Issue #2732 - Part 2: Stop accepting <a> as a valid image map <area>

This was part of the HTML4 standard but only ever implemented by Mozilla
and removed again in HTML5 due to lack of adoption. Retaining this could
cause web compat issues and unspecified behavior in the layout engine.

layout/generic/nsImageMap.cpp

@@ -9,6 +9,7 @@
 
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/Event.h" // for nsIDOMEvent::InternalDOMEvent()
+#include "mozilla/dom/HTMLAreaElement.h"
 #include "mozilla/gfx/PathHelpers.h"
 #include "mozilla/UniquePtr.h"
 #include "nsString.h"
@@ -29,10 +30,11 @@
 
 using namespace mozilla;
 using namespace mozilla::gfx;
+using namespace mozilla::dom;
 
 class Area {
 public:
-  explicit Area(nsIContent* aArea);
+  explicit Area(HTMLAreaElement* aArea);
   virtual ~Area();
 
   virtual void ParseCoords(const nsAString& aSpec);
@@ -45,17 +47,17 @@ public:
 
   void HasFocus(bool aHasFocus);
 
-  nsCOMPtr<nsIContent> mArea;
+  RefPtr<HTMLAreaElement> mArea;
   UniquePtr<nscoord[]> mCoords;
   int32_t mNumCoords;
   bool mHasFocus;
 };
 
-Area::Area(nsIContent* aArea)
+Area::Area(HTMLAreaElement* aArea)
   : mArea(aArea)
 {
   MOZ_COUNT_CTOR(Area);
-  NS_PRECONDITION(mArea, "How did that happen?");
+  MOZ_ASSERT(mArea, "How did that happen?");
   mNumCoords = 0;
   mHasFocus = false;
 }
@@ -266,7 +268,7 @@ void Area::HasFocus(bool aHasFocus)
 
 class DefaultArea : public Area {
 public:
-  explicit DefaultArea(nsIContent* aArea);
+  explicit DefaultArea(HTMLAreaElement* aArea);
 
   virtual bool IsInside(nscoord x, nscoord y) const override;
   virtual void Draw(nsIFrame* aFrame, DrawTarget& aDrawTarget,
@@ -275,7 +277,7 @@ public:
   virtual void GetRect(nsIFrame* aFrame, nsRect& aRect) override;
 };
 
-DefaultArea::DefaultArea(nsIContent* aArea)
+DefaultArea::DefaultArea(HTMLAreaElement* aArea)
   : Area(aArea)
 {
 }
@@ -310,7 +312,7 @@ void DefaultArea::GetRect(nsIFrame* aFrame, nsRect& aRect)
 
 class RectArea : public Area {
 public:
-  explicit RectArea(nsIContent* aArea);
+  explicit RectArea(HTMLAreaElement* aArea);
 
   virtual void ParseCoords(const nsAString& aSpec) override;
   virtual bool IsInside(nscoord x, nscoord y) const override;
@@ -320,7 +322,7 @@ public:
   virtual void GetRect(nsIFrame* aFrame, nsRect& aRect) override;
 };
 
-RectArea::RectArea(nsIContent* aArea)
+RectArea::RectArea(HTMLAreaElement* aArea)
   : Area(aArea)
 {
 }
@@ -416,7 +418,7 @@ void RectArea::GetRect(nsIFrame* aFrame, nsRect& aRect)
 
 class PolyArea : public Area {
 public:
-  explicit PolyArea(nsIContent* aArea);
+  explicit PolyArea(HTMLAreaElement* aArea);
 
   virtual void ParseCoords(const nsAString& aSpec) override;
   virtual bool IsInside(nscoord x, nscoord y) const override;
@@ -426,7 +428,7 @@ public:
   virtual void GetRect(nsIFrame* aFrame, nsRect& aRect) override;
 };
 
