From c1cdb57bef0c2b3c666331f01c952098c6f81888 Mon Sep 17 00:00:00 2001
From: Kris Kowal <kris@agoric.com>
Date: Wed, 8 May 2024 16:33:17 -0700
Subject: [PATCH] feat(module-source): Specialize for XS native ModuleSource

---
 packages/module-source/.gitignore             |  1 +
 packages/module-source/NEWS.md                |  2 +
 packages/module-source/README.md              |  9 +++
 packages/module-source/package.json           |  8 ++-
 .../module-source/scripts/generate-test-xs.js | 41 +++++++++++++
 packages/module-source/shim.js                |  6 +-
 packages/module-source/src-xs/index.js        | 59 +++++++++++++++++++
 packages/module-source/test/_native.js        |  3 +
 packages/module-source/test/_xs.js            | 41 +++++++++++++
 9 files changed, 167 insertions(+), 3 deletions(-)
 create mode 100644 packages/module-source/.gitignore
 create mode 100644 packages/module-source/scripts/generate-test-xs.js
 create mode 100644 packages/module-source/src-xs/index.js
 create mode 100644 packages/module-source/test/_native.js
 create mode 100644 packages/module-source/test/_xs.js

diff --git a/packages/module-source/.gitignore b/packages/module-source/.gitignore
new file mode 100644
index 0000000000..a9a5aecf42
--- /dev/null
+++ b/packages/module-source/.gitignore
@@ -0,0 +1 @@
+tmp
diff --git a/packages/module-source/NEWS.md b/packages/module-source/NEWS.md
index 3e981409b0..0d54abc096 100644
--- a/packages/module-source/NEWS.md
+++ b/packages/module-source/NEWS.md
@@ -4,6 +4,8 @@ User-visible changes in `@endo/module-source`:
 
 - Adds `@endo/module-source/shim.js` to shim `globalThis.ModuleSource`.
   The shim currently replaces the native `globalThis.ModuleSource` if present.
+- Provides an XS-specific variant of `@endo/module-source` that adapts the
+  native `ModuleSource` instead of entraining Babel.
 
 # v1.0.0 (2024-07-30)
 
diff --git a/packages/module-source/README.md b/packages/module-source/README.md
index 077c632aec..88988a857d 100644
--- a/packages/module-source/README.md
+++ b/packages/module-source/README.md
@@ -74,6 +74,15 @@ the hook returns a promise, it will be dropped and rejections will go uncaught.
 If the hook must do async work, these should be queued up as a job that the
 caller can later await.
 
+## XS Specific Variant
+
+With the `xs` condition, `@endo/module-source` will not entrain Babel and will
+just adapt the native `ModuleSource` to the older interface presented by this
+package.
+That is, the XS native `bindings` will be translated to `imports`, `exports`,
+and `reexports` getters.
+This form of `ModuleSource` ignores all options.
+
 ## Bug Disclosure
 
 Please help us practice coordinated security bug disclosure, by using the
diff --git a/packages/module-source/package.json b/packages/module-source/package.json
index 822b012b56..118820326f 100644
--- a/packages/module-source/package.json
+++ b/packages/module-source/package.json
@@ -22,7 +22,10 @@
   "type": "module",
   "main": "./index.js",
   "exports": {
-    ".": "./index.js",
+    ".": {
+      "xs": "./src-xs/index.js",
+      "default": "./index.js"
+    },
     "./shim.js": "./shim.js",
     "./package.json": "./package.json"
   },
@@ -35,7 +38,8 @@
     "lint:types": "tsc",
     "lint:eslint": "eslint .",
     "lint-fix": "eslint --fix .",
-    "test": "ava"
+    "test": "ava",
+    "test:xs": "node scripts/generate-test-xs.js && xst tmp/test-xs.js"
   },
   "dependencies": {
     "@agoric/babel-generator": "^7.17.6",
diff --git a/packages/module-source/scripts/generate-test-xs.js b/packages/module-source/scripts/generate-test-xs.js
new file mode 100644
index 0000000000..e74e88577a
--- /dev/null
+++ b/packages/module-source/scripts/generate-test-xs.js
@@ -0,0 +1,41 @@
+/* global process */
+import 'ses';
+import { promises as fs } from 'fs';
+// Lerna does not like dependency cycles.
+// With an explicit devDependency from module-source to compartment-mapper,
+// the build script stalls before running every package's build script.
+//   yarn lerna run build
+// Omitting the dependency from package.json solves the problem and works
+// by dint of shared workspace node_modules.
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { makeBundle } from '@endo/compartment-mapper/bundle.js';
+import { fileURLToPath } from 'url';
+
+const read = async location => {
+  const path = fileURLToPath(location);
+  return fs.readFile(path);
+};
+const write = async (location, content) => {
+  const path = fileURLToPath(location);
+  await fs.writeFile(path, content);
+};
+
+const main = async () => {
+  const xsPrelude = await makeBundle(
+    read,
+    new URL('../test/_xs.js', import.meta.url).href,
+    {
+      tags: new Set(['xs']),
+    },
+  );
+
+  await fs.mkdir(fileURLToPath(new URL('../tmp', import.meta.url)), {
+    recursive: true,
+  });
+  await write(new URL('../tmp/test-xs.js', import.meta.url).href, xsPrelude);
+};
+
+main().catch(err => {
+  console.error('Error running main:', err);
+  process.exitCode = 1;
+});
diff --git a/packages/module-source/shim.js b/packages/module-source/shim.js
index e1d8c5b98e..f3357fc276 100644
--- a/packages/module-source/shim.js
+++ b/packages/module-source/shim.js
@@ -1,6 +1,10 @@
 /* global globalThis */
 
