typescript-eslint · bradzacher · Feb 28, 2020 · Dec 24, 2019 · Feb 23, 2020 · Feb 23, 2020
diff --git a/packages/eslint-plugin/docs/rules/ban-types.md b/packages/eslint-plugin/docs/rules/ban-types.md
@@ -58,6 +58,23 @@ The banned type can either be a type name literal (`Foo`), a type name with gene
 }
 ```
 
+By default, this rule includes types which are likely to be mistakes, such as `String` and `Number`. If you don't want these enabled, set the `extendDefaults` option to `false`:
+
+```CJSON
+{
+    "@typescript-eslint/ban-types": ["error", {
+        "types": {
+            // add a custom message, AND tell the plugin how to fix it
+            "String": {
+                "message": "Use string instead",
+                "fixWith": "string"
+            }
+        },
+        "extendDefaults": false
+    }]
+}
+```
+
 ### Example
 
 ```json

diff --git a/packages/eslint-plugin/src/rules/ban-types.ts b/packages/eslint-plugin/src/rules/ban-types.ts
@@ -13,7 +13,8 @@ type Types = Record<
 
 type Options = [
   {
-    types: Types;
+    types?: Types;
+    extendDefaults?: boolean;
   },
 ];
 type MessageIds = 'bannedTypeMessage';
@@ -51,6 +52,35 @@ function getCustomMessage(
   return '';
 }
 
+/*
+  Defaults for this rule should be treated as an "all or nothing"
+  merge, so we need special handling here.
+
+  See: https://github.com/typescript-eslint/typescript-eslint/issues/686
+ */
+const defaultTypes = {
+  String: {
+    message: 'Use string instead',
+    fixWith: 'string',
+  },
+  Boolean: {
+    message: 'Use boolean instead',
+    fixWith: 'boolean',
+  },
+  Number: {
+    message: 'Use number instead',
+    fixWith: 'number',
+  },
+  Object: {
+    message: 'Use Record<string, any> instead',
+    fixWith: 'Record<string, any>',
+  },
+  Symbol: {
+    message: 'Use symbol instead',
+    fixWith: 'symbol',
+  },
+};
+
 export default util.createRule<Options, MessageIds>({
   name: 'ban-types',
   meta: {
@@ -85,38 +115,22 @@ export default util.createRule<Options, MessageIds>({
               ],
             },
           },
+          extendDefaults: {
+            type: 'boolean',
+          },
         },
         additionalProperties: false,
       },
     ],
   },
-  defaultOptions: [
-    {
-      types: {
-        String: {
-          message: 'Use string instead',
-          fixWith: 'string',
-        },
-        Boolean: {
-          message: 'Use boolean instead',
-          fixWith: 'boolean',
-        },
-        Number: {
-          message: 'Use number instead',
-          fixWith: 'number',
-        },
-        Object: {
-          message: 'Use Record<string, any> instead',
-          fixWith: 'Record<string, any>',
-        },
-        Symbol: {
-          message: 'Use symbol instead',
-          fixWith: 'symbol',
-        },
-      },
-    },
-  ],
-  create(context, [{ types }]) {
+  defaultOptions: [{}],
+  create(context, [options]) {
+    const extendDefaults = options.extendDefaults ?? true;
+    const customTypes = options.types ?? {};
+    const types: Types = {
+      ...(extendDefaults ? defaultTypes : {}),
+      ...customTypes,
+    };
     const bannedTypes = new Map(
       Object.entries(types).map(([type, data]) => [removeSpaces(type), data]),
     );

diff --git a/packages/eslint-plugin/tests/rules/ban-types.test.ts b/packages/eslint-plugin/tests/rules/ban-types.test.ts
@@ -72,6 +72,21 @@ ruleTester.run('ban-types', rule, {
       code: 'let a: NS.Bad._',
       options,
     },
+    // Replace default options instead of merging with extendDefaults: false
+    {
+      code: 'let a: String;',
+      options: [
+        {
+          types: {
+            Number: {
+              message: 'Use number instead.',
+              fixWith: 'number',
+            },
+          },
+          extendDefaults: false,
+        },
+      ],
+    },
     {
       code: 'let a: undefined',
       options: options2,
@@ -82,6 +97,16 @@ ruleTester.run('ban-types', rule, {
     },
   ],
   invalid: [
+    {
+      code: 'let a: String;',
+      errors: [
+        {
+          messageId: 'bannedTypeMessage',
+          line: 1,
+          column: 8,
+        },
+      ],
+    },
     {
       code: 'let a: Object;',
       errors: [