Add support for extension .mjs in no-unsupported-configs rule (#540)

Fixes #532

.changeset/spotty-buckets-fry.md

@@ -0,0 +1,5 @@
+---
+'eslint-plugin-next-on-pages': patch
+---
+
+Support for file extensions .mjs in no-unsupported-configs ESLint rule

packages/eslint-plugin-next-on-pages/src/rules/no-unsupported-configs.ts

@@ -93,7 +93,7 @@ const ruleSchema = {
 const rule: Rule.RuleModule = {
 	create: context => {
 		const code = context.sourceCode;
-		const exportedConfigName = context.filename.match(/next\.config\.js$/)
+		const exportedConfigName = context.filename.match(/next\.config\.m?js$/)
 			? getConfigVariableName(code)
 			: null;
 
@@ -217,6 +217,10 @@ function getConfigVariableName(code: SourceCode): string | null {
 		if (exportedValue?.type === 'Identifier') {
 			return exportedValue.name;
 		}
+		const esmExportedValue = extractESMExportValue(node);
+		if (esmExportedValue?.type === 'Identifier') {
+			return esmExportedValue.name;
+		}
 	}
 
 	const nodeAfterNextConfigComment = getNodeAfterNextConfigTypeComment(code);
@@ -273,3 +277,15 @@ function extractModuleExportValue(node: Node): Node | null {
 
 	return null;
 }
+
+/**
+ * Gets the value of a node potentially representing: `export default ...`
+ * Returns the node of the value, or null if the input node doesn't represent the code
+ */
+function extractESMExportValue(node: Node): Node | null {
+	if (node.type === 'ExportDefaultDeclaration') {
+		return node.declaration;
+	}
+
+	return null;
+}

packages/eslint-plugin-next-on-pages/tests/rules/no-unsupported-configs.test.ts

@@ -136,12 +136,12 @@ describe('no-unsupported-configs', () => {
 
 						/**
 						 *
-						 * @type {import(    "next"   )   .     
+						 * @type {import(    "next"   )   .
 						 *  NextConfig}
-						 * 
+						 *
 						 * The following is my config object
 						 * */
-						
+
 						/* this is another comment, surprisingly it doesn't break the type import! */
 						const nextConfig = {
 							experimental: {
@@ -463,4 +463,38 @@ describe('no-unsupported-configs', () => {
 			],
 		});
 	});
+
+	test('should work with .mjs config file extension', () => {
+		tester.run('', rule, {
+			valid: [
+				{
+					filename: 'next.config.mjs',
+					code: `
+						const nextConfig = {
+						}
+
+						export default nextConfig;
+					`,
+				},
+			],
+			invalid: [
+				{
+					filename: 'next.config.mjs',
+					code: `
+						const nextConfig = {
+							compress: true,
+						}
+
+						export default nextConfig;
+					`,
+					errors: [
+						{
+							message:
+								'The "compress" configuration is not supported by next-on-pages (and is unlikely to be supported in the future).',
+						},
+					],
+				},
+			],
+		});
+	});
 });