feat(ops): fast calls for Wasm (#16776)

This PR introduces Wasm ops. These calls are optimized for entry from
Wasm land.

The `#[op(wasm)]` attribute is opt-in. 

Last parameter `Option<&mut [u8]>` is the memory slice of the Wasm
module *when entered from a Fast API call*. Otherwise, the user is
expected to implement logic to obtain the memory if `None`

```rust
#[op(wasm)]
pub fn op_args_get(
  offset: i32,
  buffer_offset: i32,
  memory: Option<&mut [u8]>,
) {
  // ...
}
```

1 files changed, 67 insertions, 0 deletions

diff --git a/core/examples/wasm.rs b/core/examples/wasm.rs
new file mode 100644
index 000000000..ef68d8aa4
--- /dev/null
+++ b/core/examples/wasm.rs
@@ -0,0 +1,67 @@
+// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
+
+use deno_core::op;
+use deno_core::Extension;
+use deno_core::JsRuntime;
+use deno_core::RuntimeOptions;
+use std::mem::transmute;
+use std::ptr::NonNull;
+
+// This is a hack to make the `#[op]` macro work with
+// deno_core examples.
+// You can remove this:
+
+use deno_core::*;
+
+struct WasmMemory(NonNull<v8::WasmMemoryObject>);
+
+fn wasm_memory_unchecked(state: &mut OpState) -> &mut [u8] {
+  let WasmMemory(global) = state.borrow::<WasmMemory>();
+  // SAFETY: `v8::Local` is always non-null pointer; the `HandleScope` is
+  // already on the stack, but we don't have access to it.
+  let memory_object = unsafe {
+    transmute::<NonNull<v8::WasmMemoryObject>, v8::Local<v8::WasmMemoryObject>>(
+      *global,
+    )
+  };
+  let backing_store = memory_object.buffer().get_backing_store();
+  let ptr = backing_store.data().unwrap().as_ptr() as *mut u8;
+  let len = backing_store.byte_length();
+  // SAFETY: `ptr` is a valid pointer to `len` bytes.
+  unsafe { std::slice::from_raw_parts_mut(ptr, len) }
+}
+
+#[op(wasm)]
+fn op_wasm(state: &mut OpState, memory: Option<&mut [u8]>) {
+  let memory = memory.unwrap_or_else(|| wasm_memory_unchecked(state));
+  memory[0] = 69;
+}
+
+#[op(v8)]
+fn op_set_wasm_mem(
+  scope: &mut v8::HandleScope,
+  state: &mut OpState,
+  memory: serde_v8::Value,
+) {
+  let memory =
+    v8::Local::<v8::WasmMemoryObject>::try_from(memory.v8_value).unwrap();
+  let global = v8::Global::new(scope, memory);
+  state.put(WasmMemory(global.into_raw()));
+}
+
+fn main() {
+  // Build a deno_core::Extension providing custom ops
+  let ext = Extension::builder()
+    .ops(vec![op_wasm::decl(), op_set_wasm_mem::decl()])
+    .build();
+
+  // Initialize a runtime instance
+  let mut runtime = JsRuntime::new(RuntimeOptions {
+    extensions: vec![ext],
+    ..Default::default()
+  });
+
+  runtime
+    .execute_script("<usage>", include_str!("wasm.js"))
+    .unwrap();
+}