make ScrollBar check wrapped widgets for SupportsScroll (Fixes #878)

[rsekman]

Checklist

• I've ensured that similar functionality has not already been implemented
• I've ensured that similar functionality has not earlier been proposed and declined
• I've branched off the master or python-dual-support branch
• I've merged fresh upstream into my branch recently
• I've ran tox successfully in local environment
• I've included docstrings and/or documentation and/or examples for my code (if this is a new feature)

Description:

Fixes #878 .

[coveralls]

Pull Request Test Coverage Report for Build 9075496246

Details

• 9 of 10 (90.0%) changed or added relevant lines in 1 file are covered.
• 64 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.04%) to 74.72%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
urwid/widget/scrollable.py	9	10	90.0%

Files with Coverage Reduction	New Missed Lines	%
urwid/widget/widget_decoration.py	7	80.6%
urwid/display/_raw_display_base.py	57	50.0%

Totals
Change from base Build 8873706490:	0.04%
Covered Lines:	9401
Relevant Lines:	12728

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💛 - Coveralls

[wardi]

http://urwid.org/reference/widget.html#urwid.WidgetDecoration.base_widget exists to get the "most" .original_widget

[wardi]

Or are there decorations that are scrollable?

[rsekman]

http://urwid.org/reference/widget.html#urwid.WidgetDecoration.base_widget exists to get the "most" .original_widget

Looking at the code, it is implemented like this generator was originally, i.e., vulnerable to infinite loops. So the fix in e5377cf should be applied also in widget_decoration.py, at least.

I have no idea if there are scrollable decorations; this is my first time working with the urwid code. It seems like a silly thing to implement, but if someone did they might be hit with an extremely confusing bug if we only check the base_widget.

[penguinolog]

Or are there decorations that are scrollable?

Scrollable is a decoration adding scroll support to the widgets:

urwid/urwid/widget/scrollable.py

Line 140 in ba5c1c0

class Scrollable(WidgetDecoration[WrappedWidget]):