Bug 1720570 - Support fetching css module scripts; r=dom-core,smaug

Differential Revision: https://phabricator.services.mozilla.com/D263415

Author: dminor

dom/base/nsContentUtils.cpp

@@ -8659,6 +8659,11 @@ bool nsContentUtils::IsJsonMimeType(const nsAString& aMimeType) {
   return StringEndsWith(subtype, u"+json"_ns);
 }
 
+// https://html.spec.whatwg.org/#fetch-a-single-module-script, 7.3
+bool nsContentUtils::IsCssMimeType(const nsAString& aMimeType) {
+  return aMimeType.LowerCaseEqualsLiteral("text/css");
+}
+
 bool nsContentUtils::PrefetchPreloadEnabled(nsIDocShell* aDocShell) {
   //
   // SECURITY CHECK: disable prefetching and preloading from mailnews!

dom/base/nsContentUtils.h

@@ -2740,6 +2740,12 @@ class nsContentUtils {
    */
   static bool IsJsonMimeType(const nsAString& aMimeType);
 
+  /**
+   * Returns true if the given MIME type string is a valid CSS MIME type,
+   * otherwise false.
+   */
+  static bool IsCssMimeType(const nsAString& aMimeType);
+
   static void SplitMimeType(const nsAString& aValue, nsString& aType,
                             nsString& aParams);
 

dom/script/ScriptLoader.cpp

@@ -430,20 +430,32 @@ nsContentPolicyType ScriptLoadRequestToContentPolicyType(
     ScriptLoadRequest* aRequest) {
   if (aRequest->GetScriptLoadContext()->IsPreload()) {
     if (aRequest->IsModuleRequest()) {
-      return aRequest->AsModuleRequest()->mModuleType ==
-                     JS::ModuleType::JavaScript
-                 ? nsIContentPolicy::TYPE_INTERNAL_MODULE_PRELOAD
-                 : nsIContentPolicy::TYPE_INTERNAL_JSON_PRELOAD;
+      switch (aRequest->AsModuleRequest()->mModuleType) {
+        case JS::ModuleType::JavaScript:
+          return nsIContentPolicy::TYPE_INTERNAL_MODULE_PRELOAD;
+        case JS::ModuleType::JSON:
+          return nsIContentPolicy::TYPE_INTERNAL_JSON_PRELOAD;
+        case JS::ModuleType::CSS:
+          return nsIContentPolicy::TYPE_INTERNAL_STYLESHEET_PRELOAD;
+        case JS::ModuleType::Unknown:
+          MOZ_ASSERT_UNREACHABLE("Unknown module type");
+      }
     }
 
     return nsIContentPolicy::TYPE_INTERNAL_SCRIPT_PRELOAD;
   }
 
   if (aRequest->IsModuleRequest()) {
-    return aRequest->AsModuleRequest()->mModuleType ==
-                   JS::ModuleType::JavaScript
-               ? nsIContentPolicy::TYPE_INTERNAL_MODULE
-               : nsIContentPolicy::TYPE_JSON;
+    switch (aRequest->AsModuleRequest()->mModuleType) {
+      case JS::ModuleType::Unknown:
+        MOZ_CRASH("Unexpected module type");
+      case JS::ModuleType::JavaScript:
+        return nsIContentPolicy::TYPE_INTERNAL_MODULE;
+      case JS::ModuleType::JSON:
+        return nsIContentPolicy::TYPE_JSON;
+      case JS::ModuleType::CSS:
+        return nsIContentPolicy::TYPE_STYLESHEET;
+    }
   }
 
   return nsIContentPolicy::TYPE_INTERNAL_SCRIPT;
@@ -1963,10 +1975,12 @@ nsresult ScriptLoader::AttemptOffThreadScriptCompile(
     return NS_OK;
   }
 
-  // Don't off-thread compile JSON modules.
-  // https://bugzilla.mozilla.org/show_bug.cgi?id=1912112
+  // Don't off-thread compile JSON or CSS modules.
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1912112 (JSON)
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1987143 (CSS)
   if (aRequest->IsModuleRequest() &&
-      aRequest->AsModuleRequest()->mModuleType == JS::ModuleType::JSON) {
+      (aRequest->AsModuleRequest()->mModuleType == JS::ModuleType::JSON ||
+       aRequest->AsModuleRequest()->mModuleType == JS::ModuleType::CSS)) {
     return NS_OK;
   }
 
@@ -4419,6 +4433,11 @@ static bool MimeTypeMatchesExpectedModuleType(
     return true;
   }
 
+  if (expectedModuleType == JS::ModuleType::CSS &&
+      nsContentUtils::IsCssMimeType(typeString)) {
+    return true;
+  }
+
   return false;
 }