Bug 1350671 - stylo: Allow resolving out of date styles when explicitly reconstructing frames for an element. r=bholley

MozReview-Commit-ID: A7ssy7ygWLh

--HG--
extra : rebase_source : 7f8fa109f1a739b68525e3ff662024267189d93f

layout/base/PresShell.cpp

@@ -2953,6 +2953,10 @@ PresShell::RecreateFramesFor(nsIContent* aContent)
   nsStyleChangeList changeList(mPresContext->StyleSet()->BackendType());
   changeList.AppendChange(nullptr, aContent, nsChangeHint_ReconstructFrame);
 
+  // We might have restyles pending when we're asked to recreate frames.
+  // Record that we're OK with stale styles being returned, to avoid assertions.
+  ServoStyleSet::AutoAllowStaleStyles guard(mStyleSet->GetAsServo());
+
   // Mark ourselves as not safe to flush while we're doing frame construction.
   ++mChangeNestCount;
   RestyleManager* restyleManager = mPresContext->RestyleManager();

layout/style/ServoBindingList.h

@@ -291,7 +291,8 @@ SERVO_BINDING_FUNC(Servo_NoteExplicitHints, void, RawGeckoElementBorrowed elemen
 SERVO_BINDING_FUNC(Servo_TakeChangeHint, nsChangeHint, RawGeckoElementBorrowed element)
 SERVO_BINDING_FUNC(Servo_ResolveStyle, ServoComputedValuesStrong,
                    RawGeckoElementBorrowed element,
-                   RawServoStyleSetBorrowed set)
+                   RawServoStyleSetBorrowed set,
+                   bool allow_stale)
 SERVO_BINDING_FUNC(Servo_ResolvePseudoStyle, ServoComputedValuesStrong,
                    RawGeckoElementBorrowed element, nsIAtom* pseudo_tag,
                    bool is_probe, RawServoStyleSetBorrowed set)

layout/style/ServoStyleSet.cpp

@@ -27,6 +27,7 @@ using namespace mozilla::dom;
 ServoStyleSet::ServoStyleSet()
   : mPresContext(nullptr)
   , mBatching(0)
+  , mAllowResolveStaleStyles(false)
 {
 }
 
@@ -783,7 +784,8 @@ ServoStyleSet::RebuildData()
 already_AddRefed<ServoComputedValues>
 ServoStyleSet::ResolveServoStyle(Element* aElement)
 {
-  return Servo_ResolveStyle(aElement, mRawSet.get()).Consume();
+  return Servo_ResolveStyle(aElement, mRawSet.get(),
+                            mAllowResolveStaleStyles).Consume();
 }
 
 void

layout/style/ServoStyleSet.h

@@ -46,6 +46,29 @@ class ServoStyleSet
 {
   friend class ServoRestyleManager;
 public:
+  class AutoAllowStaleStyles
+  {
+  public:
+    AutoAllowStaleStyles(ServoStyleSet* aStyleSet)
+      : mStyleSet(aStyleSet)
+    {
+      if (mStyleSet) {
+        MOZ_ASSERT(!mStyleSet->mAllowResolveStaleStyles);
+        mStyleSet->mAllowResolveStaleStyles = true;
+      }
+    }
+
+    ~AutoAllowStaleStyles()
+    {
+      if (mStyleSet) {
+        mStyleSet->mAllowResolveStaleStyles = false;
+      }
+    }
+
+  private:
+    ServoStyleSet* mStyleSet;
+  };
+
   static bool IsInServoTraversal()
   {
     // The callers of this function are generally main-thread-only _except_
@@ -296,6 +319,7 @@ private:
   EnumeratedArray<SheetType, SheetType::Count,
                   nsTArray<RefPtr<ServoStyleSheet>>> mSheets;
   int32_t mBatching;
+  bool mAllowResolveStaleStyles;
 
   // Stores pointers to our cached style contexts for non-inheriting anonymous
   // boxes.

servo/components/style/gecko_bindings/bindings.rs

@@ -1812,7 +1812,8 @@ extern "C" {
 }
 extern "C" {
     pub fn Servo_ResolveStyle(element: RawGeckoElementBorrowed,
-                              set: RawServoStyleSetBorrowed)
+                              set: RawServoStyleSetBorrowed,
+                              allow_stale: bool)
      -> ServoComputedValuesStrong;
 }
 extern "C" {

servo/ports/geckolib/glue.rs

@@ -1473,15 +1473,22 @@ pub extern "C" fn Servo_TakeChangeHint(element: RawGeckoElementBorrowed) -> nsCh
 
 #[no_mangle]
 pub extern "C" fn Servo_ResolveStyle(element: RawGeckoElementBorrowed,
-                                     raw_data: RawServoStyleSetBorrowed)
+                                     raw_data: RawServoStyleSetBorrowed,
+                                     allow_stale: bool)
                                      -> ServoComputedValuesStrong
 {
     let element = GeckoElement(element);
     debug!("Servo_ResolveStyle: {:?}", element);
     let data = unsafe { element.ensure_data() }.borrow_mut();
 
-    if !data.has_current_styles() {
-        warn!("Resolving style on unstyled element with lazy computation forbidden.");
+    let valid_styles = if allow_stale {
+      data.has_styles()
+    } else {
+      data.has_current_styles()
+    };
+
+    if !valid_styles {
+        warn!("Resolving style on element without current styles with lazy computation forbidden.");
         let per_doc_data = PerDocumentStyleData::from_ffi(raw_data).borrow();
         return per_doc_data.default_computed_values().clone().into_strong();
     }