6 files changed, 260 insertions, 171 deletions

diff --git a/dom/script/ModuleLoadRequest.cpp b/dom/script/ModuleLoadRequest.cpp
index e72edca2e..d62214304 100644
--- a/dom/script/ModuleLoadRequest.cpp
+++ b/dom/script/ModuleLoadRequest.cpp
@@ -43,15 +43,29 @@ void ModuleLoadRequest::Cancel()
   ScriptLoadRequest::Cancel();
   mModuleScript = nullptr;
   mProgress = ScriptLoadRequest::Progress::Ready;
+  CancelImports();
+  mReady.RejectIfExists(NS_ERROR_DOM_ABORT_ERR, __func__);
+}
+
+void
+ModuleLoadRequest::CancelImports()
+{
   for (size_t i = 0; i < mImports.Length(); i++) {
     mImports[i]->Cancel();
   }
-  mReady.RejectIfExists(NS_ERROR_FAILURE, __func__);
 }
 
 void
 ModuleLoadRequest::SetReady()
 {
+  // Mark a module as ready to execute. This means that this module and all it
+  // dependencies have had their source loaded, parsed as a module and the
+  // modules instantiated.
+  //
+  // The mReady promise is used to ensure that when all dependencies of a module
+  // have become ready, DependenciesLoaded is called on that module
+  // request. This is set up in StartFetchingModuleDependencies.
+
 #ifdef DEBUG
   for (size_t i = 0; i < mImports.Length(); i++) {
     MOZ_ASSERT(mImports[i]->IsReadyToRun());
@@ -69,30 +83,53 @@ ModuleLoadRequest::ModuleLoaded()
   // been loaded.
 
   mModuleScript = mLoader->GetFetchedModule(mURI);
+  if (!mModuleScript || mModuleScript->IsErrored()) {
+    ModuleErrored();
+    return;
+  }
+
   mLoader->StartFetchingModuleDependencies(this);
 }
 
 void
+ModuleLoadRequest::ModuleErrored()
+{
+  mLoader->CheckModuleDependenciesLoaded(this);
+  MOZ_ASSERT(!mModuleScript || mModuleScript->IsErrored());
+
+  CancelImports();
+  SetReady();
+  LoadFinished();
+}
+
+void
 ModuleLoadRequest::DependenciesLoaded()
 {
   // The module and all of its dependencies have been successfully fetched and
   // compiled.
 
-  if (!mLoader->InstantiateModuleTree(this)) {
-    LoadFailed();
-    return;
-  }
+  MOZ_ASSERT(mModuleScript);
 
+  mLoader->CheckModuleDependenciesLoaded(this);
   SetReady();
-  mLoader->ProcessLoadedModuleTree(this);
-  mLoader = nullptr;
-  mParent = nullptr;
+  LoadFinished();
 }
 
 void
 ModuleLoadRequest::LoadFailed()
 {
+  // We failed to load the source text or an error occurred unrelated to the
+  // content of the module (e.g. OOM).
+
+  MOZ_ASSERT(!mModuleScript);
+
   Cancel();
+  LoadFinished();
+}
+
+void
+ModuleLoadRequest::LoadFinished()
+{
   mLoader->ProcessLoadedModuleTree(this);
   mLoader = nullptr;
   mParent = nullptr;
diff --git a/dom/script/ModuleLoadRequest.h b/dom/script/ModuleLoadRequest.h
index 0119fad38..7b06dd2cf 100644
--- a/dom/script/ModuleLoadRequest.h
+++ b/dom/script/ModuleLoadRequest.h
@@ -45,9 +45,15 @@ public:
   void Cancel() override;
 
   void ModuleLoaded();
+  void ModuleErrored();
   void DependenciesLoaded();
   void LoadFailed();
 
