beads-rs: Skill for Claude Code

Writing Rust Lints with Dylint

Create custom Rust lints that run as dynamic libraries via Dylint.

When to Use

• Creating project-specific lints for code patterns
• Enforcing team conventions that Clippy doesn't cover
• Building reusable lint libraries
• Any task involving LateLintPass, EarlyLintPass, or rustc internals

Quick Start

cargo dylint new my_lint_name
cd my_lint_name
# Edit src/lib.rs, ui/main.rs
cargo build && cargo test

Macro Selection

digraph macro_selection {
    "Need custom lint?" [shape=diamond];
    "Has state/config?" [shape=diamond];
    "Multiple lints?" [shape=diamond];
    "Use declare_late_lint!" [shape=box];
    "Use impl_late_lint!" [shape=box];
    "Manual register_lints" [shape=box];

    "Need custom lint?" -> "Has state/config?" [label="yes"];
    "Has state/config?" -> "Multiple lints?" [label="no"];
    "Has state/config?" -> "Use impl_late_lint!" [label="yes"];
    "Multiple lints?" -> "Use declare_late_lint!" [label="no"];
    "Multiple lints?" -> "Manual register_lints" [label="yes"];
}

• declare_late_lint!: Single lint, no state. Generates everything.
• impl_late_lint!: Single lint WITH state/config. Pass initializer.
• Manual register_lints: Multiple lints in one library. Use dylint_library!().

NEVER mix: If using declare_late_lint!, do NOT manually write dylint_library!() or register_lints.

EarlyLintPass (AST-level)

For lints that don't need type information (AST-only):

#![feature(rustc_private)]

extern crate rustc_ast;
extern crate rustc_lint;
extern crate rustc_session;

use rustc_ast::ast::{Expr, ExprKind};
use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
use rustc_session::{declare_lint, declare_lint_pass};

declare_lint! {
    pub MY_EARLY_LINT,
    Warn,
    "description"
}

declare_lint_pass!(MyEarlyLint => [MY_EARLY_LINT]);

impl EarlyLintPass for MyEarlyLint {
    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
        // AST-level checks - NO type info available
        if let ExprKind::MethodCall(method_call) = &expr.kind {
            if method_call.seg.ident.name.as_str() == "unwrap" {
                cx.lint(MY_EARLY_LINT, |diag| {
                    diag.primary_message("found unwrap");
                });
            }
        }
    }
}

// IMPORTANT: Still need this for Dylint
dylint_linting::dylint_library!();