refactor: make XXXDecisionRoot fns return js.String

[spiral-ladder]

extracted from #347

IBeaconStateView expects RootHex (66-char string) for these outputs. it also happens that it's cheaper to just create a string upfront than go through a typed array

see: https://github.com/ChainSafe/lodestar/blob/35940ffd61ad7e29f5de376e13587d044b27b246/packages/state-transition/src/stateView/interface.ts#L78-L82

[gemini-code-assist]

Summary of Changes

Hello, 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 refactors the decision root retrieval methods in the NAPI bindings to return hexadecimal strings directly. This change improves performance by bypassing intermediate typed array allocations and ensures compatibility with the IBeaconStateView interface requirements.

Highlights

• Type Conversion Update: Updated decision root functions to return js.String instead of js.Uint8Array to align with expected RootHex formats.
• Performance Optimization: Introduced a helper function rootToHexString to perform direct hex string conversion, avoiding unnecessary typed array overhead.

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[spiral-ladder]

u32 autowidens to u64 when used as an arg into calculateShufflingDecisionRoot, so changed it to inline

this is somewhat of a unrelated change to this PR but also a small change so i did a driveby

[gemini-code-assist]

Code Review

This pull request refactors decision root getters in BeaconStateView.zig to return hex strings instead of byte arrays, utilizing a new rootToHexString helper. The review identifies a critical compilation error caused by a dangling function signature for previousDecisionRoot. Furthermore, the update to getShufflingDecisionRoot incorrectly uses toU32() for 64-bit epoch values, risking data truncation. Across all modified functions, the reviewer noted a violation of the repository's style guide regarding minimum assertion density and provided specific code suggestions to address these issues.

[gemini-code-assist]

The original function signature at line 374 was not removed, resulting in a dangling signature followed by a new function definition. This will cause a compilation error. Additionally, the repository style guide (lines 51-55) requires a minimum of two assertions per function to enforce invariants and detect programmer errors. I have included suggested assertions for the helper and the function body below.

fn rootToHexString(root: *const [32]u8) !js.String {
    const env = js.env();
    var hex_buf: [66]u8 = undefined;
    try @import("hex").rootIntoHex(&hex_buf, root);
    const result = try env.createStringUtf8(&hex_buf);
    std.debug.assert(hex_buf.len == 66);
    std.debug.assert(root.len == 32);
    return js_types.wrap(js.String, result);
}

pub fn previousDecisionRoot(self: *const BeaconStateView) !js.String {
    const cached_state = try self.requireState();
    std.debug.assert(self.cached_state != null);
    const root = cached_state.previousDecisionRoot();
    std.debug.assert(root.len == 32);
    return rootToHexString(&root);
}

References

1. Assert all function arguments and return values, pre/postconditions and invariants. The assertion density of the code must average a minimum of two assertions per function. ^(link)

[spiral-ladder]

outdated; fixed in new push

[gemini-code-assist]

The use of toU32() for the epoch value is inconsistent with the rest of the file, which uses toI64() and @intCast to u64. Since Ethereum epochs are 64-bit values, using toU32() introduces an unnecessary limitation and breaks consistency with other getters in this class. Additionally, the function lacks the required assertions per the repository style guide.

pub fn getShufflingDecisionRoot(self: *const BeaconStateView, epoch_arg: js.Number) !js.String {
    const cached_state = try self.requireState();
    std.debug.assert(self.cached_state != null);
    const epoch_value: u64 = @intCast(try epoch_arg.toI64());
    const root = st.calculateShufflingDecisionRoot(cached_state.state, epoch_value) catch {
        return throwNullAs(js.String, "STATE_ERROR", "Failed to calculate shuffling decision root");
    };
    std.debug.assert(root.len == 32);
    return rootToHexString(&root);
}

References

1. The assertion density of the code must average a minimum of two assertions per function. ^(link)

[gemini-code-assist]

This function is missing the required assertions per the repository style guide (lines 51-55). Each function should have at least two assertions to verify invariants and state.

pub fn currentDecisionRoot(self: *const BeaconStateView) !js.String {
    const cached_state = try self.requireState();
    std.debug.assert(self.cached_state != null);
    const root = cached_state.currentDecisionRoot();
    std.debug.assert(root.len == 32);
    return rootToHexString(&root);
}

References

1. The assertion density of the code must average a minimum of two assertions per function. ^(link)

[gemini-code-assist]

This function is missing the required assertions per the repository style guide (lines 51-55).

pub fn nextDecisionRoot(self: *const BeaconStateView) !js.String {
    const cached_state = try self.requireState();
    std.debug.assert(self.cached_state != null);
    const root = cached_state.nextDecisionRoot();
    std.debug.assert(root.len == 32);
    return rootToHexString(&root);
}

References

1. The assertion density of the code must average a minimum of two assertions per function. ^(link)