+private:
+  void LoadFinished();
+  void CancelImports();
+
+public:
   // Is this a request for a top level module script or an import?
   bool mIsTopLevel;
 
diff --git a/dom/script/ModuleScript.cpp b/dom/script/ModuleScript.cpp
index 34ef4dec4..28b97a3cb 100644
--- a/dom/script/ModuleScript.cpp
+++ b/dom/script/ModuleScript.cpp
@@ -26,6 +26,7 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(ModuleScript)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mLoader)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mBaseURL)
   tmp->UnlinkModuleRecord();
+  tmp->mError.setUndefined();
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(ModuleScript)
@@ -34,28 +35,20 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(ModuleScript)
   NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mModuleRecord)
-  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mException)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mError)
 NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
 NS_IMPL_CYCLE_COLLECTING_ADDREF(ModuleScript)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(ModuleScript)
 
-ModuleScript::ModuleScript(ScriptLoader *aLoader, nsIURI* aBaseURL,
-                           JS::Handle<JSObject*> aModuleRecord)
+ModuleScript::ModuleScript(ScriptLoader *aLoader, nsIURI* aBaseURL)
  : mLoader(aLoader),
-   mBaseURL(aBaseURL),
-   mModuleRecord(aModuleRecord),
-   mInstantiationState(Uninstantiated)
+   mBaseURL(aBaseURL)
 {
   MOZ_ASSERT(mLoader);
   MOZ_ASSERT(mBaseURL);
-  MOZ_ASSERT(mModuleRecord);
-  MOZ_ASSERT(mException.isUndefined());
-
-  // Make module's host defined field point to this module script object.
-  // This is cleared in the UnlinkModuleRecord().
-  JS::SetModuleHostDefinedField(mModuleRecord, JS::PrivateValue(this));
-  HoldJSObjects(this);
+  MOZ_ASSERT(!mModuleRecord);
+  MOZ_ASSERT(mError.isUndefined());
 }
 
 void
@@ -66,34 +59,63 @@ ModuleScript::UnlinkModuleRecord()
     MOZ_ASSERT(JS::GetModuleHostDefinedField(mModuleRecord).toPrivate() ==
                this);
     JS::SetModuleHostDefinedField(mModuleRecord, JS::UndefinedValue());
+    mModuleRecord = nullptr;
   }
-  mModuleRecord = nullptr;
-  mException.setUndefined();
 }
 
 ModuleScript::~ModuleScript()
 {
-  if (mModuleRecord) {
-    // The object may be destroyed without being unlinked first.
-    UnlinkModuleRecord();
-  }
+  // The object may be destroyed without being unlinked first.
+  UnlinkModuleRecord();
   DropJSObjects(this);
 }
 
 void
-ModuleScript::SetInstantiationResult(JS::Handle<JS::Value> aMaybeException)
+ModuleScript::SetModuleRecord(JS::Handle<JSObject*> aModuleRecord)
 {
-  MOZ_ASSERT(mInstantiationState == Uninstantiated);
-  MOZ_ASSERT(mModuleRecord);
-  MOZ_ASSERT(mException.isUndefined());
+  MOZ_ASSERT(!mModuleRecord);
+  MOZ_ASSERT(mError.isUndefined());
 
-  if (aMaybeException.isUndefined()) {
-    mInstantiationState = Instantiated;
-  } else {
-    mModuleRecord = nullptr;
-    mException = aMaybeException;
-    mInstantiationState = Errored;
+  mModuleRecord = aModuleRecord;
+
+  // Make module's host defined field point to this module script object.
+  // This is cleared in the UnlinkModuleRecord().
+  JS::SetModuleHostDefinedField(mModuleRecord, JS::PrivateValue(this));
+  HoldJSObjects(this);
+}
+
+void
+ModuleScript::SetPreInstantiationError(const JS::Value& aError)
+{
+  MOZ_ASSERT(!aError.isUndefined());
+
+  UnlinkModuleRecord();
+  mError = aError;
+
+  HoldJSObjects(this);
+}
+
+bool
+ModuleScript::IsErrored() const
+{
+  if (!mModuleRecord) {
+    MOZ_ASSERT(!mError.isUndefined());
+    return true;
   }
+
+  return JS::IsModuleErrored(mModuleRecord);
+}
+
+JS::Value
+ModuleScript::Error() const
+{
+  MOZ_ASSERT(IsErrored());
+
+  if (!mModuleRecord) {
+    return mError;
+  }
+
+  return JS::GetModuleError(mModuleRecord);
 }
 
