@studnicky/adapter-only-import

Restricts a configurable list of concrete third-party dependencies — HTTP frameworks, database drivers, external API clients — to the adapters layer of a hexagonal architecture. Business logic in domain, application, ports, or even infrastructure files should depend on a port/interface, not directly on a specific library; only the adapters layer (configurable via adapterLayerName, default "adapters") is exempt. The rule resolves each file's layer the same way layer-import-boundary does (via layers/sourceRoot), then reports any import whose specifier matches (or is a submodule of) an entry in adapterOnlyImports. Files outside the configured layer tree are never checked; notably, infrastructure — which can otherwise import any configured layer — is still bound by this restriction, since infrastructure bootstrap code should still route concrete dependencies through adapters. This rule is typically wired together with layer-import-boundary, domain-purity, and known-types-outside-adapters via the HexagonalSuite.create({...}) factory export, since all four share the same layers/sourceRoot configuration — but it is fully usable and configurable on its own.

Fixable: No · Options: Yes · Suggested severity: error

Options

Name	Type	Default	Description
layers	string[]	(required)	Ordered list of enforced layer names, e.g. ["domain", "ports", "application", "adapters", "infrastructure"].
sourceRoot	string	(required)	Path segment(s) after which the layer name appears, e.g. "src".
aliasPrefixes	object	undefined	Map of path-alias prefixes (e.g. "@domain/") to their layer name.
allowedImports	object	undefined	Override of the default allow-matrix: source layer name → list of layers it may import from.
adapterLayerName	string	"adapters"	Name of the layer treated as the adapters layer for exemption purposes.
adapterOnlyImports	string[]	undefined	Package names/roots restricted to the adapters layer, e.g. ["express", "pg", "axios"].

✗ Incorrect

// domain-layer file (/repo/src/domain/user/User.ts) importing an
// adapter-only package directly — forbidden
import axios from 'axios';

// application-layer file importing an adapter-only package — forbidden
import axios from 'axios';

// infrastructure-layer file importing an adapter-only package — forbidden,
// despite infrastructure otherwise being able to import any configured layer
import axios from 'axios';

// domain-layer file importing a submodule of an adapter-only root — forbidden,
// exercises prefix match against adapterOnlyImports
import { Client } from 'pg/lib/client';

✓ Correct

// adapters-layer file (/repo/src/adapters/HttpAdapter.ts) importing an
// adapter-only package — allowed, adapters are exempt
import axios from 'axios';

// domain-layer file importing something not in adapterOnlyImports — not flagged
import { User } from './User';

// file outside the configured layer tree (/repo/scripts/build.ts) — out of scope
import axios from 'axios';