From 3e63774e9978b4552ce0b7c21fe57bd1c9babacd Mon Sep 17 00:00:00 2001
From: Nick Fitzgerald <fitzgen@gmail.com>
Date: Tue, 7 Jul 2020 11:02:00 -0700
Subject: [PATCH] wasmtime: Add support for `Option<Func>` args and returns in
 `Func::wrap`

---
 crates/wasmtime/src/func.rs   | 59 +++++++++++++++++++++++++++++++++++
 crates/wasmtime/src/values.rs | 16 ++--------
 2 files changed, 61 insertions(+), 14 deletions(-)

diff --git a/crates/wasmtime/src/func.rs b/crates/wasmtime/src/func.rs
index 70f5023850..ea060198ac 100644
--- a/crates/wasmtime/src/func.rs
+++ b/crates/wasmtime/src/func.rs
@@ -307,6 +307,22 @@ impl Func {
         }
     }
 
+    pub(crate) unsafe fn from_caller_checked_anyfunc(
+        store: &Store,
+        anyfunc: *mut wasmtime_runtime::VMCallerCheckedAnyfunc,
+    ) -> Option<Self> {
+        let anyfunc = NonNull::new(anyfunc)?;
+        debug_assert!(
+            anyfunc.as_ref().type_index != wasmtime_runtime::VMSharedSignatureIndex::default()
+        );
+
+        let instance_handle = wasmtime_runtime::InstanceHandle::from_vmctx(anyfunc.as_ref().vmctx);
+        let export = wasmtime_runtime::ExportFunction { anyfunc };
+        let instance = store.existing_instance_handle(instance_handle);
+        let f = Func::from_wasmtime_function(export, instance);
+        Some(f)
+    }
+
     /// Creates a new `Func` from the given Rust closure.
     ///
     /// This function will create a new `Func` which, when called, will
@@ -1186,6 +1202,49 @@ unsafe impl WasmTy for Option<ExternRef> {
     }
 }
 
+unsafe impl WasmTy for Option<Func> {
+    type Abi = *mut wasmtime_runtime::VMCallerCheckedAnyfunc;
+
+    #[inline]
+    fn into_abi_for_arg<'a>(self, _store: WeakStore<'a>) -> Self::Abi {
+        if let Some(f) = self {
+            f.caller_checked_anyfunc().as_ptr()
+        } else {
+            ptr::null_mut()
+        }
+    }
+
+    #[inline]
+    unsafe fn from_abi<'a>(abi: Self::Abi, store: WeakStore<'a>) -> Self {
+        let store = Store::upgrade(store.0).unwrap();
+        Func::from_caller_checked_anyfunc(&store, abi)
+    }
+
+    fn push(dst: &mut Vec<ValType>) {
+        dst.push(ValType::FuncRef);
+    }
+
+    fn matches(mut tys: impl Iterator<Item = ValType>) -> anyhow::Result<()> {
+        let next = tys.next();
+        ensure!(
+            next == Some(ValType::FuncRef),
+            "Type mismatch, expected funcref, got {:?}",
+            next
+        );
+        Ok(())
+    }
+
+    unsafe fn load_from_args(ptr: &mut *const u128) -> Self::Abi {
+        let ret = **ptr as usize as *mut wasmtime_runtime::VMCallerCheckedAnyfunc;
+        *ptr = (*ptr).add(1);
+        ret
+    }
+
+    unsafe fn store_to_args(abi: Self::Abi, ptr: *mut u128) {
+        ptr::write(ptr, abi as usize as u128);
+    }
+}
+
 unsafe impl<T> WasmRet for T
 where
     T: WasmTy,
diff --git a/crates/wasmtime/src/values.rs b/crates/wasmtime/src/values.rs
index 053e539e53..2ec507a037 100644
--- a/crates/wasmtime/src/values.rs
+++ b/crates/wasmtime/src/values.rs
@@ -1,7 +1,7 @@
 use crate::r#ref::ExternRef;
 use crate::{Func, Store, ValType};
 use anyhow::{bail, Result};
-use std::ptr::{self, NonNull};
+use std::ptr;
 use wasmtime_runtime::{self as runtime, VMExternRef};
 
 /// Possible runtime values that a WebAssembly module can either consume or
@@ -270,17 +270,5 @@ pub(crate) unsafe fn from_checked_anyfunc(
     anyfunc: *mut wasmtime_runtime::VMCallerCheckedAnyfunc,
     store: &Store,
 ) -> Val {
-    let anyfunc = match NonNull::new(anyfunc) {
-        None => return Val::FuncRef(None),
-        Some(f) => f,
-    };
-
-    debug_assert!(
-        anyfunc.as_ref().type_index != wasmtime_runtime::VMSharedSignatureIndex::default()
-    );
-    let instance_handle = wasmtime_runtime::InstanceHandle::from_vmctx(anyfunc.as_ref().vmctx);
-    let export = wasmtime_runtime::ExportFunction { anyfunc };
-    let instance = store.existing_instance_handle(instance_handle);
-    let f = Func::from_wasmtime_function(export, instance);
-    Val::FuncRef(Some(f))
+    Val::FuncRef(Func::from_caller_checked_anyfunc(store, anyfunc))
 }