I don't actually think it was correct to allow the future to borrow a mutable app reference. I went back to passing a wrapper around the refcell to async tests. They'll be a bit more annoying to write but also totally safe.
Previously, when splicing an edit that deleted all transforms, we would
leave the `FoldMap` empty, thus violating a bunch of downstream
invariants and e.g. causing the `BufferRows` iterator to not return any
buffer row.
This commit ensures we always have at least one transform (an isomorphic
one, specifically) and adds additional test coverage for the
`FoldMap::buffer_rows` method by adding it to the randomized tests.
Nathan SoboandMax Brunsfeld
Nathan Sobo
Antonio Scandurra