feat(eslint-plugin): [no-empty-func] private/protected construct (typescript-eslint#1267)

a-tarasyuk · bradzacher · bradzacher · commit 3b931acf563c · 2019-11-26T22:24:30.000-08:00
Co-authored-by: Brad Zacher &lt;brad.zacher@gmail.com&gt;
diff --git a/packages/eslint-plugin/docs/rules/no-empty-function.md b/packages/eslint-plugin/docs/rules/no-empty-function.md
@@ -44,4 +44,37 @@ See the [ESLint documentation](https://eslint.org/docs/rules/no-empty-function)
 }
 ```
 
+## Options
+
+This rule has an object option:
+
+- `allow` (`string[]`)
+  - `"protected-constructors"` - Protected class constructors.
+  - `"private-constructors"` - Private class constructors.
+  - [See the other options allowed](https://github.com/eslint/eslint/blob/master/docs/rules/no-empty-function.md#options)
+
+#### allow: protected-constructors
+
+Examples of **correct** code for the `{ "allow": ["protected-constructors"] }` option:
+
+```ts
+/*eslint @typescript-eslint/no-empty-function: ["error", { "allow": ["protected-constructors"] }]*/
+
+class Foo {
+  protected constructor() {}
+}
+```
+
+#### allow: private-constructors
+
+Examples of **correct** code for the `{ "allow": ["private-constructors"] }` option:
+
+```ts
+/*eslint @typescript-eslint/no-empty-function: ["error", { "allow": ["private-constructors"] }]*/
+
+class Foo {
+  private constructor() {}
+}
+```
+
 <sup>Taken with ❤️ [from ESLint core](https://github.com/eslint/eslint/blob/master/docs/rules/no-empty-function.md)</sup>
diff --git a/packages/eslint-plugin/src/rules/no-empty-function.ts b/packages/eslint-plugin/src/rules/no-empty-function.ts
@@ -8,6 +8,32 @@ import * as util from '../util';
 type Options = util.InferOptionsTypeFromRule<typeof baseRule>;
 type MessageIds = util.InferMessageIdsTypeFromRule<typeof baseRule>;
 
+const schema = util.deepMerge(
+  Array.isArray(baseRule.meta.schema)
+    ? baseRule.meta.schema[0]
+    : baseRule.meta.schema,
+  {
+    properties: {
+      allow: {
+        items: {
+          enum: [
+            'functions',
+            'arrowFunctions',
+            'generatorFunctions',
+            'methods',
+            'generatorMethods',
+            'getters',
+            'setters',
+            'constructors',
+            'private-constructors',
+            'protected-constructors',
+          ],
+        },
+      },
+    },
+  },
+);
+
 export default util.createRule<Options, MessageIds>({
   name: 'no-empty-function',
   meta: {
@@ -17,32 +43,21 @@ export default util.createRule<Options, MessageIds>({
       category: 'Best Practices',
       recommended: 'error',
     },
-    schema: baseRule.meta.schema,
+    schema: [schema],
     messages: baseRule.meta.messages,
   },
   defaultOptions: [
     {
       allow: [],
     },
   ],
-  create(context) {
+  create(context, [{ allow = [] }]) {
     const rules = baseRule.create(context);
 
-    /**
-     * Checks if the node is a constructor
-     * @param node the node to ve validated
-     * @returns true if the node is a constructor
-     * @private
-     */
-    function isConstructor(
-      node: TSESTree.FunctionDeclaration | TSESTree.FunctionExpression,
-    ): boolean {
-      return !!(
-        node.parent &&
-        node.parent.type === 'MethodDefinition' &&
-        node.parent.kind === 'constructor'
-      );
-    }
+    const isAllowedProtectedConstructors = allow.includes(
+      'protected-constructors',
+    );
+    const isAllowedPrivateConstructors = allow.includes('private-constructors');
 
     /**
      * Check if the method body is empty
@@ -74,30 +89,44 @@ export default util.createRule<Options, MessageIds>({
     }
 
     /**
-     * Checks if the method is a concise constructor (no function body, but has parameter properties)
      * @param node the node to be validated
-     * @returns true if the method is a concise constructor
+     * @returns true if the constructor is allowed to be empty
      * @private
      */
-    function isConciseConstructor(
+    function isAllowedEmptyConstructor(
       node: TSESTree.FunctionDeclaration | TSESTree.FunctionExpression,
     ): boolean {
-      // Check TypeScript specific nodes
-      return (
-        isConstructor(node) && isBodyEmpty(node) && hasParameterProperties(node)
-      );
+      const parent = node.parent;
+      if (
+        isBodyEmpty(node) &&
+        parent?.type === 'MethodDefinition' &&
+        parent.kind === 'constructor'
+      ) {
+        const { accessibility } = parent;
+
+        return (
+          // allow protected constructors
+          (accessibility === 'protected' && isAllowedProtectedConstructors) ||
+          // allow private constructors
+          (accessibility === 'private' && isAllowedPrivateConstructors) ||
+          // allow constructors which have parameter properties
+          hasParameterProperties(node)
+        );
+      }
+
+      return false;
     }
 
     return {
       FunctionDeclaration(node): void {
-        if (!isConciseConstructor(node)) {
-          rules.FunctionDeclaration(node);
-        }
+        rules.FunctionDeclaration(node);
       },
       FunctionExpression(node): void {
-        if (!isConciseConstructor(node)) {
-          rules.FunctionExpression(node);
+        if (isAllowedEmptyConstructor(node)) {
+          return;
         }
+
+        rules.FunctionExpression(node);
       },
     };
   },
diff --git a/packages/eslint-plugin/tests/rules/no-empty-function.test.ts b/packages/eslint-plugin/tests/rules/no-empty-function.test.ts
@@ -32,6 +32,29 @@ ruleTester.run('no-empty-function', rule, {
       }`,
       options: [{ allow: ['methods'] }],
     },
+    {
+      code: `
+class Foo {
+  private constructor() {}
+}
+      `,
+      options: [{ allow: ['private-constructors'] }],
+    },
+    {
+      code: `
+class Foo {
+  protected constructor() {}
+}
+      `,
+      options: [{ allow: ['protected-constructors'] }],
+    },
+    {
+      code: `
+function foo() {
+  const a = null;
+}
+      `,
+    },
   ],
 
   invalid: [
@@ -65,5 +88,55 @@ ruleTester.run('no-empty-function', rule, {
         },
       ],
     },
+    {
+      code: `
+class Foo {
+  private constructor() {}
+}
+      `,
+      errors: [
+        {
+          messageId: 'unexpected',
+          data: {
+            name: 'constructor',
+          },
+          line: 3,
+          column: 25,
+        },
+      ],
+    },
+    {
+      code: `
+class Foo {
+  protected constructor() {}
+}
+      `,
+      errors: [
+        {
+          messageId: 'unexpected',
+          data: {
+            name: 'constructor',
+          },
+          line: 3,
+          column: 27,
+        },
+      ],
+    },
+    {
+      code: `
+function foo() {
+}
+      `,
+      errors: [
+        {
+          messageId: 'unexpected',
+          data: {
+            name: "function 'foo'",
+          },
+          line: 2,
+          column: 16,
+        },
+      ],
+    },
   ],
 });
