From c05bca316875ca90c56468e70b54a355bd4ca3c6 Mon Sep 17 00:00:00 2001
From: Moonchild <moonchild@palemoon.org>
Date: Fri, 8 Jan 2021 14:15:50 +0000
Subject: Issue #1705 - Part 5: Implement scrollbar-width:none for all target
 platforms.

---
 layout/generic/nsGfxScrollFrame.cpp | 39 +++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

(limited to 'layout')

diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index 8e7b208e4..d1053da86 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -1054,6 +1054,15 @@ nsHTMLScrollFrame::Reflow(nsPresContext* aPresContext,
       reflowScrollCorner = showResizer == mHelper.mCollapsedResizer;
       mHelper.mCollapsedResizer = !showResizer;
     }
+
+    // Hide the scrollbar when the scrollbar-width is set to none.
+    // This is only needed for root element because scrollbars of non-
+    // root elements with "scrollbar-width: none" is already suppressed
+    // in ScrollFrameHelper::CreateAnonymousContent.
+    if (this->StyleUserInterface()->mScrollbarWidth == StyleScrollbarWidth::None) {
+      state.mVScrollbar = ShowScrollbar::Never;
+      state.mHScrollbar = ShowScrollbar::Never;
+    }
   }
 
   nsRect oldScrollAreaBounds = mHelper.mScrollPort;
@@ -4404,24 +4413,30 @@ ScrollFrameHelper::CreateAnonymousContent(
 
   nsIScrollableFrame *scrollable = do_QueryFrame(mOuter);
 
-  // If we're the scrollframe for the root, then we want to construct
-  // our scrollbar frames no matter what.  That way later dynamic
-  // changes to propagated overflow styles will show or hide
-  // scrollbars on the viewport without requiring frame reconstruction
-  // of the viewport (good!).
   bool canHaveHorizontal;
   bool canHaveVertical;
-  if (!mIsRoot) {
-    ScrollStyles styles = scrollable->GetScrollStyles();
-    canHaveHorizontal = styles.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN;
-    canHaveVertical = styles.mVertical != NS_STYLE_OVERFLOW_HIDDEN;
+  if (mIsRoot) {
+    // If we're the scrollframe for the root, then we want to construct
+    // our scrollbar frames no matter what. That way, later dynamic
+    // changes to propagated overflow styles will show or hide
+    // scrollbars on the viewport without requiring frame reconstruction
+    // of the viewport (which is a Good Thing(tm)!).
+    canHaveHorizontal = true;
+    canHaveVertical = true;
+  } else {
+    if (mOuter->StyleUserInterface()->mScrollbarWidth == StyleScrollbarWidth::None) {
+      // If scrollbar-width is none, don't generate scrollbars.
+      canHaveHorizontal = false;
+      canHaveVertical = false;
+    } else {
+      ScrollStyles styles = scrollable->GetScrollStyles();
+      canHaveHorizontal = styles.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN;
+      canHaveVertical = styles.mVertical != NS_STYLE_OVERFLOW_HIDDEN;
+    }
     if (!canHaveHorizontal && !canHaveVertical && !isResizable) {
       // Nothing to do.
       return NS_OK;
     }
-  } else {
-    canHaveHorizontal = true;
-    canHaveVertical = true;
   }
 
   // The anonymous <div> used by <inputs> never gets scrollbars.
-- 
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