module: enable existing machinery for deferred import of static modules

This commit enables deferred import for statically imported modules,
by using the corresponding functionality in V8. It also adds a single
smoke test, so more test coverage should be added.

Refs: https://github.com/tc39/proposal-defer-import-eval
Signed-off-by: Maya Lekova <maya@igalia.com>

Author: MayaLekova

eslint.config.mjs

@@ -19,6 +19,7 @@ const { globalIgnores } = await importEslintTool('eslint/config');
 const { default: js } = await importEslintTool('@eslint/js');
 const { default: babelEslintParser } = await importEslintTool('@babel/eslint-parser');
 const babelPluginSyntaxImportSource = resolveEslintTool('@babel/plugin-syntax-import-source');
+const babelPluginImportDefer = resolveEslintTool('@babel/plugin-syntax-import-defer');
 const { default: jsdoc } = await importEslintTool('eslint-plugin-jsdoc');
 const { default: regexpPlugin } = await importEslintTool('eslint-plugin-regexp');
 const { default: markdown } = await importEslintTool('@eslint/markdown');
@@ -105,6 +106,7 @@ export default [
         babelOptions: {
           plugins: [
             babelPluginSyntaxImportSource,
+            babelPluginImportDefer,
           ],
         },
         requireConfigFile: false,

src/module_wrap.cc

@@ -555,6 +555,8 @@ ModulePhase to_phase_constant(ModuleImportPhase phase) {
   switch (phase) {
     case ModuleImportPhase::kEvaluation:
       return kEvaluationPhase;
+    case ModuleImportPhase::kDefer:
+      return kDeferPhase;
     case ModuleImportPhase::kSource:
       return kSourcePhase;
     default:
@@ -1682,6 +1684,7 @@ void ModuleWrap::CreatePerContextProperties(Local<Object> target,
   V(Module::Status, kErrored);
 
   V(ModulePhase, kEvaluationPhase);
+  V(ModulePhase, kDeferPhase);
   V(ModulePhase, kSourcePhase);
 #undef V
 }

src/module_wrap.h

@@ -35,7 +35,8 @@ enum HostDefinedOptions : int {
 
 enum ModulePhase : int {
   kSourcePhase = 1,
-  kEvaluationPhase = 2,
+  kDeferPhase = 2,
+  kEvaluationPhase = 3,
 };
 
 /**

test/es-module/test-defer-import-eval.mjs

@@ -0,0 +1,24 @@
+// Flags: --js-defer-import-eval
+
+// Tests that defer import actually evaluates the imported module
+// only when properties that it exports are accessed.
+
+import '../common/index.mjs';
+import * as assert from 'assert';
+
+globalThis.eval_list = [];
+
+import defer * as deferred from '../fixtures/es-modules/module-deferred-eval.mjs';
+
+assert.strictEqual(globalThis.eval_list.length, 0);
+
+// Attempts to define a property on the deferred module. This should
+// trigger its execution, similar to accessing the `foo` property.
+// assert.throws(() => Object.defineProperty(deferred, 'newProp', { value: 15 }), TypeError);
+assert.strictEqual(deferred.foo, 42);
+
+// Check that the module has been evaluated at this point.
+assert.partialDeepStrictEqual(['defer-1'], globalThis.eval_list);
+
+// Clean-up
+delete globalThis.eval_list;

test/fixtures/es-modules/module-deferred-eval.mjs

@@ -0,0 +1,8 @@
+if (!globalThis.eval_list) {
+  globalThis.eval_list = [];
+}
+globalThis.eval_list.push('defer-1');
+
+export const foo = 42;
+
+console.log('executed');

tools/eslint/package-lock.json

@@ -5,6 +5,7 @@
   "dependencies": {
     "@babel/core": "^8.0.0-rc.6",
     "@babel/eslint-parser": "^8.0.0-rc.6",
+    "@babel/plugin-syntax-import-defer": "^7.29.7",
     "@babel/plugin-syntax-import-source": "^8.0.0-rc.6",
     "@eslint/js": "^10.0.1",
     "@eslint/markdown": "^8.0.2",