Split the ComponentValue trait into... components (#4236)

This commit splits the current `ComponentValue` trait into three
separate traits:

* `ComponentType` - contains size/align/typecheck information in
  addition to the "lower" representation.
* `Lift` - only contains `lift` and `load`
* `Lower` - only contains `lower` and `store`

When describing the original implementation of host functions to Nick he
immediately pointed out this superior solution to the traits involved
with Wasmtime's support for typed parameters/returns in exported and
imported functions. Instead of having dynamic errors at runtime for
things like "you can't lift a `String`" that's instead a static
compile-time error now.

While I was doing this split I also refactored the `ComponentParams`
trait a bit to have `ComponentType` as a supertrait instead of a subtype
which made its implementations a bit more compact. Additionally its impl
blocks were folded into the existing tuple impl blocks.

crates/wasmtime/src/component/func.rs

@@ -196,8 +196,8 @@ impl Func {
     /// ```
     pub fn typed<Params, Return, S>(&self, store: S) -> Result<TypedFunc<Params, Return>>
     where
-        Params: ComponentParams,
+        Params: ComponentParams + Lower,
-        Return: ComponentValue,
+        Return: Lift,
         S: AsContext,
     {
         self.typecheck::<Params, Return>(store.as_context().0)?;
@@ -206,16 +206,15 @@ impl Func {
 
     fn typecheck<Params, Return>(&self, store: &StoreOpaque) -> Result<()>
     where
-        Params: ComponentParams,
+        Params: ComponentParams + Lower,
-        Return: ComponentValue,
+        Return: Lift,
     {
         let data = &store[self.0];
         let ty = &data.types[data.ty];
 
-        Params::typecheck(&ty.params, &data.types, Op::Lower)
+        Params::typecheck_params(&ty.params, &data.types)
             .context("type mismatch with parameters")?;
-        Return::typecheck(&ty.result, &data.types, Op::Lift)
+        Return::typecheck(&ty.result, &data.types).context("type mismatch with result")?;
-            .context("type mismatch with result")?;
 
         Ok(())
     }

crates/wasmtime/src/component/func/host.rs

@@ -1,5 +1,5 @@
 use crate::component::func::{MAX_STACK_PARAMS, MAX_STACK_RESULTS};
-use crate::component::{ComponentParams, ComponentValue, Memory, MemoryMut, Op, Options};
+use crate::component::{ComponentParams, ComponentType, Lift, Lower, Memory, MemoryMut, Options};
 use crate::{AsContextMut, StoreContextMut, ValRaw};
 use anyhow::{bail, Context, Result};
 use std::any::Any;
@@ -46,8 +46,8 @@ impl HostFunc {
     fn new<F, P, R>(func: F, entrypoint: VMLoweringCallee) -> Arc<HostFunc>
     where
         F: Send + Sync + 'static,
-        P: ComponentParams,
+        P: ComponentParams + Lift,
-        R: ComponentValue,
+        R: Lower,
     {
         Arc::new(HostFunc {
             entrypoint,
@@ -71,12 +71,12 @@ impl HostFunc {
 
 fn typecheck<P, R>(ty: FuncTypeIndex, types: &ComponentTypes) -> Result<()>
 where
-    P: ComponentParams,
+    P: ComponentParams + Lift,
-    R: ComponentValue,
+    R: Lower,
 {
     let ty = &types[ty];
-    P::typecheck(&ty.params, types, Op::Lift).context("type mismatch with parameters")?;
+    P::typecheck_params(&ty.params, types).context("type mismatch with parameters")?;
-    R::typecheck(&ty.result, types, Op::Lower).context("type mismatch with result")?;
+    R::typecheck(&ty.result, types).context("type mismatch with result")?;
     Ok(())
 }
 
@@ -110,8 +110,8 @@ unsafe fn call_host<T, Params, Return, F>(
     closure: F,
 ) -> Result<()>
 where
-    Params: ComponentValue,
+    Params: Lift,
-    Return: ComponentValue,
+    Return: Lower,
     F: FnOnce(StoreContextMut<'_, T>, Params) -> Result<Return>,
 {
     /// Representation of arguments to this function when a return pointer is in
@@ -227,7 +227,7 @@ where
     }
 }
 
