Issue #2721 - Create special case exception for <A>.Click() outside of DOM

This removes the requirement for there to be a non-null PresShell to
dispatch `Click()` events on `<A>` elements (only), since the exception
to the rule has propagated to the spec.

With these changes it should now be possible do create an anchor and
`Click()` on it from JS without actually first attaching it to the DOM
of the presented document, as abused by scripted downloads in pages
(instead of using the A attribute to custom-name downloads).

dom/base/Element.cpp

@@ -149,6 +149,8 @@
 #include "nsDOMStringMap.h"
 #include "DOMIntersectionObserver.h"
 
+#include "nsDocShell.h" // for ::Cast
+
 using namespace mozilla;
 using namespace mozilla::dom;
 
@@ -2259,12 +2261,15 @@ Element::GetPrimaryFrame(mozFlushType aType)
 nsresult
 Element::LeaveLink(nsPresContext* aPresContext)
 {
-  nsILinkHandler *handler = aPresContext->GetLinkHandler();
-  if (!handler) {
+  if (!aPresContext || !aPresContext->Document()->LinkHandlingEnabled()) {
     return NS_OK;
   }
 
-  return handler->OnLeaveLink();
+  nsIDocShell* shell = aPresContext->Document()->GetDocShell();
+  if (!shell) {
+    return NS_OK;
+  }
+  return nsDocShell::Cast(shell)->OnLeaveLink();
 }
 
 nsresult
@@ -3175,7 +3180,6 @@ Element::CheckHandleEventForLinksPrecondition(EventChainVisitor& aVisitor,
        (aVisitor.mEvent->mMessage != eMouseClick) &&
        (aVisitor.mEvent->mMessage != eKeyPress) &&
        (aVisitor.mEvent->mMessage != eLegacyDOMActivate)) ||
-      !aVisitor.mPresContext ||
       aVisitor.mEvent->mFlags.mMultipleActionsPrevented) {
     return false;
   }
@@ -3220,7 +3224,7 @@ Element::GetEventTargetParentForLinks(EventChainPreVisitor& aVisitor)
     if (!focusEvent || !focusEvent->mIsRefocus) {
       nsAutoString target;
       GetLinkTarget(target);
-      nsContentUtils::TriggerLink(this, aVisitor.mPresContext, absURI, target,
+      nsContentUtils::TriggerLink(this, absURI, target,
                                   false, true, true);
       // Make sure any ancestor links don't also TriggerLink
       aVisitor.mEvent->mFlags.mMultipleActionsPrevented = true;
@@ -3272,20 +3276,20 @@ Element::PostHandleEventForLinks(EventChainPostVisitor& aVisitor)
   switch (aVisitor.mEvent->mMessage) {
   case eMouseDown:
     {
-      if (aVisitor.mEvent->AsMouseEvent()->button ==
-            WidgetMouseEvent::eLeftButton) {
-        // don't make the link grab the focus if there is no link handler
-        nsILinkHandler *handler = aVisitor.mPresContext->GetLinkHandler();
-        nsIDocument *document = GetComposedDoc();
-        if (handler && document) {
+      if (aVisitor.mEvent->AsMouseEvent()->button == WidgetMouseEvent::eLeftButton &&
+          OwnerDoc()->LinkHandlingEnabled()) {
+        aVisitor.mEvent->mFlags.mMultipleActionsPrevented = true;
+        
+        if (IsInComposedDoc()) {
           nsIFocusManager* fm = nsFocusManager::GetFocusManager();
           if (fm) {
-            aVisitor.mEvent->mFlags.mMultipleActionsPrevented = true;
             nsCOMPtr<nsIDOMElement> elem = do_QueryInterface(this);
             fm->SetFocus(elem, nsIFocusManager::FLAG_BYMOUSE |
                                nsIFocusManager::FLAG_NOSCROLL);
           }
-
+        }
+        
+        if (aVisitor.mPresContext) {
           EventStateManager::SetActiveManager(
             aVisitor.mPresContext->EventStateManager(), this);
         }
@@ -3302,19 +3306,18 @@ Element::PostHandleEventForLinks(EventChainPostVisitor& aVisitor)
       }
 
