Add partial tests for import defer

- syntax
- Deferred namespace objects
- Behavior of synchronous deferred modules
- Errors for synchronous cases

I will open another PR (or push another commit here) for tests about
async modules, since I still have to finish polishing it up.

There are a few details of the proposal that are still in flux because
of some bugs, so this PR does not include tests for them:
- `Symbol.toStringTag` of deferred namespace objects
- `test/language/import/import-defer/evaluation-sync/evaluation-*` for the other object operations
- `import.defer`, which currently doesn't actually defer due to a problem with `.then`

features.txt

@@ -84,6 +84,10 @@ Atomics.pause
 # https://github.com/tc39/proposal-is-error
 Error.isError
 
+# Deferred import evaluation
+# https://tc39.es/proposal-defer-import-eval
+import-defer
+
 ## Standard language features
 #
 # Language features that have been included in a published version of the

test/language/import/import-defer/deferred-namespace-object/dep-defer-ns_FIXTURE.js

@@ -0,0 +1,6 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+import defer * as depDeferredNamespace from "./dep.js";
+
+export { depDeferredNamespace };

test/language/import/import-defer/deferred-namespace-object/dep_FIXTURE.js

@@ -0,0 +1,5 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+export const foo = 1;
+export const bar = 2;

test/language/import/import-defer/deferred-namespace-object/identity.js

@@ -0,0 +1,42 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-getmodulenamespace
+description: >
+  Deferred namespace objects are created and cached appropriately
+info: |
+  GetModuleNamespace ( _module_, _phase_ )
+    1. ...
+    1. If _phase_ is ~defer~, let _namespace_ be _module_.[[DeferredNamespace]], otherwise let _namespace_ be _module_.[[Namespace]].
+    1. If _namespace_ is ~empty~, then
+      1. ...
+      1. Set _namespace_ to ModuleNamespaceCreate(_module_, _unambiguousNames_, _phase_).
+    1. Return _namespace_.
+
+  ModuleNamespaceCreate ( _module_, _exports_, _phase_ )
+    1. ...
+    1. Let _M_ be MakeBasicObject(_internalSlotsList_).
+    1. ...
+    1. If _phase_ is ~defer~, then
+      1. Set _module_.[[DeferredNamespace]] to _M_.
+      1. ...
+    1. Else,
+      1. Set _module_.[[Namespace]] to _M_.
+      1. ...
+    1. Return _M_.
+
+features: [import-defer]
+---*/
+
+import * as nsEager from "./dep_FIXTURE.js";
+
+import defer * as nsDeferred1 from "./dep_FIXTURE.js";
+import defer * as nsDeferred2 from "./dep_FIXTURE.js";
+import { depDeferredNamespace as nsDeferred3 } from "./dep-defer-ns_FIXTURE.js";
+const nsDeferred4 = await import.defer("./dep_FIXTURE.js");
+
+assert(nsDeferred1 === nsDeferred2, "Deferred import of the same module twice gives the same object");
+assert(nsDeferred1 === nsDeferred3, "Deferred import of the same module twice from different files gives the same object");
+assert(nsDeferred1 === nsDeferred4, "Static and dynamic deferred import of the same module gives the same object");
+assert(nsDeferred1 !== nsEager, "Deferred namespaces are distinct from eager namespaces");

