Custom eslint rule for disallowing cross-package references

Summary:
Added infra for writing and using custom eslint rules and created a rule for disallowing cross-package file imports. Such imports are anti-pattern and they also break standalone plugin bundling.

We still have a bunch of places where Flipper core references code directly from plugins. I've ignored these places for now and added task T71355623 to revisit them.

Reviewed By: passy

Differential Revision: D22998955

fbshipit-source-id: d04cff8fc115ba1300a7e6830306ec134046e927

desktop/eslint-plugin-flipper/src/rules/__tests__/noRelativeImportsAcrossPackages.node.ts

@@ -0,0 +1,56 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {TSESLint} from '@typescript-eslint/experimental-utils';
+import rule, {RULE_NAME} from '../noRelativeImportsAcrossPackages';
+
+const tester = new TSESLint.RuleTester({
+  parser: require.resolve('@typescript-eslint/parser'),
+  parserOptions: {
+    sourceType: 'module',
+    ecmaVersion: 2020,
+  },
+});
+
+tester.run(RULE_NAME, rule, {
+  valid: [
+    {
+      code: `import * as testUtils from 'flipper-test-utils';`,
+      filename: __filename,
+    },
+    {
+      code: `const testUtils = require('flipper-test-utils');`,
+      filename: __filename,
+    },
+    {
+      code: `import rule, {RULE_NAME} from '../noRelativeImportsAcrossPackages';`,
+      filename: __filename,
+    },
+    {
+      code: `require('../noRelativeImportsAcrossPackages');`,
+      filename: __filename,
+    },
+    {
+      code: `import m from './subdir/module';`,
+      filename: __filename,
+    },
+  ],
+  invalid: [
+    {
+      code: `import * as pathUtils from '../../../../test-utils/src/pathUtils';`,
+      filename: __filename,
+      errors: [{messageId: 'noRelativeImportsAcrossPackages'}],
+    },
+    {
+      code: `require('../../../../test-utils/src/pathUtils');`,
+      filename: __filename,
+      errors: [{messageId: 'noRelativeImportsAcrossPackages'}],
+    },
+  ],
+});