       // The default action is simply to dispatch DOMActivate
-      nsCOMPtr<nsIPresShell> shell = aVisitor.mPresContext->GetPresShell();
-      if (shell) {
-        // single-click
-        nsEventStatus status = nsEventStatus_eIgnore;
-        // DOMActive event should be trusted since the activation is actually
-        // occurred even if the cause is an untrusted click event.
-        InternalUIEvent actEvent(true, eLegacyDOMActivate, mouseEvent);
-        actEvent.mDetail = 1;
-
-        rv = shell->HandleDOMEventWithTarget(this, &actEvent, &status);
-        if (NS_SUCCEEDED(rv)) {
-          aVisitor.mEventStatus = nsEventStatus_eConsumeNoDefault;
-        }
+      nsEventStatus status = nsEventStatus_eIgnore;
+      // The DOMActive event should be trusted since the activation has actually
+      // occurred even if the cause is an untrusted click event.
+      // This is a hack to allow click events to happen on anchors outside document
+      // contexts (where there is no presShell)... Thanks, Google, for another ugly one.
+      InternalUIEvent actEvent(true, eLegacyDOMActivate, mouseEvent);
+      actEvent.mDetail = 1;
+      
+      rv = EventDispatcher::Dispatch(this, aVisitor.mPresContext, &actEvent,
+                                     nullptr, &status);
+      if (NS_SUCCEEDED(rv)) {
+        aVisitor.mEventStatus = nsEventStatus_eConsumeNoDefault;
       }
     }
     break;
@@ -3326,7 +3329,7 @@ Element::PostHandleEventForLinks(EventChainPostVisitor& aVisitor)
         GetLinkTarget(target);
         const InternalUIEvent* activeEvent = aVisitor.mEvent->AsUIEvent();
         MOZ_ASSERT(activeEvent);
-        nsContentUtils::TriggerLink(this, aVisitor.mPresContext, absURI, target,
+        nsContentUtils::TriggerLink(this, absURI, target,
                                     true, true, activeEvent->IsTrustable());
         aVisitor.mEventStatus = nsEventStatus_eConsumeNoDefault;
       }

dom/base/nsContentUtils.cpp

@@ -89,6 +89,7 @@
 #include "nsCycleCollectionParticipant.h"
 #include "nsCycleCollector.h"
 #include "nsDataHashtable.h"
+#include "nsDocShell.h"
 #include "nsDocShellCID.h"
 #include "nsDocument.h"
 #include "nsDOMCID.h"
@@ -5336,25 +5337,24 @@ nsContentUtils::CombineResourcePrincipals(nsCOMPtr<nsIPrincipal>* aResourcePrinc
 
 /* static */
 void
-nsContentUtils::TriggerLink(nsIContent *aContent, nsPresContext *aPresContext,
+nsContentUtils::TriggerLink(nsIContent *aContent,
                             nsIURI *aLinkURI, const nsString &aTargetSpec,
                             bool aClick, bool aIsUserTriggered,
                             bool aIsTrusted)
 {
-  NS_ASSERTION(aPresContext, "Need a nsPresContext");
   NS_PRECONDITION(aLinkURI, "No link URI");
 
-  if (aContent->IsEditable()) {
+  if (aContent->IsEditable() || !aContent->OwnerDoc()->LinkHandlingEnabled()) {
     return;
   }
 
-  nsILinkHandler *handler = aPresContext->GetLinkHandler();
-  if (!handler) {
+  nsCOMPtr<nsIDocShell> docShell = aContent->OwnerDoc()->GetDocShell();
+  if (!docShell) {
     return;
   }
 
   if (!aClick) {
-    handler->OnOverLink(aContent, aLinkURI, aTargetSpec.get());
+    nsDocShell::Cast(docShell)->OnOverLink(aContent, aLinkURI, aTargetSpec.get());
     return;
   }
 
@@ -5397,9 +5397,9 @@ nsContentUtils::TriggerLink(nsIContent *aContent, nsPresContext *aPresContext,
       }
     }
 
-    handler->OnLinkClick(aContent, aLinkURI,
-                         fileName.IsVoid() ? aTargetSpec.get() : EmptyString().get(),
-                         fileName, nullptr, nullptr, aIsTrusted, aContent->NodePrincipal());
+    nsDocShell::Cast(docShell)->OnLinkClick(aContent, aLinkURI,
+                                            fileName.IsVoid() ? aTargetSpec.get() : EmptyString().get(),
+                                            fileName, nullptr, nullptr, aIsTrusted, aContent->NodePrincipal());
   }
 }
 

dom/base/nsContentUtils.h

@@ -1711,7 +1711,6 @@ public:
    * security check using aContent's principal.
    *
    * @param aContent the node on which a link was triggered.
-   * @param aPresContext the pres context, must be non-null.
    * @param aLinkURI the URI of the link, must be non-null.
    * @param aTargetSpec the target (like target=, may be empty).
    * @param aClick whether this was a click or not (if false, this method
@@ -1722,7 +1721,7 @@ public:
    * @param aIsTrusted If false, JS Context will be pushed to stack
    *                   when the link is triggered.
    */
-  static void TriggerLink(nsIContent *aContent, nsPresContext *aPresContext,
+  static void TriggerLink(nsIContent *aContent,
                           nsIURI *aLinkURI, const nsString& aTargetSpec,
                           bool aClick, bool aIsUserTriggered,
                           bool aIsTrusted);

dom/base/nsDocument.cpp

@@ -1288,6 +1288,7 @@ nsIDocument::nsIDocument()
 
 nsDocument::nsDocument(const char* aContentType)
   : nsIDocument()
+  , mLinksEnabled(true)
   , mViewportType(Unknown)
 {
   SetContentTypeInternal(nsDependentCString(aContentType));

dom/base/nsDocument.h

@@ -412,6 +412,14 @@ public:
   virtual void RemoveIDTargetObserver(nsIAtom* aID, IDTargetObserver aObserver,
                                       void* aData, bool aForImage) override;
 
