Typed service path inventory

This page inventories typed callpaths that can reach parser services or the TypeScript checker.

Source document: docs/internal/typed-paths.md

Guard model

The plugin follows a syntax-first design.

• Shared typed access flows through getTypeOfNode(node, context) in src/util/rule.ts.
• That helper calls ESLintUtils.getParserServices(context, true) and returns null when parser services or a program are unavailable.
• Rules consuming the helper treat null as a normal fallback path rather than crashing.

Core typed helper

Path	Typed dependency	Current callers	Fallback behavior	Max expected expensive calls/file
src/util/rule.ts#getTypeOfNode	parserServices.program, checker, ESTree→TS node map	immutable-data, readonly-array	Catches parser-service failures and returns null	Up to 4 lookups in one immutable-data mutator path; per implicit candidate in readonly-array

Rule callpath inventory

immutable-data

• Uses type lookups to distinguish mutating array/object operations from freshly-created values.
• Consults checker-backed type information for chained array constructors and Object.assign(...) targets.
• Falls back to its conservative assumeTypes behavior when type services are unavailable.

readonly-array

• Uses type lookups only for implicit mutable-array inference when a declaration or parameter lacks an explicit annotation.
• Still reports explicit T[], Array<T>, and tuple syntax without any parser services.
• Skips the implicit inference branch when getTypeOfNode(...) returns null.

Operational guidance

• Enable projectService: true when you want the highest semantic precision.
• Treat null from getTypeOfNode(...) as an expected soft-failure path.
• Keep typed lookups narrow and local to already-filtered AST nodes.