Issue #1219 - Align computed DOM styles with mainstream behvior.

This updates our behavior for computed DOM styling to no longer return
null on elements that have no display, but return a 0-length (empty)
style instead and don't throw. For this we stop looking at having a
presentation for the style and just look at the document instead.

This resolves #1219

6 files changed, 47 insertions, 74 deletions

diff --git a/config/milestone.txt b/config/milestone.txt
index 210727cac2..e74505029c 100644
--- a/config/milestone.txt
+++ b/config/milestone.txt
@@ -10,4 +10,4 @@
 # hardcoded milestones in the tree from these two files.
 #--------------------------------------------------------
 
-4.4.2
\ No newline at end of file
+4.5.0
\ No newline at end of file
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 1288b34353..47b46dda06 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -10950,35 +10950,12 @@ nsGlobalWindow::GetComputedStyleHelperOuter(Element& aElt,
 {
   MOZ_RELEASE_ASSERT(IsOuterWindow());
 
-  if (!mDocShell) {
+  if (!mDoc) {
     return nullptr;
   }
 
-  nsCOMPtr<nsIPresShell> presShell = mDocShell->GetPresShell();
-
-  if (!presShell) {
-    // Try flushing frames on our parent in case there's a pending
-    // style change that will create the presshell.
-    auto* parent = nsGlobalWindow::Cast(GetPrivateParent());
-    if (!parent) {
-      return nullptr;
-    }
-
-    parent->FlushPendingNotifications(Flush_Frames);
-
-    // Might have killed mDocShell
-    if (!mDocShell) {
-      return nullptr;
-    }
-
-    presShell = mDocShell->GetPresShell();
-    if (!presShell) {
-      return nullptr;
-    }
-  }
-
   RefPtr<nsComputedDOMStyle> compStyle =
-    NS_NewComputedDOMStyle(&aElt, aPseudoElt, presShell,
+    NS_NewComputedDOMStyle(&aElt, aPseudoElt, mDoc,
                            aDefaultStylesOnly ? nsComputedDOMStyle::eDefaultOnly :
                                                 nsComputedDOMStyle::eAll);
 
diff --git a/dom/smil/nsSMILCSSProperty.cpp b/dom/smil/nsSMILCSSProperty.cpp
index 53f3e0fbf7..e745124432 100644
--- a/dom/smil/nsSMILCSSProperty.cpp
+++ b/dom/smil/nsSMILCSSProperty.cpp
@@ -38,14 +38,8 @@ GetCSSComputedValue(Element* aElem,
     return false;
   }
 
-  nsIPresShell* shell = doc->GetShell();
-  if (!shell) {
-    NS_WARNING("Unable to look up computed style -- no pres shell");
-    return false;
-  }
-
   RefPtr<nsComputedDOMStyle> computedStyle =
-    NS_NewComputedDOMStyle(aElem, EmptyString(), shell);
+    NS_NewComputedDOMStyle(aElem, EmptyString(), doc);
 
   computedStyle->GetPropertyValue(aPropID, aResult);
   return true;
diff --git a/editor/libeditor/CSSEditUtils.cpp b/editor/libeditor/CSSEditUtils.cpp
index 5199838c01..d8146ca654 100644
--- a/editor/libeditor/CSSEditUtils.cpp
+++ b/editor/libeditor/CSSEditUtils.cpp
@@ -569,11 +569,8 @@ CSSEditUtils::GetComputedStyle(Element* aElement)
   nsIDocument* doc = aElement->GetUncomposedDoc();
   NS_ENSURE_TRUE(doc, nullptr);
 
-  nsIPresShell* presShell = doc->GetShell();
-  NS_ENSURE_TRUE(presShell, nullptr);
-
   RefPtr<nsComputedDOMStyle> style =
-    NS_NewComputedDOMStyle(aElement, EmptyString(), presShell);
+    NS_NewComputedDOMStyle(aElement, EmptyString(), doc);
 
   return style.forget();
 }
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index 65c1d698c6..647f7f6dc5 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -64,13 +64,13 @@ using namespace mozilla::dom;
  */
 
 already_AddRefed<nsComputedDOMStyle>
-NS_NewComputedDOMStyle(dom::Element* aElement, const nsAString& aPseudoElt,
-                       nsIPresShell* aPresShell,
+NS_NewComputedDOMStyle(dom::Element* aElement,
+                       const nsAString& aPseudoElt,
+                       nsIDocument* aDocument,
                        nsComputedDOMStyle::StyleType aStyleType)
 {
   RefPtr<nsComputedDOMStyle> computedStyle;
-  computedStyle = new nsComputedDOMStyle(aElement, aPseudoElt, aPresShell,
-                                         aStyleType);
+  computedStyle = new nsComputedDOMStyle(aElement, aPseudoElt, aDocument, aStyleType);
   return computedStyle.forget();
 }
 
