bc-isolation

A bounded context is closed. The only way into it is its open host service, and the only place allowed to use it is an anti-corruption layer of the other context, or that context's composition root. Nothing else crosses the boundary.

❌ Avoid: src/ordering/driven/pg/adapters/stock.adapter.ts

import type { Product } from "../../../../catalog/domain/aggregates/product.aggregate";
import type { ProductRepresentation } from "../../../../catalog/published-language/product.representation";

✅ Prefer: src/ordering/driven/catalog/adapters/catalog-price-list.adapter.ts

import type { AntiCorruptionLayer } from "@alveolus/core";

import type { CatalogApi } from "../../../../catalog/driving/in-process/catalog-api";
import { PriceList } from "../../../domain/ports/price-list.port";

export class CatalogPriceList extends PriceList implements AntiCorruptionLayer {
	constructor(private readonly catalog: CatalogApi) {
		super();
	}
}

What it checks

When a file of one bounded context imports a file of another one:

• the imported names must all be classes that implement OpenHostService;
• the importing file must declare a class that implements AntiCorruptionLayer, or be the composition root of its context;
• a composition root may also import another context's composition root, to reach its open host services;
• the published language of another context is never imported, not even its types.

The shared kernel imports no bounded context at all. Every context may import the shared kernel.

Why

Two contexts that import each other's classes share one model without saying so: renaming a field in the catalog breaks ordering. Going through an open host service and an anti-corruption layer gives one entry point on one side, one translation on the other, and everything in between is free to change.

The downstream context redeclares the fields it reads in its own published-language/, instead of importing the upstream types. When the open host service is called in the same process, TypeScript still checks that both shapes match, at the anti-corruption layer and nowhere else.

What it reports

src/ordering/driven/pg/adapters/stock.adapter.ts:1
  bc-isolation: Imports src/catalog/domain/aggregates/product.aggregate.ts (catalog domain): only an OpenHostService of another bounded context may be imported.

src/ordering/driven/pg/adapters/stock.adapter.ts:2
  bc-isolation: Imports the published language of catalog: redeclare the fields you read in your own published-language/.

An open host service imported by a class that is not an anti-corruption layer reports Uses the open host service of catalog outside an AntiCorruptionLayer.

Turn it off

rules: { "bc-isolation": "off" }

See also

• Project layout: bounded contexts
• layer-direction, for dependencies inside a context