[
{
"pattern": "chrono",
"replacement": "time",
"kind": "ModernAlternative",
"reason": "time is a strong modern option for smaller/simple datetime needs, but chrono is still maintained and may be correct for timezone-heavy projects",
"source": "blessed.rs",
"condition": "UTC-only or simple datetime usage",
"confidence": "Low",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "lazy_static",
"replacement": "std::sync::LazyLock",
"kind": "StdReplacement",
"reason": "LazyLock is stable since Rust 1.80 and can remove an extra dependency after source imports are updated",
"source": "std docs",
"confidence": "High",
"migration_risk": "Low",
"autofix_safety": "ManualOnly",
"evidence_source": "StdDocs"
},
{
"pattern": "once_cell",
"replacement": "std::sync::LazyLock / OnceLock",
"kind": "StdReplacement",
"reason": "LazyLock and OnceLock are stable since Rust 1.80 and may cover common once_cell usage after source imports are updated",
"source": "std docs",
"confidence": "High",
"migration_risk": "Low",
"autofix_safety": "ManualOnly",
"evidence_source": "StdDocs"
},
{
"pattern": "structopt",
"replacement": "clap v4 (derive)",
"kind": "ModernAlternative",
"reason": "structopt functionality was folded into clap derive; migrate when you are ready to update CLI derives and attributes",
"source": "blessed.rs",
"confidence": "High",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "actix-web",
"replacement": "axum",
"kind": "ModernAlternative",
"reason": "axum is a common Tokio-native choice for new services, but actix-web remains maintained; treat this as an ecosystem preference, not a mandatory migration",
"source": "blessed.rs",
"confidence": "Low",
"migration_risk": "High",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "iron",
"replacement": "axum",
"kind": "Unmaintained",
"reason": "Iron is no longer a good foundation for new Rust web services; axum is a maintained Tokio-native migration target",
"source": "blessed.rs",
"confidence": "High",
"migration_risk": "High",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "memmap",
"replacement": "memmap2",
"kind": "Unmaintained",
"reason": "memmap is unmaintained; memmap2 is the maintained fork, but source imports and API details still need review",
"source": "RustSec",
"confidence": "High",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "RustSec"
},
{
"pattern": "failure",
"replacement": "anyhow + thiserror",
"kind": "Unmaintained",
"reason": "failure is deprecated and unmaintained; anyhow for application errors and thiserror for library errors is the common modern split",
"source": "blessed.rs",
"confidence": "High",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "log",
"replacement": "tracing",
"kind": "ModernAlternative",
"reason": "tracing adds structured spans and async-aware instrumentation, but log is still maintained and may be enough for simple libraries",
"source": "blessed.rs",
"confidence": "Medium",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "reqwest+serde_json",
"replacement": "reqwest with \"json\" feature",
"kind": "FeatureOptimization",
"reason": "reqwest can deserialize JSON directly when its json feature is enabled; cargo-bless only suggests this when serde_json is not used directly in source",
"source": "reqwest docs",
"confidence": "High",
"migration_risk": "Low",
"autofix_safety": "CargoTomlOnly",
"evidence_source": "CrateDocs"
},
{
"pattern": "tokio+async-std",
"replacement": "tokio only",
"kind": "ComboWin",
"reason": "using two async runtimes usually adds complexity; consolidate only after checking runtime boundaries and dependencies",
"source": "blessed.rs",
"confidence": "Medium",
"migration_risk": "High",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "env_logger",
"replacement": "tracing-subscriber",
"kind": "ModernAlternative",
"reason": "tracing-subscriber pairs with tracing for structured, filterable logging; keep env_logger if log-based output is intentionally simple",
"source": "blessed.rs",
"confidence": "Medium",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "log+env_logger",
"replacement": "tracing + tracing-subscriber",
"kind": "ComboWin",
"reason": "tracing plus tracing-subscriber is the modern observability stack, but migration requires source instrumentation choices",
"source": "blessed.rs",
"confidence": "Medium",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "warp",
"replacement": "axum",
"kind": "ModernAlternative",
"reason": "axum is the more active Tokio-native web framework choice for new projects; migration from warp should be deliberate",
"source": "blessed.rs",
"confidence": "Medium",
"migration_risk": "High",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "rocket",
"replacement": "axum",
"kind": "ModernAlternative",
"reason": "axum is a common lightweight Tokio-native choice, but Rocket may still be appropriate if its ergonomics are important to the project",
"source": "blessed.rs",
"confidence": "Low",
"migration_risk": "High",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "maplit",
"replacement": "std::collections::HashMap::from / BTreeMap::from",
"kind": "StdReplacement",
"reason": "std collection constructors cover many maplit use cases after source macros are rewritten",
"source": "std docs",
"confidence": "High",
