Merge pull request #68 from azat-io/feat/ts-declarations

allow var in TypeScript ambient declarations

Author: cowboyd

.changeset/tidy-coats-peel.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-prefer-let": patch
+---
+
+allow var in TypeScript ambient declarations

packages/eslint-plugin-prefer-let/lib/rules/prefer-let.js

@@ -51,13 +51,27 @@ module.exports = {
       return isGlobalScope(node) || isModuleScope(node) || isProgramScope(node);
     }
 
+    function isInAmbientContext(node) {
+      let current = node.parent;
+      while (current) {
+        if (current.type === 'TSModuleDeclaration' && current.declare === true) {
+          return true;
+        }
+        current = current.parent;
+      }
+      return false;
+    }
+
     //----------------------------------------------------------------------
     // Public
     //----------------------------------------------------------------------
 
     return {
       VariableDeclaration(node) {
         if (node.kind === 'var') {
+          if (isInAmbientContext(node)) {
+            return;
+          }
           context.report({
             message: 'prefer `let` over `var` to declare value bindings',
             node

packages/eslint-plugin-prefer-let/package.json

@@ -20,6 +20,7 @@
     "requireindex": "~1.2.0"
   },
   "devDependencies": {
+    "@typescript-eslint/parser": "^8.0.0",
     "eslint": "^9.3.0",
     "globals": "^15.3.0",
     "mocha": "^9.1.3"

packages/eslint-plugin-prefer-let/tests/lib/rules/prefer-let.js

@@ -46,6 +46,24 @@ ruleTester.run("prefer-let", rule, {
         }
       },
       code: "const PI = 3.14;"
+    },
+    {
+      code: "declare global { var foo: any; }",
+      languageOptions: {
+        parser: require("@typescript-eslint/parser")
+      }
+    },
+    {
+      code: "declare module 'foo' { var bar: any; }",
+      languageOptions: {
+        parser: require("@typescript-eslint/parser")
+      }
+    },
+    {
+      code: "declare namespace MyNamespace { var baz: any; }",
+      languageOptions: {
+        parser: require("@typescript-eslint/parser")
+      }
     }
   ],