From 7b5ea1d438d56c4f5aadcc82d97c1ad091bf56b7 Mon Sep 17 00:00:00 2001
From: cherryblossom <31467609+cherryblossom000@users.noreply.github.com>
Date: Sun, 1 Nov 2020 15:11:51 +1100
Subject: [PATCH] fix(eslint-plugin): [no-shadow] ignore module augmentation 
 (fixes #2724)

---
 .../eslint-plugin/docs/rules/no-shadow.md     |  2 +-
 packages/eslint-plugin/src/rules/no-shadow.ts | 16 +++++++
 .../tests/rules/no-shadow.test.ts             | 43 +++++++++++++++++++
 3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/packages/eslint-plugin/docs/rules/no-shadow.md b/packages/eslint-plugin/docs/rules/no-shadow.md
index ed241b807882..bcb40d4fb5a0 100644
--- a/packages/eslint-plugin/docs/rules/no-shadow.md
+++ b/packages/eslint-plugin/docs/rules/no-shadow.md
@@ -3,7 +3,7 @@
 ## Rule Details
 
 This rule extends the base [`eslint/no-shadow`](https://eslint.org/docs/rules/no-shadow) rule.
-It adds support for TypeScript's `this` parameters, and adds options for TypeScript features.
+It adds support for TypeScript's `this` parameters and global augmentation, and adds options for TypeScript features.
 
 ## How to use
 
diff --git a/packages/eslint-plugin/src/rules/no-shadow.ts b/packages/eslint-plugin/src/rules/no-shadow.ts
index 05761572b216..1d1f894b651f 100644
--- a/packages/eslint-plugin/src/rules/no-shadow.ts
+++ b/packages/eslint-plugin/src/rules/no-shadow.ts
@@ -3,6 +3,7 @@ import {
   TSESLint,
   AST_NODE_TYPES,
 } from '@typescript-eslint/experimental-utils';
+import { ScopeType } from '@typescript-eslint/scope-manager';
 import * as util from '../util';
 
 type MessageIds = 'noShadow';
@@ -67,6 +68,16 @@ export default util.createRule<Options, MessageIds>({
     },
   ],
   create(context, [options]) {
+    /**
+     * Check if a scope is a TypeScript module augmenting the global namespace.
+     */
+    function isGlobalAugmentation(scope: TSESLint.Scope.Scope): boolean {
+      return (
+        (scope.type === ScopeType.tsModule && !!scope.block.global) ||
+        (!!scope.upper && isGlobalAugmentation(scope.upper))
+      );
+    }
+
     /**
      * Check if variable is a `this` parameter.
      */
@@ -261,6 +272,11 @@ export default util.createRule<Options, MessageIds>({
      * @param {Scope} scope Fixme
      */
     function checkForShadows(scope: TSESLint.Scope.Scope): void {
+      // ignore global augmentation
+      if (isGlobalAugmentation(scope)) {
+        return;
+      }
+
       const variables = scope.variables;
 
       for (const variable of variables) {
diff --git a/packages/eslint-plugin/tests/rules/no-shadow.test.ts b/packages/eslint-plugin/tests/rules/no-shadow.test.ts
index d7c81d834492..abc78ee5f3ec 100644
--- a/packages/eslint-plugin/tests/rules/no-shadow.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-shadow.test.ts
@@ -116,6 +116,49 @@ type Fn = (Foo: string) => typeof Foo;
         Foo: 'writable',
       },
     },
+    // https://github.com/typescript-eslint/typescript-eslint/issues/2724
+    {
+      code: `
+        declare global {
+          interface ArrayConstructor {}
+        }
+        export {};
+      `,
+      options: [{ builtinGlobals: true }],
+    },
+    `
+      declare global {
+        const a: string;
+
+        namespace Foo {
+          const a: number;
+        }
+      }
+      export {};
+    `,
+    {
+      code: `
+        declare global {
+          type A = 'foo';
+
+          namespace Foo {
+            type A = 'bar';
+          }
+        }
+        export {};
+      `,
+      options: [{ ignoreTypeValueShadow: false }],
+    },
+    {
+      code: `
+        declare global {
+          const foo: string;
+          type Fn = (foo: number) => void;
+        }
+        export {};
+      `,
+      options: [{ ignoreFunctionTypeParameterNameValueShadow: false }],
+    },
   ],
   invalid: [
     {