-import { ModuleSource } from './index.js';
+// We are using a reflexive import to make sure we pass through the conditional
+// export in package.json.
+// Eslint does not yet seem to have a carve-out for package-reflexive imports.
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { ModuleSource } from '@endo/module-source';
 
 Object.defineProperty(globalThis, 'ModuleSource', {
   value: ModuleSource,
diff --git a/packages/module-source/src-xs/index.js b/packages/module-source/src-xs/index.js
new file mode 100644
index 0000000000..93863c350b
--- /dev/null
+++ b/packages/module-source/src-xs/index.js
@@ -0,0 +1,59 @@
+// @ts-check
+/* global globalThis */
+/* eslint-disable @endo/no-nullish-coalescing */
+
+/** @typedef {{ import: string, as?: string, from: string } & { importAllFrom: string, as: string, from: string } & { export: string, as?: string, from?: string } & { exportAllFrom: string, as?: string } & {importFrom: string }} Binding */
+
+/** @param {Binding[]} bindings */
+function* getImports(bindings) {
+  for (const binding of bindings) {
+    if (binding.import !== undefined) {
+      yield binding.from;
+    } else if (binding.importFrom !== undefined) {
+      yield binding.importFrom;
+    } else if (binding.importAllFrom !== undefined) {
+      yield binding.importAllFrom;
+    } else if (binding.exportAllFrom !== undefined) {
+      yield binding.exportAllFrom;
+    }
+  }
+}
+
+/** @param {Binding[]} bindings */
+function* getExports(bindings) {
+  for (const binding of bindings) {
+    if (binding.export !== undefined) {
+      yield binding.as ?? binding.export;
+    }
+  }
+}
+
+/** @param {Binding[]} bindings */
+function* getReexports(bindings) {
+  for (const binding of bindings) {
+    if (binding.exportAllFrom !== undefined) {
+      yield binding.exportAllFrom;
+    }
+  }
+}
+
+const ModuleSource = globalThis.ModuleSource;
+
+Object.defineProperties(
+  ModuleSource.prototype,
+  Object.getOwnPropertyDescriptors({
+    get imports() {
+      return Array.from(new Set(getImports(this.bindings)));
+    },
+
+    get exports() {
+      return Array.from(new Set(getExports(this.bindings)));
+    },
+
+    get reexports() {
+      return Array.from(new Set(getReexports(this.bindings)));
+    },
+  }),
+);
+
+export { ModuleSource };
diff --git a/packages/module-source/test/_native.js b/packages/module-source/test/_native.js
new file mode 100644
index 0000000000..85ff89518a
--- /dev/null
+++ b/packages/module-source/test/_native.js
@@ -0,0 +1,3 @@
+/* global globalThis */
+export const NativeModuleSource = globalThis.ModuleSource;
+export const NativeCompartment = globalThis.Compartment;
diff --git a/packages/module-source/test/_xs.js b/packages/module-source/test/_xs.js
new file mode 100644
index 0000000000..47573b12f5
--- /dev/null
+++ b/packages/module-source/test/_xs.js
@@ -0,0 +1,41 @@
+// This is a test fixture for XS validation (yarn test:xs with Moddable's xst
+// on the PATH)
+// This must be bundled with the -C xs condition to produce an artifact
+// (tmp/test-xs.js) suitable for running with xst.
+import { NativeModuleSource, NativeCompartment } from './_native.js';
+// Eslint does not know about package reflexive imports (importing your own
+// package), which in this case is necessary to go through the conditional
+// export in package.json.
+// eslint-disable-next-line import/no-extraneous-dependencies
+import '@endo/module-source/shim.js';
+import 'ses';
+
+lockdown();
+
+// spot checks
+assert(Object.isFrozen(Object));
+
+const source = new ModuleSource(`
+  import name from 'imported';
+  export * from 'reexported';
+  export default 42;
+  throw new Error('unreached');
+`);
+assert(source.imports[0] === 'imported');
+assert(source.exports[0] === 'default');
+assert(source.reexports[0] === 'reexported');
+
+assert(source instanceof NativeModuleSource);
+
+const compartment = new NativeCompartment({
+  modules: {
+    '.': {
+      source: new ModuleSource(`
+        export default 42;
+      `),
+    },
+  },
+});
+assert(compartment.importNow('.').default === 42);
+
+// to be continued with XS-specific adapters for Compartment in SES...