enforce-ianitor-check-type

Require Ianitor.Check<T> validators when a TypeScript type gets too complex to trust at runtime.

Rule details Roblox

TypeScript types evaporate at runtime. If your code reads data from a DataStore, RemoteEvent, or any other IO boundary, TypeScript has no way to prove the data matches your type. This rule scores the structural complexity of your types and reports an error when the score crosses a threshold, nudging you to add an Ianitor runtime validator.

Runtime safety

TypeScript types don’t exist at runtime. Ianitor fills the gap by validating data shape before your code touches it.

How it works

1. Score the type — The rule recursively walks the type, adding weight for nesting depth, property count, unions, intersections, and structural complexity.
2. Check the threshold — If the score exceeds baseThreshold (default 10), the rule reports an error.
3. Define an Ianitor schema — Create an Ianitor validator that matches your TypeScript interface.
4. Derive the type — Use type MyType = Ianitor.Static<typeof myValidator> so the runtime check and the TypeScript type stay in sync.

Examples

Incorrect

Complex type without validation

This type is too deeply nested to trust without a runtime check.

type UserPayload = {
  data: {
    preferences: {
      theme: string;
      blurEnabled: boolean;
    };
    lastLogin: number;
  };
};

Correct

Schema-derived type

Define the validator once and extract the TypeScript type from it.

const userValidator = Ianitor.interface({
  data: Ianitor.interface({
    preferences: Ianitor.interface({ ... }),
    lastLogin: Ianitor.number(),
  }),
});

type UserPayload = Ianitor.Static<typeof userValidator>;

Configuration options

The rule accepts a single options object with these fields:

Option	Type	Default	What it controls
baseThreshold	number	10	Minimum complexity score before the rule reports.
warnThreshold	number	15	Score at which the rule starts warning.
errorThreshold	number	25	Score at which the violation becomes an error.
interfacePenalty	number	20	Base score added to all interface declarations.
performanceMode	boolean	true	Cap scores at 2x errorThreshold to avoid expensive walks.

What drives the score up

Structural weight

Unions, intersections, and optional properties add more weight than simple primitives.

Nesting depth

Each level of nesting multiplies the score via log2(depth + 1).

Property count

Large objects with many fields are penalized to encourage smaller sub-interfaces.

Caching

The rule caches complexity scores per node so re-checking stays cheap.

Related rules

require-serialized-numeric-data-type Correct types for binary data

Further reading

Ianitor on GitHub Source code for the Ianitor runtime validation library