 } // dom namespace
diff --git a/dom/script/ModuleScript.h b/dom/script/ModuleScript.h
index dd0d07e84..571359859 100644
--- a/dom/script/ModuleScript.h
+++ b/dom/script/ModuleScript.h
@@ -20,17 +20,10 @@ class ScriptLoader;
 
 class ModuleScript final : public nsISupports
 {
-  enum InstantiationState {
-    Uninstantiated,
-    Instantiated,
-    Errored
-  };
-
   RefPtr<ScriptLoader> mLoader;
   nsCOMPtr<nsIURI> mBaseURL;
   JS::Heap<JSObject*> mModuleRecord;
-  JS::Heap<JS::Value> mException;
-  InstantiationState mInstantiationState;
+  JS::Heap<JS::Value> mError;
 
   ~ModuleScript();
 
@@ -39,24 +32,17 @@ public:
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(ModuleScript)
 
   ModuleScript(ScriptLoader* aLoader,
-               nsIURI* aBaseURL,
-               JS::Handle<JSObject*> aModuleRecord);
+               nsIURI* aBaseURL);
+
+  void SetModuleRecord(JS::Handle<JSObject*> aModuleRecord);
+  void SetPreInstantiationError(const JS::Value& aError);
 
   ScriptLoader* Loader() const { return mLoader; }
   JSObject* ModuleRecord() const { return mModuleRecord; }
-  JS::Value Exception() const { return mException; }
   nsIURI* BaseURL() const { return mBaseURL; }
 
-  void SetInstantiationResult(JS::Handle<JS::Value> aMaybeException);
-  bool IsUninstantiated() const {
-    return mInstantiationState == Uninstantiated;
-  }
-  bool IsInstantiated() const {
-    return mInstantiationState == Instantiated;
-  }
-  bool InstantiationFailed() const {
-    return mInstantiationState == Errored;
-  }
+  bool IsErrored() const;
+  JS::Value Error() const;
 
   void UnlinkModuleRecord();
 };
diff --git a/dom/script/ScriptLoader.cpp b/dom/script/ScriptLoader.cpp
index adc046b7c..a53098974 100644
--- a/dom/script/ScriptLoader.cpp
+++ b/dom/script/ScriptLoader.cpp
@@ -418,21 +418,23 @@ void
 ScriptLoader::SetModuleFetchFinishedAndResumeWaitingRequests(ModuleLoadRequest *aRequest,
                                                              nsresult aResult)
 {
-  // Update module map with the result of fetching a single module script.  The
-  // module script pointer is nullptr on error.
-
-  MOZ_ASSERT(!aRequest->IsReadyToRun());
+  // Update module map with the result of fetching a single module script.
+  //
+  // If any requests for the same URL are waiting on this one to complete, they
+  // will have ModuleLoaded or LoadFailed on them when the promise is
+  // resolved/rejected. This is set up in StartLoad.
 
   RefPtr<GenericPromise::Private> promise;
   MOZ_ALWAYS_TRUE(mFetchingModules.Get(aRequest->mURI, getter_AddRefs(promise)));
   mFetchingModules.Remove(aRequest->mURI);
 
