typescript-eslint · bradzacher · Apr 26, 2020 · Apr 4, 2020 · Apr 5, 2020 · Apr 5, 2020
diff --git a/packages/eslint-plugin/README.md b/packages/eslint-plugin/README.md
@@ -119,6 +119,7 @@ Pro Tip: For larger codebases you may want to consider splitting our linting int
 | [`@typescript-eslint/no-for-in-array`](./docs/rules/no-for-in-array.md)                                               | Disallow iterating over an array with a for-in loop                                                                     | :heavy_check_mark: |          | :thought_balloon: |
 | [`@typescript-eslint/no-implied-eval`](./docs/rules/no-implied-eval.md)                                               | Disallow the use of `eval()`-like methods                                                                               |                    |          | :thought_balloon: |
 | [`@typescript-eslint/no-inferrable-types`](./docs/rules/no-inferrable-types.md)                                       | Disallows explicit type declarations for variables or parameters initialized to a number, string, or boolean            | :heavy_check_mark: | :wrench: |                   |
+| [`@typescript-eslint/no-invalid-void-type`](./docs/rules/no-invalid-void-type.md)                                     | Disallows usage of `void` type outside of generic or return types                                                       |                    |          |                   |
 | [`@typescript-eslint/no-misused-new`](./docs/rules/no-misused-new.md)                                                 | Enforce valid definition of `new` and `constructor`                                                                     | :heavy_check_mark: |          |                   |
 | [`@typescript-eslint/no-misused-promises`](./docs/rules/no-misused-promises.md)                                       | Avoid using promises in places not designed to handle them                                                              | :heavy_check_mark: |          | :thought_balloon: |
 | [`@typescript-eslint/no-namespace`](./docs/rules/no-namespace.md)                                                     | Disallow the use of custom TypeScript modules and namespaces                                                            | :heavy_check_mark: |          |                   |

diff --git a/packages/eslint-plugin/ROADMAP.md b/packages/eslint-plugin/ROADMAP.md
@@ -18,7 +18,7 @@ It lists all TSLint rules along side rules from the ESLint ecosystem that are th
 | [`adjacent-overload-signatures`]  | ✅  | [`@typescript-eslint/adjacent-overload-signatures`]  |
 | [`ban-ts-ignore`]                 | ✅  | [`@typescript-eslint/ban-ts-ignore`]                 |
 | [`ban-types`]                     | 🌓  | [`@typescript-eslint/ban-types`]<sup>[1]</sup>       |
-| [`invalid-void`]                  | 🛑  | N/A                                                  |
+| [`invalid-void`]                  | ✅  | [`@typescript-eslint/no-invalid-void-type`]          |
 | [`member-access`]                 | ✅  | [`@typescript-eslint/explicit-member-accessibility`] |
 | [`member-ordering`]               | ✅  | [`@typescript-eslint/member-ordering`]               |
 | [`no-any`]                        | ✅  | [`@typescript-eslint/no-explicit-any`]               |
@@ -623,6 +623,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
 [`@typescript-eslint/restrict-plus-operands`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/restrict-plus-operands.md
 [`@typescript-eslint/strict-boolean-expressions`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/strict-boolean-expressions.md
 [`@typescript-eslint/indent`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/indent.md
+[`@typescript-eslint/no-invalid-void-type`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-invalid-void-type.md
 [`@typescript-eslint/no-require-imports`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-require-imports.md
 [`@typescript-eslint/array-type`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/array-type.md
 [`@typescript-eslint/class-name-casing`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/class-name-casing.md

diff --git a/packages/eslint-plugin/docs/rules/no-invalid-void-type.md b/packages/eslint-plugin/docs/rules/no-invalid-void-type.md
@@ -0,0 +1,101 @@
+# Disallows usage of `void` type outside of generic or return types (`no-invalid-void-type`)
+
+Disallows usage of `void` type outside of return types or generic type arguments.
+If `void` is used as return type, it shouldn’t be a part of intersection/union type.
