feat(ses): Add XS variant of shim

packages/ses/.gitignore

@@ -0,0 +1 @@
+tmp

packages/ses/NEWS.md

@@ -13,8 +13,18 @@ User-visible changes in `ses`:
   - Node 18, Node 20, and all browsers have `structuredClone`
   - Node <= 16 have neither, but are also no longer supported by Endo.
 - Now exports separate layer for console shim: `ses/console-shim.js`.
+
+Incubating: Please do not rely on these features as they are under development
+and subject to breaking changes that will not be signaled by semver.
+
 - Adds permits for `ModuleSource`, either the native implementation or from
   `@endo/module-source/shim.js`.
+- Adds support for an XS-specific variant of the SES shim that is triggered
+  with the `xs` package export condition.
+  This version of SES preserves all the features of `Compartment` provided
+  uniquely by the SES shim, but with the `__native__` constructor option,
+  loses support for importing precompiled module records and gains support
+  for native `ModuleSource`.
 
 # v1.8.0 (2024-08-27)
 

packages/ses/package.json

@@ -38,6 +38,7 @@
     ".": {
       "import": {
         "types": "./types.d.ts",
+        "xs": "./src-xs/index.js",
         "default": "./index.js"
       },
       "require": {
@@ -57,8 +58,14 @@
     },
     "./tools.js": "./tools.js",
     "./assert-shim.js": "./assert-shim.js",
-    "./lockdown-shim.js": "./lockdown-shim.js",
-    "./compartment-shim.js": "./compartment-shim.js",
+    "./lockdown-shim.js": {
+      "xs": "./src-xs/shim.js",
+      "default": "./lockdown-shim.js"
+    },
+    "./compartment-shim.js": {
+      "xs": "./src-xs/shim.js",
+      "default": "./compartment-shim.js"
+    },
     "./console-shim.js": "./console-shim.js",
     "./package.json": "./package.json"
   },
@@ -74,7 +81,7 @@
     "prepare": "npm run clean && npm run build",
     "qt": "ava",
     "test": "tsd && ava",
-    "test:xs": "xst dist/ses.umd.js test/_lockdown-safe.js",
+    "test:xs": "xst dist/ses.umd.js test/_lockdown-safe.js && node scripts/generate-test-xs.js && xst tmp/test-xs.js",
     "postpack": "git clean -f '*.d.ts*' '*.tsbuildinfo'"
   },
   "dependencies": {

packages/ses/scripts/generate-test-xs.js

@@ -0,0 +1,56 @@
+/* eslint-env node */
+/* glimport/no-extraneous-dependenciesobal process */
+import '../index.js';
+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';
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { ModuleSource } from '@endo/module-source';
+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 () => {
+  await fs.mkdir(fileURLToPath(new URL('../tmp', import.meta.url)), {
+    recursive: true,
+  });
+
+  const meaningText = await fs.readFile(
+    fileURLToPath(new URL('../test/_meaning.js', import.meta.url)),
+    'utf8',
+  );
+  const meaningModuleSource = new ModuleSource(meaningText);
+
+  await fs.writeFile(
+    fileURLToPath(new URL('../tmp/_meaning.pre-mjs.json', import.meta.url)),
+    JSON.stringify(meaningModuleSource),
+  );
+
+  const xsPrelude = await makeBundle(
+    read,
+    new URL('../test/_xs.js', import.meta.url).href,
+    {
+      tags: new Set(['xs']),
+    },
+  );
+
+  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;
+});