-  RefPtr<ModuleScript> ms(aRequest->mModuleScript);
-  MOZ_ASSERT(NS_SUCCEEDED(aResult) == (ms != nullptr));
-  mFetchedModules.Put(aRequest->mURI, ms);
+  RefPtr<ModuleScript> moduleScript(aRequest->mModuleScript);
+  MOZ_ASSERT(NS_FAILED(aResult) == !moduleScript);
+
+  mFetchedModules.Put(aRequest->mURI, moduleScript);
 
   if (promise) {
-    if (ms) {
+    if (moduleScript) {
       promise->Resolve(true, __func__);
     } else {
       promise->Reject(aResult, __func__);
@@ -478,19 +480,29 @@ ScriptLoader::ProcessFetchedModuleSource(ModuleLoadRequest* aRequest)
   MOZ_ASSERT(!aRequest->mModuleScript);
 
   nsresult rv = CreateModuleScript(aRequest);
+  MOZ_ASSERT(NS_FAILED(rv) == !aRequest->mModuleScript);
+
   SetModuleFetchFinishedAndResumeWaitingRequests(aRequest, rv);
 
   free(aRequest->mScriptTextBuf);
   aRequest->mScriptTextBuf = nullptr;
   aRequest->mScriptTextLength = 0;
 
-  if (NS_SUCCEEDED(rv)) {
+  if (NS_FAILED(rv)) {
+    aRequest->LoadFailed();
+    return rv;
+  }
+
+  if (!aRequest->mModuleScript->IsErrored()) {
     StartFetchingModuleDependencies(aRequest);
   }
 
-  return rv;
+  return NS_OK;
 }
 
+static nsresult
+ResolveRequestedModules(ModuleLoadRequest* aRequest, nsCOMArray<nsIURI>& aUrls);
+
 nsresult
 ScriptLoader::CreateModuleScript(ModuleLoadRequest* aRequest)
 {
@@ -544,9 +556,34 @@ ScriptLoader::CreateModuleScript(ModuleLoadRequest* aRequest)
       }
     }
     MOZ_ASSERT(NS_SUCCEEDED(rv) == (module != nullptr));
-    if (module) {
-      aRequest->mModuleScript =
-        new ModuleScript(this, aRequest->mBaseURL, module);
+    RefPtr<ModuleScript> moduleScript = new ModuleScript(this, aRequest->mBaseURL);
+    aRequest->mModuleScript = moduleScript;
+
+    if (!module) {
+      // Compilation failed
+      MOZ_ASSERT(aes.HasException());
+      JS::Rooted<JS::Value> error(cx);
+      if (!aes.StealException(&error)) {
+        aRequest->mModuleScript = nullptr;
+        return NS_ERROR_FAILURE;
+      }
+
+      moduleScript->SetPreInstantiationError(error);
+      aRequest->ModuleErrored();
+      return NS_OK;
+    }
+
+    moduleScript->SetModuleRecord(module);
+
+    // Validate requested modules and treat failure to resolve module specifiers
+    // the same as a parse error.
+    nsCOMArray<nsIURI> urls;
+    rv = ResolveRequestedModules(aRequest, urls);
+    if (NS_FAILED(rv)) {
+      // ResolveRequestedModules sets pre-instanitation error on failure.
+      MOZ_ASSERT(moduleScript->IsErrored());
+      aRequest->ModuleErrored();
+      return NS_OK;
     }
   }
 
@@ -556,8 +593,8 @@ ScriptLoader::CreateModuleScript(ModuleLoadRequest* aRequest)
 }
 
 static bool
-ThrowTypeError(JSContext* aCx, ModuleScript* aScript,
-               const nsString& aMessage)
+CreateTypeError(JSContext* aCx, ModuleScript* aScript, const nsString& aMessage,
+                JS::MutableHandle<JS::Value> aError)
 {
   JS::Rooted<JSObject*> module(aCx, aScript->ModuleRecord());
   JS::Rooted<JSScript*> script(aCx, JS::GetModuleScript(aCx, module));
@@ -572,17 +609,11 @@ ThrowTypeError(JSContext* aCx, ModuleScript* aScript,
     return false;
   }
 
-  JS::Rooted<JS::Value> error(aCx);
-  if (!JS::CreateError(aCx, JSEXN_TYPEERR, nullptr, filename, 0, 0, nullptr,
-                       message, &error)) {
-    return false;
-  }
-
-  JS_SetPendingException(aCx, error);
-  return false;
+  return JS::CreateError(aCx, JSEXN_TYPEERR, nullptr, filename, 0, 0, nullptr,
+                         message, aError);
 }
 
