Adding a New Lint Rule

Linting operates on HIR trees. Rules live in src/lint/rules.rs; the tree walker lives in src/hir/lint.rs.

Files to modify (in order)

1. src/lint/rules.rs — Implement the rule function.

2. src/hir/lint.rs — Call the rule from the appropriate HirKind arm in HirLinter::check().

3. src/lint/mod.rs — Re-export if the rule is public.

Step by step

Step 1: src/lint/rules.rs — Write the rule. Rules take context and push Diagnostics:

use super::diagnostics::{Diagnostic, Severity};
use crate::reader::SourceLoc;

pub fn check_my_rule(
    context_data: &str,
    location: &Option<SourceLoc>,
    diagnostics: &mut Vec<Diagnostic>,
) {
    if /* violation detected */ {
        diagnostics.push(Diagnostic::new(
            Severity::Warning,
            "W004",                    // unique code
            "my-rule-name",            // kebab-case rule name
            "description of the issue",
            location.clone(),
        ).with_suggestions(vec![
            "how to fix it".to_string(),
        ]));
    }
}

Step 2: src/hir/lint.rs — Call the rule from the tree walker. Find the appropriate HirKind match arm in check():

// Example: check all let bindings for some property
HirKind::Let { bindings, body } | HirKind::Letrec { bindings, body } => {
    for (binding, init) in bindings {
        // Call your rule here:
        if let Some(sym_name) = symbols.name(binding.name()) {
            rules::check_my_rule(sym_name, &loc, &mut self.diagnostics);
        }
        self.check(init, symbols);
    }
    self.check(body, symbols);
}

Key types

Diagnostic codes

• W001 — naming-kebab-case
• W002 — arity-mismatch
• W003 — non-exhaustive-match
• Use W004+ for new warnings, E00x for errors, I00x for info.

How linting runs

1. Linter::lint_str() (in src/lint/cli.rs) calls analyze_all() to get HIR. 2. For each analysis result, it creates a HirLinter and calls hir_linter.lint(&analysis.hir, &symbols). 3. HirLinter::check() recursively walks the HIR tree, calling rule functions that push Diagnostics. 4. The LSP (src/lsp/state.rs) uses the same HirLinter for real-time diagnostics.

See also

• Cookbook index