+
+## Rationale
+
+The `void` type means “nothing” or that a function does not return any value,
+in contrast with implicit `undefined` type which means that a function returns a value `undefined`.
+So “nothing” cannot be mixed with any other types. If you need this - use the `undefined` type instead.
+
+## Rule Details
+
+This rule aims to ensure that the `void` type is only used in valid places.
+
+The following patterns are considered warnings:
+
+```ts
+type PossibleValues = string | number | void;
+type MorePossibleValues = string | ((number & any) | (string | void));
+
+function logSomething(thing: void) {}
+function printArg<T = void>(arg: T) {}
+
+logAndReturn<void>(undefined);
+
+interface Interface {
+  lambda: () => void;
+  prop: void;
+}
+
+class MyClass {
+  private readonly propName: void;
+}
+```
+
+The following patterns are not considered warnings:
+
+```ts
+type NoOp = () => void;
+
+function noop(): void {}
+
+let trulyUndefined = void 0;
+
+async function promiseMeSomething(): Promise<void> {}
+```
+
+### Options
+
+```ts
+interface Options {
+  allowInGenericTypeArguments?: boolean | string[];
+}
+
+const defaultOptions: Options = {
+  allowInGenericTypeArguments: true,
+};
+```
+
+#### `allowInGenericTypeArguments`
+
+This option lets you control if `void` can be used as a valid value for generic type parameters.
+
+Alternatively, you can provide an array of strings which whitelist which types may accept `void` as a generic type parameter.
+
+This option is `true` by default.
+
+The following patterns are considered warnings with `{ allowInGenericTypeArguments: false }`:
+
+```ts
+logAndReturn<void>(undefined);
+
+let voidPromise: Promise<void> = new Promise<void>(() => {});
+let voidMap: Map<string, void> = new Map<string, void>();
+```
+
+The following patterns are considered warnings with `{ allowInGenericTypeArguments: ['Ex.Mx.Tx'] }`:
+
+```ts
+logAndReturn<void>(undefined);
+
+type NotAllowedVoid1 = Mx.Tx<void>;
+type NotAllowedVoid2 = Tx<void>;
+type NotAllowedVoid3 = Promise<void>;
+```
+
+The following patterns are not considered warnings with `{ allowInGenericTypeArguments: ['Ex.Mx.Tx'] }`:
+
+```ts
+type AllowedVoid = Ex.MX.Tx<void>;
+```
+
+## When Not To Use It
+
+If you don't care about if `void` is used with other types,
+or in invalid places, then you don't need this rule.
+
+## Compatibility
+
+- TSLint: [invalid-void](https://palantir.github.io/tslint/rules/invalid-void/)
diff --git a/packages/eslint-plugin/src/configs/all.json b/packages/eslint-plugin/src/configs/all.json
@@ -50,6 +50,7 @@
     "@typescript-eslint/no-for-in-array": "error",
     "@typescript-eslint/no-implied-eval": "error",
     "@typescript-eslint/no-inferrable-types": "error",
+    "@typescript-eslint/no-invalid-void-type": "error",
     "no-magic-numbers": "off",
     "@typescript-eslint/no-magic-numbers": "error",
     "@typescript-eslint/no-misused-new": "error",

diff --git a/packages/eslint-plugin/src/rules/index.ts b/packages/eslint-plugin/src/rules/index.ts
@@ -40,6 +40,7 @@ import noFloatingPromises from './no-floating-promises';
 import noForInArray from './no-for-in-array';
 import noImpliedEval from './no-implied-eval';
 import noInferrableTypes from './no-inferrable-types';
+import noInvalidVoidType from './no-invalid-void-type';
 import noMagicNumbers from './no-magic-numbers';
 import noMisusedNew from './no-misused-new';
 import noMisusedPromises from './no-misused-promises';
@@ -142,6 +143,7 @@ export default {
   'no-for-in-array': noForInArray,
   'no-implied-eval': noImpliedEval,
   'no-inferrable-types': noInferrableTypes,