+  virtual void SetLinkHandlingEnabled(bool aValue) override {
+    mLinksEnabled = aValue;
+  }
+  
+  virtual bool LinkHandlingEnabled() override {
+    return mLinksEnabled;
+  }  
+  
   /**
    * Access HTTP header data (this may also get set from other sources, like
    * HTML META tags).
@@ -1223,6 +1231,10 @@ public:
   // Recorded time of change to 'loading' state.
   mozilla::TimeStamp mLoadingTimeStamp;
 
+  // False if we've disabled link handling for elements inside this document,
+  // true otherwise.
+  bool mLinksEnabled : 1;
+
   // True if the document has been detached from its content viewer.
   bool mIsGoingAway:1;
   // True if the document is being destroyed.

dom/base/nsIDocument.h

@@ -767,6 +767,9 @@ public:
     mSandboxFlags = sandboxFlags;
   }
 
+  virtual void SetLinkHandlingEnabled(bool aValue) = 0;
+  virtual bool LinkHandlingEnabled() = 0;
+
   /**
    * Access HTTP header data (this may also get set from other
    * sources, like HTML META tags).

dom/html/HTMLAnchorElement.cpp

@@ -199,16 +199,9 @@ HTMLAnchorElement::IsHTMLFocusable(bool aWithMouse,
   }
 
   // cannot focus links if there is no link handler
-  nsIDocument* doc = GetComposedDoc();
-  if (doc) {
-    nsIPresShell* presShell = doc->GetShell();
-    if (presShell) {
-      nsPresContext* presContext = presShell->GetPresContext();
-      if (presContext && !presContext->GetLinkHandler()) {
-        *aIsFocusable = false;
-        return false;
-      }
-    }
+  if (!OwnerDoc()->LinkHandlingEnabled()) {
+    *aIsFocusable = false;
+    return false;
   }
 
   // Links that are in an editable region should never be focusable, even if

dom/html/nsGenericHTMLElement.cpp

@@ -581,17 +581,16 @@ nsGenericHTMLElement::FindAncestorForm(HTMLFormElement* aCurrentForm)
 }
 
 bool
-nsGenericHTMLElement::CheckHandleEventForAnchorsPreconditions(
-                        EventChainVisitor& aVisitor)
+nsGenericHTMLElement::CheckHandleEventForAnchorsPreconditions(EventChainVisitor& aVisitor)
 {
   NS_PRECONDITION(nsCOMPtr<Link>(do_QueryObject(this)),
                   "should be called only when |this| implements |Link|");
 
   if (!aVisitor.mPresContext) {
-    // We need a pres context to do link stuff. Some events (e.g. mutation
-    // events) don't have one.
-    // XXX: ideally, shouldn't we be able to do what we need without one?
-    return false; 
+    // When not in the composed document DOM, only <a> should navigate away per
+    // the exception in https://html.spec.whatwg.org/#cannot-navigate
+    // Thanks, Google, for another ugly one. :|
+    return IsInComposedDoc() || IsHTMLElement(nsGkAtoms::a); 
   }
 
   //Need to check if we hit an imagemap area and if so see if we're handling

editor/libeditor/HTMLEditor.cpp

@@ -165,11 +165,10 @@ HTMLEditor::~HTMLEditor()
   // free any default style propItems
   RemoveAllDefaultProperties();
 
-  if (mLinkHandler && IsInitialized()) {
-    nsCOMPtr<nsIPresShell> ps = GetPresShell();
-
-    if (ps && ps->GetPresContext()) {
-      ps->GetPresContext()->SetLinkHandler(mLinkHandler);
+  if (mDisabledLinkHandling) {
+    nsCOMPtr<nsIDocument> doc = GetDocument();
+    if (doc) {
+      doc->SetLinkHandlingEnabled(mOldLinkHandlingEnabled);
     }
   }
 
@@ -290,13 +289,14 @@ HTMLEditor::Init(nsIDOMDocument* aDoc,
     mCSSEditUtils = MakeUnique<CSSEditUtils>(this);
 
