feat(no-empty-interface): add allowSingleExtend option (#215)

Author: timkraut

Diff for: packages/eslint-plugin/docs/rules/no-empty-interface.md

@@ -38,6 +38,23 @@ interface Bar {
 interface Baz extends Foo, Bar {}
 ```
 
+### Options
+
+This rule accepts a single object option with the following default configuration:
+
+```json
+{
+  "@typescript-eslint/no-empty-interface": [
+    "error",
+    {
+      "allowSingleExtends": false
+    }
+  ]
+}
+```
+
+- `allowSingleExtends: true` will silence warnings about extending a single interface without adding additional members
+
 ## When Not To Use It
 
 If you don't care about having empty/meaningless interfaces, then you will not need this rule.

Diff for: packages/eslint-plugin/src/rules/no-empty-interface.ts

@@ -6,7 +6,14 @@
 import { TSESTree } from '@typescript-eslint/typescript-estree';
 import * as util from '../util';
 
-export default util.createRule({
+type Options = [
+  {
+    allowSingleExtends?: boolean;
+  }
+];
+type MessageIds = 'noEmpty' | 'noEmptyWithSuper';
+
+export default util.createRule<Options, MessageIds>({
   name: 'no-empty-interface',
   meta: {
     type: 'suggestion',
@@ -21,13 +28,28 @@ export default util.createRule({
       noEmptyWithSuper:
         'An interface declaring no members is equivalent to its supertype.'
     },
-    schema: []
+    schema: [
+      {
+        type: 'object',
+        additionalProperties: false,
+        properties: {
+          allowSingleExtends: {
+            type: 'boolean'
+          }
+        }
+      }
+    ]
   },
-  defaultOptions: [],
-  create(context) {
+  defaultOptions: [
+    {
+      allowSingleExtends: false
+    }
+  ],
+  create(context, [{ allowSingleExtends }]) {
     return {
       TSInterfaceDeclaration(node: TSESTree.TSInterfaceDeclaration) {
         if (node.body.body.length !== 0) {
+          // interface contains members --> Nothing to report
           return;
         }
 
@@ -37,10 +59,15 @@ export default util.createRule({
             messageId: 'noEmpty'
           });
         } else if (node.extends.length === 1) {
-          context.report({
-            node: node.id,
-            messageId: 'noEmptyWithSuper'
-          });
+          // interface extends exactly 1 interface --> Report depending on rule setting
+          if (allowSingleExtends) {
+            return;
+          } else {
+            context.report({
+              node: node.id,
+              messageId: 'noEmptyWithSuper'
+            });
+          }
         }
       }
     };

Diff for: packages/eslint-plugin/tests/rules/no-empty-interface.test.ts

@@ -23,7 +23,17 @@ interface Bar {
 
 // valid because extending multiple interfaces can be used instead of a union type
 interface Baz extends Foo, Bar {}
-        `
+        `,
+    {
+      code: `
+interface Foo {
+    name: string;
+}
+
+interface Bar extends Foo {}
+        `,
+      options: [{ allowSingleExtends: true }]
+    }
   ],
   invalid: [
     {
@@ -54,6 +64,7 @@ interface Foo {
 
 interface Bar extends Foo {}
             `,
+      options: [{ allowSingleExtends: false }],
       errors: [
         {
           messageId: 'noEmptyWithSuper',