Transactions with no ops in them are generally undesirable. They take up
space in the change log but do nothing else. They are not useless
though, it may occasionally be necessary to create an empty change in
order to list all the current heads of the document as dependents of the
empty change.
The current API makes no distinction between empty changes and non-empty
changes. If the user calls `Transaction::commit` a change is created
regardless of whether there are ops to commit. To provide a more useful
API modify `commit` so that if there is a no-op transaction then no
changes are created, but provide explicit methods to create an empty
change via `Transaction::empty_change`, `Automerge::empty_change` and
`Autocommit::empty_change`. Also make these APIs available in Javascript
and C.
It's tricky to modify these structs with the fields public as every
change requires scanning the codebase for references to make sure you're
not breaking any invariants. Make the fields private to ease
development.
Sometimes it is necessary to query the heads of a document at the time a
transaction started without having a mutable reference to the
transactable. Add `Transactable::base_heads` to do this.
The API of Automerge::generate_sync_message requires that the user keep
track of in flight messages themselves if they want to avoid sending
duplicate messages. To avoid this add a flag to `automerge::sync::State`
to track if there are any in flight messages and return `None` from
`generate_sync_message` if there are.
Generating patches to text objects (a la the edit-trace benchmark) was
very slow due to appending to the back of a Vec. Use the SequenceTree
(effectively a B-tree) instead so as to speed up sequence patch
generation.
The assert_doc and assert_obj macros in automerge/tests::helpers are
useful for writing tests for any application working with automerge
documents. Typically however, you only want these utilities in tests so
rather than packaging them in the main `automerge` crate move them to a
new crate (in the spirit of `tokio_test`)
The logic for `clone` which was updated to support cloning a viewed
document inadverantly left the heads of the cloned document state in
place, which meant that cloned documents could not be `change`d. Set
state.heads to undefined when cloning to allow changing them.
Sometimes you need a cheap copy of a document at a given set of heads
just so you can see what has changed. Cloning the document to do this is
quite expensive when you don't need a writable copy. Add automerge.view
to allow a cheap read only copy of a document at a given set of heads
and add an additional heads argument to clone for when you do want a
writable copy.
The cmake CI seemed to reference a few nonexistent targets for docs and
tests. Remove the doc generation step and point the test CI script at
the generated test program.
