From 186a0ce621e03b796e3224f337da55037fca61d6 Mon Sep 17 00:00:00 2001
From: Fedor <fedor@mail.ru>
Date: Wed, 25 Dec 2019 15:40:03 +0300
Subject: [PATCH] 1330657 - Enable script type=/module/ behind a pref.

---
 dom/base/nsScriptLoader.cpp                  | 18 +++++++++++++++---
 dom/base/nsScriptLoader.h                    |  2 ++
 js/src/jit-test/tests/modules/bug-1320993.js |  2 ++
 modules/libpref/init/all.js                  |  3 +++
 4 files changed, 22 insertions(+), 3 deletions(-)
 create mode 100644 js/src/jit-test/tests/modules/bug-1320993.js

diff --git a/dom/base/nsScriptLoader.cpp b/dom/base/nsScriptLoader.cpp
index 1e23d6c5f..5577df20b 100644
--- a/dom/base/nsScriptLoader.cpp
+++ b/dom/base/nsScriptLoader.cpp
@@ -653,6 +653,19 @@ nsScriptLoader::CheckContentPolicy(nsIDocument* aDocument,
   return NS_OK;
 }
 
+bool
+nsScriptLoader::ModuleScriptsEnabled()
+{
+  static bool sEnabledForContent = false;
+  static bool sCachedPref = false;
+  if (!sCachedPref) {
+    sCachedPref = true;
+    Preferences::AddBoolVarCache(&sEnabledForContent, "dom.moduleScripts.enabled", false);
+  }
+
+  return nsContentUtils::IsChromeDoc(mDocument) || sEnabledForContent;
+}
+
 bool
 nsScriptLoader::ModuleMapContainsModule(nsModuleLoadRequest *aRequest) const
 {
@@ -1448,8 +1461,7 @@ nsScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
 
   nsScriptKind scriptKind = nsScriptKind::Classic;
   if (!type.IsEmpty()) {
-    // Support type="module" only for chrome documents.
-    if (nsContentUtils::IsChromeDoc(mDocument) && type.LowerCaseEqualsASCII("module")) {
+    if (ModuleScriptsEnabled() && type.LowerCaseEqualsASCII("module")) {
       scriptKind = nsScriptKind::Module;
     } else {
       NS_ENSURE_TRUE(ParseTypeAttribute(type, &version), false);
@@ -2768,7 +2780,7 @@ nsScriptLoader::PreloadURI(nsIURI *aURI, const nsAString &aCharset,
   }
 
   // TODO: Preload module scripts.
-  if (nsContentUtils::IsChromeDoc(mDocument) && aType.LowerCaseEqualsASCII("module")) {
+  if (ModuleScriptsEnabled() && aType.LowerCaseEqualsASCII("module")) {
     return;
   }
 
diff --git a/dom/base/nsScriptLoader.h b/dom/base/nsScriptLoader.h
index d30a58441..a00239be5 100644
--- a/dom/base/nsScriptLoader.h
+++ b/dom/base/nsScriptLoader.h
@@ -568,6 +568,8 @@ private:
   JS::SourceBufferHolder GetScriptSource(nsScriptLoadRequest* aRequest,
                                          nsAutoString& inlineData);
 
+  bool ModuleScriptsEnabled();
+
   void SetModuleFetchStarted(nsModuleLoadRequest *aRequest);
   void SetModuleFetchFinishedAndResumeWaitingRequests(nsModuleLoadRequest *aRequest,
                                                       nsresult aResult);
diff --git a/js/src/jit-test/tests/modules/bug-1320993.js b/js/src/jit-test/tests/modules/bug-1320993.js
new file mode 100644
index 000000000..bece5731a
--- /dev/null
+++ b/js/src/jit-test/tests/modules/bug-1320993.js
@@ -0,0 +1,2 @@
+parseModule("export default (class {})");
+parseModule("export default (class A {})");
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 9eb9c2a7b..1c6c3af09 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -5468,3 +5468,6 @@ pref("dom.storageManager.enabled", false);
 // >0 = suppress further prompts after the user has canceled the dialog n times
 // See application preferences for appropriate defaults.
 pref("prompts.authentication_dialog_abuse_limit", 0);
+
+// Whether module scripts (<script type="module">) are enabled for content.
+pref("dom.moduleScripts.enabled", true);