feat: rule warns when token duplicates type

src/rules/check-inject-decorator.rule.ts

@@ -0,0 +1,44 @@
+import { ESLintUtils } from '@typescript-eslint/utils';
+
+const createRule = ESLintUtils.RuleCreator(
+  (name) => `https://eslint.org/docs/latest/rules/${name}`
+);
+
+export type MessageIds =
+  | 'tokenDuplicatesType'
+  | 'typeIsInterface'
+  | 'propertyMissingInject';
+
+const defaultOptions: unknown[] = [];
+
+export default createRule({
+  name: 'check-inject-decorator',
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'Ensure proper use of the @Inject decorator',
+      recommended: 'recommended',
+    },
+    fixable: undefined,
+    schema: [], // no options
+    messages: {
+      tokenDuplicatesType: '⚠️ Token duplicates type',
+      typeIsInterface: '⚠️ Type is an interface and cannot be injected',
+      propertyMissingInject: '⚠️ Did you want to `@Inject({{type}})`?',
+    },
+  },
+  defaultOptions,
+  create(context) {
+    return {
+      // Matches code that defines a variable of type TestingModule
+      // e.g. `let testingModule: TestingModule;`
+      'Program:exit': (node) => {
+        context.report({
+          node,
+          messageId: 'tokenDuplicatesType',
+          loc: node.loc,
+        });
+      },
+    };
+  },
+});

tests/rules/check-inject-decorator.spec.ts

@@ -0,0 +1,47 @@
+import { RuleTester } from '@typescript-eslint/rule-tester';
+import checkInjectDecorator from '../../src/rules/check-inject-decorator.rule';
+
+// This test required changes to the tsconfig file to allow importing from the rule-tester package.
+// See https://github.com/typescript-eslint/typescript-eslint/issues/7284
+
+const ruleTester = new RuleTester({
+  parserOptions: {
+    project: './tsconfig.json',
+  },
+  parser: '@typescript-eslint/parser',
+  defaultFilenames: {
+    // We need to specify a filename that will be used by the rule parser.
+    // Since the test process starts at the root of the project, we need to point to the sub folder containing it.
+    ts: './tests/rules/file.ts',
+    tsx: '',
+  },
+});
+
+ruleTester.run('check-inject-decorator', checkInjectDecorator, {
+  valid: [
+    // TODO: add following tests:
+    // 1 - 🆗 Type is a class and was injected in the constructor
+    // 2 - 🆗 Token differs from type
+    // 3 - 🆗 Token duplicates type, but class properties are not injected automatically
+  ],
+  invalid: [
+    {
+      code: `
+      class FooBarController {      
+        constructor(
+          @Inject(BazService) // ⚠️ Token duplicates type
+          private readonly bazService: BazService,
+        ) {}
+      }
+      `,
+      errors: [
+        {
+          messageId: 'tokenDuplicatesType',
+        },
+      ],
+    },
+    // TODO: add following tests:
+    // 1 - 🚫 Type is an interface and cannot be injected
+    // 2 - private readonly fooService: FooService; // ⚠️ Did you want to `@Inject(FooService)`?
+  ],
+});