+  'no-invalid-void-type': noInvalidVoidType,
   'no-magic-numbers': noMagicNumbers,
   'no-misused-new': noMisusedNew,
   'no-misused-promises': noMisusedPromises,

diff --git a/packages/eslint-plugin/src/rules/no-invalid-void-type.ts b/packages/eslint-plugin/src/rules/no-invalid-void-type.ts
@@ -0,0 +1,116 @@
+import {
+  AST_NODE_TYPES,
+  TSESTree,
+} from '@typescript-eslint/experimental-utils';
+import * as util from '../util';
+
+interface Options {
+  allowInGenericTypeArguments: boolean | string[];
+}
+
+type MessageIds =
+  | 'invalidVoidForGeneric'
+  | 'invalidVoidNotReturnOrGeneric'
+  | 'invalidVoidNotReturn';
+
+export default util.createRule<[Options], MessageIds>({
+  name: 'no-invalid-void-type',
+  meta: {
+    type: 'problem',
+    docs: {
+      description:
+        'Disallows usage of `void` type outside of generic or return types',
+      category: 'Best Practices',
+      recommended: false,
+    },
+    messages: {
+      invalidVoidForGeneric:
+        '{{ generic }} may not have void as a type variable',
+      invalidVoidNotReturnOrGeneric:
+        'void is only valid as a return type or generic type variable',
+      invalidVoidNotReturn: 'void is only valid as a return type',
+    },
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          allowInGenericTypeArguments: {
+            oneOf: [
+              { type: 'boolean' },
+              {
+                type: 'array',
+                items: { type: 'string' },
+                minLength: 1,
+              },
+            ],
+          },
+        },
+        additionalProperties: false,
+      },
+    ],
+  },
+  defaultOptions: [{ allowInGenericTypeArguments: true }],
+  create(context, [{ allowInGenericTypeArguments }]) {
+    const validParents: AST_NODE_TYPES[] = [
+      AST_NODE_TYPES.TSTypeAnnotation, //
+    ];
+    const invalidGrandParents: AST_NODE_TYPES[] = [
+      AST_NODE_TYPES.TSPropertySignature,
+      AST_NODE_TYPES.CallExpression,
+      AST_NODE_TYPES.ClassProperty,
+      AST_NODE_TYPES.Identifier,
+    ];
+
+    if (allowInGenericTypeArguments === true) {
+      validParents.push(AST_NODE_TYPES.TSTypeParameterInstantiation);
+    }
+
+    return {
+      TSVoidKeyword(node: TSESTree.TSVoidKeyword): void {
+        /* istanbul ignore next */
+        if (!node.parent?.parent) {
+          return;
+        }
+
+        if (
+          validParents.includes(node.parent.type) &&
+          !invalidGrandParents.includes(node.parent.parent.type)
+        ) {
+          return;
+        }
+
+        if (
+          node.parent.type === AST_NODE_TYPES.TSTypeParameterInstantiation &&
+          node.parent.parent.type === AST_NODE_TYPES.TSTypeReference &&
+          Array.isArray(allowInGenericTypeArguments)
+        ) {
+          const sourceCode = context.getSourceCode();
+          const fullyQualifiedName = sourceCode
+            .getText(node.parent.parent.typeName)
+            .replace(/ /gu, '');
+
+          if (
+            !allowInGenericTypeArguments
+              .map(s => s.replace(/ /gu, ''))
+              .includes(fullyQualifiedName)
+          ) {
+            context.report({
+              messageId: 'invalidVoidForGeneric',
+              data: { generic: fullyQualifiedName },
+              node,
+            });
+          }
+
+          return;
+        }
+
+        context.report({
+          messageId: allowInGenericTypeArguments
+            ? 'invalidVoidNotReturnOrGeneric'
+            : 'invalidVoidNotReturn',
+          node,
+        });
+      },
+    };
+  },
+});