fix (labs/ssr): move to enhanced-resolve for package exports support (#…

…3367)

The resolve package doesn't support package exports and various other
more modern resolution features. It seems `enhanced-resolve` (from
webpack) introduces this support.

.changeset/fuzzy-gorillas-wait.md

@@ -0,0 +1,5 @@
+---
+'@lit-labs/ssr': minor
+---
+
+Module resolution within SSR now supports package exports (via `package.json`)

packages/labs/ssr/package.json

@@ -134,9 +134,9 @@
     "@open-wc/testing-karma": "^4.0.9",
     "@types/command-line-args": "^5.0.0",
     "@types/koa": "^2.0.49",
+    "@types/koa__router": "^8.0.2",
     "@types/koa-cors": "*",
     "@types/koa-static": "^4.0.1",
-    "@types/koa__router": "^8.0.2",
     "@types/parse5": "^6.0.1",
     "@types/resolve": "^1.20.2",
     "@webcomponents/template-shadowroot": "^0.1.0",
@@ -151,12 +151,12 @@
     "@lit-labs/ssr-client": "^1.0.0",
     "@lit/reactive-element": "^1.4.0",
     "@types/node": "^16.0.0",
+    "enhanced-resolve": "^5.10.0",
     "lit": "^2.3.0",
     "lit-element": "^3.1.0",
     "lit-html": "^2.3.0",
     "node-fetch": "^3.2.8",
-    "parse5": "^6.0.1",
-    "resolve": "^1.10.1"
+    "parse5": "^6.0.1"
   },
   "engines": {
     "node": ">=13.9.0"

packages/labs/ssr/src/lib/module-loader.ts

@@ -8,11 +8,9 @@ import * as path from 'path';
 import {promises as fs} from 'fs';
 import {URL, fileURLToPath, pathToFileURL} from 'url';
 import * as vm from 'vm';
-import resolveAsync from 'resolve';
+import enhancedResolve from 'enhanced-resolve';
 import {builtinModules} from 'module';
 
-type PackageJSON = {main?: string; module?: string; 'jsnext:main'?: string};
-
 const builtIns = new Set(builtinModules);
 
 const specifierMatches = (specifier: string, match: string) =>
@@ -276,17 +274,11 @@ export const resolveSpecifier = async (
       // a single version.
       referrerPath = fileURLToPath(import.meta.url);
     }
-    const modulePath = await resolve(specifier, {
-      basedir: path.dirname(referrerPath),
-      moduleDirectory: ['node_modules'],
+    const modulePath = await resolve(specifier, path.dirname(referrerPath), {
+      modules: ['node_modules'],
       extensions: ['.js'],
-      // Some packages use a non-standard alternative to the "main" field
-      // in their package.json to differentiate their ES module version.
-      packageFilter: (packageJson: PackageJSON) => {
-        packageJson.main =
-          packageJson.module ?? packageJson['jsnext:main'] ?? packageJson.main;
-        return packageJson;
-      },
+      mainFields: ['module', 'jsnext:main', 'main'],
+      conditionNames: ['node'],
     });
     return pathToFileURL(modulePath);
   }
@@ -301,10 +293,12 @@ const initializeImportMeta = (meta: {url: string}, module: vm.Module) => {
 
 const resolve = async (
   id: string,
-  opts: resolveAsync.AsyncOpts
+  path: string,
+  opts: Partial<enhancedResolve.ResolveOptions>
 ): Promise<string> => {
+  const resolver = enhancedResolve.create(opts);
   return new Promise((res, rej) => {
-    resolveAsync(id, opts, (err, resolved) => {
+    resolver({}, path, id, {}, (err: unknown, resolved?: string) => {
       if (err != null) {
         rej(err);
       } else {

packages/labs/ssr/src/test/lib/module-loader_test.ts

@@ -53,4 +53,38 @@ test('loads a module with a built-in import', async () => {
   assert.ok(module.namespace.join);
 });
 
+test('resolves an exact exported path', async () => {
+  const loader = new ModuleLoader({global: window});
+  const result = await loader.importModule('./lit-import.js', testIndex);
+  const {module, path: modulePath} = result;
+  assert.is(module.namespace.litIsServer, true);
+  assert.ok(loader.cache.has(modulePath));
+  const isServerPath = path.resolve(
+    path.dirname(testIndex),
+    '../../../../../lit-html/node/is-server.js'
+  );
+  assert.ok(loader.cache.has(isServerPath));
+});
+
+test('resolves a root exported path (.)', async () => {
+  const loader = new ModuleLoader({global: window});
+  const result = await loader.importModule(
+    './lit-import-from-root.js',
+    testIndex
+  );
+  const {module, path: modulePath} = result;
+  assert.is(module.namespace.litIsServer, true);
+  assert.ok(loader.cache.has(modulePath));
+  const litPath = path.resolve(
+    path.dirname(testIndex),
+    '../../../../../lit/index.js'
+  );
+  const isServerPath = path.resolve(
+    path.dirname(testIndex),
+    '../../../../../lit-html/node/is-server.js'
+  );
+  assert.ok(loader.cache.has(litPath));
+  assert.ok(loader.cache.has(isServerPath));
+});
+
 test.run();

packages/labs/ssr/src/test/test-files/module-loader/lit-import-from-root.js

@@ -0,0 +1,2 @@
+import {isServer} from 'lit';
+export const litIsServer = isServer;

packages/labs/ssr/src/test/test-files/module-loader/lit-import.js

@@ -0,0 +1,2 @@
+import {isServer} from 'lit-html/is-server.js';
+export const litIsServer = isServer;