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Phoebe Goldman
dcd8640543
# Description of Changes
This commit adds a macro attribute `#[procedure]` which applies to
functions, and various in-WASM machinery for defining, calling and
running procedures.
A simple example of a procedure, included in `modules/module-test`:
```rust
fn sleep_one_second(ctx: &mut ProcedureContext) {
let prev_time = ctx.timestamp;
let target = prev_time + Duration::from_secs(1);
ctx.sleep_until(target);
let new_time = ctx.timestamp;
let actual_delta = new_time.duration_since(prev_time).unwrap();
log::info!("Slept from {prev_time} to {new_time}, a total of {actual_delta:?}");
}
```
We intend eventually to make procedures be `async` functions (with the
trivial `now_or_never` executor from `future-util`), but I found that
making the types work for this was giving me a lot of trouble, and
decided to put it off in the interest of unblocking more parallelizable
work.
Host-side infrastructure for executing procedures is not included in
this commit. I have a prototype working, but cleaning it up for review
and merge will come a bit later.
One item of complexity in this PR is enabling scheduled tables to
specify either reducers or procedures, while still providing
compile-time diagnostics for ill-typed scheduled functions (as opposed
to publish-time). I had to rewrite the previous
`schedule_reducer_typecheck` into a more complex `schedule_typecheck`
with a trait `ExportFunctionForScheduledTable`, which takes a "tacit
trait parameter" encoding reducer-ness or procedure-ness, as described
in https://willcrichton.net/notes/defeating-coherence-rust/ .
The trait name `ExportFunctionForScheduledTable` is user-facing in the
sense that it will appear in compiler diagnostics in ill-typed modules.
As such, I am open to bikeshedding.
# API and ABI breaking changes
Adds a new user-facing API, which we intend to change before releasing.
# Expected complexity level and risk
2? Mostly pretty mechanical changes to macros and bindings.
# Testing
- [x] Added a procedure definition to `module-test`, saw that it
typechecks.
- [x] Executed same procedure definition using #3390 , the prototype
implementation this PR draws from.