test/language/import/import-defer/deferred-namespace-object/object-properties.js

@@ -0,0 +1,51 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-modulenamespacecreate
+description: >
+  `defer` is a valid name for default imports
+info: |
+  ModuleNamespaceCreate ( _module_, _exports_, _phase_ )
+    1. Let _internalSlotsList_ be the internal slots listed in <emu-xref href="#table-internal-slots-of-module-namespace-exotic-objects"></emu-xref>.
+    1. Let _M_ be MakeBasicObject(_internalSlotsList_).
+    1. Set _M_'s essential internal methods to the definitions specified in <emu-xref href="#sec-module-namespace-exotic-objects"></emu-xref>.
+    1. ...
+
+  [[GetPrototypeOf]] ( )
+    1. Return null.
+
+  [[IsExtensible]] ( )
+    1. Return false.
+
+features: [import-defer]
+includes: [propertyHelper.js]
+---*/
+
+import defer * as ns from "./dep_FIXTURE.js";
+
+assert(typeof ns === "object", "Deferred namespaces are objects");
+
+assert(Reflect.isExtensible(ns) === false, "Deferred namespaces are not extensible");
+assert(Reflect.preventExtensions(ns) === true, "Deferred namespaces can made non-extensible");
+
+assert(Reflect.getPrototypeOf(ns) === null, "Deferred namespaces have a null prototype");
+asserts(Reflect.setPrototypeOf(ns, {}) === false, "Deferred namespaces' prototype cannot be changed");
+asserts(Reflect.setPrototypeOf(ns, null) === true, "Deferred namespaces' prototype can be 'set' to null");
+
+assert.throws(TypeError, () => Reflect.apply(ns, null, []), "Deferred namespaces are not callable");
+assert.throws(TypeError, () => Reflect.construct(ns, null, []), "Deferred namespaces are not constructable");
+
+assert.deepEqual(
+  Reflect.ownKeys(ns),
+  ["bar", "foo", Symbol.toStringTag],
+  "Deferred namespaces' keys are the exports sorted alphabetically, followed by @@toStringTag"
+);
+
+verifyProperty(ns, "foo", {
+  value: 1,
+  writable: true,
+  enumerable: true,
+  configurable: false,
+});
+assert(Reflect.getOwnPropertyDescriptor(ns, "non-existent") === undefined, "No descriptors for non-exports");

test/language/import/import-defer/errors/get-other-while-dep-evaluating/dep-1_FIXTURE.js

@@ -0,0 +1,8 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+import defer * as dep2 from "./dep-2_FIXTURE.js";
+
+globalThis.dep3evaluated = false;
+assert.throws(TypeError, () => dep2.foo);
+assert(globalThis.dep3evaluated === false, "the 'evaluable' dependencies of dep-2 are not evaluated");

test/language/import/import-defer/errors/get-other-while-dep-evaluating/dep-2_FIXTURE.js

@@ -0,0 +1,5 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+import "./dep-3_FIXTURE.js";
+import "./main.js";

test/language/import/import-defer/errors/get-other-while-dep-evaluating/dep-3_FIXTURE.js

@@ -0,0 +1,4 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+globalThis.dep3evaluated = true;

test/language/import/import-defer/errors/get-other-while-dep-evaluating/main.js

@@ -0,0 +1,37 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-module-namespace-exotic-objects-get-p-receiver-EnsureDeferredNamespaceEvaluation
+description: >
+  Modules cannot try to trigger their own evaluation
+info: |
+  10.4.6.8 [[Get]] ( _P_, _Receiver_ )
+    1. ...
+    1. If _O_.[[Deferred]] is **true**, perform ? EnsureDeferredNamespaceEvaluation(_O_).
+    1. ...
+
+  EnsureDeferredNamespaceEvaluation ( _O_ )
+    1. Assert: _O_.[[Deferred]] is *false*.
+    1. Let _m_ be _O_.[[Module]].
+    1. If _m_ is a Cyclic Module Record, _m_.[[Status]] is not ~evaluated~, and ReadyForSyncExecution(_m_) is *false*, throw a *TypeError* exception.
+    1. ...
+
+  ReadyForSyncExecution( _module_, _seen_ )
+    1. If _seen_ is not provided, let _seen_ be a new empty List.
+    1. If _seen_ contains _module_, return *true*.
+    1. Append _module_ to _seen_.
+    1. If _module_.[[Status]] is ~evaluated~, return *true*.
+    1. If _module_.[[Status]] is ~evaluating~ or ~evaluating-async~, return *false*.
+    1. Assert: _module_.[[Status]] is ~linked~.
+    1. If _module_.[[HasTLA]] is *true*, return *false*.
+    1. For each ModuleRequest Record _required_ of _module_.[[RequestedModules]], do
+      1. Let _requiredModule_ be GetImportedModule(_module_, _required_.[[Specifier]]).
+      1. If ReadyForSyncExecution(_requiredModule_, _seen_) is *false*, then
+        1. Return *false*.
+    1. Return *true*.
+
+features: [import-defer]
+---*/
+
+import "./dep-1_FIXTURE.js";

test/language/import/import-defer/errors/get-other-while-evaluating/dep_FIXTURE.js

