Allow linking additional modules via CommonJS modules

Author: mrbbot

packages/runner-vm/src/linker.ts

@@ -101,6 +101,7 @@ export class ModuleLinker {
         const exports = this.loadCommonJSModule(
           errorBase,
           identifier,
+          spec,
           referencing.context
         );
         module = new vm.SyntheticModule<{ default: Context }>(
@@ -151,13 +152,24 @@ export class ModuleLinker {
   private loadCommonJSModule(
     errorBase: string,
     identifier: string,
+    spec: string,
     context: vm.Context
   ): any {
     // If we've already seen a module with the same identifier, return it, to
     // handle import cycles
     const cached = this.#cjsModuleCache.get(identifier);
     if (cached) return cached.exports;
 
+    const additionalModule = this.additionalModules[spec];
+    const module: CommonJSModule = { exports: {} };
+
+    // If this is an additional module, return it immediately
+    if (additionalModule) {
+      module.exports.default = additionalModule.default;
+      this.#cjsModuleCache.set(identifier, module);
+      return module.exports;
+    }
+
     // Find first matching module rule ("ignore" requires relative paths)
     const relativeIdentifier = path.relative("", identifier);
     const rule = this.moduleRules.find((rule) =>
@@ -170,9 +182,8 @@ export class ModuleLinker {
       );
     }
 
-    // Create module and store in cache now as require is sync, so may load
-    // this module again before this function returns
-    const module: CommonJSModule = { exports: {} };
+    // Store in cache now as require is sync, so may load this module again
+    // before this function returns
     this.#cjsModuleCache.set(identifier, module);
 
     // Load module based on rule type
@@ -221,7 +232,7 @@ export class ModuleLinker {
       const errorBase = `Unable to resolve "${relative}" dependency "${spec}"`;
       // Get path to specified module relative to referencing module
       const identifier = path.resolve(referencingDirname, spec);
-      return this.loadCommonJSModule(errorBase, identifier, context);
+      return this.loadCommonJSModule(errorBase, identifier, spec, context);
     };
   }
 }

packages/runner-vm/test/fixtures/cjsadditional.cjs

@@ -0,0 +1,2 @@
+const additional = require("ADDITIONAL");
+module.exports = `CommonJS ${additional.default}`;

packages/runner-vm/test/linker.spec.ts

@@ -207,6 +207,18 @@ test("ModuleLinker: stack trace references correct line for CommonJS modules", a
     t.regex(e.stack, /cjserror\.cjs:2:9/);
   }
 });
+test("ModuleLinker: links additional module via CommonJS module", async (t) => {
+  const callback = (defaultExport: string) => {
+    t.is(defaultExport, "CommonJS test");
+  };
+  const additionalModules = { ADDITIONAL: { default: "test" } };
+  await runner.run(
+    { callback },
+    { code: 'import s from "./cjsadditional.cjs"; callback(s);', filePath },
+    processedModuleRules,
+    additionalModules
+  );
+});
 
 const sizePath = path.join(fixturesPath, "size");
 const sizeEntryPath = path.join(sizePath, "entry.mjs");