content/msglist: Fix vertical position of horizontal scrollbar in codeblock

[chrisbobbe]

In the issue, Greg said:

#736 (comment)

Wrapping in a SliverSafeArea would mean that the actual list stays out of the bottom inset area, right? That doesn't seem like the desired behavior — I think it's expected that the messages scroll visibly through that bottom area.

But that's not what I'm seeing. There is a visible change: the blank space that you can scroll into view, under the messages, is now taller by the height of the bottom inset. (Before, the height was just 36px hard-coded.) But you can still scroll this blank space out of view, and when you do, the messages scroll visibly through that bottom area.

Before	After

GIF from after:

Fixes: #736

[chrisbobbe]

Ah and of course screenshots of the bugfix itself:

Before	After

[gnprice]

I see. I guess it makes sense that that's what happens once I think about it again, and particularly after looking at the implementation of SliverSafeArea — it turns out to be quite simple, just a SliverPadding and a MediaQuery.removePadding:

  Widget build(BuildContext context) {
    assert(debugCheckHasMediaQuery(context));
    final EdgeInsets padding = MediaQuery.paddingOf(context);
    return SliverPadding(
      padding: EdgeInsets.only(
        left: math.max(left ? padding.left : 0.0, minimum.left),
        top: math.max(top ? padding.top : 0.0, minimum.top),
        right: math.max(right ? padding.right : 0.0, minimum.right),
        bottom: math.max(bottom ? padding.bottom : 0.0, minimum.bottom),
      ),
      sliver: MediaQuery.removePadding(
        context: context,
        removeLeft: left,
        removeTop: top,
        removeRight: right,
        removeBottom: bottom,
        child: sliver,
      ),
    );
  }

Seems fine; merging. Thanks for the fix!

I don't love the extra space this causes below the mark-read button, but I think that's mostly that I don't love that extra space in general; this can reasonably be seen as just bringing the combined-feed narrow in line with the others in showing that extra space.