fix: config path problem on windows (#4501)

* add test

* fix

cli/run/loadConfigFile.ts

@@ -1,4 +1,3 @@
-import { promises as fs } from 'fs';
 import { extname, isAbsolute } from 'path';
 import { version } from 'process';
 import { pathToFileURL } from 'url';
@@ -103,8 +102,8 @@ async function getDefaultFromTranspiledConfigFile(
 	return loadConfigFromBundledFile(fileName, code);
 }
 
-async function loadConfigFromBundledFile(fileName: string, bundledCode: string): Promise<unknown> {
-	const resolvedFileName = await fs.realpath(fileName);
+function loadConfigFromBundledFile(fileName: string, bundledCode: string): unknown {
+	const resolvedFileName = require.resolve(fileName);
 	const extension = extname(resolvedFileName);
 	const defaultLoader = require.extensions[extension];
 	require.extensions[extension] = (module: NodeModule, requiredFileName: string) => {

test/cli/samples/config-cwd-case-insensitive-es6/_config.js

@@ -0,0 +1,11 @@
+function toggleCase(s) {
+	return s == s.toLowerCase() ? s.toUpperCase() : s.toLowerCase();
+}
+
+module.exports = {
+	onlyWindows: true,
+	description: "can load ES6 config with cwd that doesn't match realpath",
+	command: 'rollup -c',
+	cwd: __dirname.replace(/^[A-Z]:\\/i, toggleCase),
+	execute: true
+};

test/cli/samples/config-cwd-case-insensitive-es6/main.js

@@ -0,0 +1 @@
+assert.equal( ANSWER, 42 );

test/cli/samples/config-cwd-case-insensitive-es6/rollup.config.js

@@ -0,0 +1,9 @@
+import replace from '@rollup/plugin-replace';
+
+export default {
+	input: 'main.js',
+	output: {
+		format: 'cjs'
+	},
+	plugins: [replace({ preventAssignment: true, ANSWER: 42 })]
+};