This had two unexpected consequences, one unfortunate, one "medium":
* All `salsa::Database` must be `'static`. This falls out from
`Q::DynDb` not having access to any lifetimes, but also the defaulting
rules for `dyn QueryGroup` that make it `dyn QueryGroup + 'static`. We
don't really support generic databases anyway yet so this isn't a big
deal, and we can add workarounds later (ideally via GATs).
* It is now statically impossible to invoke `snapshot` from a query,
and so we don't need to test that it panics. This is because the
signature of `snapshot` returns a `Snapshot<Self>` and that is not
accessible to a `dyn QueryGroup` type. Similarly, invoking
`Runtime::snapshot` directly is not possible becaues it is
crate-private. So I removed the test. This seems ok, but eventually I
would like to expose ways for queries to do parallel
execution (matklad and I had talked about a "speculation" primitive
for enabling that).
* This commit is 99% boilerplate I did with search-and-replace. I also
rolled in a few other changes I might have preferred to factor out,
most notably removing the `GetQueryTable` plumbing trait in favor of
free-methods, but it was awkward to factor them out and get all the
generics right (so much simpler in this version).
We now track the last revision in which constants were modified. When
we see a constant query result, we record the current revision as
well. Then later we can check if the result is "still" constant. This
lets us cut out a lot of intermediate work.
Switch to a procedural implementation of the `query_group!` macro,
residing in the `components/salsa_macros` subcrate.
Allow the user to override the invoked function via `salsa::invoke(...)`
and the name of the generated query type via `salsa::query_type(...)`.
In all tests, replace the `salsa::query_group! { ... }` invocations with
the new attribute-style `#[salsa::query_group]` macro, and change them
to the new naming scheme for query types (`...Query`).
Update README, examples, and documentation.
