Fix scrolling comments list

AppBarLayout mostly gets it, but we still need to uphold our own part -
expanding it back after focus returns to it

app/src/main/java/com/google/android/material/appbar/FlingBehavior.java

@@ -1,10 +1,13 @@
 package com.google.android.material.appbar;
 
+import android.annotation.SuppressLint;
 import android.content.Context;
+import android.graphics.Rect;
 import android.util.AttributeSet;
 import android.view.MotionEvent;
 import android.widget.OverScroller;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.coordinatorlayout.widget.CoordinatorLayout;
 
@@ -13,10 +16,46 @@ import java.lang.reflect.Field;
 // check this https://stackoverflow.com/questions/56849221/recyclerview-fling-causes-laggy-while-appbarlayout-is-scrolling/57997489#57997489
 public final class FlingBehavior extends AppBarLayout.Behavior {
 
+    private final Rect focusScrollRect = new Rect();
+
     public FlingBehavior(Context context, AttributeSet attrs) {
         super(context, attrs);
     }
 
+    @Override
+    public boolean onRequestChildRectangleOnScreen(@NonNull CoordinatorLayout coordinatorLayout, @NonNull AppBarLayout child, @NonNull Rect rectangle, boolean immediate) {
+        focusScrollRect.set(rectangle);
+
+        coordinatorLayout.offsetDescendantRectToMyCoords(child, focusScrollRect);
+
+        int height = coordinatorLayout.getHeight();
+
+        if (focusScrollRect.top <= 0 && focusScrollRect.bottom >= height) {
+            // the child is too big to fit inside ourselves completely, ignore request
+            return false;
+        }
+
+        int offset = getTopAndBottomOffset();
+
+        int dy;
+
+        if (focusScrollRect.bottom > height) {
+            dy =  focusScrollRect.top;
+        } else if (focusScrollRect.top < 0) {
+            // scrolling up
+            dy = -(height - focusScrollRect.bottom);
+        } else {
+            // nothing to do
+            return false;
+        }
+
+        //int newOffset = offset + dy;
+
+        int consumed = scroll(coordinatorLayout, child, dy, getMaxDragOffset(child), 0);
+
+        return consumed == dy;
+    }
+
     @Override
     public boolean onInterceptTouchEvent(CoordinatorLayout parent, AppBarLayout child, MotionEvent ev) {
         switch (ev.getActionMasked()) {

app/src/main/java/org/schabi/newpipe/fragments/list/BaseListFragment.java

@@ -34,6 +34,7 @@ import org.schabi.newpipe.util.NavigationHelper;
 import org.schabi.newpipe.util.OnClickGesture;
 import org.schabi.newpipe.util.StateSaver;
 import org.schabi.newpipe.util.StreamDialogEntry;
+import org.schabi.newpipe.views.SuperScrollLayoutManager;
 
 import java.util.List;
 import java.util.Queue;
@@ -147,7 +148,7 @@ public abstract class BaseListFragment<I, N> extends BaseStateFragment<I> implem
     }
 
     protected RecyclerView.LayoutManager getListLayoutManager() {
-        return new LinearLayoutManager(activity);
+        return new SuperScrollLayoutManager(activity);
     }
 
     protected RecyclerView.LayoutManager getGridLayoutManager() {

app/src/main/java/org/schabi/newpipe/views/SuperScrollLayoutManager.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) Eltex ltd 2019 <eltex@eltex-co.ru>
+ * SuperScrollLayoutManager.java is part of NewPipe.
+ *
+ * NewPipe is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * NewPipe is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with NewPipe.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.schabi.newpipe.views;
+
+import android.content.Context;
+import android.graphics.Rect;
+import android.view.FocusFinder;
+import android.view.View;
+
+import androidx.annotation.NonNull;
+import androidx.recyclerview.widget.LinearLayoutManager;
+import androidx.recyclerview.widget.RecyclerView;
+
+public final class SuperScrollLayoutManager extends LinearLayoutManager {
+    private final Rect handy = new Rect();
+
+    public SuperScrollLayoutManager(Context context) {
+        super(context);
+    }
+
+    @Override
+    public boolean requestChildRectangleOnScreen(@NonNull RecyclerView parent, @NonNull View child, @NonNull Rect rect, boolean immediate, boolean focusedChildVisible) {
+        if (!parent.isInTouchMode()) {
+            // only activate when in directional navigation mode (Android TV etc) — fine grained
+            // touch scrolling is better served by nested scroll system
+
+            if (!focusedChildVisible || getFocusedChild() == child) {
+                handy.set(rect);
+
+                parent.offsetDescendantRectToMyCoords(child, handy);
+
+                parent.requestRectangleOnScreen(handy, immediate);
+            }
+        }
+
+        return super.requestChildRectangleOnScreen(parent, child, rect, immediate, focusedChildVisible);
+    }
+}