"migration_risk": "Low",
"autofix_safety": "ManualOnly",
"evidence_source": "StdDocs"
},
{
"pattern": "error-chain",
"replacement": "anyhow + thiserror",
"kind": "Unmaintained",
"reason": "error-chain is in maintenance mode; anyhow for app errors and thiserror for library errors is the common modern split",
"source": "blessed.rs",
"confidence": "High",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "proc-macro-error",
"replacement": "syn::Error or proc-macro-error2",
"kind": "ModernAlternative",
"reason": "proc-macro diagnostics need compile-time errors with spans; syn::Error is the standard baseline and proc-macro-error2 is an ergonomic option",
"source": "crate docs",
"confidence": "Medium",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "CrateDocs"
},
{
"pattern": "derivative",
"replacement": "derive_more",
"kind": "Unmaintained",
"reason": "derivative appears inactive; derive_more may cover many derive helper use cases, but macro behavior needs source review",
"source": "crates.io",
"confidence": "Medium",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "CratesIo"
},
{
"pattern": "anyhow+error-chain",
"replacement": "anyhow only (app) or thiserror (lib)",
"kind": "ComboWin",
"reason": "error-chain and anyhow overlap; pick one error handling pattern based on whether this is an application or library boundary",
"source": "blessed.rs",
"confidence": "High",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "bytes+try_from_bytes",
"replacement": "bytes with built-in zero-copy slicing",
"kind": "FeatureOptimization",
"reason": "bytes already provides the core zero-copy byte buffer primitives; verify the helper crate is not adding project-specific parsing behavior",
"source": "bytes docs",
"confidence": "Medium",
"migration_risk": "Low",
"autofix_safety": "ManualOnly",
"evidence_source": "CrateDocs"
},
{
"pattern": "num_cpus",
"replacement": "std::thread::available_parallelism",
"kind": "StdReplacement",
"reason": "available_parallelism covers common CPU count queries in std after source calls are updated",
"source": "std docs",
"confidence": "High",
"migration_risk": "Low",
"autofix_safety": "ManualOnly",
"evidence_source": "StdDocs"
},
{
"pattern": "rustc-serialize",
"replacement": "serde",
"kind": "Unmaintained",
"reason": "rustc-serialize is obsolete; serde is the standard serialization ecosystem, but migration is a real source change",
"source": "blessed.rs",
"confidence": "High",
"migration_risk": "High",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "serde_derive",
"replacement": "serde with \"derive\" feature",
"kind": "FeatureOptimization",
"reason": "serde exposes derive through its own feature; this can usually remove the separate serde_derive dependency without source rewrites",
"source": "serde docs",
"confidence": "High",
"migration_risk": "Low",
"autofix_safety": "CargoTomlOnly",
"evidence_source": "CrateDocs"
},
{
"pattern": "crossbeam-utils",
"replacement": "std::sync primitives or parking_lot",
"kind": "ModernAlternative",
"reason": "some crossbeam-utils use cases are now covered by std, while parking_lot may fit some locking needs; inspect actual APIs before changing",
"source": "blessed.rs",
"confidence": "Low",
"migration_risk": "Medium",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "hyper+serde_json",
"replacement": "axum with built-in JSON support",
"kind": "ComboWin",
"reason": "axum can reduce boilerplate for application HTTP JSON handling, but hyper remains right for lower-level HTTP code",
"source": "blessed.rs",
"confidence": "Low",
"migration_risk": "High",
"autofix_safety": "ManualOnly",
"evidence_source": "BlessedRs"
},
{
"pattern": "clap+clap_derive",
"replacement": "clap with \"derive\" feature",
"kind": "FeatureOptimization",
"reason": "clap exposes derive through its own feature; this can usually remove the separate clap_derive dependency without source rewrites",
"source": "clap docs",
"confidence": "High",
"migration_risk": "Low",
"autofix_safety": "CargoTomlOnly",
"evidence_source": "CrateDocs"
},
{
"pattern": "quick-error",
"replacement": "anyhow + thiserror",
"kind": "Unmaintained",
"reason": "quick-error is unmaintained since 2018 \u2014 anyhow (app) + thiserror (lib) is the modern standard",
"source": "crates.io"
},
{
"pattern": "failure_derive",
"replacement": "thiserror",
"kind": "Unmaintained",
"reason": "failure_derive was part of the deprecated failure crate \u2014 thiserror provides better derive macros",
"source": "blessed.rs"
},
{
"pattern": "proc-macro-nested",
"replacement": "no replacement needed (modern Rust handles nested macros)",
"kind": "ModernAlternative",
"reason": "proc-macro-nested was a workaround for old macro limitations \u2014 no longer needed in modern Rust",
"source": "Rust RFC"
},
{
"pattern": "version_check",
"replacement": "rust-version in Cargo.toml or cfg_attr",
"kind": "ModernAlternative",
"reason": "version_check is a legacy crate for MSRV detection \u2014 use package.rust-version field instead",
"source": "Cargo docs"
},
{
"pattern": "semver",
"replacement": "built-in version parsing or cargo_metadata",
"kind": "ModernAlternative",
"reason": "semver crate is rarely needed directly \u2014 use cargo_metadata for dependency resolution",
"source": "blessed.rs"
}
]