Summary:
Fixes https://github.com/facebook/react-native/issues/13784
The section footer was only rendered with the last item of the section. However, that meant in sections where no items were rendered, no section footer would be rendered. This patch makes sure that when there are no items the section footer is rendered with the section header in addition to adding tests asserting the existance of section footers in empty lists.
One potential point of contention is whether or not a section separator (as defined by the `SectionSeparatorComponent` prop to `<SectionList>`) should be rendered in an empty list. I did not include a section separator for empty lists, but let me know if you think one should be included. See the test plan below for an image of an empty section rendered without a section separator.
I was also running into a lint error, `no-alert`, in `SectionListExample.js` around line 135 that blocked me from publishing. This error looks to be triggered when the `alert()` global function is called, so to fix the error I added an import for the `Alert` module and called the `alert()` function on that module.
To help debug the `scrollToLocation()` behavior that was modified as a part of this PR I added three buttons (can be seen in the test plan image) which scroll to arbitrary points in the list.
Reviewed By: sahrens
Differential Revision: D5084095
fbshipit-source-id: 4c98bebc1c3f1ceaa5a634fa144685d83d1072df
Caleb Meredith
Eric Vicenti