@@ -0,0 +1,6 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+import defer * as main from "./main.js";
+
+assert.throws(TypeError, () => main.foo);

test/language/import/import-defer/errors/get-other-while-evaluating/main.js

@@ -0,0 +1,37 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-module-namespace-exotic-objects-get-p-receiver-EnsureDeferredNamespaceEvaluation
+description: >
+  Modules cannot try to trigger their own evaluation
+info: |
+  10.4.6.8 [[Get]] ( _P_, _Receiver_ )
+    1. ...
+    1. If _O_.[[Deferred]] is **true**, perform ? EnsureDeferredNamespaceEvaluation(_O_).
+    1. ...
+
+  EnsureDeferredNamespaceEvaluation ( _O_ )
+    1. Assert: _O_.[[Deferred]] is *false*.
+    1. Let _m_ be _O_.[[Module]].
+    1. If _m_ is a Cyclic Module Record, _m_.[[Status]] is not ~evaluated~, and ReadyForSyncExecution(_m_) is *false*, throw a *TypeError* exception.
+    1. ...
+
+  ReadyForSyncExecution( _module_, _seen_ )
+    1. If _seen_ is not provided, let _seen_ be a new empty List.
+    1. If _seen_ contains _module_, return *true*.
+    1. Append _module_ to _seen_.
+    1. If _module_.[[Status]] is ~evaluated~, return *true*.
+    1. If _module_.[[Status]] is ~evaluating~ or ~evaluating-async~, return *false*.
+    1. Assert: _module_.[[Status]] is ~linked~.
+    1. If _module_.[[HasTLA]] is *true*, return *false*.
+    1. For each ModuleRequest Record _required_ of _module_.[[RequestedModules]], do
+      1. Let _requiredModule_ be GetImportedModule(_module_, _required_.[[Specifier]]).
+      1. If ReadyForSyncExecution(_requiredModule_, _seen_) is *false*, then
+        1. Return *false*.
+    1. Return *true*.
+
+features: [import-defer]
+---*/
+
+import "./dep_FIXTURE.js";

test/language/import/import-defer/errors/get-self-while-defer-evaluating/dep_FIXTURE.js

@@ -0,0 +1,6 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+import defer * as ns from "./dep_FIXTURE.js";
+
+assert.throws(TypeError, () => ns.foo);

test/language/import/import-defer/errors/get-self-while-defer-evaluating/main.js

@@ -0,0 +1,39 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-module-namespace-exotic-objects-get-p-receiver-EnsureDeferredNamespaceEvaluation
+description: >
+  Modules cannot try to trigger their own evaluation
+info: |
+  10.4.6.8 [[Get]] ( _P_, _Receiver_ )
+    1. ...
+    1. If _O_.[[Deferred]] is **true**, perform ? EnsureDeferredNamespaceEvaluation(_O_).
+    1. ...
+
+  EnsureDeferredNamespaceEvaluation ( _O_ )
+    1. Assert: _O_.[[Deferred]] is *false*.
+    1. Let _m_ be _O_.[[Module]].
+    1. If _m_ is a Cyclic Module Record, _m_.[[Status]] is not ~evaluated~, and ReadyForSyncExecution(_m_) is *false*, throw a *TypeError* exception.
+    1. ...
+
+  ReadyForSyncExecution( _module_, _seen_ )
+    1. If _seen_ is not provided, let _seen_ be a new empty List.
+    1. If _seen_ contains _module_, return *true*.
+    1. Append _module_ to _seen_.
+    1. If _module_.[[Status]] is ~evaluated~, return *true*.
+    1. If _module_.[[Status]] is ~evaluating~ or ~evaluating-async~, return *false*.
+    1. Assert: _module_.[[Status]] is ~linked~.
+    1. If _module_.[[HasTLA]] is *true*, return *false*.
+    1. For each ModuleRequest Record _required_ of _module_.[[RequestedModules]], do
+      1. Let _requiredModule_ be GetImportedModule(_module_, _required_.[[Specifier]]).
+      1. If ReadyForSyncExecution(_requiredModule_, _seen_) is *false*, then
+        1. Return *false*.
+    1. Return *true*.
+
+features: [import-defer]
+---*/
+
+import defer * as ns from "./dep_FIXTURE.js";
+
+ns.foo;

