From c9dc273cb0a1bb513e214d5c24776ecff766c8b7 Mon Sep 17 00:00:00 2001
From: Bruno Windels <brunow@matrix.org>
Date: Tue, 6 Nov 2018 10:20:04 +0100
Subject: [PATCH] better native scrollbar width compensation for FF

instead of having to offset the padding of children of the
autohiding scrollbar container, which gets fiddly quickly,
add a new child to the scrollbar container that gets a negative
margin of the scrollbar width when needed
(on hover and overflowing when overlay is not supported).

This needs an extra DOM element, but as it doesn't do anything weird
layout-wise (like set position), it shouldn't affect styling at all.

It also makes the auto hide scrollbar workarounds completely transparent
to the rest of the code.
---
 res/css/structures/_AutoHideScrollbar.scss    | 22 +++++++++----------
 res/css/structures/_RoomSubList.scss          | 13 ++---------
 res/css/views/rooms/_RoomTile.scss            |  2 +-
 .../structures/AutoHideScrollbar.js           |  4 +++-
 4 files changed, 16 insertions(+), 25 deletions(-)

diff --git a/res/css/structures/_AutoHideScrollbar.scss b/res/css/structures/_AutoHideScrollbar.scss
index 0b8558a61e..70dbbe8d07 100644
--- a/res/css/structures/_AutoHideScrollbar.scss
+++ b/res/css/structures/_AutoHideScrollbar.scss
@@ -18,6 +18,7 @@ limitations under the License.
 1. for browsers that support native overlay auto-hiding scrollbars
 */
 .mx_AutoHideScrollbar {
+    overflow-x: hidden;
     overflow-y: auto;
     -ms-overflow-style: -ms-autohiding-scrollbar;
 }
@@ -34,23 +35,20 @@ body.mx_scrollbar_overlay_noautohide .mx_AutoHideScrollbar:hover {
 }
 /*
 3. as a last fallback, compensate for the scrollbar taking up space in the layout
-by playing with the paddings. the default below will add a right padding
-of the scrollbar width and clear that on hover.
-this won't work well on classes that also need to set their padding,
-so this needs to be overriden and adjust the padding with calc like so:
-```
-body.mx_scrollbar_nooverlay .componentClass.mx_AutoHideScrollbar_overflow:hover {
-    padding-right: calc(15px - var(--scrollbar-width)) !important;
-}
-```
+by having giving the child element (.mx_AutoHideScrollbar_offset) a
+negative right margin of the width of the scrollbar when the container
+is overflowing. This is what Firefox ends up using. Overflow is detected
+in javascript, and adds the mx_AutoHideScrollbar_overflow class to the container.
+This only works in Firefox, which should be fine as this fallback is only needed there.
 */
 body.mx_scrollbar_nooverlay .mx_AutoHideScrollbar {
-    box-sizing: border-box;
     overflow-y: hidden;
-    padding-right: var(--scrollbar-width);
 }
 
 body.mx_scrollbar_nooverlay .mx_AutoHideScrollbar:hover {
     overflow-y: auto;
-    padding-right: 0;
+}
+
+body.mx_scrollbar_nooverlay .mx_AutoHideScrollbar:hover.mx_AutoHideScrollbar_overflow > .mx_AutoHideScrollbar_offset {
+    margin-right: calc(-1 * var(--scrollbar-width));
 }
diff --git a/res/css/structures/_RoomSubList.scss b/res/css/structures/_RoomSubList.scss
index 2b83e4ee03..1a92a792d6 100644
--- a/res/css/structures/_RoomSubList.scss
+++ b/res/css/structures/_RoomSubList.scss
@@ -118,22 +118,13 @@ limitations under the License.
 .mx_RoomSubList_scroll {
     /* let rooms list grab all available space */
     flex: 0 1 auto;
-    padding: 0 15px !important;
-    overflow-x: hidden;
-}
-/*
-for browsers that don't support overlay scrollbars,
-subtract scrollbar width from right padding on hover when overflowing
-so the content doesn't jump when showing the scrollbars
-*/
-body.mx_scrollbar_nooverlay .mx_RoomSubList_scroll.mx_AutoHideScrollbar_overflow:hover {
-    padding-right: calc(15px - var(--scrollbar-width)) !important;
+    padding: 0 8px;
 }
 
 .collapsed {
 
     .mx_RoomSubList_scroll {
-        padding: 0px !important;
+        padding: 0;
     }
     .mx_RoomSubList_label {
         height: 17px;
diff --git a/res/css/views/rooms/_RoomTile.scss b/res/css/views/rooms/_RoomTile.scss
index f13e0ea2fd..1ea62b8ca8 100644
--- a/res/css/views/rooms/_RoomTile.scss
+++ b/res/css/views/rooms/_RoomTile.scss
@@ -36,7 +36,7 @@ limitations under the License.
 }
 
 // toggle menuButton and badge on hover/menu displayed
-.mx_RoomTile:hover, .mx_RoomTile_menuDisplayed {
+.mx_LeftPanel_container:not(.collapsed) .mx_RoomTile:hover, .mx_RoomTile_menuDisplayed {
     .mx_RoomTile_menuButton {
         display: block;
     }
diff --git a/src/components/structures/AutoHideScrollbar.js b/src/components/structures/AutoHideScrollbar.js
index 507af2c5f0..a462b2bf14 100644
--- a/src/components/structures/AutoHideScrollbar.js
+++ b/src/components/structures/AutoHideScrollbar.js
@@ -112,7 +112,9 @@ export default class AutoHideScrollbar extends React.Component {
                     ref={this._collectContainerRef}
                     className={["mx_AutoHideScrollbar", this.props.className].join(" ")}
                 >
-            { this.props.children }
+            <div className="mx_AutoHideScrollbar_offset">
+                { this.props.children }
+            </div>
         </div>);
     }
 }