implement fuzzing for component types (#4537)

This addresses #4307.

For the static API we generate 100 arbitrary test cases at build time, each of
which includes 0-5 parameter types, a result type, and a WAT fragment containing
an imported function and an exported function.  The exported function calls the
imported function, which is implemented by the host.  At runtime, the fuzz test
selects a test case at random and feeds it zero or more sets of arbitrary
parameters and results, checking that values which flow host-to-guest and
guest-to-host make the transition unchanged.

The fuzz test for the dynamic API follows a similar pattern, the only difference
being that test cases are generated at runtime.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

crates/misc/component-test-util/src/lib.rs

@@ -0,0 +1,112 @@
+use anyhow::Result;
+use arbitrary::Arbitrary;
+use std::mem::MaybeUninit;
+use wasmtime::component::__internal::{
+    ComponentTypes, InterfaceType, Memory, MemoryMut, Options, StoreOpaque,
+};
+use wasmtime::component::{ComponentParams, ComponentType, Func, Lift, Lower, TypedFunc, Val};
+use wasmtime::{AsContextMut, Config, Engine, StoreContextMut};
+
+pub trait TypedFuncExt<P, R> {
+    fn call_and_post_return(&self, store: impl AsContextMut, params: P) -> Result<R>;
+}
+
+impl<P, R> TypedFuncExt<P, R> for TypedFunc<P, R>
+where
+    P: ComponentParams + Lower,
+    R: Lift,
+{
+    fn call_and_post_return(&self, mut store: impl AsContextMut, params: P) -> Result<R> {
+        let result = self.call(&mut store, params)?;
+        self.post_return(&mut store)?;
+        Ok(result)
+    }
+}
+
+pub trait FuncExt {
+    fn call_and_post_return(&self, store: impl AsContextMut, args: &[Val]) -> Result<Val>;
+}
+
+impl FuncExt for Func {
+    fn call_and_post_return(&self, mut store: impl AsContextMut, args: &[Val]) -> Result<Val> {
+        let result = self.call(&mut store, args)?;
+        self.post_return(&mut store)?;
+        Ok(result)
+    }
+}
+
+pub fn engine() -> Engine {
+    drop(env_logger::try_init());
+
+    let mut config = Config::new();
+    config.wasm_component_model(true);
+
+    // When `WASMTIME_TEST_NO_HOG_MEMORY` is set it means we're in qemu. The
+    // component model tests create a disproportionate number of instances so
+    // try to cut down on virtual memory usage by avoiding 4G reservations.
+    if std::env::var("WASMTIME_TEST_NO_HOG_MEMORY").is_ok() {
+        config.static_memory_maximum_size(0);
+        config.dynamic_memory_guard_size(0);
+    }
+    Engine::new(&config).unwrap()
+}
+
+/// Newtype wrapper for `f32` whose `PartialEq` impl considers NaNs equal to each other.
+#[derive(Copy, Clone, Debug, Arbitrary)]
+pub struct Float32(pub f32);
+
+/// Newtype wrapper for `f64` whose `PartialEq` impl considers NaNs equal to each other.
+#[derive(Copy, Clone, Debug, Arbitrary)]
+pub struct Float64(pub f64);
+
+macro_rules! forward_impls {
+    ($($a:ty => $b:ty,)*) => ($(
+        unsafe impl ComponentType for $a {
+            type Lower = <$b as ComponentType>::Lower;
+
+            const SIZE32: usize = <$b as ComponentType>::SIZE32;
+            const ALIGN32: u32 = <$b as ComponentType>::ALIGN32;
+
+            #[inline]
+            fn typecheck(ty: &InterfaceType, types: &ComponentTypes) -> Result<()> {
+                <$b as ComponentType>::typecheck(ty, types)
+            }
+        }
+
+        unsafe impl Lower for $a {
+            fn lower<U>(
+                &self,
+                store: &mut StoreContextMut<U>,
+                options: &Options,
+                dst: &mut MaybeUninit<Self::Lower>,
+            ) -> Result<()> {
+                <$b as Lower>::lower(&self.0, store, options, dst)
+            }
+
+            fn store<U>(&self, memory: &mut MemoryMut<'_, U>, offset: usize) -> Result<()> {
+                <$b as Lower>::store(&self.0, memory, offset)
+            }
+        }
+
+        unsafe impl Lift for $a {
+            fn lift(store: &StoreOpaque, options: &Options, src: &Self::Lower) -> Result<Self> {
+                Ok(Self(<$b as Lift>::lift(store, options, src)?))
+            }
+
+            fn load(memory: &Memory<'_>, bytes: &[u8]) -> Result<Self> {
+                Ok(Self(<$b as Lift>::load(memory, bytes)?))
+            }
+        }
+
+        impl PartialEq for $a {
+            fn eq(&self, other: &Self) -> bool {
+                self.0 == other.0 || (self.0.is_nan() && other.0.is_nan())
+            }
+        }
+    )*)
+}
+
+forward_impls! {
+    Float32 => f32,
+    Float64 => f64,
+}