[blink] Add ModuleRecordEvaluationResult

The newly introduced will make the return type of
ModuleRecord::Evaluation explicit.

Currently an empty v8::Local return value corresponds to a successful
evaluation and any returned value is treated as an exception.

This is different when top-level await is enabled. In this case
ModuleRecord::Evaluation always returns a Promise on success. Thus
simply checking for an empty or non-empty v8::Local is no longer
sufficient and we need a dedicated flag to detect Exceptions.

Bug: 1022182, v8:9344
Change-Id: Ida7684bff79d68624548c99aee6e7b6f2e334afc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2105315
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750914}

third_party/blink/renderer/bindings/core/v8/module_record.cc

@@ -3,7 +3,8 @@
 // found in the LICENSE file.
 
 #include "third_party/blink/renderer/bindings/core/v8/module_record.h"
-
+#include "base/feature_list.h"
+#include "third_party/blink/public/common/features.h"
 #include "third_party/blink/renderer/bindings/core/v8/boxed_v8_module.h"
 #include "third_party/blink/renderer/bindings/core/v8/referrer_script_info.h"
 #include "third_party/blink/renderer/bindings/core/v8/v8_binding_for_core.h"
@@ -18,6 +19,49 @@
 
 namespace blink {
 
+// static
+ModuleEvaluationResult ModuleEvaluationResult::Empty() {
+  DCHECK(!base::FeatureList::IsEnabled(features::kTopLevelAwait));
+  return ModuleEvaluationResult(true, {});
+}
+
+// static
+ModuleEvaluationResult ModuleEvaluationResult::FromResult(
+    v8::Local<v8::Value> promise) {
+  DCHECK(base::FeatureList::IsEnabled(features::kTopLevelAwait) ||
+         promise.IsEmpty());
+  DCHECK(!base::FeatureList::IsEnabled(features::kTopLevelAwait) ||
+         promise->IsPromise());
+  return ModuleEvaluationResult(true, promise);
+}
+
+// static
+ModuleEvaluationResult ModuleEvaluationResult::FromException(
+    v8::Local<v8::Value> exception) {
+  DCHECK(!exception.IsEmpty());
+  return ModuleEvaluationResult(false, exception);
+}
+
+ModuleEvaluationResult& ModuleEvaluationResult::Escape(
+    ScriptState::EscapableScope* scope) {
+  value_ = scope->Escape(value_);
+  return *this;
+}
+
+v8::Local<v8::Value> ModuleEvaluationResult::GetException() const {
+  DCHECK(IsException());
+  DCHECK(!value_.IsEmpty());
+  return value_;
+}
+
+ScriptPromise ModuleEvaluationResult::GetPromise(
+    ScriptState* script_state) const {
+  DCHECK(base::FeatureList::IsEnabled(features::kTopLevelAwait));
+  DCHECK(IsSuccess());
+  DCHECK(!value_.IsEmpty());
+  return ScriptPromise(script_state, value_);
+}
+
 ModuleRecordProduceCacheData::ModuleRecordProduceCacheData(
     v8::Isolate* isolate,
     SingleCachedMetadataHandler* cache_handler,

third_party/blink/renderer/bindings/core/v8/module_record.h

@@ -23,6 +23,48 @@ class KURL;
 class ScriptFetchOptions;
 class ScriptState;
 class ScriptValue;
+class ScriptPromise;
+
+// ModuleEvaluationResult encapsulates the result of a module evaluation.
+// - Without top-level-await
+//   - succeed and not return a value, or
+//     (IsSuccess() == true), no return value is available.
+//   - throw any object.
+//     (IsException() == true && GetException()) returns the thrown exception
+// - With top-level-await a module can either
+//   - return a promise, or
+//     (IsSuccess() == true && GetPromise()) returns a valid ScriptPromise())
+//   - throw any object.
+//     (IsException() == true && GetException()) returns the thrown exception
+class CORE_EXPORT ModuleEvaluationResult final {
+  STACK_ALLOCATED();
+
+ public:
+  ModuleEvaluationResult() = delete;
+  static ModuleEvaluationResult Empty();
+  static ModuleEvaluationResult FromResult(v8::Local<v8::Value> promise);
+  static ModuleEvaluationResult FromException(v8::Local<v8::Value> exception);
+
+  ModuleEvaluationResult(const ModuleEvaluationResult& value) = default;
+  ModuleEvaluationResult& operator=(const ModuleEvaluationResult& value) =
+      default;
+  ~ModuleEvaluationResult() = default;
+
+  ModuleEvaluationResult& Escape(ScriptState::EscapableScope* scope);
+
+  bool IsSuccess() const { return is_success_; }
+  bool IsException() const { return !is_success_; }
+
+  v8::Local<v8::Value> GetException() const;
+  ScriptPromise GetPromise(ScriptState* script_state) const;
+
+ private:
+  ModuleEvaluationResult(bool is_success, v8::Local<v8::Value> value)
+      : is_success_(is_success), value_(value) {}
+
+  bool is_success_;
+  v8::Local<v8::Value> value_;
+};
 
 // ModuleRecordProduceCacheData is a parameter object for
 // ModuleRecord::ProduceCache().
@@ -78,7 +120,7 @@ class CORE_EXPORT ModuleRecord final {
                                  v8::Local<v8::Module> record,
                                  const KURL& source_url);
 
-  // Returns exception, if any.
+  // Returns exception, if any
   static ScriptValue Evaluate(ScriptState*,
                               v8::Local<v8::Module> record,
                               const KURL& source_url);