@lint-suite/eslint-plugin-type-placement

An ESLint rule for TypeScript and Angular-style feature code that enforces predictable locations for exported types, constants, and internal type-only imports. It keeps shared exported types in common/*.type.ts, limits *.type.ts and *.const.ts exports, and ensures internal import type declarations target type-oriented modules.

Install

Requires Node.js 24+, ESLint ^10.9.1, and TypeScript >=6.0.3.

pnpm add -D @lint-suite/eslint-plugin-type-placement eslint@^10.9.1 typescript@">=6.0.3" typescript-eslint

The plugin does not configure a TypeScript parser. Use typescript-eslint for TypeScript files:

// eslint.config.js
import typePlacement from '@lint-suite/eslint-plugin-type-placement';
import tseslint from 'typescript-eslint';

export default [{
  files: ['**/*.ts'],
  languageOptions: { parser: tseslint.parser },
  plugins: { typePlacement },
  rules: { 'typePlacement/type-placement': 'error' }
}];

Options

internalPatterns defaults to []. Each supplied string becomes a regular expression. A matching non-relative import type source is treated as internal and must be a *.type.ts, *.schema.ts, or common barrel.

rules: {
  'typePlacement/type-placement': ['error', {
    internalPatterns: ['^@workspace/']
  }]
}

This non-default option makes @workspace/* type-only imports subject to the internal-source restriction. Without it, non-relative package and workspace-alias imports are allowed.

Filename rules and exemptions

Filename is part of this rule's contract. Exported type aliases and interfaces belong in common/*.type.ts or test/common/*.type.ts. A *.type.ts file may export only type aliases and interfaces; a *.const.ts file may export only const variable declarations.

Relative import type sources are internal. Their companion module must have a final filename segment ending in .type.ts or .schema.ts, unless the source is a common barrel such as ../common or ./common/index.ts. The same requirement applies to non-relative imports that match internalPatterns.

The rule does not inspect files ending in .spec.ts, .stub.ts, .schema.ts, or .d.ts; state.type.ts files; or files below a /fixtures/ path. The exemption applies to the entire file.

Examples

Each snippet below is checked by this rule alone, not by an entire ESLint configuration. Every example states its filename; import examples also state the required companion filename. The internalPatterns option is called out where it is non-default.

Valid examples

1. Exported type in a common type file

// Filename: src/orders/common/order.type.ts
export type Order = { readonly id: string };

2. Exported interface in a test common type file

// Filename: src/orders/test/common/order.type.ts
export interface Order { readonly id: string }

3. Const-only export in a const file

// Filename: src/orders/order.const.ts
export const PAGE_SIZE = 20;

4. Relative type import from a type file

// Filename: src/orders/order.ts
// Companion file: src/orders/common/order.type.ts
import type { Order } from './common/order.type.ts';

5. Relative type import from a common barrel

// Filename: src/orders/order.ts
// Companion barrel: src/orders/common/index.ts
import type { Order } from './common/index.ts';

6. External alias import with default options

// Filename: src/orders/order.ts
import type { Signal } from '@angular/core';

This remains valid because internalPatterns defaults to [].

Invalid examples

1. Exported type outside a common type file

// Filename: src/orders/order.ts
export interface Order {}

Move the type to src/orders/common/order.type.ts.

2. Type file outside a common directory

// Filename: src/orders/order.type.ts
export type Order = { readonly id: string };

The .type.ts suffix alone is insufficient; the file must be under common.

3. Value export in a common type file

// Filename: src/orders/common/order.type.ts
export const DEFAULT_ORDER = { id: 'new' };

*.type.ts files may export only type aliases and interfaces.

4. Function export in a const file

// Filename: src/orders/order.const.ts
export function createOrder() {}

*.const.ts files may export only const variable declarations.

5. Relative type import from a regular module

// Filename: src/orders/order.service.ts
// Companion file: src/orders/order.ts
import type { Order } from './order.ts';

The companion must instead be a .type.ts, .schema.ts, or common barrel module.

6. Internal alias type import from a regular module

// Filename: src/orders/order.ts
// Non-default rule option: { internalPatterns: ['^@workspace/'] }
// Companion module: @workspace/orders
import type { Order } from '@workspace/orders';

Because the non-default option marks this alias as internal, its companion must be a type file, schema file, or common barrel.

The named typePlacementRule export is for composed plugin registries.