-static bool
+static nsresult
 HandleResolveFailure(JSContext* aCx, ModuleScript* aScript,
                      const nsAString& aSpecifier)
 {
@@ -591,19 +622,13 @@ HandleResolveFailure(JSContext* aCx, ModuleScript* aScript,
   nsAutoString message(NS_LITERAL_STRING("Error resolving module specifier: "));
   message.Append(aSpecifier);
 
-  return ThrowTypeError(aCx, aScript, message);
-}
-
-static bool
-HandleModuleNotFound(JSContext* aCx, ModuleScript* aScript,
-                     const nsAString& aSpecifier)
-{
-  // TODO: How can we get the line number of the failed import?
-
-  nsAutoString message(NS_LITERAL_STRING("Resolved module not found in map: "));
-  message.Append(aSpecifier);
+  JS::Rooted<JS::Value> error(aCx);
+  if (!CreateTypeError(aCx, aScript, message, &error)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
 
-  return ThrowTypeError(aCx, aScript, message);
+  aScript->SetPreInstantiationError(error);
+  return NS_OK;
 }
 
 static already_AddRefed<nsIURI>
@@ -701,7 +726,8 @@ ResolveRequestedModules(ModuleLoadRequest* aRequest, nsCOMArray<nsIURI> &aUrls)
     ModuleScript* ms = aRequest->mModuleScript;
     nsCOMPtr<nsIURI> uri = ResolveModuleSpecifier(ms, specifier);
     if (!uri) {
-      HandleResolveFailure(cx, ms, specifier);
+      nsresult rv = HandleResolveFailure(cx, ms, specifier);
+      NS_ENSURE_SUCCESS(rv, rv);
       return NS_ERROR_FAILURE;
     }
 
@@ -720,13 +746,15 @@ void
 ScriptLoader::StartFetchingModuleDependencies(ModuleLoadRequest* aRequest)
 {
   MOZ_ASSERT(aRequest->mModuleScript);
+  MOZ_ASSERT(!aRequest->mModuleScript->IsErrored());
   MOZ_ASSERT(!aRequest->IsReadyToRun());
+
   aRequest->mProgress = ModuleLoadRequest::Progress::FetchingImports;
 
   nsCOMArray<nsIURI> urls;
   nsresult rv = ResolveRequestedModules(aRequest, urls);
   if (NS_FAILED(rv)) {
-    aRequest->LoadFailed();
+    aRequest->ModuleErrored();
     return;
   }
 
@@ -750,7 +778,7 @@ ScriptLoader::StartFetchingModuleDependencies(ModuleLoadRequest* aRequest)
     GenericPromise::All(AbstractThread::GetCurrent(), importsReady);
   allReady->Then(AbstractThread::GetCurrent(), __func__, aRequest,
                  &ModuleLoadRequest::DependenciesLoaded,
-                 &ModuleLoadRequest::LoadFailed);
+                 &ModuleLoadRequest::ModuleErrored);
 }
 
 RefPtr<GenericPromise>
@@ -773,6 +801,7 @@ ScriptLoader::StartFetchingModuleAndDependencies(ModuleLoadRequest* aRequest,
 
   nsresult rv = StartLoad(childRequest, NS_LITERAL_STRING("module"), false);
   if (NS_FAILED(rv)) {
+    MOZ_ASSERT(!childRequest->mModuleScript);
     childRequest->mReady.Reject(rv, __func__);
     return ready;
   }
@@ -781,6 +810,7 @@ ScriptLoader::StartFetchingModuleAndDependencies(ModuleLoadRequest* aRequest,
   return ready;
 }
 
+// 8.1.3.8.1 HostResolveImportedModule(referencingModule, specifier)
 bool
 HostResolveImportedModule(JSContext* aCx, unsigned argc, JS::Value* vp)
 {
@@ -795,31 +825,25 @@ HostResolveImportedModule(JSContext* aCx, unsigned argc, JS::Value* vp)
   MOZ_ASSERT(script->ModuleRecord() == module);
 
