Previously, when trying to use block decorations on non-empty markers,
Atom could sometimes throw an error if such markers ended or started at
a position that was not currently rendered.
In fact, even if we already restricted the decoration query to markers
that intersected the visible row range, markers that were only partially
visible would still be considered for rendering. If, depending on the
`reversed` property, we decided to render the tail or head of the marker
in question and this was outside the viewport, Atom would throw the
aforementioned exception.
This commit addresses the above issue by explicitly ignoring block
decorations that are located on rows that are not yet rendered.
Previously, we were hiding scrollbars when their height/width was 0. On
macOS, however, users can decide to only show scrollbars while
scrolling, which causes Atom to detect scrollbars as being invisible
during measurements. As a result, we were mistakenly setting the
visibility property to `hidden` when this setting was on, thus
preventing users from seeing the scrollbar on scroll.
With this commit we are changing the dummy scrollbar components to only
become invisible when the content is not scrollable rather than when the
scrollbars have zero width or height.
As part of this, we have also renamed the
`is{Horizontal,Vertical}ScrollbarVisible` functions to
`canScroll{Horizontally,Vertically}`, to better express their intent.
This was fixed back in bac9922 and, due to the same reasons, not having
a separate layer causes the "Show scrollbars only when scrolling"
setting on macOS to not work properly.
Previously, when a marker became invalid we would delete the
corresponding block decoration from the DOM, without however removing it
from the `lineTopIndex`. Also, we had a similar issue when decorating a
marker that was already invalid: we would account for it in the index
without adding it to the DOM.
This commit addresses the above problems by ensuring that block
decorations are never added for invalid markers. At the same time, the
editor component will still keep track of changes on the marker that was
decorated, so that it can detect when its validity changes and render it
appropriately.
