bug#58921: Tab completion hangs in eshell

[Jim Porter <jporterbugs@gmail.com>]

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X-Debbugs-Cc: monnier@iro.umontreal.ca

On 10/31/2022 2:04 AM, reza via Bug reports for GNU Emacs, the Swiss 
army knife of text editors wrote:
> Open an eshell:
> 
>       M-x eshell <enter>
> 
> Type this command in the eshell
> 
>       tab --warning=no-timestamp -xf <tab>
> 
> emacs will hang and has to be killed.
> 
> This behavior does not occur when only typing
> 
>       tar -xf <tab>

I believe the attached patch fixes this. It ensures that even when 
'pcomplete/tar' encounters an option it doesn't recognize, it continues 
to make forward progress.

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From b11cfb6fc1cbb52b88425f66b4dc503b9e3cd543 Mon Sep 17 00:00:00 2001
From: Jim Porter <jporterbugs@gmail.com>
Date: Thu, 9 Feb 2023 23:27:50 -0800
Subject: [PATCH] Fix Pcompletion of "tar" when using unrecognized arguments

Previously, arguments to tar like "--warning=no-timestamp" would cause
Pcompletion to hang (bug#58921).

* lisp/pcmpl-gnu.el (pcomplete/tar): Properly handle completion of
arguments that look like "--ARG=", even if they're not recognized by
this function.  (This also lets us coalesce a lot of the different
cases into one.)
---
 lisp/pcmpl-gnu.el | 24 +++---------------------
 1 file changed, 3 insertions(+), 21 deletions(-)

diff --git a/lisp/pcmpl-gnu.el b/lisp/pcmpl-gnu.el
index 7d270ea789f..00e9af3a974 100644
--- a/lisp/pcmpl-gnu.el
+++ b/lisp/pcmpl-gnu.el
@@ -276,20 +276,12 @@ pcomplete/tar
       (cond
        ((pcomplete-match "\\`-\\'" 0)
         (pcomplete-here*))
-       ((pcomplete-match "\\`--after-date=" 0)
-        (pcomplete-here*))
-       ((pcomplete-match "\\`--backup=" 0)
-        (pcomplete-here*))
-       ((pcomplete-match "\\`--blocking-factor=" 0)
-        (pcomplete-here*))
        ((pcomplete-match "\\`--directory=\\(.*\\)" 0)
         (pcomplete-here* (pcomplete-dirs)
                          (pcomplete-match-string 1 0)))
        ((pcomplete-match "\\`--exclude-from=\\(.*\\)" 0)
         (pcomplete-here* (pcomplete-entries)
                          (pcomplete-match-string 1 0)))
-       ((pcomplete-match "\\`--exclude=" 0)
-        (pcomplete-here*))
        ((pcomplete-match "\\`--\\(extract\\|list\\)\\'" 0)
         (setq complete-within t))
        ((pcomplete-match "\\`--file=\\(.*\\)" 0)
@@ -304,36 +296,26 @@ pcomplete/tar
        ((pcomplete-match "\\`--info-script=\\(.*\\)" 0)
         (pcomplete-here* (pcomplete-entries)
                          (pcomplete-match-string 1 0)))
-       ((pcomplete-match "\\`--label=" 0)
-        (pcomplete-here*))
-       ((pcomplete-match "\\`--mode=" 0)
-        (pcomplete-here*))
        ((pcomplete-match "\\`--new-volume-script=\\(.*\\)" 0)
         (pcomplete-here* (pcomplete-entries)
                          (pcomplete-match-string 1 0)))
-       ((pcomplete-match "\\`--newer=" 0)
-        (pcomplete-here*))
        ((pcomplete-match "\\`--owner=\\(.*\\)" 0)
         (pcomplete-here* (pcmpl-unix-user-names)
                          (pcomplete-match-string 1 0)))
-       ((pcomplete-match "\\`--record-size=" 0)
-        (pcomplete-here*))
        ((pcomplete-match "\\`--rsh-command=\\(.*\\)" 0)
         (pcomplete-here* (funcall pcomplete-command-completion-function)
                          (pcomplete-match-string 1 0)))
        ((pcomplete-match "\\`--starting-file=\\(.*\\)" 0)
         (pcomplete-here* (pcomplete-entries)
                          (pcomplete-match-string 1 0)))
-       ((pcomplete-match "\\`--suffix=" 0)
-        (pcomplete-here*))
-       ((pcomplete-match "\\`--tape-length=" 0)
-        (pcomplete-here*))
        ((pcomplete-match "\\`--use-compress-program=\\(.*\\)" 0)
         (pcomplete-here* (funcall pcomplete-command-completion-function)
                          (pcomplete-match-string 1 0)))
        ((pcomplete-match "\\`--volno-file=\\(.*\\)" 0)
         (pcomplete-here* (pcomplete-entries)
-                         (pcomplete-match-string 1 0)))))
+                         (pcomplete-match-string 1 0)))
+       ((pcomplete-match "\\`--.*=" 0)
+        (pcomplete-here*))))
     (unless saw-option
       (pcomplete-here
        (mapcar #'char-to-string
-- 
2.25.1