   // Let url be the result of resolving a module specifier given referencing
-  // module script and specifier. If the result is failure, throw a TypeError
-  // exception and abort these steps.
+  // module script and specifier.
   nsAutoJSString string;
   if (!string.init(aCx, specifier)) {
     return false;
   }
 
   nsCOMPtr<nsIURI> uri = ResolveModuleSpecifier(script, string);
-  if (!uri) {
-    return HandleResolveFailure(aCx, script, string);
-  }
 
-  // Let resolved module script be the value of the entry in module map whose
-  // key is url. If no such entry exists, throw a TypeError exception and abort
-  // these steps.
+  // This cannot fail because resolving a module specifier must have been
+  // previously successful with these same two arguments.
+  MOZ_ASSERT(uri, "Failed to resolve previously-resolved module specifier");
+
+  // Let resolved module script be moduleMap[url]. (This entry must exist for us
+  // to have gotten to this point.)
+
   ModuleScript* ms = script->Loader()->GetFetchedModule(uri);
-  if (!ms) {
-    return HandleModuleNotFound(aCx, script, string);
-  }
+  MOZ_ASSERT(ms, "Resolved module not found in module map");
 
-  if (ms->InstantiationFailed()) {
-    JS::Rooted<JS::Value> exception(aCx, ms->Exception());
-    JS_SetPendingException(aCx, exception);
-    return false;
-  }
+  MOZ_ASSERT(!ms->IsErrored());
 
   *vp = JS::ObjectValue(*ms->ModuleRecord());
   return true;
@@ -844,9 +868,35 @@ EnsureModuleResolveHook(JSContext* aCx)
 }
 
 void
+ScriptLoader::CheckModuleDependenciesLoaded(ModuleLoadRequest* aRequest)
+{
+  RefPtr<ModuleScript> moduleScript = aRequest->mModuleScript;
+  if (moduleScript && !moduleScript->IsErrored()) {
+    for (auto childRequest : aRequest->mImports) {
+      ModuleScript* childScript = childRequest->mModuleScript;
+      if (!childScript) {
+        // Load error
+        aRequest->mModuleScript = nullptr;
+        return;
+      } else if (childScript->IsErrored()) {
+        // Script error
+        moduleScript->SetPreInstantiationError(childScript->Error());
+        return;
+      }
+    }
+  }
+}
+
+void
 ScriptLoader::ProcessLoadedModuleTree(ModuleLoadRequest* aRequest)
 {
   if (aRequest->IsTopLevel()) {
+    ModuleScript* moduleScript = aRequest->mModuleScript;
+    if (moduleScript && !moduleScript->IsErrored()) {
+      if (!InstantiateModuleTree(aRequest)) {
+        aRequest->mModuleScript = nullptr;
+      }
+    }
     MaybeMoveToLoadedList(aRequest);
     ProcessPendingRequests();
   }
@@ -859,60 +909,35 @@ ScriptLoader::ProcessLoadedModuleTree(ModuleLoadRequest* aRequest)
 bool
 ScriptLoader::InstantiateModuleTree(ModuleLoadRequest* aRequest)
 {
-  // Perform eager instantiation of the loaded module tree.
+  // Instantiate a top-level module and record any error.
 
   MOZ_ASSERT(aRequest);
+  MOZ_ASSERT(aRequest->IsTopLevel());
 
-  ModuleScript* ms = aRequest->mModuleScript;
-  MOZ_ASSERT(ms);
-  if (!ms || !ms->ModuleRecord()) {
-    return false;
-  }
+  ModuleScript* moduleScript = aRequest->mModuleScript;
+  MOZ_ASSERT(moduleScript);
+  MOZ_ASSERT(moduleScript->ModuleRecord());
 