@@ -243,7 +243,7 @@ nsComputedStyleMap::Update()
 
 nsComputedDOMStyle::nsComputedDOMStyle(dom::Element* aElement,
                                        const nsAString& aPseudoElt,
-                                       nsIPresShell* aPresShell,
+                                       nsIDocument* aDocument,
                                        StyleType aStyleType)
   : mDocumentWeak(nullptr)
   , mOuterFrame(nullptr)
@@ -254,11 +254,13 @@ nsComputedDOMStyle::nsComputedDOMStyle(dom::Element* aElement,
   , mExposeVisitedStyle(false)
   , mResolvedStyleContext(false)
 {
-  MOZ_ASSERT(aElement && aPresShell);
+  MOZ_ASSERT(aElement);
+  MOZ_ASSERT(aDocument);
+  // TODO(emilio, bug 548397, https://github.com/w3c/csswg-drafts/issues/2403):
+  // Should use aElement->OwnerDoc() instead.
+  mDocumentWeak = do_GetWeakReference(aDocument);
 
-  mDocumentWeak = do_GetWeakReference(aPresShell->GetDocument());
-
-  mContent = aElement;
+  mElement = aElement;
 
   if (!DOMStringIsNull(aPseudoElt) && !aPseudoElt.IsEmpty() &&
       aPseudoElt.First() == char16_t(':')) {
@@ -285,8 +287,6 @@ nsComputedDOMStyle::nsComputedDOMStyle(dom::Element* aElement,
       mPseudo = nullptr;
     }
   }
-
-  MOZ_ASSERT(aPresShell->GetPresContext());
 }
 
 nsComputedDOMStyle::~nsComputedDOMStyle()
@@ -297,13 +297,13 @@ nsComputedDOMStyle::~nsComputedDOMStyle()
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsComputedDOMStyle)
 
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsComputedDOMStyle)
-  tmp->ClearStyleContext();  // remove observer before clearing mContent
-  NS_IMPL_CYCLE_COLLECTION_UNLINK(mContent)
+  tmp->ClearStyleContext();  // remove observer before clearing mElement
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mElement)
   NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsComputedDOMStyle)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mContent)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mElement)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(nsComputedDOMStyle)
@@ -366,8 +366,6 @@ nsComputedDOMStyle::SetCssText(const nsAString& aCssText)
 NS_IMETHODIMP
 nsComputedDOMStyle::GetLength(uint32_t* aLength)
 {
-  NS_PRECONDITION(aLength, "Null aLength!  Prepare to die!");
-
   uint32_t length = GetComputedStyleMap()->Length();
 
   // Make sure we have up to date style so that we can include custom
@@ -375,6 +373,8 @@ nsComputedDOMStyle::GetLength(uint32_t* aLength)
   UpdateCurrentStyleSources(false);
   if (mStyleContext) {
     length += StyleVariables()->mVariables.Count();
+  } else {
+    length = 0;
   }
 
   *aLength = length;
@@ -616,7 +616,7 @@ nsComputedDOMStyle::ClearStyleContext()
 {
   if (mResolvedStyleContext) {
     mResolvedStyleContext = false;
-    mContent->RemoveMutationObserver(this);
+    mElement->RemoveMutationObserver(this);
   }
   mStyleContext = nullptr;
 }
@@ -626,7 +626,7 @@ nsComputedDOMStyle::SetResolvedStyleContext(RefPtr<nsStyleContext>&& aContext)
 {
   if (!mResolvedStyleContext) {
     mResolvedStyleContext = true;
-    mContent->AddMutationObserver(this);
+    mElement->AddMutationObserver(this);
   }
   mStyleContext = aContext;
 }
@@ -651,7 +651,7 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
 
   // Flush _before_ getting the presshell, since that could create a new
   // presshell.  Also note that we want to flush the style on the document
-  // we're computing style in, not on the document mContent is in -- the two
+  // we're computing style in, not on the document mElement is in -- the two
   // may be different.
   document->FlushPendingNotifications(
     aNeedsLayoutFlush ? Flush_Layout : Flush_Style);
@@ -659,7 +659,7 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
   mFlushedPendingReflows = aNeedsLayoutFlush;
 #endif
 
-  nsCOMPtr<nsIPresShell> presShellForContent = GetPresShellForContent(mContent);
+  nsCOMPtr<nsIPresShell> presShellForContent = GetPresShellForContent(mElement);
   if (presShellForContent && presShellForContent != document->GetShell()) {
     presShellForContent->FlushPendingNotifications(Flush_Style);
   }
@@ -674,7 +674,11 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
     mPresShell->GetPresContext()->GetRestyleGeneration();
 
   if (mStyleContext) {
-    if (mStyleContextGeneration == currentGeneration) {
+    // We can't rely on the undisplayed restyle generation if mElement is

+    // out-of-document, since that generation is not incremented for DOM changes

+    // on out-of-document elements.

