feat: comptime fork by wemeetagain · Pull Request #190 · ChainSafe/lodestar-z

wemeetagain · 2026-01-24T16:24:43Z

Refactor fork-specific consensus types into a fork_types module
- runtime dispatched fork types are exported as Any* types. Only AnySignedBeaconBlock and AnyBeaconState are currently used
- comptime fork types are exported as ForkTypes(f) (for all types) and Fork* for block and state, eg: ForkBeaconState(comptime f: ForkSeq)
state transition code is refactored to use comptime f: ForkSeq internally. The top-level stfn takes AnyBeaconState/CachedBeaconState and AnySignedBeaconBlock, and then does a single dispatch into fork-specific code.
state transition code is refactored to "decompose" CachedBeaconState from being passed deeply into utility functions and only pass the pieces required per function, Eg: converting functions like getFinalityDelay(cached_state: *CachedBeaconState) !u64 into getFinalityDelay(current_epoch: u64, finalized_epoch: u64) u64

Signed-off-by: Chen Kai <281165273grape@gmail.com>

gemini-code-assist · 2026-01-24T16:27:35Z

Summary of Changes

Hello @wemeetagain, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly refactors the codebase to implement a more robust and type-safe approach to handling different Ethereum Beacon Chain forks. By leveraging Zig's compile-time generics, the changes introduce specialized types for each fork, enhancing type safety and enabling compiler optimizations. This refactoring centralizes fork-related logic within a new fork_types module and updates numerous state transition and utility functions to seamlessly integrate with the new fork-aware type system, streamlining future development and maintenance across various network upgrades.

Highlights

Compile-time Fork Generics: Introduced ForkBeaconState(fork) and ForkBeaconBlock(fork, block_type) to enable compile-time specialization for different Beacon Chain forks, improving type safety and potentially performance.
Dynamic Fork Handling: New AnyBeaconState and AnySignedBeaconBlock unions provide a unified interface for handling state and blocks across various forks when the specific fork is not known at compile time.
Refactored State Transition Functions: All core state_transition functions (e.g., processBlock, processEpoch, processWithdrawals) have been updated to accept comptime fork: ForkSeq and utilize the new fork-aware types.
Centralized Fork Type Definitions: A new src/fork_types module has been added to encapsulate all fork-specific type definitions and their dynamic/compile-time wrappers.

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Code Review

This is an impressive and large-scale refactoring that introduces compile-time generics for handling fork-specific logic. The new fork_types module with Any* and Fork* types is a great architectural improvement that enhances type safety and likely performance. The changes are consistent and significantly improve the maintainability of the codebase, especially with the removal of the old types directory and the simplification of tests. I've found one critical issue that will cause a compilation error and a couple of style guide violations regarding function length that should be addressed.

gemini-code-assist · 2026-01-24T16:32:12Z

        switch (self.*) {
            .bellatrix => |*state| try state.setValue("latest_execution_payload_header", &header.bellatrix),
            .capella => |*state| try state.setValue("latest_execution_payload_header", &header.capella),


The switch statement is not exhaustive. It's missing cases for .deneb, .electra, .fulu, and an else case. This will result in a compilation error.

Similar to how latestExecutionPayloadHeader handles these forks by mapping them to .deneb (since they share the same payload header structure), you should do the same here.

switch (self.*) { .bellatrix => |*state| try state.setValue("latest_execution_payload_header", &header.bellatrix), .capella => |*state| try state.setValue("latest_execution_payload_header", &header.capella), .deneb, .electra, .fulu => |*state| try state.setValue("latest_execution_payload_header", &header.deneb), else => return error.InvalidAtFork, }

