Bug 1938290 - Add a continuation mechanism for the parsers returning early due to there being a current script. r=peterv

Differential Revision: https://phabricator.services.mozilla.com/D233329

dom/base/nsContentSink.cpp

@@ -883,6 +883,12 @@ bool nsContentSink::IsScriptExecutingImpl() {
   return !!mScriptLoader->GetCurrentScript();
 }
 
+void nsContentSink::ContinueParsingDocumentAfterCurrentScriptImpl() {
+  if (mScriptLoader) {
+    mScriptLoader->ContinueParsingDocumentAfterCurrentScript();
+  }
+}
+
 nsresult nsContentSink::WillParseImpl(void) {
   if (mRunsToCompletion || !mDocument) {
     return NS_OK;

dom/base/nsContentSink.h

@@ -105,6 +105,7 @@ class nsContentSink : public nsICSSLoaderObserver,
   void DidBuildModelImpl(bool aTerminated);
   void DropParserAndPerfHint(void);
   bool IsScriptExecutingImpl();
+  void ContinueParsingDocumentAfterCurrentScriptImpl();
 
   void NotifyAppend(nsIContent* aContent, uint32_t aStartIndex);
 

dom/script/ScriptLoader.cpp

@@ -207,6 +207,7 @@ ScriptLoader::ScriptLoader(Document* aDocument)
       mBlockingDOMContentLoaded(false),
       mLoadEventFired(false),
       mGiveUpEncoding(false),
+      mContinueParsingDocumentAfterCurrentScript(false),
       mReporter(new ConsoleReportCollector()) {
   LOG(("ScriptLoader::ScriptLoader %p", this));
 
@@ -2721,7 +2722,8 @@ nsresult ScriptLoader::EvaluateScriptElement(ScriptLoadRequest* aRequest) {
   Document* ownerDoc =
       aRequest->GetScriptLoadContext()->GetScriptOwnerDocument();
   if (ownerDoc != mDocument) {
-    // Willful violation of HTML5 as of 2010-12-01
+    // https://html.spec.whatwg.org/#prepare-the-script-element step 16
+    // as of 2025-01-15
     return NS_ERROR_FAILURE;
   }
 
@@ -2749,6 +2751,23 @@ nsresult ScriptLoader::EvaluateScriptElement(ScriptLoadRequest* aRequest) {
     globalObject = scriptGlobal;
   }
 
+  // This mechanism is currently only used when the parser returns
+  // early due to this script loader having a current script. However,
+  // now that we have this, we could migrate continuing after a
+  // parser-blocking script to this same mechanism. Not doing it right
+  // away to reduce risk of introducing bugs.
+  auto maybeContinueParser = MakeScopeExit([&] {
+    if (mContinueParsingDocumentAfterCurrentScript) {
+      mContinueParsingDocumentAfterCurrentScript = false;
+      if (mDocument) {
+        nsCOMPtr<nsIParser> parser = mDocument->CreatorParserOrNull();
+        if (parser) {
+          parser->ContinueInterruptedParsingAsync();
+        }
+      }
+    }
+  });
+
   // Update our current script.
   // This must be destroyed after destroying nsAutoMicroTask, see:
   // https://bugzilla.mozilla.org/show_bug.cgi?id=1620505#c4

dom/script/ScriptLoader.h

@@ -224,6 +224,11 @@ class ScriptLoader final : public JS::loader::ScriptLoaderInterface {
    */
   nsIScriptElement* GetCurrentScript() { return mCurrentScript; }
 
+  void ContinueParsingDocumentAfterCurrentScript() {
+    MOZ_ASSERT(mCurrentScript);
+    mContinueParsingDocumentAfterCurrentScript = true;
+  }
+
   nsIScriptElement* GetCurrentParserInsertedScript() {
     return mCurrentParserInsertedScript;
   }
@@ -817,6 +822,7 @@ class ScriptLoader final : public JS::loader::ScriptLoaderInterface {
   bool mBlockingDOMContentLoaded;
   bool mLoadEventFired;
   bool mGiveUpEncoding;
+  bool mContinueParsingDocumentAfterCurrentScript;
 
