This is ready for Android Rust-y components: it no longer references Mentat.
The standalone toolchains are installed into
$ANDROID_NDK_TOOLCHAIN_DIR/arch-$ANDROID_NDK_API_VERSION.
This leverages JNA to test the Android SDK on the host machine using
Robolectric, which is significantly faster and easier to debug than
the equivalent on-device instrumentation tests.
We'll still want instrumentation smoke tests, but they won't need to
cover the entire range of the Android SDK.
Locally, I witnessed very slow tests. Profiling with Visual VM
revealed a lot of time spent in `wait`.
Digging in, we were trying to be clever, with a `wait(1000)/notify`
mechanism. However, there were never multiple threads in play, so the
waiter wasn't waiting when `notify` was invoked. That means we always
timed out. I think this never worked and using bare `wait()` would
have revealed that.
Anyway, `CountDownLatch` maintains the one bit of state (was I
notified) and generalizes smoothly to when we have threads.
Being able to derive partition map from partition definitions and current
state of the world (transactions), segmented by timelines, is useful
because it lets us not worry about keeping materialized partition maps
up-to-date - since there's no need for materialized partition maps at that point.
This comes in very handy when we start moving chunks of transactions off of our mainline.
Alternative to this work would look like materializing partition maps per timeline,
growing support for incremental "backwards update" of the materialized maps, etc.
Our core partitions are defined in 'known_parts' table during bootstrap,
and what used to be 'parts' table is a generated view that operates over
transactions to figure out partition index.
'parts' is defined for the main timeline. Querying parts for other timelines
or for particular timeline+tx combinations will look similar.
Normally we want to both materialize our changes (into 'datoms')
as well as commit source transactions into 'transactions' table.
However, when moving transactions from timeline to timeline
we don't want to persist artifacts (rewind assertions), just their
materializations.
This patch expands the 'db' interface to allow for this split,
and changes transactor's functions to take a crate-private 'action'
which defines desired behaviour.
This is necessary for the timelines work ahead. When schema is being
moved off of a main timeline, we need to be able to retract it cleanly.
Retractions are only processed if the whole defining attribute set
is being retracted at once (:db/ident, :db/valueType, :db/cardinality).
