Previously, we would use `Project::serialize_buffer_for_peer` and
`Project::deserialize_buffer` respectively in the host and in the
guest to create a new buffer or just send its ID if the host thought
the buffer had already been sent.
These methods would be called as part of other methods, such as
`Project::open_buffer_by_id` or `Project::open_buffer_for_symbol`.
However, if any of the tasks driving the futures that eventually
called `Project::deserialize_buffer` were dropped after the host
responded with the buffer state but (crucially) before the guest
deserialized it and registered it, there could be a situation where
the host thought the guest had the buffer (thus sending them just the
buffer id) and the guest would wait indefinitely.
Given how crucial this interaction is, this commit switches to creating
remote buffers for peers out of band. The host will push buffers to guests,
who will always refer to buffers via IDs and wait for the host to send them,
as opposed to including the buffer's payload as part of some other operation.
As part of #1405, we changed the way we performed undo and redo to
support combining transactions that were not temporally adjacent for
IME purposes.
We introduced a bug with that release that caused divergence
when performing undo: the bug was caused by only changing the visibility
of fragments whose insertion id was contained in the undo operation. However,
an undo operation also affects deletions which we were mistakenly not
considering. Randomized tests caught this but I guess we didn't run enough
of them.
Previously, a change on a given line would cause that whole line to be
replaced. In turn, this caused anchors on that line to go to the start
of that line because they would lie inside of a deleted region after applying
the diff.
By switching to a character-wise diff, we perform smaller edits to the buffer
which stabilizes anchor positions.
Now, instead of using these versioned offset ranges, we locate the
fragments associated with a transaction using the transaction's
edit ids. To make this possible, buffers now store a new map called
`insertion_slices`, which lets you look up the ranges of insertions
that were affected by a given edit.
Co-authored-by: Antonio Scandurra <antonio@zed.dev>
