fix(eslint-plugin): [no-empty-interface] use suggestion fixer for ambient contexts (#1880)

Author: vapurrmaid

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

@@ -1,4 +1,8 @@
 import * as util from '../util';
+import {
+  AST_NODE_TYPES,
+  TSESLint,
+} from '@typescript-eslint/experimental-utils';
 
 type Options = [
   {
@@ -43,6 +47,7 @@ export default util.createRule<Options, MessageIds>({
     return {
       TSInterfaceDeclaration(node): void {
         const sourceCode = context.getSourceCode();
+        const filename = context.getFilename();
 
         if (node.body.body.length !== 0) {
           // interface contains members --> Nothing to report
@@ -58,21 +63,46 @@ export default util.createRule<Options, MessageIds>({
         } else if (extend.length === 1) {
           // interface extends exactly 1 interface --> Report depending on rule setting
           if (!allowSingleExtends) {
+            const fix = (fixer: TSESLint.RuleFixer): TSESLint.RuleFix => {
+              let typeParam = '';
+              if (node.typeParameters) {
+                typeParam = sourceCode.getText(node.typeParameters);
+              }
+              return fixer.replaceText(
+                node,
+                `type ${sourceCode.getText(
+                  node.id,
+                )}${typeParam} = ${sourceCode.getText(extend[0])}`,
+              );
+            };
+
+            // Check if interface is within ambient declaration
+            let useAutoFix = true;
+            if (util.isDefinitionFile(filename)) {
+              const scope = context.getScope();
+              if (
+                scope.block.parent &&
+                scope.block.parent.type ===
+                  AST_NODE_TYPES.TSModuleDeclaration &&
+                scope.block.parent.declare
+              ) {
+                useAutoFix = false;
+              }
+            }
+
             context.report({
               node: node.id,
               messageId: 'noEmptyWithSuper',
-              fix: fixer => {
-                let typeParam = '';
-                if (node.typeParameters) {
-                  typeParam = sourceCode.getText(node.typeParameters);
-                }
-                return fixer.replaceText(
-                  node,
-                  `type ${sourceCode.getText(
-                    node.id,
-                  )}${typeParam} = ${sourceCode.getText(extend[0])}`,
-                );
-              },
+              ...(useAutoFix
+                ? { fix }
+                : {
+                    suggest: [
+                      {
+                        messageId: 'noEmptyWithSuper',
+                        fix,
+                      },
+                    ],
+                  }),
             });
           }
         }

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

@@ -148,5 +148,41 @@ type Foo<T> = Bar<T>
         },
       ],
     },
+    {
+      filename: 'test.d.ts',
+      code: `
+declare module FooBar {
+  type Baz = typeof baz;
+  export interface Bar extends Baz {}
+}
+      `.trimRight(),
+      errors: [
+        {
+          messageId: 'noEmptyWithSuper',
+          line: 4,
+          column: 20,
+          endLine: 4,
+          endColumn: 23,
+          suggestions: [
+            {
+              messageId: 'noEmptyWithSuper',
+              output: noFormat`
+declare module FooBar {
+  type Baz = typeof baz;
+  export type Bar = Baz
+}
+              `.trimRight(),
+            },
+          ],
+        },
+      ],
+      // output matches input because a suggestion was made
+      output: `
+declare module FooBar {
+  type Baz = typeof baz;
+  export interface Bar extends Baz {}
+}
+      `.trimRight(),
+    },
   ],
 });