bug#7779: Miserable widget completion for type 'directory on w32

[Mauro Aranda <maurooaranda@gmail.com>]

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I can reproduce the bug in the latest master.  On a Windows machine,
and starting with emacs -Q, I do:
M-x customize-option RET tutorial-directory
and try to complete with C-M-i inside the editable-field, with different
names,
and different cases.
It doesn't work, because the completion is made case sensitive, even though
read-file-name-completion-ignore-case is t.

Also, the completion is made not only for directory names,
but also for file names.  This also happens on a GNU/Linux machine.

Since the 'file widget suffers from the first mentioned bug as well,
the attached patch tries to improve the completion for both of these
widgets.

Best regards,
Mauro.

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From 24be0bc9760e16af80747b4bc06fd953e050be4f Mon Sep 17 00:00:00 2001
From: Mauro Aranda <maurooaranda@gmail.com>
Date: Wed, 28 Aug 2019 08:29:57 -0300
Subject: [PATCH] Improve file name completion in file and directory widgets
 (Bug#7779)

* lisp/wid-edit.el (widget 'file, widget 'directory): Respect the option
read-file-name-completion-ignore-case.
(widget 'directory): Filter the file names, to only perform directory name
completion.
---
 lisp/wid-edit.el | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/lisp/wid-edit.el b/lisp/wid-edit.el
index 1ddc461..ad65ca6 100644
--- a/lisp/wid-edit.el
+++ b/lisp/wid-edit.el
@@ -3083,7 +3083,9 @@ widget-regexp-validate
 (define-widget 'file 'string
   "A file widget.
 It reads a file name from an editable text field."
-  :completions #'completion-file-name-table
+  :completions (completion-table-case-fold
+                #'completion-file-name-table
+                (not read-file-name-completion-ignore-case))
   :prompt-value 'widget-file-prompt-value
   :format "%{%t%}: %v"
   ;; Doesn't work well with terminating newline.
@@ -3118,6 +3120,11 @@ widget-file-prompt-value
 (define-widget 'directory 'file
   "A directory widget.
 It reads a directory name from an editable text field."
+  :completions (apply-partially #'completion-table-with-predicate
+                                (completion-table-case-fold
+                                 #'completion-file-name-table
+                                 (not read-file-name-completion-ignore-case))
+                                #'directory-name-p 'strict)
   :tag "Directory")
 
 (defvar widget-symbol-prompt-value-history nil
-- 
2.7.4