Bug 1899316 - Add ModuleScript::{FromCache,ToCache}. r=nbp

In order to store ModuleScript in SharedScriptCache, we need to strip off
all GC-things and runtime-related flags.
All fields in ModuleScript matches either of them, so just converting to
base class LoadedScript fits this purpose.

Differential Revision: https://phabricator.services.mozilla.com/D242305

js/loader/LoadedScript.cpp

@@ -6,7 +6,9 @@
 
 #include "LoadedScript.h"
 
+#include "mozilla/AlreadyAddRefed.h"  // already_AddRefed
 #include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/RefPtr.h"     // RefPtr, mozilla::MakeRefPtr
 #include "mozilla/UniquePtr.h"  // mozilla::UniquePtr
 
 #include "mozilla/dom/ScriptLoadContext.h"  // ScriptLoadContext
@@ -54,6 +56,26 @@ LoadedScript::LoadedScript(ScriptKind aKind,
   MOZ_ASSERT(mURI);
 }
 
+LoadedScript::LoadedScript(const LoadedScript& aOther)
+    : mKind(aOther.mKind),
+      mReferrerPolicy(aOther.mReferrerPolicy),
+      mFetchOptions(aOther.mFetchOptions),
+      mURI(aOther.mURI),
+      mBaseURL(aOther.mBaseURL),
+      mDataType(DataType::eStencil),
+      mReceivedScriptTextLength(0),
+      mBytecodeOffset(0),
+      mStencil(aOther.mStencil) {
+  MOZ_ASSERT(mFetchOptions);
+  MOZ_ASSERT(mURI);
+  // NOTE: This is only for the stencil case.
+  //       The script text and the bytecode are not reflected.
+  MOZ_DIAGNOSTIC_ASSERT(aOther.mDataType == DataType::eStencil);
+  MOZ_DIAGNOSTIC_ASSERT(mStencil);
+  MOZ_ASSERT(!mScriptData);
+  MOZ_ASSERT(mScriptBytecode.empty());
+}
+
 LoadedScript::~LoadedScript() {
   mozilla::UnregisterWeakMemoryReporter(this);
   mozilla::DropJSObjects(this);
@@ -262,14 +284,35 @@ NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
 ModuleScript::ModuleScript(mozilla::dom::ReferrerPolicy aReferrerPolicy,
                            ScriptFetchOptions* aFetchOptions, nsIURI* aURI)
-    : LoadedScript(ScriptKind::eModule, aReferrerPolicy, aFetchOptions, aURI),
-      mHadImportMap(false),
-      mDebuggerDataInitialized(false) {
+    : LoadedScript(ScriptKind::eModule, aReferrerPolicy, aFetchOptions, aURI) {
   MOZ_ASSERT(!ModuleRecord());
   MOZ_ASSERT(!HasParseError());
   MOZ_ASSERT(!HasErrorToRethrow());
 }
 
+ModuleScript::ModuleScript(const LoadedScript& aOther) : LoadedScript(aOther) {
+  MOZ_ASSERT(!ModuleRecord());
+  MOZ_ASSERT(!HasParseError());
+  MOZ_ASSERT(!HasErrorToRethrow());
+}
+
+/* static */
+already_AddRefed<ModuleScript> ModuleScript::FromCache(
+    const LoadedScript& aScript) {
+  MOZ_DIAGNOSTIC_ASSERT(aScript.IsModuleScript());
+  MOZ_DIAGNOSTIC_ASSERT(aScript.IsStencil());
+
+  return mozilla::MakeRefPtr<ModuleScript>(aScript).forget();
+}
+
+already_AddRefed<LoadedScript> ModuleScript::ToCache() {
+  MOZ_DIAGNOSTIC_ASSERT(IsStencil());
+  MOZ_DIAGNOSTIC_ASSERT(!HasParseError());
+  MOZ_DIAGNOSTIC_ASSERT(!HasErrorToRethrow());
+
+  return mozilla::MakeRefPtr<LoadedScript>(*this).forget();
+}
+
 void ModuleScript::Shutdown() {
   if (mModuleRecord) {
     JS::ClearModuleEnvironment(mModuleRecord);

js/loader/LoadedScript.h

@@ -65,6 +65,11 @@ class LoadedScript : public nsIMemoryReporter {
   LoadedScript(ScriptKind aKind, mozilla::dom::ReferrerPolicy aReferrerPolicy,
                ScriptFetchOptions* aFetchOptions, nsIURI* aURI);
 
+  LoadedScript(const LoadedScript& aOther);
+
+  template <typename T, typename... Args>
+  friend RefPtr<T> mozilla::MakeRefPtr(Args&&... aArgs);
+
   virtual ~LoadedScript();
 
  public:
@@ -383,12 +388,14 @@ class EventScript final : public LoadedScript {
 // A single module script. May be used to satisfy multiple load requests.
 
 class ModuleScript final : public LoadedScript {
+  // Those fields are used only after instantiated, and they're reset to
+  // null and false when stored into the cache as LoadedScript instance.
   JS::Heap<JSObject*> mModuleRecord;
   JS::Heap<JS::Value> mParseError;
   JS::Heap<JS::Value> mErrorToRethrow;
-  bool mForPreload;
-  bool mHadImportMap;
-  bool mDebuggerDataInitialized;
+  bool mForPreload = false;
+  bool mHadImportMap = false;
+  bool mDebuggerDataInitialized = false;
 
   ~ModuleScript();
 
@@ -402,9 +409,19 @@ class ModuleScript final : public LoadedScript {
   ModuleScript(mozilla::dom::ReferrerPolicy aReferrerPolicy,
                ScriptFetchOptions* aFetchOptions, nsIURI* aURI);
 
+  explicit ModuleScript(const LoadedScript& other);
+
+  template <typename T, typename... Args>
+  friend RefPtr<T> mozilla::MakeRefPtr(Args&&... aArgs);
+
   friend class ScriptLoadRequest;
 
  public:
+  // Convert between cacheable LoadedScript instance, which is used by
+  // mozilla::dom::SharedScriptCache.
+  static already_AddRefed<ModuleScript> FromCache(const LoadedScript& aScript);
+  already_AddRefed<LoadedScript> ToCache();
+
   void SetModuleRecord(JS::Handle<JSObject*> aModuleRecord);
   void SetParseError(const JS::Value& aError);
   void SetErrorToRethrow(const JS::Value& aError);