no-barrel-files

Avoid Barrel Files and Re-exports

Core Principle

Always avoid barrel files (index.ts files that only re-export from other modules) and prefer explicit, direct imports. This improves build performance, reduces bundle size, and makes dependencies clearer.

Guidelines

1. No Barrel Files

• Never create index.ts files that only contain export * from './other-module'
• Never create index.ts files that only contain export { something } from './other-module'
• Prefer explicit imports: import { connect } from '@prisma/runtime/connection'

2. Explicit Exports Only

• Only create index.ts files when they contain actual implementation code
• Use exports/index.ts pattern only for explicit, intentional API surfaces
• Each package should have a clear, minimal public API

3. Direct Imports

• Import directly from the specific module: import { sql } from '@prisma/sql/builder'
• Avoid: import { sql } from '@prisma/sql' (barrel import)
• This makes dependencies explicit and improves tree-shaking

4. Package Structure

• Each package should expose specific subpaths in package.json exports
• Example: "./builder": { "types": "./dist/builder.d.ts", "import": "./dist/builder.js" }
• Consumers import from specific subpaths, not from barrel files

5. Benefits

• Build Performance: Faster builds due to fewer re-export chains
• Bundle Size: Better tree-shaking and smaller bundles
• Dependency Clarity: Clear understanding of what each module depends on
• IDE Performance: Faster IntelliSense and type checking
• Debugging: Easier to trace where code comes from

6. Examples

BAD - Barrel file:

// packages/sql/src/index.ts
export { sql } from './builder';
export { makeT } from './maket';
export { compileToSQL } from './compiler';
export * from './types';

GOOD - Direct imports:

// Consumer code
import { sql } from '@prisma/sql/builder';
import { makeT } from '@prisma/sql/maket';
import { compileToSQL } from '@prisma/sql/compiler';