gemini-code-assist · 2026-01-24T16:32:12Z

+    pub fn deserialize(allocator: std.mem.Allocator, block_type: BlockType, fork_seq: ForkSeq, bytes: []const u8) !AnySignedBeaconBlock {
+        switch (fork_seq) {
+            .phase0 => {
+                if (block_type != .full) return error.InvalidBlockTypeForFork;
+                const signed_block = try allocator.create(ct.phase0.SignedBeaconBlock.Type);
+                errdefer allocator.destroy(signed_block);
+                signed_block.* = ct.phase0.SignedBeaconBlock.default_value;
+                try ct.phase0.SignedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                return .{ .phase0 = signed_block };
+            },
+            .altair => {
+                if (block_type != .full) return error.InvalidBlockTypeForFork;
+                const signed_block = try allocator.create(ct.altair.SignedBeaconBlock.Type);
+                errdefer allocator.destroy(signed_block);
+                signed_block.* = ct.altair.SignedBeaconBlock.default_value;
+                try ct.altair.SignedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                return .{ .altair = signed_block };
+            },
+            .bellatrix => {
+                if (block_type == .full) {
+                    const signed_block = try allocator.create(ct.bellatrix.SignedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.bellatrix.SignedBeaconBlock.default_value;
+                    try ct.bellatrix.SignedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .full_bellatrix = signed_block };
+                } else {
+                    const signed_block = try allocator.create(ct.bellatrix.SignedBlindedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.bellatrix.SignedBlindedBeaconBlock.default_value;
+                    try ct.bellatrix.SignedBlindedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .blinded_bellatrix = signed_block };
+                }
+            },
+            .capella => {
+                if (block_type == .full) {
+                    const signed_block = try allocator.create(ct.capella.SignedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.capella.SignedBeaconBlock.default_value;
+                    try ct.capella.SignedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .full_capella = signed_block };
+                } else {
+                    const signed_block = try allocator.create(ct.capella.SignedBlindedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.capella.SignedBlindedBeaconBlock.default_value;
+                    try ct.capella.SignedBlindedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .blinded_capella = signed_block };
+                }
+            },
+            .deneb => {
+                if (block_type == .full) {
+                    const signed_block = try allocator.create(ct.deneb.SignedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.deneb.SignedBeaconBlock.default_value;
+                    try ct.deneb.SignedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .full_deneb = signed_block };
+                } else {
+                    const signed_block = try allocator.create(ct.deneb.SignedBlindedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.deneb.SignedBlindedBeaconBlock.default_value;
+                    try ct.deneb.SignedBlindedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .blinded_deneb = signed_block };
+                }
+            },
+            .electra => {
+                if (block_type == .full) {
+                    const signed_block = try allocator.create(ct.electra.SignedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.electra.SignedBeaconBlock.default_value;
+                    try ct.electra.SignedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .full_electra = signed_block };
+                } else {
+                    const signed_block = try allocator.create(ct.electra.SignedBlindedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.electra.SignedBlindedBeaconBlock.default_value;
+                    try ct.electra.SignedBlindedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .blinded_electra = signed_block };
+                }
+            },
+            .fulu => {
+                if (block_type == .full) {
+                    const signed_block = try allocator.create(ct.fulu.SignedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.fulu.SignedBeaconBlock.default_value;
+                    try ct.fulu.SignedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .full_fulu = signed_block };
+                } else {
+                    const signed_block = try allocator.create(ct.fulu.SignedBlindedBeaconBlock.Type);
+                    errdefer allocator.destroy(signed_block);
+                    signed_block.* = ct.fulu.SignedBlindedBeaconBlock.default_value;
+                    try ct.fulu.SignedBlindedBeaconBlock.deserializeFromBytes(allocator, bytes, signed_block);
+                    return .{ .blinded_fulu = signed_block };
+                }
+            },
+        }
+    }


This function exceeds the 70-line limit specified in the style guide (line 104). Please refactor it to be shorter. You could extract the logic for each fork into a separate helper function.

References

Functions should not exceed a hard limit of 70 lines to reduce complexity and improve readability. ^(link)