test/language/import/import-defer/errors/get-self-while-evaluating.js

@@ -0,0 +1,39 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-module-namespace-exotic-objects-get-p-receiver-EnsureDeferredNamespaceEvaluation
+description: >
+  Modules cannot try to trigger their own evaluation
+info: |
+  10.4.6.8 [[Get]] ( _P_, _Receiver_ )
+    1. ...
+    1. If _O_.[[Deferred]] is **true**, perform ? EnsureDeferredNamespaceEvaluation(_O_).
+    1. ...
+
+  EnsureDeferredNamespaceEvaluation ( _O_ )
+    1. Assert: _O_.[[Deferred]] is *false*.
+    1. Let _m_ be _O_.[[Module]].
+    1. If _m_ is a Cyclic Module Record, _m_.[[Status]] is not ~evaluated~, and ReadyForSyncExecution(_m_) is *false*, throw a *TypeError* exception.
+    1. ...
+
+  ReadyForSyncExecution( _module_, _seen_ )
+    1. If _seen_ is not provided, let _seen_ be a new empty List.
+    1. If _seen_ contains _module_, return *true*.
+    1. Append _module_ to _seen_.
+    1. If _module_.[[Status]] is ~evaluated~, return *true*.
+    1. If _module_.[[Status]] is ~evaluating~ or ~evaluating-async~, return *false*.
+    1. Assert: _module_.[[Status]] is ~linked~.
+    1. If _module_.[[HasTLA]] is *true*, return *false*.
+    1. For each ModuleRequest Record _required_ of _module_.[[RequestedModules]], do
+      1. Let _requiredModule_ be GetImportedModule(_module_, _required_.[[Specifier]]).
+      1. If ReadyForSyncExecution(_requiredModule_, _seen_) is *false*, then
+        1. Return *false*.
+    1. Return *true*.
+
+features: [import-defer]
+---*/
+
+import defer * self from "./get-self-while-evaluating.js";
+
+assert.throws(TypeError, () => self.foo);

test/language/import/import-defer/errors/module-throws/defer-import-after-evaluation.js

@@ -0,0 +1,34 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-module-namespace-exotic-objects-get-p-receiver-EnsureDeferredNamespaceEvaluation
+description: >
+  Module evaluation errors are thrown
+info: |
+  [[Get]] ( _P_, _Receiver_ )
+    1. ...
+    1. If _O_.[[Deferred]] is **true**, perform ? EnsureDeferredNamespaceEvaluation(_O_).
+    1. ...
+
+  EnsureDeferredNamespaceEvaluation( _O_ )
+    1. ...
+    1. Perform ? EvaluateSync(_m_).
+    1. ...
+
+  EvaluateSync ( _module_ )
+    1. ...
+    1. Let _promise_ be ! _module_.Evaluate().
+    1. Assert: _promise_.[[PromiseState]] is either ~fulfilled~ or ~rejected~.
+    1. If _promise_.[[PromiseState]] is ~rejected~, then
+      1. Return ThrowCompletion(_promise_.[[PromiseResult]]).
+    1. ...
+
+features: [import-defer, top-level-await]
+---*/
+
+await import("./throws_FIXTURE.js").catch(() => {});
+
+const { ns } = await import("./import-defer-throws_FIXTURE.js");
+
+assert.throws(URIError, () => ns.foo, "Evaluation errors are thrown for modules evaluated before getting the deferred namespace");

test/language/import/import-defer/errors/module-throws/import-defer-throws_FIXTURE.js

@@ -0,0 +1,5 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+import defer * as ns from "./import-defer-throws_FIXTURE.js";
+export { ns };

test/language/import/import-defer/errors/module-throws/third-party-evaluation-after-defer-import.js

@@ -0,0 +1,34 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-module-namespace-exotic-objects-get-p-receiver-EnsureDeferredNamespaceEvaluation
+description: >
+  Module evaluation errors are thrown
+info: |
+  [[Get]] ( _P_, _Receiver_ )
+    1. ...
+    1. If _O_.[[Deferred]] is **true**, perform ? EnsureDeferredNamespaceEvaluation(_O_).
+    1. ...
+
+  EnsureDeferredNamespaceEvaluation( _O_ )
+    1. ...
+    1. Perform ? EvaluateSync(_m_).
+    1. ...
+
+  EvaluateSync ( _module_ )
+    1. ...
+    1. Let _promise_ be ! _module_.Evaluate().
+    1. Assert: _promise_.[[PromiseState]] is either ~fulfilled~ or ~rejected~.
+    1. If _promise_.[[PromiseState]] is ~rejected~, then
+      1. Return ThrowCompletion(_promise_.[[PromiseResult]]).
+    1. ...
+
+features: [import-defer, top-level-await]
+---*/
+
+import defer * as ns from "./throws_FIXTURE.js";
+
+await import("./throws_FIXTURE.js").catch(() => {});
+
+assert.throws(URIError, () => ns.foo, "Evaluation errors are thrown for modules evaluated after getting the deferred namespace");

test/language/import/import-defer/errors/module-throws/throws_FIXTURE.js

@@ -0,0 +1,4 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+throw new URIError("hello");