Support conditional export resolution with custom resolver

lib/resolver-compat.js

@@ -322,8 +322,13 @@ function resolverFromOptions(vm, options, override, compiler) {
 			}
 			const resolved = customResolver(x, path);
 			if (!resolved) return undefined;
-			if (externals) externals.push(new RegExp('^' + escapeRegExp(resolved)));
-			return resolver.loadAsFileOrDirecotry(resolved, extList);
+			if (typeof resolved === 'string') {
+				if (externals) externals.push(new RegExp('^' + escapeRegExp(resolved)));
+				return resolver.loadAsFileOrDirecotry(resolved, extList);
+			}
+			const {module=x, path: resolvedPath} = resolved;
+			if (externals) externals.push(new RegExp('^' + escapeRegExp(resolvedPath)));
+			return resolver.loadNodeModules(module, [resolvedPath], extList);
 		};
 	}
 

test/additional-modules/my-es-module/index.cjs

@@ -0,0 +1 @@
+module.exports = {additional_cjs_module: true};

test/additional-modules/my-es-module/index.js

@@ -0,0 +1 @@
+export default {additional_es_module: true};

test/additional-modules/my-es-module/package.json

@@ -0,0 +1,11 @@
+{
+    "main": "index.js",
+    "exports": {
+        ".": {
+          "default": {
+            "require": "./index.cjs",
+            "default": "./index.js"
+          }
+        }
+    }
+}

test/nodevm.js

@@ -239,6 +239,17 @@ describe('modules', () => {
 		assert.ok(vm.run("require('my-module')", __filename));
 	});
 
+	it('can resolve conditional exports with a custom resolver', () => {
+		const vm = new NodeVM({
+			require: {
+				external: ['my-es-module'],
+				resolve: () => ({ path: path.resolve(__dirname, 'additional-modules') })
+			}
+		});
+
+		assert.ok(vm.run("require('my-es-module')", __filename));
+	})
+
 	it('allows for multiple root folders', () => {
 		const vm = new NodeVM({
 			require: {