EpicGames/lore · error · syn::Error

expected `state`

Error message

expected `state`

What it means

The `lore_instrument` attribute macro parses its arguments manually and requires the first token to be the exact identifier `state`, followed by `=` and a string literal path. When the attribute is invoked with any other key name (or a bare value), the macro raises this compile-time error pointing at the unexpected identifier. It is a macro-input validation failure, not a runtime fault.

Solutions

1. Change the attribute's first argument to the exact form `state = "<path>"`.
2. Check the lore-macro docs/tests for the accepted invocation syntax of `lore_instrument`.
3. If the error points at a token that isn't yours, verify you are attaching the attribute to a supported item.

Example fix

// before
#[lore_instrument(path = "state.json")]
fn handler() {}

// after
#[lore_instrument(state = "state.json")]
fn handler() {}

// Compile-time: the attribute must literally be: #[lore_instrument(state = "<path>")]
// Verify before building:
// grep -R '#\[lore_instrument(' src/ | grep -v 'state = '

When it happens

Trigger: Writing `#[lore_instrument(path = "state.json")]`, `#[lore_instrument("state.json")]`, a misspelled key like `#[lore_instrument(states = ...)]`, or any attribute argument that does not start with the literal token `state`.

Common situations: Copying an attribute from a different macro, misreading the macro's docs, refactoring the attribute name after a library API change, or IDE autocompletion inserting the wrong key.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

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• {e}
• Networking not supported on this OS
• [environment.endpoint] auth_url is set but [server.auth] is…
• [environment.endpoint] auth_url and [server.auth]…

AI-assisted analysis of EpicGames/lore@074eb0b0d1 (2026-09-13). Data as JSON: /api/errors/7035c7379a30b6c3. Report an issue: GitHub.

Appendix: source

Thrown at lore-macro/src/lore_instrument.rs:21

use proc_macro::TokenStream;
use quote::quote;
use syn::ItemFn;
use syn::parse::Parse;
use syn::parse::ParseStream;

struct LoreInstrumentArgs {
    state_path: Option<syn::Path>,
}

impl Parse for LoreInstrumentArgs {
    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
        if input.is_empty() {
            return Ok(LoreInstrumentArgs { state_path: None });
        }

        let ident: syn::Ident = input.parse()?;
        if ident != "state" {
            return Err(syn::Error::new(ident.span(), "expected `state`"));
        }
        let _eq: syn::Token![=] = input.parse()?;
        let lit: syn::LitStr = input.parse()?;
        let path: syn::Path = lit.parse()?;
        Ok(LoreInstrumentArgs {
            state_path: Some(path),
        })
    }
}

pub fn lore_instrument_impl(args: TokenStream, item: TokenStream) -> TokenStream {
    let args = syn::parse_macro_input!(args as LoreInstrumentArgs);
    let input = syn::parse_macro_input!(item as ItemFn);

    let state_path = args.state_path.unwrap_or_else(|| {
        syn::parse_str("lore_telemetry::execution_state::ServerExecutionState").unwrap()
    });

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