bug#59956: 29.0.60: Failure when completing arguments in Eshell after variable interpolation

[Gregory Heytings <gregory@heytings.org>]

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>
> Sounds good to me,
>

Thanks.

Augusto and Jim, can you please try the attached patch and tell us if it 
fixes the issue without introducing regressions?

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From 5bee9d8bec42ddf38bb7e8d8f2a1b36adb96a506 Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Mon, 19 Dec 2022 22:18:22 +0000
Subject: [PATCH] Handle non-string values in pcomplete

* lisp/pcomplete.el (pcomplete-arg): When
pcomplete-parse-arguments-function returns a non-string value,
return the string the user typed in, and attach the value as a
text property to that string.  Fixes bug#59956 and bug#60021.
---
 lisp/pcomplete.el | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/lisp/pcomplete.el b/lisp/pcomplete.el
index 4e3a88bbda8..b1fbd88a377 100644
--- a/lisp/pcomplete.el
+++ b/lisp/pcomplete.el
@@ -645,13 +645,26 @@ pcomplete-arg
 
 The OFFSET argument is added to/taken away from the index that will be
 used.  This is really only useful with `first' and `last', for
-accessing absolute argument positions."
-  (nth (+ (pcase index
-	   ('first 0)
-	   ('last  pcomplete-last)
-	   (_      (- pcomplete-index (or index 0))))
-	  (or offset 0))
-       pcomplete-args))
+accessing absolute argument positions.
+
+When the argument has been transformed into something that is not
+a string by `pcomplete-parse-arguments-function', the text
+representation of the argument, namely what the user actually
+typed in, is returned, and the value of the argument is stored in
+the pcomplete-arg-value text property of that string."
+  (let ((arg
+         (nth (+ (pcase index
+	           ('first 0)
+	           ('last  pcomplete-last)
+	           (_      (- pcomplete-index (or index 0))))
+	         (or offset 0))
+              pcomplete-args)))
+    (if (stringp arg)
+        arg
+      (propertize
+       (buffer-substring (pcomplete-begin index offset)
+                         (pcomplete-begin (1- (or index 0)) offset))
+       'pcomplete-arg-value arg))))
 
 (defun pcomplete-begin (&optional index offset)
   "Return the beginning position of the INDEXth argument.
-- 
2.35.1