gemini-code-assist · 2026-01-24T16:32:12Z

+    pub fn serialize(self: AnySignedBeaconBlock, allocator: std.mem.Allocator) ![]u8 {
+        switch (self) {
+            .phase0 => |signed_block| {
+                const out = try allocator.alloc(u8, ct.phase0.SignedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.phase0.SignedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .altair => |signed_block| {
+                const out = try allocator.alloc(u8, ct.altair.SignedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.altair.SignedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .full_bellatrix => |signed_block| {
+                const out = try allocator.alloc(u8, ct.bellatrix.SignedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.bellatrix.SignedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .blinded_bellatrix => |signed_block| {
+                const out = try allocator.alloc(u8, ct.bellatrix.SignedBlindedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.bellatrix.SignedBlindedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .full_capella => |signed_block| {
+                const out = try allocator.alloc(u8, ct.capella.SignedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.capella.SignedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .blinded_capella => |signed_block| {
+                const out = try allocator.alloc(u8, ct.capella.SignedBlindedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.capella.SignedBlindedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .full_deneb => |signed_block| {
+                const out = try allocator.alloc(u8, ct.deneb.SignedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.deneb.SignedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .blinded_deneb => |signed_block| {
+                const out = try allocator.alloc(u8, ct.deneb.SignedBlindedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.deneb.SignedBlindedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .full_electra => |signed_block| {
+                const out = try allocator.alloc(u8, ct.electra.SignedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.electra.SignedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .blinded_electra => |signed_block| {
+                const out = try allocator.alloc(u8, ct.electra.SignedBlindedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.electra.SignedBlindedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .full_fulu => |signed_block| {
+                const out = try allocator.alloc(u8, ct.fulu.SignedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.fulu.SignedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+            .blinded_fulu => |signed_block| {
+                const out = try allocator.alloc(u8, ct.fulu.SignedBlindedBeaconBlock.serializedSize(signed_block));
+                errdefer allocator.free(out);
+                _ = ct.fulu.SignedBlindedBeaconBlock.serializeIntoBytes(signed_block, out);
+                return out;
+            },
+        }
+    }


This function exceeds the 70-line limit specified in the style guide (line 104). Please refactor it to be shorter, for example by extracting the logic for each fork into a helper function.

References

Functions should not exceed a hard limit of 70 lines to reduce complexity and improve readability. ^(link)

Signed-off-by: Chen Kai <281165273grape@gmail.com>

chatgpt-codex-connector

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Signed-off-by: Chen Kai <281165273grape@gmail.com>

spiral-ladder

partial review

spiral-ladder · 2026-01-28T09:08:26Z

@@ -0,0 +1,24 @@
+const ct = @import("consensus_types");
+
+pub const AnyAttestations = union(enum) {


Is there a benefit to the Any prefix for this (and all other types)? Most data structures differ by fork types anyway, so I'm not sure if the Any prefix is helpful

Feels like we can either go with:

ForkBeaconState versus BeaconState, or

BeaconState versus AnyBeaconState

Preference for 2. or keeping as is

went with option 2.

spiral-ladder · 2026-01-28T09:16:53Z

+    full_bellatrix: *ct.bellatrix.SignedBeaconBlock.Type,
+    blinded_bellatrix: *ct.bellatrix.SignedBlindedBeaconBlock.Type,


nit: I personally prefer <name>_<variant> for naming, think it makes more sense naming wise for fork to come before the type of block since we have alphabetical ordering.

Suggested change

full_bellatrix: *ct.bellatrix.SignedBeaconBlock.Type,

blinded_bellatrix: *ct.bellatrix.SignedBlindedBeaconBlock.Type,

bellatrix_full: *ct.bellatrix.SignedBeaconBlock.Type,

bellatrix_blinded: *ct.bellatrix.SignedBlindedBeaconBlock.Type,

One thing that needs to be more consistent in this PR is the ordering between block type and fork.

Its not clear that fork needs to be first, nor vice versa.

I think that block type being primary reads slightly better, and would like to see (bt, f) everywhere. Eg BeaconBlockBody(.full, .fulu)

made that update, now (bt, f) is consistently everywhere.

Signed-off-by: Chen Kai <281165273grape@gmail.com>

spiral-ladder

lgtm w some comments

spiral-ladder · 2026-01-29T15:22:46Z

+    };
+}
+
+pub fn BeaconBlock(comptime bt: BlockType, comptime f: ForkSeq) type {


nit and maybe in a followup PR: should we capitalize comptime types? eg. BT and F

I think we should only capitalize types

spiral-ladder · 2026-01-29T15:25:53Z

+        }
+
+        pub fn nextWithdrawalIndex(self: *Self) !u64 {
+            if (comptime (f == .phase0 or f == .altair or f == .bellatrix)) return error.InvalidAtFork;


can we use lt() for these and the other checks? Seems pretty long and unreadable

yeah, current impl isn't great. (currently unused codepath)

spiral-ladder · 2026-01-29T15:34:02Z

    var state_eth1_data_view = try state.eth1Data();
    var state_eth1_data: Eth1Data = undefined;
-    try state_eth1_data_view.toValue(allocator, &state_eth1_data);
+    try state_eth1_data_view.toValue(undefined, &state_eth1_data);


i know this is because this doesn't require an allocator but this seems like a smell maybe for a future refactor

yes this is annoying, this is why the ssz types are split into fixed and variable types, so that we avoid this ^. (eg ct.phase0.Checkpoint.deserializeFromBytes doesn't take an allocator bc of the FixedContainerType function signature).
Our tree view code is not splt between fixed and variable, so we have situations like this...