   TimeDuration mMainThreadParseTime;
 

dom/xml/nsXMLContentSink.cpp

@@ -792,8 +792,6 @@ void nsXMLContentSink::SetDocumentCharset(NotNull<const Encoding*> aEncoding) {
 
 nsISupports* nsXMLContentSink::GetTarget() { return ToSupports(mDocument); }
 
-bool nsXMLContentSink::IsScriptExecuting() { return IsScriptExecutingImpl(); }
-
 nsresult nsXMLContentSink::FlushText(bool aReleaseTextNode) {
   nsresult rv = NS_OK;
 

dom/xml/nsXMLContentSink.h

@@ -69,7 +69,10 @@ class nsXMLContentSink : public nsContentSink,
   virtual void FlushPendingNotifications(mozilla::FlushType aType) override;
   virtual void SetDocumentCharset(NotNull<const Encoding*> aEncoding) override;
   virtual nsISupports* GetTarget() override;
-  virtual bool IsScriptExecuting() override;
+  bool IsScriptExecuting() override { return IsScriptExecutingImpl(); }
+  void ContinueParsingDocumentAfterCurrentScript() override {
+    ContinueParsingDocumentAfterCurrentScriptImpl();
+  }
   virtual void ContinueInterruptedParsingAsync() override;
   bool IsPrettyPrintXML() const override { return mPrettyPrintXML; }
   bool IsPrettyPrintHasSpecialRoot() const override {

parser/html/nsHtml5TreeOpExecutor.cpp

@@ -516,6 +516,8 @@ void nsHtml5TreeOpExecutor::RunFlushLoop() {
 
   if (mRunFlushLoopOnStack) {
     // There's already a RunFlushLoop() on the call stack.
+    // The instance of RunFlushLoop() already on the stack is
+    // expected to ensure that we don't stall.
     return;
   }
 
@@ -544,18 +546,26 @@ void nsHtml5TreeOpExecutor::RunFlushLoop() {
 
     if (!parserKungFuDeathGrip->IsParserEnabled()) {
       // The parser is blocked.
+      // Whatever blocked the parser is responsible for ensuring that
+      // we don't stall.
       return;
     }
 
     if (mFlushState != eNotFlushing) {
-      // XXX Can this happen? In case it can, let's avoid crashing.
+      // It's not clear whether this case can ever happen. It's not
+      // supposed to, but in case this can happen, let's return
+      // early to avoid an even worse state. In case this happens,
+      // there in no obvious other mechanism to prevent stalling,
+      // so let's call `ContinueInterruptedParsingAsync()` to
+      // make sure we don't stall.
+      nsHtml5TreeOpExecutor::ContinueInterruptedParsingAsync();
       return;
     }
 
-    // If there are scripts executing, then the content sink is jumping the gun
-    // (probably due to a synchronous XMLHttpRequest) and will re-enable us
-    // later, see bug 460706.
+    // If there are scripts executing, this is probably due to a synchronous
+    // XMLHttpRequest, see bug 460706 and 1938290.
     if (IsScriptExecuting()) {
+      ContinueParsingDocumentAfterCurrentScript();
       return;
     }
 

parser/html/nsHtml5TreeOpExecutor.h

@@ -161,6 +161,10 @@ class nsHtml5TreeOpExecutor final
 
   bool IsScriptExecuting() override { return IsScriptExecutingImpl(); }
 
+  void ContinueParsingDocumentAfterCurrentScript() override {
+    ContinueParsingDocumentAfterCurrentScriptImpl();
+  }
+
   // Not from interface
 
   void SetStreamParser(nsHtml5StreamParser* aStreamParser) {

parser/htmlparser/nsIContentSink.h

@@ -28,12 +28,8 @@ namespace mozilla {
 class Encoding;
 }
 
-#define NS_ICONTENT_SINK_IID                         \
-  {                                                  \
-    0xcf9a7cbb, 0xfcbc, 0x4e13, {                    \
-      0x8e, 0xf5, 0x18, 0xef, 0x2d, 0x3d, 0x58, 0x29 \
-    }                                                \
-  }
+#define NS_ICONTENT_SINK_IID \
+  {0xcf9a7cbb, 0xfcbc, 0x4e13, {0x8e, 0xf5, 0x18, 0xef, 0x2d, 0x3d, 0x58, 0x29}}
 
 class nsIContentSink : public nsISupports {
  protected:
@@ -130,6 +126,8 @@ class nsIContentSink : public nsISupports {
    */
   virtual bool IsScriptExecuting() { return false; }
 
+  virtual void ContinueParsingDocumentAfterCurrentScript() {};
+
   /**
    * Posts a runnable that continues parsing.
    */