bug#55588: pgtk: child-frame-border-width cannot be set to nil

[Florian Rommel <mail@florommel.de>]

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In pgtk, child-frame-border-width is set to 0 by default, and it cannot
be set to nil.
According to the manual it should be possible for child-frame-border-
width to be nil. In such cases, the value of internal-border-width is
used as the border width (see 30.4.3.4 "Layout Parameters"; and
function FRAME_INTERNAL_BORDER_WIDTH in frame.h).

The problem causes missing child-frame borders for code that depends on
this behavior (e.g., lsp-doc-ui in the lsp-ui package), and it will
cause errors for code that tries to set child-frame-border-width to
nil.

The attached patch fixes this. It essentially replicates the respective
behavior of xfns.c.


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From 05479840c12174baa8b1de61c80156ee7d56dd38 Mon Sep 17 00:00:00 2001
From: Florian Rommel <mail@florommel.de>
Date: Sun, 22 May 2022 23:30:52 +0200
Subject: [PATCH] pgtk: Allow child-frame-border-width to be nil

* src/pgtkfns.c (pgtk_set_child_frame_border_width, x-create-frame):
Allow child-frame-border-width to be set to nil, and set its default
value to nil.

Copyright-paperwork-exempt: yes
---
 src/pgtkfns.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/pgtkfns.c b/src/pgtkfns.c
index 1feb3fe250..0764e4a2d5 100644
--- a/src/pgtkfns.c
+++ b/src/pgtkfns.c
@@ -566,7 +566,14 @@ pgtk_set_tool_bar_lines (struct frame *f, Lisp_Object value, Lisp_Object oldval)
 static void
 pgtk_set_child_frame_border_width (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
 {
-  int border = check_int_nonnegative (arg);
+  int border;
+
+  if (NILP (arg))
+    border = -1;
+  else if (RANGED_FIXNUMP (0, arg, INT_MAX))
+    border = XFIXNAT (arg);
+  else
+    signal_error ("Invalid child frame border width", arg);
 
   if (border != FRAME_CHILD_FRAME_BORDER_WIDTH (f))
     {
@@ -1429,8 +1436,7 @@ This function is an internal primitive--use `make-frame' instead.  */ )
 
     }
 
-  gui_default_parameter (f, parms, Qchild_frame_border_width,
-			 make_fixnum (0),
+  gui_default_parameter (f, parms, Qchild_frame_border_width, Qnil,
 			 "childFrameBorderWidth", "childFrameBorderWidth",
 			 RES_TYPE_NUMBER);
   gui_default_parameter (f, parms, Qright_divider_width, make_fixnum (0),
-- 
2.36.1