would there be any value in having toValue and toValueAlloc?

wemeetagain and others added 17 commits January 19, 2026 19:00

wip

3ee0cc3

wip

4b2fd98

chore: remove unused imports

1bd6cab

Signed-off-by: Chen Kai <281165273grape@gmail.com>

refactor: move beacon_state to fork types to prepare refactor

8c2b1dd

Signed-off-by: Chen Kai <281165273grape@gmail.com>

refactor: change some processXX to use comptime fork

b80bba7

Signed-off-by: Chen Kai <281165273grape@gmail.com>

refactor: continue change func using comptime fork

1e37e44

Signed-off-by: Chen Kai <281165273grape@gmail.com>

chore: fork_types tweaks

011ea81

chore: more processXX updates, top-level stateTransition update

064c413

Merge main (int tests migration)

a13ffb1

refactor: continue use comptimee fork

ab58507

Signed-off-by: Chen Kai <281165273grape@gmail.com>

refactor: continue to use comptime fork

1876bfe

Signed-off-by: Chen Kai <281165273grape@gmail.com>

refactor: continue translate functions using comptime fork

600beaa

Signed-off-by: Chen Kai <281165273grape@gmail.com>

chore: continue refactor

a689e5f

fix: fix state transition test

fbbb1a3

Signed-off-by: Chen Kai <281165273grape@gmail.com>

fix: fix spec test

71b16d8

Signed-off-by: Chen Kai <281165273grape@gmail.com>

fix: fix build compile error

a951492

Signed-off-by: Chen Kai <281165273grape@gmail.com>

fix: fix bench

8616e50

Signed-off-by: Chen Kai <281165273grape@gmail.com>

gemini-code-assist Bot reviewed Jan 24, 2026

View reviewed changes

GrapeBaBa and others added 4 commits January 25, 2026 22:01

chore: use ForkBeaconBlockBody in stf util

9f754ff

Signed-off-by: Chen Kai <281165273grape@gmail.com>

Merge branch 'main' into comptime-fork

b856f10

chore: bring CachedBeaconState back to top-level stfn

54623fd

fix: fix the spec and bench tests

cae6099

Signed-off-by: Chen Kai <281165273grape@gmail.com>

wemeetagain changed the title ~~chore: comptime fork~~ feat: comptime fork Jan 27, 2026

wemeetagain marked this pull request as ready for review January 27, 2026 19:33

wemeetagain requested a review from a team as a code owner January 27, 2026 19:33

chatgpt-codex-connector Bot reviewed Jan 27, 2026

View reviewed changes

Comment thread src/state_transition/block/process_block_header.zig Outdated

fix: fix some error not called

947046a

Signed-off-by: Chen Kai <281165273grape@gmail.com>

spiral-ladder reviewed Jan 28, 2026

View reviewed changes

chore: consistent order of block_type, fork

d155063

wemeetagain and others added 4 commits January 28, 2026 18:00

chore: remove Fork prefix from fork-specific types

44c3af6

chore: add more tests

e62ca1e

chore: standardize blockType and forkSeq anyblock methods

e04cf66

fix: remove wrong import

463178b

Signed-off-by: Chen Kai <281165273grape@gmail.com>

spiral-ladder approved these changes Jan 29, 2026

View reviewed changes

wemeetagain merged commit ce37c88 into main Jan 29, 2026
9 checks passed

wemeetagain deleted the comptime-fork branch January 29, 2026 15:55

twoeths added a commit that referenced this pull request Mar 3, 2026

feat: comptime fork (#190)

cd06c84

lodekeeper-z mentioned this pull request Mar 26, 2026

chore: remove merge transition code #145

Open

		@@ -0,0 +1,24 @@
		const ct = @import("consensus_types");

		pub const AnyAttestations = union(enum) {

		full_bellatrix: *ct.bellatrix.SignedBeaconBlock.Type,
		blinded_bellatrix: *ct.bellatrix.SignedBlindedBeaconBlock.Type,

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wemeetagain commented Jan 24, 2026 •

edited

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