bug#67112: 30.0.50; [PATCH] Fix completion annotations when using 'pcomplete-here-using-help'

[Jim Porter <jporterbugs@gmail.com>]

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

Starting from "emacs -Q -f shell" (or eshell, doesn't matter) on a 
GNU/Linux system, type "cp -" and then press TAB. The completions buffer 
shows a list of completions. However, they don't show the annotations, 
which in this case should be a helpful string for any option taking an 
argument.

For example, one completion is "--backup". This takes an optional 
"CONTROL" argument, which should show in the completions list. However, 
it doesn't. With the attached patch, the completions list now correctly 
shows "--backup[=CONTROL]".

This was happening because 'pcomplete-here-using-help' passes along the 
annotation as a text property on the first character of each completion 
candidate. That property failed to propagate through 
'completion-table-with-quoting' though. So the fix is to propagate text 
properties on the first character of the candidate, since that's already 
a convention in a couple places with completion tables.

(There's a larger question about whether 'pcomplete-here-using-help' is 
doing this in the right way. Maybe instead of returning a list of 
candidates with text properties for annotations and such, it should 
instead return a programmed completion table that specifies an 
'annotation-function' for the table's metadata. However, that's both a 
much more invasive change, and I think we'd still want this patch to 
help improve other parts of completion tables. For example, with this 
patch, 'completion-table-merge' could annotate which table each 
candidate is from, and then we could resolve the FIXME in that function.)

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From b4cb492ebe4c7905b83bfbcd81e6bc8385d0a760 Mon Sep 17 00:00:00 2001
From: Jim Porter <jporterbugs@gmail.com>
Date: Sat, 11 Nov 2023 13:26:44 -0800
Subject: [PATCH] Forward completion text properties when using
 'completion-table-with-quoting'

This fixes an issue with 'pcomplete-here-using-help', which passes
annotation strings along as text properties.  Previously, those got
clobbered when the completions got requoted.

* lisp/minibuffer.el (completion--twq-all): Apply text properties from
the first character of the unquoted completion to the quoted
completion.
---
 lisp/minibuffer.el | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 3e2e3b6c6f2..fc75cd9cb66 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -677,6 +677,13 @@ completion--twq-all
                                              'completions-common-part)
                                qprefix))))
                         (qcompletion (concat qprefix qnew)))
+                   ;; Some completion tables (including this one) pass
+                   ;; along necessary information as text properties
+                   ;; on the first character of the completion.  Make
+                   ;; sure the quoted completion has these properties
+                   ;; too.
+                   (add-text-properties 0 1 (text-properties-at 0 completion)
+                                        qcompletion)
                    ;; Attach unquoted completion string, which is needed
                    ;; to score the completion in `completion--flex-score'.
                    (put-text-property 0 1 'completion--unquoted
-- 
2.25.1