Move the construction of HostFunc out of Config.

This commit moves the implementation for constructing a host function into
`HostFunc::new` and `HostFunc::wrap` so that `Config` has minimal
implementation for creating host functions.

crates/wasmtime/src/config.rs

@@ -1,8 +1,7 @@
 use crate::memory::MemoryCreator;
 use crate::trampoline::MemoryCreatorProxy;
-use crate::{func::HostFunc, Caller, Func, FuncType, IntoFunc, Store, Trap, Val};
+use crate::{func::HostFunc, Caller, FuncType, IntoFunc, Trap, Val};
 use anyhow::{bail, Result};
-use std::any::Any;
 use std::cmp;
 use std::collections::HashMap;
 use std::convert::TryFrom;
@@ -781,25 +780,8 @@ impl Config {
         ty: FuncType,
         func: impl Fn(Caller<'_>, &[Val], &mut [Val]) -> Result<(), Trap> + Send + Sync + 'static,
     ) {
-        let ty_clone = ty.clone();
-
-        // Create a trampoline that converts raw u128 values to `Val`
-        let func = Box::new(move |caller_vmctx, values_vec: *mut u128| {
-            // Lookup the last registered store as host functions have no associated store
-            let store = wasmtime_runtime::with_last_info(|last| {
-                last.and_then(Any::downcast_ref::<Store>)
-                    .cloned()
-                    .expect("Host function called without thread state")
-            });
-
-            Func::invoke(&store, &ty_clone, caller_vmctx, values_vec, &func)
-        });
-
-        let (instance, trampoline) = crate::trampoline::create_function(&ty, func, &self, None)
-            .expect("failed to create host function");
-
         self.host_funcs
-            .insert(module, name, HostFunc::new(ty, instance, trampoline));
+            .insert(module, name, HostFunc::new(self, ty, func));
     }
 
     /// Defines a host function for the [`Config`] from the given Rust closure.
@@ -816,9 +798,7 @@ impl Config {
         name: &str,
         func: impl IntoFunc<Params, Results> + Send + Sync,
     ) {
-        let (ty, instance, trampoline) = func.into_func(None);
-        self.host_funcs
-            .insert(module, name, HostFunc::new(ty, instance, trampoline));
+        self.host_funcs.insert(module, name, HostFunc::wrap(func));
     }
 
     pub(crate) fn get_host_func(&self, module: &str, name: &str) -> Option<&HostFunc> {

crates/wasmtime/src/func.rs

@@ -1,5 +1,5 @@
 use crate::{sig_registry::SignatureRegistry, trampoline::StoreInstanceHandle};
-use crate::{Extern, ExternRef, FuncType, Store, Trap, Val, ValType};
+use crate::{Config, Extern, ExternRef, FuncType, Store, Trap, Val, ValType};
 use anyhow::{bail, ensure, Context as _, Result};
 use smallvec::{smallvec, SmallVec};
 use std::any::Any;
@@ -25,7 +25,44 @@ pub(crate) struct HostFunc {
 }
 
 impl HostFunc {
-    pub fn new(ty: FuncType, instance: InstanceHandle, trampoline: VMTrampoline) -> Self {
+    /// Creates a new host function from a callback.
+    ///
+    /// This is analogous to [`Func::new`].
+    pub fn new(
+        config: &Config,
+        ty: FuncType,
+        func: impl Fn(Caller<'_>, &[Val], &mut [Val]) -> Result<(), Trap> + Send + Sync + 'static,
+    ) -> Self {
+        let ty_clone = ty.clone();
+
+        // Create a trampoline that converts raw u128 values to `Val`
+        let func = Box::new(move |caller_vmctx, values_vec: *mut u128| {
+            // Lookup the last registered store as host functions have no associated store
+            let store = wasmtime_runtime::with_last_info(|last| {
+                last.and_then(Any::downcast_ref::<Store>)
+                    .cloned()
+                    .expect("Host function called without thread state")
+            });
+
+            Func::invoke(&store, &ty_clone, caller_vmctx, values_vec, &func)
+        });
+
+        let (instance, trampoline) = crate::trampoline::create_function(&ty, func, config, None)
+            .expect("failed to create host function");
+
+        Self {
+            ty,
+            instance,
+            trampoline,
+        }
+    }
+
+    /// Creates a new host function from wrapping a closure.
+    ///
+    /// This is analogous to [`Func::wrap`].
+    pub fn wrap<Params, Results>(func: impl IntoFunc<Params, Results> + Send + Sync) -> Self {
+        let (ty, instance, trampoline) = func.into_func(None);
+
         Self {
             ty,
             instance,