Issue #618 - Remove eager instantiation

This backs out the stuff added in Bug 1295978.
Ref: BZ 1295978, 1388728

6 files changed, 10 insertions, 129 deletions

diff --git a/dom/base/nsJSUtils.cpp b/dom/base/nsJSUtils.cpp
index c294cfdbad..65965d74bf 100644
--- a/dom/base/nsJSUtils.cpp
+++ b/dom/base/nsJSUtils.cpp
@@ -315,6 +315,7 @@ nsJSUtils::ModuleInstantiate(JSContext* aCx, JS::Handle<JSObject*> aModule)
 
   MOZ_ASSERT(aCx == nsContentUtils::GetCurrentJSContext());
   MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(nsContentUtils::IsInMicroTask());
 
   NS_ENSURE_TRUE(xpc::Scriptability::Get(aModule).Allowed(), NS_OK);
 
diff --git a/dom/script/ModuleLoadRequest.cpp b/dom/script/ModuleLoadRequest.cpp
index 98106df1b9..8871dcdab2 100644
--- a/dom/script/ModuleLoadRequest.cpp
+++ b/dom/script/ModuleLoadRequest.cpp
@@ -86,11 +86,6 @@ ModuleLoadRequest::DependenciesLoaded()
   // The module and all of its dependencies have been successfully fetched and
   // compiled.
 
-  if (!mLoader->InstantiateModuleTree(this)) {
-    LoadFailed();
-    return;
-  }
-
   SetReady();
   mLoader->ProcessLoadedModuleTree(this);
   mLoader = nullptr;
diff --git a/dom/script/ModuleScript.cpp b/dom/script/ModuleScript.cpp
index 34ef4dec46..bf02f522de 100644
--- a/dom/script/ModuleScript.cpp
+++ b/dom/script/ModuleScript.cpp
@@ -34,7 +34,6 @@ 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_END
 
 NS_IMPL_CYCLE_COLLECTING_ADDREF(ModuleScript)
@@ -44,13 +43,11 @@ ModuleScript::ModuleScript(ScriptLoader *aLoader, nsIURI* aBaseURL,
                            JS::Handle<JSObject*> aModuleRecord)
  : mLoader(aLoader),
    mBaseURL(aBaseURL),
-   mModuleRecord(aModuleRecord),
-   mInstantiationState(Uninstantiated)
+   mModuleRecord(aModuleRecord)
 {
   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().
@@ -68,7 +65,6 @@ ModuleScript::UnlinkModuleRecord()
     JS::SetModuleHostDefinedField(mModuleRecord, JS::UndefinedValue());
   }
   mModuleRecord = nullptr;
-  mException.setUndefined();
 }
 
 ModuleScript::~ModuleScript()
@@ -80,21 +76,5 @@ ModuleScript::~ModuleScript()
   DropJSObjects(this);
 }
 
-void
-ModuleScript::SetInstantiationResult(JS::Handle<JS::Value> aMaybeException)
-{
-  MOZ_ASSERT(mInstantiationState == Uninstantiated);
-  MOZ_ASSERT(mModuleRecord);
-  MOZ_ASSERT(mException.isUndefined());
-
-  if (aMaybeException.isUndefined()) {
-    mInstantiationState = Instantiated;
-  } else {
-    mModuleRecord = nullptr;
-    mException = aMaybeException;
-    mInstantiationState = Errored;
-  }
-}
-
 } // dom namespace
 } // mozilla namespace
diff --git a/dom/script/ModuleScript.h b/dom/script/ModuleScript.h
index dd0d07e847..97fdb8ed19 100644
--- a/dom/script/ModuleScript.h
+++ b/dom/script/ModuleScript.h
@@ -20,17 +20,9 @@ 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;
 
   ~ModuleScript();
 
@@ -44,20 +36,8 @@ public:
 
   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;
-  }
-
   void UnlinkModuleRecord();
 };
 
diff --git a/dom/script/ScriptLoader.cpp b/dom/script/ScriptLoader.cpp
index 736bb43499..cf7f06e713 100644
--- a/dom/script/ScriptLoader.cpp
+++ b/dom/script/ScriptLoader.cpp
@@ -726,11 +726,6 @@ ScriptLoader::StartFetchingModuleDependencies(ModuleLoadRequest* aRequest)
   MOZ_ASSERT(aRequest->mModuleScript);
   MOZ_ASSERT(!aRequest->IsReadyToRun());
 
-  if (aRequest->mModuleScript->InstantiationFailed()) {
-    aRequest->LoadFailed();
-    return;
-  }
-
   aRequest->mProgress = ModuleLoadRequest::Progress::FetchingImports;
 
   nsCOMArray<nsIURI> urls;
@@ -825,12 +820,6 @@ HostResolveImportedModule(JSContext* aCx, unsigned argc, JS::Value* vp)
     return HandleModuleNotFound(aCx, script, string);
   }
 
-  if (ms->InstantiationFailed()) {
-    JS::Rooted<JS::Value> exception(aCx, ms->Exception());
-    JS_SetPendingException(aCx, exception);
-    return false;
-  }
-
   *vp = JS::ObjectValue(*ms->ModuleRecord());
   return true;
 }
@@ -866,68 +855,6 @@ ScriptLoader::ProcessLoadedModuleTree(ModuleLoadRequest* aRequest)
   }
 }
 
-bool
-ScriptLoader::InstantiateModuleTree(ModuleLoadRequest* aRequest)
-{
-  // Perform eager instantiation of the loaded module tree.
-
-  MOZ_ASSERT(aRequest);
-
-  ModuleScript* ms = aRequest->mModuleScript;
-  MOZ_ASSERT(ms);
-  if (!ms || !ms->ModuleRecord()) {
-    return false;
-  }
-
-  AutoJSAPI jsapi;
-  if (NS_WARN_IF(!jsapi.Init(ms->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::ModuleInstantiate(jsapi.cx(), module));
-
-  JS::RootedValue exception(jsapi.cx());
-  if (!ok) {
-    MOZ_ASSERT(jsapi.HasException());
-    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;
-      }
-    }
-  }
-
-  return true;
-}
-
 nsresult
 ScriptLoader::StartLoad(ScriptLoadRequest *aRequest, const nsAString &aType,
                         bool aScriptFromHead)
@@ -1941,18 +1868,17 @@ ScriptLoader::EvaluateScript(ScriptLoadRequest* aRequest)
     }
 
     if (aRequest->IsModuleRequest()) {
+      rv = EnsureModuleResolveHook(aes.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);
+      JS::Rooted<JSObject*> module(aes.cx(),
+                                   request->mModuleScript->ModuleRecord());
+      MOZ_ASSERT(module);
+      rv = nsJSUtils::ModuleInstantiate(aes.cx(), module);
+      if (NS_SUCCEEDED(rv)) {
         rv = nsJSUtils::ModuleEvaluate(aes.cx(), module);
       }
     } else {
diff --git a/dom/script/ScriptLoader.h b/dom/script/ScriptLoader.h
index 3c428deea6..32401d1b6b 100644
--- a/dom/script/ScriptLoader.h
+++ b/dom/script/ScriptLoader.h
@@ -581,7 +581,6 @@ private:
   nsresult CreateModuleScript(ModuleLoadRequest* aRequest);
   nsresult ProcessFetchedModuleSource(ModuleLoadRequest* aRequest);
   void ProcessLoadedModuleTree(ModuleLoadRequest* aRequest);
-  bool InstantiateModuleTree(ModuleLoadRequest* aRequest);
   void StartFetchingModuleDependencies(ModuleLoadRequest* aRequest);
 
   RefPtr<mozilla::GenericPromise>