module: enable existing machinery for import defer

This commit enables deferred module imports by using the corresponding
functionality in V8. It also adds a single test, but more test coverage
should be added.

Refs: https://github.com/tc39/proposal-defer-import-eval

Author: MayaLekova

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/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');

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

@@ -0,0 +1,20 @@
+// Flags: --js-defer-import-eval
+
+// Tests that defer import actually evaluates the imported module
+// only when properties that it exports are accessed.
+
+import * as assert from 'assert'
+
+globalThis.eval_list = [];
+
+import defer * as deferred from './module-deferred-eval.mjs'
+
+assert.strictEqual(0, globalThis.eval_list.length);
+
+// 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.equal(42, deferred.foo);
+
+// Check that the module has been evaluated at this point.
+assert.partialDeepStrictEqual(['defer-1'], globalThis.eval_list);