-PolyArea::PolyArea(nsIContent* aArea)
+PolyArea::PolyArea(HTMLAreaElement* aArea)
   : Area(aArea)
 {
 }
@@ -573,7 +575,7 @@ void PolyArea::GetRect(nsIFrame* aFrame, nsRect& aRect)
 
 class CircleArea : public Area {
 public:
-  explicit CircleArea(nsIContent* aArea);
+  explicit CircleArea(HTMLAreaElement* aArea);
 
   virtual void ParseCoords(const nsAString& aSpec) override;
   virtual bool IsInside(nscoord x, nscoord y) const override;
@@ -583,7 +585,7 @@ public:
   virtual void GetRect(nsIFrame* aFrame, nsRect& aRect) override;
 };
 
-CircleArea::CircleArea(nsIContent* aArea)
+CircleArea::CircleArea(HTMLAreaElement* aArea)
   : Area(aArea)
 {
 }
@@ -750,21 +752,17 @@ nsImageMap::Init(nsImageFrame* aImageFrame, nsIContent* aMap)
 
 
 nsresult
-nsImageMap::SearchForAreas(nsIContent* aParent, bool& aFoundArea,
-                           bool& aFoundAnchor)
+nsImageMap::SearchForAreas(nsIContent* aParent)
 {
   nsresult rv = NS_OK;
-  uint32_t i, n = aParent->GetChildCount();
+  uint32_t n = aParent->GetChildCount();
 
-  // Look for <area> or <a> elements. We'll use whichever type we find first.
-  for (i = 0; i < n; i++) {
-    nsIContent *child = aParent->GetChildAt(i);
-
-    // If we haven't determined that the map element contains an
-    // <a> element yet, then look for <area>.
-    if (!aFoundAnchor && child->IsHTMLElement(nsGkAtoms::area)) {
-      aFoundArea = true;
-      rv = AddArea(child);
+  // Look for <area> elements.
+  for (nsIContent* child = aParent->GetFirstChild();
+       child;
+       child = child->GetNextSibling()) {
+    if (auto* area = static_cast<HTMLAreaElement*>(HTMLAreaElement::FromContent(child))) {
+      rv = AddArea(area);
       NS_ENSURE_SUCCESS(rv, rv);
 
       // Continue to next child. This stops mConsiderWholeSubtree from
@@ -774,17 +772,9 @@ nsImageMap::SearchForAreas(nsIContent* aParent, bool& aFoundArea,
       continue;
     }
 
-    // If we haven't determined that the map element contains an
-    // <area> element yet, then look for <a>.
-    if (!aFoundArea && child->IsHTMLElement(nsGkAtoms::a)) {
-      aFoundAnchor = true;
-      rv = AddArea(child);
-      NS_ENSURE_SUCCESS(rv, rv);
-    }
-
     if (child->IsElement()) {
       mConsiderWholeSubtree = true;
-      rv = SearchForAreas(child, aFoundArea, aFoundAnchor);
+      rv = SearchForAreas(child);
       NS_ENSURE_SUCCESS(rv, rv);
     }
   }
@@ -798,11 +788,9 @@ nsImageMap::UpdateAreas()
   // Get rid of old area data
   FreeAreas();
 
-  bool foundArea = false;
-  bool foundAnchor = false;
   mConsiderWholeSubtree = false;
+  nsresult rv = SearchForAreas(mMap);
 
-  nsresult rv = SearchForAreas(mMap, foundArea, foundAnchor);
 #ifdef ACCESSIBILITY
   if (NS_SUCCEEDED(rv)) {
     nsAccessibilityService* accService = GetAccService();
@@ -815,7 +803,7 @@ nsImageMap::UpdateAreas()
 }
 
 nsresult
-nsImageMap::AddArea(nsIContent* aArea)
+nsImageMap::AddArea(HTMLAreaElement* aArea)
 {
   static nsIContent::AttrValuesArray strings[] =
     {&nsGkAtoms::rect, &nsGkAtoms::rectangle,