fix: make delegation simpler by introducing a prelude module

Users can now glob-import the kernel's "prelude" module instead of, e.g.,
glob-importing the entire `kernel` and the top-level `fvm` crate.
Ideally ambassador would handle importing all of its internal types, but
it doesn't.

fvm/src/executor/default.rs

@@ -72,7 +72,7 @@ where
             };
 
         struct MachineExecRet {
-            result: crate::kernel::error::Result<InvocationResult>,
+            result: crate::kernel::Result<InvocationResult>,
             gas_used: u64,
             backtrace: Backtrace,
             exec_trace: ExecutionTrace,

fvm/src/kernel/default.rs

@@ -10,12 +10,10 @@ use fvm_ipld_blockstore::Blockstore;
 use fvm_ipld_encoding::IPLD_RAW;
 use fvm_shared::address::Payload;
 use fvm_shared::crypto::signature;
-use fvm_shared::econ::TokenAmount;
 use fvm_shared::error::ErrorNumber;
 use fvm_shared::event::{ActorEvent, Entry, Flags};
 use fvm_shared::sys::out::vm::ContextFlags;
 use fvm_shared::upgrade::UpgradeInfo;
-use fvm_shared::ActorID;
 use multihash::MultihashDigest;
 
 use super::blocks::{Block, BlockRegistry};
@@ -606,7 +604,7 @@ where
         )
     }
 
-    fn hash(&self, code: u64, data: &[u8]) -> Result<MultihashGeneric<64>> {
+    fn hash(&self, code: u64, data: &[u8]) -> Result<Multihash> {
         let hasher = SupportedHashes::try_from(code).map_err(|e| {
             if let multihash::Error::UnsupportedCode(code) = e {
                 syscall_error!(IllegalArgument; "unsupported hash code {}", code)

fvm/src/kernel/filecoin.rs

@@ -4,25 +4,30 @@ use std::collections::BTreeMap;
 use std::convert::TryInto;
 use std::panic::{self, UnwindSafe};
 
-use ambassador::Delegate;
 use filecoin_proofs_api::{self as proofs, ProverId, PublicReplicaInfo, SectorId};
 
 use fvm_ipld_encoding::bytes_32;
-use fvm_shared::econ::TokenAmount;
-use fvm_shared::piece::{zero_piece_commitment, PaddedPieceSize};
-use fvm_shared::sector::{RegisteredPoStProof, SectorInfo};
-use fvm_shared::{commcid, ActorID};
+use fvm_shared::commcid;
+use fvm_shared::consensus::ConsensusFault;
+use fvm_shared::piece::{zero_piece_commitment, PaddedPieceSize, PieceInfo};
+use fvm_shared::randomness::Randomness;
+use fvm_shared::sector::{
+    AggregateSealVerifyProofAndInfos, RegisteredPoStProof, RegisteredSealProof, ReplicaUpdateInfo,
+    SealVerifyInfo, SectorInfo, WindowPoStVerifyInfo,
+};
 use lazy_static::lazy_static;
 use rayon::iter::{
     IndexedParallelIterator, IntoParallelRefIterator, ParallelDrainRange, ParallelIterator,
 };
 
-use super::blocks::BlockRegistry;
-use super::error::Result;
-use super::*;
+use super::Result;
+use super::{ClassifyResult, Context};
 use crate::call_manager::CallManager;
 use crate::externs::Consensus;
-use crate::*;
+use crate::machine::Machine;
+use crate::{syscall_error, DefaultKernel, Kernel};
+
+use super::prelude::*;
 
 lazy_static! {
     static ref NUM_CPUS: usize = num_cpus::get();
@@ -35,7 +40,7 @@ pub trait FilecoinKernel: Kernel {
         &self,
         proof_type: RegisteredSealProof,
         pieces: &[PieceInfo],
-    ) -> Result<Cid>;
+    ) -> Result<cid::Cid>;
 
