to make ielm file name completion work on my
system (see signature for its details) is to add ?\s to
comint-file-name-chars, e.g.:

diff --git a/lisp/ielm.el b/lisp/ielm.el
index b4ad69e4c7..4bb6e752e8 100644
--- a/lisp/ielm.el
+++ b/lisp/ielm.el
@@ -546,6 +546,8 @@ inferior-emacs-lisp-mode
   (set (make-local-variable 'paragraph-start) comint-prompt-regexp)
   (setq comint-input-sender 'ielm-input-sender)
   (setq comint-process-echoes nil)
+  (unless (string-match-p " " comint-file-name-chars)
+    (setq comint-file-name-chars (concat " " comint-file-name-chars)))
   (set (make-local-variable 'completion-at-point-functions)
        '(comint-replace-by-expanded-history
          ielm-complete-filename elisp-completion-at-point))

As for shell, file name completion only seems to breaks down for me when
completing a relative file name argument to the cd command in
particular:

0. emacs -Q
1. M-x shell RET
2. cd /tmp/
   [shell doesn't seem to support dynamic cd arguments such as
    "$(mktemp -d)".]
3. mkdir dir\ one dir\ two RET
4. cd /tmp/dir TAB
   [Completes to "/tmp/dir\ ".]
5. TAB
   [Offers "dir\ one/" and "dir\ two/" as completion candidates.]
6. o TAB
   [Completes to "/tmp/dir\ one/".]

Replacing cd with ls (or pretty much any other string, let alone valid
command) in step 4 exhibits the same correct behaviour.  Doing so in
OP's recipe (which tries to complete relative file names), however, does
not seem to struggle in the same way as cd completion:

Steps 0-3 as before.
4. ls dir TAB
   [Completes to "dir\ ".]
5. TAB
   [Offers "dir\ one/" and "dir\ two/" as completion candidates.]
5. o TAB
   [Completes to "/tmp/dir\ one/".]

I'm not familiar with the workings of shell, but it seems like it's
trying to be smart about cd completion and falling a bit short.

-- 
Basil

In GNU Emacs 27.0.50 (build 4, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll 
bars)
 of 2018-05-27 built on thunk
Repository revision: 0f48d18fd2a30f29cc3592a835d2a2254c9b0afb
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Debian GNU/Linux buster/sid

"${SHELL}" --version
GNU bash, version 4.4.19(1)-release (x86_64-pc-linux-gnu)