performance-lint-rules

Performance Guidelines

Prefer top-level node kind checks

Put node kind checks at the rule entry point. If a rule only handles a few syntactic forms, start run with an AstKind match and return for all other nodes, even when a helper filters again internally. This lets lintgen derive narrower NODE_TYPES and avoids dispatching the rule on unrelated AST nodes.

After changing the relevant node kinds for a rule, regenerate the rule runner with cargo lintgen and consider adding or updating assert_rule_runs_on_node_types coverage in crates/oxc_linter/src/rule.rs.

Implement only the needed entry point. If a rule is a whole-file pass over semantic indexes, use run_once by itself. Implementing both run and run_once prevents useful node-type narrowing.

Do cheaper checks first

Order checks from cheapest and most selective to most expensive. Return quickly for common non-matches before doing semantic lookups, allocations, or deeper traversal.

• Matching a small fixed string set with matches! before semantic checks.
• Rejecting lowercase identifiers before global-object checks when only constructors can match.
• Checking whether a JSX attribute starts with aria- before lowercasing it.
• Checking for required syntax such as a key prop before looking up callback parameter symbols.
• Checking source_range(span).contains("this") before running a visitor that only finds this.