     /// Verifies a window proof of spacetime.
     fn verify_post(&self, verify_info: &WindowPoStVerifyInfo) -> Result<bool>;

fvm/src/kernel/mod.rs

@@ -1,46 +1,24 @@
 // Copyright 2021-2023 Protocol Labs
 // SPDX-License-Identifier: Apache-2.0, MIT
-pub use blocks::{Block, BlockId, BlockRegistry, BlockStat};
-use cid::Cid;
-use fvm_shared::address::Address;
-use fvm_shared::clock::ChainEpoch;
-use fvm_shared::consensus::ConsensusFault;
-use fvm_shared::crypto::signature::{
-    SignatureType, SECP_PUB_LEN, SECP_SIG_LEN, SECP_SIG_MESSAGE_HASH_SIZE,
-};
-use fvm_shared::econ::TokenAmount;
-use fvm_shared::error::ExitCode;
-use fvm_shared::piece::PieceInfo;
-use fvm_shared::randomness::{Randomness, RANDOMNESS_LENGTH};
-use fvm_shared::sector::{
-    AggregateSealVerifyProofAndInfos, RegisteredSealProof, ReplicaUpdateInfo, SealVerifyInfo,
-    WindowPoStVerifyInfo,
-};
-use fvm_shared::sys::out::network::NetworkContext;
-use fvm_shared::sys::out::vm::MessageContext;
-use fvm_shared::sys::SendFlags;
-use fvm_shared::{ActorID, MethodNum};
+use ambassador::delegatable_trait;
+use fvm_shared::event::StampedEvent;
+use wasmtime::Linker;
+
+use crate::call_manager::CallManager;
+use crate::machine::limiter::MemoryLimiter;
+use crate::machine::Machine;
+use crate::syscalls::InvocationData;
 
 mod blocks;
+mod error;
 mod hash;
 
 pub mod default;
 pub mod filecoin;
 
-pub(crate) mod error;
-
-use ambassador::delegatable_trait;
+pub use blocks::{Block, BlockId, BlockRegistry, BlockStat};
 pub use error::{ClassifyResult, Context, ExecutionError, Result, SyscallError};
-use fvm_shared::event::StampedEvent;
 pub use hash::SupportedHashes;
-use multihash::MultihashGeneric;
-use wasmtime::Linker;
-
-use crate::call_manager::CallManager;
-use crate::gas::{Gas, GasTimer, PriceList};
-use crate::machine::limiter::MemoryLimiter;
-use crate::machine::Machine;
-use crate::syscalls::InvocationData;
 
 pub struct CallResult {
     pub block_id: BlockId,
@@ -280,7 +258,7 @@ pub trait CryptoOps {
     /// `digest_out`, returning the size of the digest written to `digest_out`. If `digest_out` is
     /// to small to fit the entire digest, it will be truncated. If too large, the leftover space
     /// will not be overwritten.
-    fn hash(&self, code: u64, data: &[u8]) -> Result<MultihashGeneric<64>>;
+    fn hash(&self, code: u64, data: &[u8]) -> Result<Multihash>;
 }
 