+  nsAutoMicroTask mt;
   AutoJSAPI jsapi;
-  if (NS_WARN_IF(!jsapi.Init(ms->ModuleRecord()))) {
+  if (NS_WARN_IF(!jsapi.Init(moduleScript->ModuleRecord()))) {
     return false;
   }
 
   nsresult rv = EnsureModuleResolveHook(jsapi.cx());
   NS_ENSURE_SUCCESS(rv, false);
 
-  JS::Rooted<JSObject*> module(jsapi.cx(), ms->ModuleRecord());
-  bool ok = NS_SUCCEEDED(nsJSUtils::ModuleDeclarationInstantiation(jsapi.cx(), module));
+  JS::Rooted<JSObject*> module(jsapi.cx(), moduleScript->ModuleRecord());
+  bool ok = NS_SUCCEEDED(nsJSUtils::ModuleInstantiate(jsapi.cx(), module));
 
-  JS::RootedValue exception(jsapi.cx());
   if (!ok) {
     MOZ_ASSERT(jsapi.HasException());
+    JS::RootedValue exception(jsapi.cx());
     if (!jsapi.StealException(&exception)) {
       return false;
     }
     MOZ_ASSERT(!exception.isUndefined());
-  }
-
-  // Mark this module and any uninstantiated dependencies found via depth-first
-  // search as instantiated and record any error.
-
-  mozilla::Vector<ModuleLoadRequest*, 1> requests;
-  if (!requests.append(aRequest)) {
-    return false;
-  }
-
-  while (!requests.empty()) {
-    ModuleLoadRequest* request = requests.popCopy();
-    ModuleScript* ms = request->mModuleScript;
-    if (!ms->IsUninstantiated()) {
-      continue;
-    }
-
-    ms->SetInstantiationResult(exception);
-
-    for (auto import : request->mImports) {
-      if (import->mModuleScript->IsUninstantiated() &&
-          !requests.append(import))
-      {
-        return false;
-      }
-    }
+    // Ignore the exception. It will be recorded in the module record.
   }
 
   return true;
@@ -1427,13 +1452,19 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
     ModuleLoadRequest* modReq = request->AsModuleRequest();
     modReq->mBaseURL = mDocument->GetDocBaseURI();
     rv = CreateModuleScript(modReq);
-    NS_ENSURE_SUCCESS(rv, false);
-    StartFetchingModuleDependencies(modReq);
+    MOZ_ASSERT(NS_FAILED(rv) == !modReq->mModuleScript);
+    if (NS_FAILED(rv)) {
+      modReq->LoadFailed();
+      return false;
+    }
     if (aElement->GetScriptAsync()) {
       mLoadingAsyncRequests.AppendElement(request);
     } else {
       AddDeferRequest(request);
     }
+    if (!modReq->mModuleScript->IsErrored()) {
+      StartFetchingModuleDependencies(modReq);
+    }
     return false;
   }
   request->mProgress = ScriptLoadRequest::Progress::Ready;
@@ -1511,11 +1542,7 @@ ScriptLoader::ProcessOffThreadRequest(ScriptLoadRequest* aRequest)
   if (aRequest->IsModuleRequest()) {
     MOZ_ASSERT(aRequest->mOffThreadToken);
     ModuleLoadRequest* request = aRequest->AsModuleRequest();
-    nsresult rv = ProcessFetchedModuleSource(request);
-    if (NS_FAILED(rv)) {
-      request->LoadFailed();
-    }
-    return rv;
+    return ProcessFetchedModuleSource(request);
   }
 
