Fixes false positives with import/extensions in ESM. (#190)

src/import.js

@@ -62,8 +62,15 @@ const config = {
 };
 
 if (packageJson.type === 'module') {
-    // Need to modify rule as file extensions are mandatory in ESM.
+    // Need to modify rules as file extensions are mandatory in ESM.
     // https://nodejs.org/api/esm.html#mandatory-file-extensions
+    config.rules['import/extensions'] = [
+        'error',
+        'ignorePackages',
+        {
+            cjs: 'never',
+        },
+    ];
     config.rules['import/no-useless-path-segments'] = [
         'error',
         {

src/import.test.js

@@ -1,9 +1,41 @@
+describe('import/extensions', () => {
+    beforeEach(() => {
+        jest.resetModules();
+    });
+
+    test('cjs', () => {
+        jest.doMock('./utils/files/contents', () => ({
+            packageJson: {},
+        }));
+
+        const {rules} = require('./import');
+
+        const [, option, config] = rules['import/extensions'];
+
+        expect(option).toBe('never');
+        expect(config.mjs).toBe('ignorePackages');
+    });
+
+    test('esm', () => {
+        jest.doMock('./utils/files/contents', () => ({
+            packageJson: {type: 'module'},
+        }));
+
+        const {rules} = require('./import');
+
+        const [, option, config] = rules['import/extensions'];
+
+        expect(option).toBe('ignorePackages');
+        expect(config.cjs).toBe('never');
+    });
+});
+
 describe('import/no-useless-path-segments', () => {
     beforeEach(() => {
         jest.resetModules();
     });
 
-    test('packageJson.type = "module"', () => {
+    test('esm', () => {
         jest.doMock('./utils/files/contents', () => ({
             packageJson: {type: 'module'},
         }));