feat: add an embryo actor (filecoin-project#667)

The embryo actor:

- Has no constructor (the system is expected to simply "set" the embryo
  code CID, not construct it).
- Immediately aborts when called with a non-zero method.

We could, alternatively, use some well-known "id" address. But it's nice
to make this actual valid wasm.

Author: Stebalien

actors/embryo/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "fil_actor_embryo"
+description = "Builtin embryo actor for Filecoin"
+version = "10.0.0-alpha.1"
+license = "MIT OR Apache-2.0"
+authors = ["Protocol Labs", "Filecoin Core Devs"]
+edition = "2021"
+keywords = ["filecoin", "web3", "wasm"]
+
+[lib]
+## lib is necessary for integration tests
+## cdylib is necessary for Wasm build
+crate-type = ["cdylib", "lib"]
+
+[dependencies]
+fvm_sdk = { version = "3.0.0-alpha.2", optional = true }
+fvm_shared = { version = "3.0.0-alpha.1", optional = true }
+
+[features]
+fil-actor = ["fvm_sdk", "fvm_shared"]

actors/embryo/src/lib.rs

@@ -0,0 +1,8 @@
+#[cfg(feature = "fil-actor")]
+#[no_mangle]
+pub extern "C" fn invoke(_: u32) -> u32 {
+    fvm_sdk::vm::abort(
+        fvm_shared::error::ExitCode::USR_UNHANDLED_MESSAGE.value(),
+        Some("embryo actors may only receive messages on method 0"),
+    )
+}

runtime/src/test_utils.rs

@@ -96,6 +96,8 @@ lazy_static::lazy_static! {
         map.insert(*PAYCH_ACTOR_CODE_ID, ());
         map.insert(*MULTISIG_ACTOR_CODE_ID, ());
         map.insert(*MINER_ACTOR_CODE_ID, ());
+        map.insert(*EMBRYO_ACTOR_CODE_ID, ());
+        map.insert(*EVM_ACTOR_CODE_ID, ());
         map
     };
 }