legacy - SKILL.md Agent Skill

name: legacy description: >- Scans Rust code for edition-specific patterns and deprecated APIs, then migrates to a target edition (2015 → 2018 → 2021 → 2024) or updates breaking crate API changes (tokio 0.x → 1.x, diesel 1.x → 2.x, failure → anyhow/thiserror, futures 0.1 → async/await). Detects extern crate declarations, old module syntax (mod.rs), try!() macro, pre-NLL borrow patterns, and deprecated std APIs. Use when the user says "migrate to Rust 2021", "upgrade edition", "this is old Rust", "update tokio", "replace failure crate", or when rustc produces edition warnings. Do NOT use for dependency management (Cargo), performance optimization (web-optimize), or general refactoring unrelated to Rust edition/API compatibility.

sc-rust Legacy

Detects edition-specific patterns and deprecated APIs in the Rust codebase, then produces a migration plan and applies changes file by file — migrating to a newer edition or updating breaking crate API changes.

Available actions

#	Action	Role	Input
01	`scan`	Detect edition/API gaps and deprecated patterns	path, target edition
02	`migrate`	Apply edition migration and crate API transformations	scan manifest

Default flow

Always sequential: scan → migrate.

scan reads Cargo.toml, detects current edition, finds deprecated patterns and outdated crate API usage, emits a structured manifest
migrate reads the manifest and applies transformations file by file

References

references/rust-editions.md — edition-by-edition change tables (2015→2018→2021→2024)
references/api-deprecations.md — std deprecations and crate migrations (failure, futures 0.1, rand, serde)

Transversal rules

Always detect the current Rust edition from Cargo.toml (edition = "2015"/"2018"/"2021"/"2024") before scanning.
Never remove a working pattern without providing its replacement inline.
For breaking changes: show a diff of what will change and ask for confirmation before writing.
extern crate removal: verify the crate is in the standard prelude or Rust 2018+ implicit imports before removing.
Error handling migration (failure/error-chain → anyhow/thiserror): prefer anyhow for binaries/applications, thiserror for library crates.
Never touch target/ or generated build.rs output.