   aRequest->SetReady();
@@ -1687,7 +1714,7 @@ ScriptLoader::ProcessRequest(ScriptLoadRequest* aRequest)
   if (aRequest->IsModuleRequest() &&
       !aRequest->AsModuleRequest()->mModuleScript)
   {
-    // There was an error parsing a module script.  Nothing to do here.
+    // There was an error fetching a module script.  Nothing to do here.
     FireScriptAvailable(NS_ERROR_FAILURE, aRequest);
     return NS_OK;
   }
@@ -1909,8 +1936,8 @@ ScriptLoader::EvaluateScript(ScriptLoadRequest* aRequest)
   // http://www.whatwg.org/specs/web-apps/current-work/#execute-the-script-block
   nsAutoMicroTask mt;
   AutoEntryScript aes(globalObject, "<script> element", true);
-  JS::Rooted<JSObject*> global(aes.cx(),
-                               globalObject->GetGlobalJSObject());
+  JSContext* cx = aes.cx();
+  JS::Rooted<JSObject*> global(cx, globalObject->GetGlobalJSObject());
 
   bool oldProcessingScriptTag = context->GetProcessingScriptTag();
   context->SetProcessingScriptTag(true);
@@ -1931,28 +1958,38 @@ ScriptLoader::EvaluateScript(ScriptLoadRequest* aRequest)
     }
 
     if (aRequest->IsModuleRequest()) {
+      rv = EnsureModuleResolveHook(cx);
+      NS_ENSURE_SUCCESS(rv, rv);
+
       ModuleLoadRequest* request = aRequest->AsModuleRequest();
       MOZ_ASSERT(request->mModuleScript);
       MOZ_ASSERT(!request->mOffThreadToken);
-      ModuleScript* ms = request->mModuleScript;
-      MOZ_ASSERT(!ms->IsUninstantiated());
-      if (ms->InstantiationFailed()) {
-        JS::Rooted<JS::Value> exception(aes.cx(), ms->Exception());
-        JS_SetPendingException(aes.cx(), exception);
-        rv = NS_ERROR_FAILURE;
-      } else {
-        JS::Rooted<JSObject*> module(aes.cx(), ms->ModuleRecord());
-        MOZ_ASSERT(module);
-        rv = nsJSUtils::ModuleEvaluation(aes.cx(), module);
+
+      ModuleScript* moduleScript = request->mModuleScript;
+      if (moduleScript->IsErrored()) {
+        // Module has an error status
+        JS::Rooted<JS::Value> error(cx, moduleScript->Error());
+        JS_SetPendingException(cx, error);
+        return NS_OK; // An error is reported by AutoEntryScript.
+      }
+
+      JS::Rooted<JSObject*> module(cx, moduleScript->ModuleRecord());
+      MOZ_ASSERT(module);
+
+      rv = nsJSUtils::ModuleEvaluate(cx, module);
+      MOZ_ASSERT(NS_FAILED(rv) == aes.HasException());
+      if (NS_FAILED(rv)) {
+        // Evaluation failed
+        rv = NS_OK; // An error is reported by AutoEntryScript.
       }
     } else {
-      JS::CompileOptions options(aes.cx());
+      JS::CompileOptions options(cx);
       rv = FillCompileOptionsForRequest(aes, aRequest, global, &options);
 
       if (NS_SUCCEEDED(rv)) {
         nsAutoString inlineData;
         SourceBufferHolder srcBuf = GetScriptSource(aRequest, inlineData);
-        rv = nsJSUtils::EvaluateString(aes.cx(), srcBuf, global, options,
+        rv = nsJSUtils::EvaluateString(cx, srcBuf, global, options,
                                        aRequest->OffThreadTokenPtr());
       }
     }
diff --git a/dom/script/ScriptLoader.h b/dom/script/ScriptLoader.h
index 3c428deea..e6b75bf3b 100644
--- a/dom/script/ScriptLoader.h
+++ b/dom/script/ScriptLoader.h
@@ -580,6 +580,7 @@ private:
 
   nsresult CreateModuleScript(ModuleLoadRequest* aRequest);
   nsresult ProcessFetchedModuleSource(ModuleLoadRequest* aRequest);
+  void CheckModuleDependenciesLoaded(ModuleLoadRequest* aRequest);
   void ProcessLoadedModuleTree(ModuleLoadRequest* aRequest);
   bool InstantiateModuleTree(ModuleLoadRequest* aRequest);
   void StartFetchingModuleDependencies(ModuleLoadRequest* aRequest);