feat: allow global type declaration in no-var (#19714)

Author: remcohaszing

docs/src/rules/no-var.md

@@ -54,6 +54,42 @@ const CONFIG = {};
 
 :::
 
+This rule additionally supports TypeScript type syntax. There are multiple ways to declare global variables in TypeScript. Only using `var` works for all cases. See this [TypeScript playground](https://www.typescriptlang.org/play/?#code/PQgEB4CcFMDNpgOwMbVAGwJYCMC8AiAEwHsBbfUYAPgFgAoew6ZdAQxlAHN1jtX1QAb3qhRGaABdQAGUkAuUAGcJkTIk4ixAN3agAauwXLV6+ptFqJCWK1SgA6mpIB3IebGjHiIyrUa6HgC+9MEMdGDcvPygtqiKivSyEvQGkPReZuHAoM5OxK6ckvS5iC4AdEnFec5lqVWl+WUZYWAlLkpFdG2NSaC4oADkA-XlqX2Dw13VTWrjQ5kRPHzoACoAFpiKXJ2Ry+ubFTtL-PuKtez0uycbZ830i1GrNx3JdFdPB73982-HH2djb6Td6nGaIOaTe7ZRTQdCwbavGFww6I2Gwc5pOhI9F3LIdOEvejYlEQolojGkrHkryU+jQAAeAAdiJApIJAkA) for reference.
+
+Examples of **incorrect** TypeScript code for this rule:
+
+:::incorrect
+
+```ts
+/*eslint no-var: "error"*/
+
+declare var x: number
+
+declare namespace ns {
+	var x: number
+}
+
+declare module 'module' {
+	var x: number
+}
+```
+
+:::
+
+Examples of **correct** TypeScript code for this rule:
+
+:::correct
+
+```ts
+/*eslint no-var: "error"*/
+
+declare global {
+    declare var x: number
+}
+```
+
+:::
+
 ## When Not To Use It
 
 In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their

lib/rules/no-var.js

@@ -199,6 +199,8 @@ function hasNameDisallowedForLetDeclarations(variable) {
 module.exports = {
 	meta: {
 		type: "suggestion",
+		dialects: ["typescript", "javascript"],
+		language: "javascript",
 
 		docs: {
 			description: "Require `let` or `const` instead of `var`",
@@ -346,9 +348,19 @@ module.exports = {
 
 		return {
 			"VariableDeclaration:exit"(node) {
-				if (node.kind === "var") {
-					report(node);
+				if (node.kind !== "var") {
+					return;
 				}
+
+				if (
+					node.parent.type === "TSModuleBlock" &&
+					node.parent.parent.type === "TSModuleDeclaration" &&
+					node.parent.parent.global
+				) {
+					return;
+				}
+
+				report(node);
 			},
 		};
 	},

tests/lib/rules/no-var.js

@@ -431,3 +431,23 @@ ruleTester.run("no-var", rule, {
 		},
 	],
 });
+
+const ruleTesterTypeScript = new RuleTester({
+	languageOptions: {
+		parser: require("@typescript-eslint/parser"),
+	},
+});
+
+ruleTesterTypeScript.run("no-var", rule, {
+	valid: ["declare global { var bar: 'car' }"],
+	invalid: [
+		{
+			code: "declare namespace ns { var bar: 'car' }",
+			errors: [{ messageId: "unexpectedVar" }],
+		},
+		{
+			code: "declare module 'module' { var bar: 'car' }",
+			errors: [{ messageId: "unexpectedVar" }],
+		},
+	],
+});