feat(eslint-plugin): add extension rule init-declarations

packages/eslint-plugin/README.md

@@ -183,6 +183,7 @@ In these cases, we create what we call an extension rule; a rule within our plug
 | [`@typescript-eslint/default-param-last`](./docs/rules/default-param-last.md)                   | Enforce default parameters to be last                                          |                    |          |                   |
 | [`@typescript-eslint/func-call-spacing`](./docs/rules/func-call-spacing.md)                     | Require or disallow spacing between function identifiers and their invocations |                    | :wrench: |                   |
 | [`@typescript-eslint/indent`](./docs/rules/indent.md)                                           | Enforce consistent indentation                                                 |                    | :wrench: |                   |
+| [`@typescript-eslint/init-declarations`](./docs/rules/init-declarations.md)                     | require or disallow initialization in variable declarations                    |                    |          |                   |
 | [`@typescript-eslint/no-array-constructor`](./docs/rules/no-array-constructor.md)               | Disallow generic `Array` constructors                                          | :heavy_check_mark: | :wrench: |                   |
 | [`@typescript-eslint/no-dupe-class-members`](./docs/rules/no-dupe-class-members.md)             | Disallow duplicate class members                                               |                    |          |                   |
 | [`@typescript-eslint/no-empty-function`](./docs/rules/no-empty-function.md)                     | Disallow empty functions                                                       | :heavy_check_mark: |          |                   |

packages/eslint-plugin/docs/rules/init-declarations.md

@@ -0,0 +1,22 @@
+# require or disallow initialization in variable declarations (`init-declarations`)
+
+## Rule Details
+
+This rule extends the base [`eslint/init-declarations`](https://eslint.org/docs/rules/init-declarations) rule.
+It adds support for TypeScript's `declare` variables.
+
+## How to use
+
+```cjson
+{
+  // note you must disable the base rule as it can report incorrect errors
+  "init-declarations": "off",
+  "@typescript-eslint/init-declarations": ["error"]
+}
+```
+
+## Options
+
+See [`eslint/init-declarations` options](https://eslint.org/docs/rules/init-declarations#options).
+
+<sup>Taken with ❤️ [from ESLint core](https://github.com/eslint/eslint/blob/master/docs/rules/init-declarations.md)</sup>

packages/eslint-plugin/src/configs/all.json

@@ -22,6 +22,8 @@
     "@typescript-eslint/func-call-spacing": "error",
     "indent": "off",
     "@typescript-eslint/indent": "error",
+    "init-declarations": "off",
+    "@typescript-eslint/init-declarations": "error",
     "@typescript-eslint/member-delimiter-style": "error",
     "@typescript-eslint/member-ordering": "error",
     "@typescript-eslint/method-signature-style": "error",

packages/eslint-plugin/src/rules/index.ts

@@ -86,6 +86,7 @@ import requireAwait from './require-await';
 import restrictPlusOperands from './restrict-plus-operands';
 import restrictTemplateExpressions from './restrict-template-expressions';
 import returnAwait from './return-await';
+import initDeclarations from './init-declarations';
 import semi from './semi';
 import spaceBeforeFunctionParen from './space-before-function-paren';
 import strictBooleanExpressions from './strict-boolean-expressions';
@@ -117,6 +118,7 @@ export default {
   'func-call-spacing': funcCallSpacing,
   'generic-type-naming': genericTypeNaming,
   indent: indent,
+  'init-declarations': initDeclarations,
   'interface-name-prefix': interfaceNamePrefix,
   'member-delimiter-style': memberDelimiterStyle,
   'member-naming': memberNaming,

packages/eslint-plugin/src/rules/init-declarations.ts

@@ -0,0 +1,53 @@
+import {
+  TSESTree,
+  AST_NODE_TYPES,
+} from '@typescript-eslint/experimental-utils';
+import baseRule from 'eslint/lib/rules/init-declarations';
+import {
+  InferOptionsTypeFromRule,
+  InferMessageIdsTypeFromRule,
+  createRule,
+} from '../util';
+
+export type Options = InferOptionsTypeFromRule<typeof baseRule>;
+export type MessageIds = InferMessageIdsTypeFromRule<typeof baseRule>;
+
+export default createRule<Options, MessageIds>({
+  name: 'init-declarations',
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description:
+        'require or disallow initialization in variable declarations',
+      category: 'Variables',
+      recommended: false,
+      extendsBaseRule: true,
+    },
+    schema: baseRule.meta.schema,
+    messages: baseRule.meta.messages,
+  },
+  defaultOptions: ['always'],
+  create(context) {
+    const rules = baseRule.create(context);
+    const mode = context.options[0] || 'always';
+
+    return {
+      'VariableDeclaration:exit'(node: TSESTree.VariableDeclaration): void {
+        if (mode === 'always') {
+          if (node.declare) {
+            return;
+          }
+          if (
+            node.parent?.type === AST_NODE_TYPES.TSModuleBlock &&
+            node.parent.parent?.type === AST_NODE_TYPES.TSModuleDeclaration &&
+            node.parent.parent?.declare
+          ) {
+            return;
+          }
+        }
+
+        rules['VariableDeclaration:exit'](node);
+      },
+    };
+  },
+});