JsValue module conversions (#2771)

* Update `linera-wasmer` to `4.4.0-linera.6`

This version includes `JsValue` conversions for `Module` that include
type hints.

* `linera-execution`: add `JsValue` conversions for `wasm::Module`

* `linera-execution`: preserve JsValue conversions in module traits

* `linera-execution`: document `DynInto`

* `linera-base`: adopt `dyn_convert`

* `linera_base::task`: adopt `linera_execution::Post`

* `linera_execution::wasm`: fix up comments

* `linera-execution`: remove redundant TODO

We actually can't remove this `Send` and `Sync` until we can send the
`ExecutionStateRequest`s via `postMessage`, i.e. issue #2552.  That
issue is far enough divorced from this code that I don't want to link
it here, so let's just remove the TODO.

Cargo.toml

@@ -161,13 +161,14 @@ wasm-bindgen-test = "0.3.42"
 wasm-encoder = "0.24.1"
 wasm-instrument = "0.4.0"
 wasm_thread = "0.3.0"
-wasmer = { package = "linera-wasmer", version = "4.4.0-linera.5", default-features = false }
-wasmer-compiler-singlepass = { package = "linera-wasmer-compiler-singlepass", version = "4.4.0-linera.5", default-features = false, features = ["std", "unwind", "avx"] }
+wasmer = { package = "linera-wasmer", version = "4.4.0-linera.6", default-features = false }
+wasmer-compiler-singlepass = { package = "linera-wasmer-compiler-singlepass", version = "4.4.0-linera.6", default-features = false, features = ["std", "unwind", "avx"] }
 wasmparser = "0.101.1"
 wasmtime = { version = "25.0.0", default-features = false, features = ["cranelift", "runtime", "std"] }
 wasmtimer = "0.2.0"
 webassembly-test = "0.1.0"
 web-sys = "0.3.69"
+js-sys = "0.3.70"
 web-time = "1.1.0"
 wit-bindgen = "0.24.0"
 zstd = "0.13.2"

linera-base/src/dyn_convert.rs

@@ -0,0 +1,18 @@
+// Copyright (c) Zefchain Labs, Inc.
+// SPDX-License-Identifier: Apache-2.0
+
+/*!
+Object-safe conversion traits.
+*/
+
+/// An object-safe version of `std::convert::Into`.
+pub trait DynInto<To> {
+    /// Converts a boxed object into the target type.
+    fn into_box(self: Box<Self>) -> To;
+}
+
+impl<To, From: Into<To>> DynInto<To> for From {
+    fn into_box(self: Box<From>) -> To {
+        (*self).into()
+    }
+}

linera-base/src/lib.rs

@@ -16,6 +16,7 @@ pub mod abi;
 pub mod command;
 pub mod crypto;
 pub mod data_types;
+pub mod dyn_convert;
 mod graphql;
 pub mod identifiers;
 mod limited_writer;

linera-base/src/task.rs

@@ -11,6 +11,13 @@ use std::future::Future;
 mod implementation {
     use super::*;
 
+    /// Types that can be _explicitly_ sent to a new thread.
+    /// This differs from `Send` in that we can provide an explicit post step
+    /// (e.g. `postMessage` on the Web).
+    pub trait Post: Send + Sync {}
+
+    impl<T: Send + Sync> Post for T {}
+
     /// The type of errors that can result from awaiting a task to completion.
     pub type Error = tokio::task::JoinError;
     /// The type of a future awaiting another task.
@@ -36,8 +43,18 @@ mod implementation {
 #[cfg(web)]
 mod implementation {
     use futures::channel::oneshot;
+    use wasm_bindgen_futures::wasm_bindgen::JsValue;
 
     use super::*;
+    use crate::dyn_convert;
+
+    /// Types that can be _explicitly_ sent to a new thread.
+    /// This differs from `Send` in that we can provide an explicit post step
+    /// (e.g. `postMessage` on the Web).
+    // TODO(#2809): this trait is overly liberal.
+    pub trait Post: dyn_convert::DynInto<JsValue> {}
+
+    impl<T: dyn_convert::DynInto<JsValue>> Post for T {}
 
     /// The type of errors that can result from awaiting a task to completion.
     pub type Error = oneshot::Canceled;

linera-execution/Cargo.toml

@@ -18,6 +18,7 @@ metrics = ["prometheus", "linera-views/metrics"]
 unstable-oracles = []
 wasmer = [
     "dep:wasmer",
+    "wasmer/enable-serde",
     "linera-witty/wasmer",
     "wasm-encoder",
     "wasm-instrument",
@@ -29,7 +30,7 @@ wasmtime = [
     "wasm-encoder",
     "wasmparser",
 ]
-web = ["linera-base/web", "linera-views/web"]
+web = ["linera-base/web", "linera-views/web", "js-sys"]
 
 [dependencies]
 anyhow.workspace = true
@@ -43,6 +44,7 @@ dashmap.workspace = true
 derive_more = { workspace = true, features = ["display"] }
 dyn-clone.workspace = true
 futures.workspace = true
+js-sys = { workspace = true, optional = true }
 linera-base.workspace = true
 linera-views.workspace = true
 linera-views-derive.workspace = true