+    if (mStyleContextGeneration == currentGeneration &&
+        mElement->IsInComposedDoc()) {
       // Our cached style context is still valid.
       return;
     }
@@ -683,12 +687,12 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
     mStyleContext = nullptr;
   }
 
-  // XXX the !mContent->IsHTMLElement(nsGkAtoms::area)
+  // XXX the !mElement->IsHTMLElement(nsGkAtoms::area)
   // check is needed due to bug 135040 (to avoid using
   // mPrimaryFrame). Remove it once that's fixed.
   if (!mPseudo && mStyleType == eAll &&
-      !mContent->IsHTMLElement(nsGkAtoms::area)) {
-    mOuterFrame = mContent->GetPrimaryFrame();
+      !mElement->IsHTMLElement(nsGkAtoms::area)) {
+    mOuterFrame = mElement->GetPrimaryFrame();
     mInnerFrame = mOuterFrame;
     if (mOuterFrame) {
       nsIAtom* type = mOuterFrame->GetType();
@@ -731,7 +735,7 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
     // Need to resolve a style context
     RefPtr<nsStyleContext> resolvedStyleContext =
       nsComputedDOMStyle::GetStyleContextForElementNoFlush(
-          mContent->AsElement(),
+          mElement,
           mPseudo,
           presShellForContent ? presShellForContent.get() : mPresShell,
           mStyleType);
@@ -824,7 +828,6 @@ nsComputedDOMStyle::GetPropertyCSSValue(const nsAString& aPropertyName, ErrorRes
 
   UpdateCurrentStyleSources(needsLayoutFlush);
   if (!mStyleContext) {
-    aRv.Throw(NS_ERROR_NOT_AVAILABLE);
     return nullptr;
   }
 
@@ -2861,7 +2864,7 @@ nsComputedDOMStyle::DoGetGridTemplateColumns()
 
   nsGridContainerFrame* gridFrame =
     nsGridContainerFrame::GetGridFrameWithComputedInfo(
-      mContent->GetPrimaryFrame());
+      mElement->GetPrimaryFrame());
 
   if (gridFrame) {
     info = gridFrame->GetComputedTemplateColumns();
@@ -2877,7 +2880,7 @@ nsComputedDOMStyle::DoGetGridTemplateRows()
 
   nsGridContainerFrame* gridFrame =
     nsGridContainerFrame::GetGridFrameWithComputedInfo(
-      mContent->GetPrimaryFrame());
+      mElement->GetPrimaryFrame());
 
   if (gridFrame) {
     info = gridFrame->GetComputedTemplateRows();
@@ -5214,8 +5217,10 @@ nsComputedDOMStyle::GetLineHeightCoord(nscoord& aCoord)
 
   // lie about font size inflation since we lie about font size (since
   // the inflation only applies to text)
-  aCoord = ReflowInput::CalcLineHeight(mContent, mStyleContext,
-                                             blockHeight, 1.0f);
+  aCoord = ReflowInput::CalcLineHeight(mElement,
+                                       mStyleContext,
+                                       blockHeight,
+                                       1.0f);
 
   // CalcLineHeight uses font->mFont.size, but we want to use
   // font->mSize as the font size.  Adjust for that.  Also adjust for
@@ -6642,7 +6647,7 @@ nsComputedDOMStyle::DoGetCustomProperty(const nsAString& aPropertyName)
 void
 nsComputedDOMStyle::ParentChainChanged(nsIContent* aContent)
 {
-  NS_ASSERTION(mContent == aContent, "didn't we register mContent?");
+  NS_ASSERTION(mElement == aContent, "didn't we register mElement?");
   NS_ASSERTION(mResolvedStyleContext,
                "should have only registered an observer when "
                "mResolvedStyleContext is true");
diff --git a/layout/style/nsComputedDOMStyle.h b/layout/style/nsComputedDOMStyle.h
index 77df71ec89..7fbf49afe7 100644
--- a/layout/style/nsComputedDOMStyle.h
+++ b/layout/style/nsComputedDOMStyle.h
@@ -76,12 +76,12 @@ public:
 
   nsComputedDOMStyle(mozilla::dom::Element* aElement,
                      const nsAString& aPseudoElt,
-                     nsIPresShell* aPresShell,
+                     nsIDocument* aDocument,
                      StyleType aStyleType);
 
-  virtual nsINode *GetParentObject() override
+  nsINode *GetParentObject() override
   {
-    return mContent;
+    return mElement;
   }
 
   static already_AddRefed<nsStyleContext>
@@ -667,9 +667,9 @@ private:
 
   // We don't really have a good immutable representation of "presentation".
   // Given the way GetComputedStyle is currently used, we should just grab the
-  // 0th presshell, if any, from the document.
+  // presshell, if any, from the document.
   nsWeakPtr mDocumentWeak;
-  nsCOMPtr<nsIContent> mContent;
+  RefPtr<mozilla::dom::Element> mElement;
 
   /**
    * Strong reference to the style context we access data from.  This can be
@@ -735,7 +735,7 @@ private:
 already_AddRefed<nsComputedDOMStyle>
 NS_NewComputedDOMStyle(mozilla::dom::Element* aElement,
                        const nsAString& aPseudoElt,
-                       nsIPresShell* aPresShell,
+                       nsIDocument* aDocument,
                        nsComputedDOMStyle::StyleType aStyleType =
                          nsComputedDOMStyle::eAll);