-fn validate_inbounds<T: ComponentValue>(memory: &[u8], ptr: &ValRaw) -> Result<usize> {
+fn validate_inbounds<T: ComponentType>(memory: &[u8], ptr: &ValRaw) -> Result<usize> {
     // FIXME: needs memory64 support
     let ptr = usize::try_from(ptr.get_u32())?;
     let end = match ptr.checked_add(T::size()) {
@@ -271,8 +271,8 @@ macro_rules! impl_into_component_func {
         impl<T, F, $($args,)* R> IntoComponentFunc<T, ($($args,)*), R> for F
         where
             F: Fn($($args),*) -> Result<R> + Send + Sync + 'static,
-            ($($args,)*): ComponentParams + ComponentValue,
+            ($($args,)*): ComponentParams + Lift,
-            R: ComponentValue,
+            R: Lower,
         {
             extern "C" fn entrypoint(
                 cx: *mut VMOpaqueContext,
@@ -307,8 +307,8 @@ macro_rules! impl_into_component_func {
         impl<T, F, $($args,)* R> IntoComponentFunc<T, (StoreContextMut<'_, T>, $($args,)*), R> for F
         where
             F: Fn(StoreContextMut<'_, T>, $($args),*) -> Result<R> + Send + Sync + 'static,
-            ($($args,)*): ComponentParams + ComponentValue,
+            ($($args,)*): ComponentParams + Lift,
-            R: ComponentValue,
+            R: Lower,
         {
             extern "C" fn entrypoint(
                 cx: *mut VMOpaqueContext,

crates/wasmtime/src/component/instance.rs

@@ -1,5 +1,5 @@
 use crate::component::func::HostFunc;
-use crate::component::{Component, ComponentParams, ComponentValue, Func, TypedFunc};
+use crate::component::{Component, ComponentParams, Func, Lift, Lower, TypedFunc};
 use crate::instance::OwnedImports;
 use crate::store::{StoreOpaque, Stored};
 use crate::{AsContextMut, Module, StoreContext, StoreContextMut};
@@ -86,8 +86,8 @@ impl Instance {
         name: &str,
     ) -> Result<TypedFunc<Params, Results>>
     where
-        Params: ComponentParams,
+        Params: ComponentParams + Lower,
-        Results: ComponentValue,
+        Results: Lift,
         S: AsContextMut,
     {
         let f = self

crates/wasmtime/src/component/mod.rs

@@ -11,7 +11,8 @@ mod matching;
 mod store;
 pub use self::component::Component;
 pub use self::func::{
-    ComponentParams, ComponentValue, Func, IntoComponentFunc, Op, TypedFunc, WasmList, WasmStr,
+    ComponentParams, ComponentType, Func, IntoComponentFunc, Lift, Lower, TypedFunc, WasmList,
+    WasmStr,
 };
 pub use self::instance::{Instance, InstancePre};
 pub use self::linker::Linker;

tests/all/component_model/func.rs

@@ -158,10 +158,6 @@ fn typecheck() -> Result<()> {
     assert!(thunk.typed::<(u32,), (), _>(&store).is_err());
     assert!(thunk.typed::<(), (), _>(&store).is_ok());
     assert!(take_string.typed::<(), (), _>(&store).is_err());
-    assert!(take_string.typed::<(), String, _>(&store).is_err());
-    assert!(take_string
-        .typed::<(String, String), String, _>(&store)
-        .is_err());
     assert!(take_string.typed::<(String,), (), _>(&store).is_ok());
     assert!(take_string.typed::<(&str,), (), _>(&store).is_ok());
     assert!(take_string.typed::<(&[u8],), (), _>(&store).is_err());
@@ -175,11 +171,7 @@ fn typecheck() -> Result<()> {
     assert!(ret_tuple1.typed::<(), (u32,), _>(&store).is_ok());
     assert!(ret_tuple1.typed::<(), u32, _>(&store).is_err());
     assert!(ret_string.typed::<(), (), _>(&store).is_err());
-    assert!(ret_string.typed::<(), String, _>(&store).is_err());
-    assert!(ret_string.typed::<(), &str, _>(&store).is_err());
     assert!(ret_string.typed::<(), WasmStr, _>(&store).is_ok());
-    assert!(ret_list_u8.typed::<(), &[u8], _>(&store).is_err());
-    assert!(ret_list_u8.typed::<(), Vec<u8>, _>(&store).is_err());
     assert!(ret_list_u8.typed::<(), WasmList<u16>, _>(&store).is_err());
     assert!(ret_list_u8.typed::<(), WasmList<i8>, _>(&store).is_err());
     assert!(ret_list_u8.typed::<(), WasmList<u8>, _>(&store).is_ok());