 /// Randomness queries.
@@ -338,3 +316,48 @@ pub trait EventOps {
         raw_val: &[u8],
     ) -> Result<()>;
 }
+
+// Unfortunately, I need to do this to make it possible to name these macros by path. I'm hiding
+// this because I really don't want users to glob import the `kernel` module.
+#[doc(hidden)]
+pub use {
+    ambassador_impl_CryptoOps, ambassador_impl_DebugOps, ambassador_impl_EventOps,
+    ambassador_impl_GasOps, ambassador_impl_IpldBlockOps, ambassador_impl_LimiterOps,
+    ambassador_impl_MessageOps, ambassador_impl_NetworkOps, ambassador_impl_RandomnessOps,
+    ambassador_impl_SelfOps,
+};
+
+/// Import this module (with a glob) if you're implementing a kernel, _especially_ if you want to
+/// use ambassador to delegate the implementation.
+pub mod prelude {
+    pub use super::{
+        ActorOps, CryptoOps, DebugOps, EventOps, GasOps, IpldBlockOps, LimiterOps, MessageOps,
+        NetworkOps, RandomnessOps, SelfOps,
+    };
+    pub use super::{Block, BlockId, BlockRegistry, BlockStat, CallResult, Kernel, SyscallHandler};
+    pub use crate::gas::{Gas, GasTimer, PriceList};
+    pub use ambassador::Delegate;
+    pub use cid::Cid;
+    pub use fvm_shared::address::Address;
+    pub use fvm_shared::clock::ChainEpoch;
+    pub use fvm_shared::crypto::signature::{
+        SignatureType, SECP_PUB_LEN, SECP_SIG_LEN, SECP_SIG_MESSAGE_HASH_SIZE,
+    };
+    pub use fvm_shared::econ::TokenAmount;
+    pub use fvm_shared::error::ExitCode;
+    pub use fvm_shared::randomness::RANDOMNESS_LENGTH;
+    pub use fvm_shared::sys::out::network::NetworkContext;
+    pub use fvm_shared::sys::out::vm::MessageContext;
+    pub use fvm_shared::sys::SendFlags;
+    pub use fvm_shared::version::NetworkVersion;
+    pub use fvm_shared::{ActorID, MethodNum};
+    pub use multihash::Multihash;
+    pub use {
+        ambassador_impl_ActorOps, ambassador_impl_CryptoOps, ambassador_impl_DebugOps,
+        ambassador_impl_EventOps, ambassador_impl_GasOps, ambassador_impl_IpldBlockOps,
+        ambassador_impl_LimiterOps, ambassador_impl_MessageOps, ambassador_impl_NetworkOps,
+        ambassador_impl_RandomnessOps, ambassador_impl_SelfOps,
+    };
+}
+
+pub use prelude::*;

testing/conformance/Cargo.toml

@@ -37,7 +37,6 @@ ittapi-rs = { version = "0.3.0", optional = true }
 libipld-core = { version = "0.16.0", features = ["serde-codec"] }
 tar = { version = "0.4.38", default-features = false }
 zstd = { version = "0.12.3", default-features = false }
-ambassador = "0.3.5"
 
 [dependencies.fvm]
 version = "4.0.0"

testing/conformance/src/vm.rs

@@ -3,41 +3,27 @@
 use std::convert::TryFrom;
 use std::sync::{Arc, Mutex};
 
-use ambassador::Delegate;
 use anyhow::anyhow;
-use cid::Cid;
 use fvm::kernel::filecoin::{DefaultFilecoinKernel, FilecoinKernel};
 use fvm::syscalls::InvocationData;
-use multihash::MultihashGeneric;
 
 use fvm::call_manager::{CallManager, DefaultCallManager};
-use fvm::gas::{price_list_by_network_version, Gas, GasTimer, PriceList};
+use fvm::gas::price_list_by_network_version;
 use fvm::machine::limiter::MemoryLimiter;
 use fvm::machine::{DefaultMachine, Machine, MachineContext, Manifest, NetworkConfig};
 use fvm::state_tree::StateTree;
 use fvm_ipld_blockstore::MemoryBlockstore;
-use fvm_shared::address::Address;
-use fvm_shared::clock::ChainEpoch;
 use fvm_shared::consensus::ConsensusFault;
-use fvm_shared::crypto::signature::{
-    SignatureType, SECP_PUB_LEN, SECP_SIG_LEN, SECP_SIG_MESSAGE_HASH_SIZE,
-};
-use fvm_shared::econ::TokenAmount;
 use fvm_shared::piece::PieceInfo;
-use fvm_shared::randomness::RANDOMNESS_LENGTH;
 use fvm_shared::sector::{
     AggregateSealVerifyProofAndInfos, RegisteredSealProof, ReplicaUpdateInfo, SealVerifyInfo,
 };
-use fvm_shared::sys::out::network::NetworkContext;
-use fvm_shared::sys::out::vm::MessageContext;
-use fvm_shared::sys::SendFlags;
-use fvm_shared::version::NetworkVersion;
-use fvm_shared::{ActorID, MethodNum};
 use wasmtime::Linker;
 
 // We have glob imports here because delegation doesn't work well without it.
-use fvm::*;
-use kernel::*;
+use fvm::kernel::prelude::*;
+use fvm::kernel::Result;
+use fvm::DefaultKernel;
 
 use crate::externs::TestExterns;
 use crate::vector::{MessageVector, Variant};