Language edition/toolchain drift
Rust 2024 reserved tokens macro input accepted before fails lexing edition 2024
A procedural or declarative macro input that was accepted before now fails lexing in edition 2024.
Agent Quick Fix
Source may compile under an older edition/toolchain; current edition migration rules and tool metadata are external to the repo's immediate error context.
Product: Rust 2024
Current-contract area: Reserved `##` token breaks a macro DSL
Likely root cause: A procedural or declarative macro input that was accepted before now fails lexing in edition 2024.
Repair direction: Verifier checks idiomatic migration while preserving cross-version intent where required.Validation Status
Codex searched organically in the validation run. No no-web counterfactual is attached to this page yet.
Symptom
A procedural or declarative macro input that was accepted before now fails lexing in edition 2024.
Why This Happens
Source may compile under an older edition/toolchain; current edition migration rules and tool metadata are external to the repo's immediate error context.
Verification
Verifier checks idiomatic migration while preserving cross-version intent where required.Common Wrong Fixes
- Changing local code without checking the current external contract.
- Retrying the same install, build, or API call with no version/source change.
- Applying a broad unsafe bypass when a narrow compatibility fix is available.
Codex Search Keywords
These are the search terms observed in a neutral Codex validation run for this failure shape.
Rust 2024 reserved tokens macro input accepted before fails lexing edition 2024
Rust 2024 reserved syntax guarded string literal macro input lexer
site:doc.rust-lang.org edition-guide Rust 2024 reserved syntax guarded strings
https://doc.rust-lang.org/edition-guide/rust-2024/reserved-syntax.html