     // disable links
-    nsCOMPtr<nsIPresShell> presShell = GetPresShell();
-    NS_ENSURE_TRUE(presShell, NS_ERROR_FAILURE);
-    nsPresContext *context = presShell->GetPresContext();
-    NS_ENSURE_TRUE(context, NS_ERROR_NULL_POINTER);
+    nsCOMPtr<nsIDocument> doc = GetDocument();
+    if (NS_WARN_IF(!doc)) {
+      return NS_ERROR_FAILURE;
+    }
     if (!IsPlaintextEditor() && !IsInteractionAllowed()) {
-      mLinkHandler = context->GetLinkHandler();
-      context->SetLinkHandler(nullptr);
+      mDisabledLinkHandling = true;
+      mOldLinkHandlingEnabled = doc->LinkHandlingEnabled();
+      doc->SetLinkHandlingEnabled(false);
     }
 
     // init the type-in state

editor/libeditor/HTMLEditor.h

@@ -41,7 +41,6 @@ class nsDocumentFragment;
 class nsIDOMKeyEvent;
 class nsITransferable;
 class nsIClipboard;
-class nsILinkHandler;
 class nsTableWrapperFrame;
 class nsIDOMRange;
 class nsRange;
@@ -1079,7 +1078,8 @@ protected:
   void AddMouseClickListener(nsIDOMElement* aElement);
   void RemoveMouseClickListener(nsIDOMElement* aElement);
 
-  nsCOMPtr<nsILinkHandler> mLinkHandler;
+  bool mDisabledLinkHandling = false;
+  bool mOldLinkHandlingEnabled = false;
 
 public:
   friend class HTMLEditorEventListener;

layout/base/nsDocumentViewer.cpp

@@ -910,12 +910,7 @@ nsDocumentViewer::InitInternal(nsIWidget* aParentWidget,
   nsCOMPtr<nsIInterfaceRequestor> requestor(mContainer);
   if (requestor) {
     if (mPresContext) {
-      nsCOMPtr<nsILinkHandler> linkHandler;
-      requestor->GetInterface(NS_GET_IID(nsILinkHandler),
-                              getter_AddRefs(linkHandler));
-
       mPresContext->SetContainer(mContainer);
-      mPresContext->SetLinkHandler(linkHandler);
     }
 
     // Set script-context-owner in the document
@@ -1421,8 +1416,6 @@ AttachContainerRecurse(nsIDocShell* aShell)
     viewer->GetPresContext(getter_AddRefs(pc));
     if (pc) {
       pc->SetContainer(static_cast<nsDocShell*>(aShell));
-      nsCOMPtr<nsILinkHandler> handler = do_QueryInterface(aShell);
-      pc->SetLinkHandler(handler);
     }
     nsCOMPtr<nsIPresShell> presShell;
     viewer->GetPresShell(getter_AddRefs(presShell));
@@ -2146,12 +2139,6 @@ nsDocumentViewer::Show(void)
       return rv;
 
     if (mPresContext && base_win) {
-      nsCOMPtr<nsILinkHandler> linkHandler(do_GetInterface(base_win));
-
-      if (linkHandler) {
-        mPresContext->SetLinkHandler(linkHandler);
-      }
-
       mPresContext->SetContainer(mContainer);
     }
 

layout/base/nsPresContext.cpp

@@ -1504,7 +1504,6 @@ nsPresContext::GetDocShell() const
 nsPresContext::Detach()
 {
   SetContainer(nullptr);
-  SetLinkHandler(nullptr);
   if (mShell) {
     mShell->CancelInvalidatePresShellIfHidden();
   }

layout/base/nsPresContext.h

@@ -457,13 +457,9 @@ public:
 
   nsIDocShell* GetDocShell() const;
 
-  // XXX this are going to be replaced with set/get container
-  void SetLinkHandler(nsILinkHandler* aHandler) { mLinkHandler = aHandler; }
-  nsILinkHandler* GetLinkHandler() { return mLinkHandler; }
-
   /**
    * Detach this pres context - i.e. cancel relevant timers,
-   * SetLinkHandler(null), SetContainer(null) etc.
+   * SetContainer(null) etc.
    * Only to be used by the DocumentViewer.
    */
   virtual void Detach();
@@ -1245,10 +1241,6 @@ protected:
   nsIAtom* MOZ_UNSAFE_REF("always a static atom") mMedium; // initialized by subclass ctors
   nsCOMPtr<nsIAtom> mMediaEmulated;
 
-  // This pointer is nulled out through SetLinkHandler() in the destructors of
-  // the classes which set it. (using SetLinkHandler() again).
-  nsILinkHandler* MOZ_NON_OWNING_REF mLinkHandler;
-
   // Formerly mLangGroup; moving from charset-oriented langGroup to
   // maintaining actual language settings everywhere (see bug 524107).
   // This may in fact hold a langGroup such as x-western rather than

layout/base/nsPresShell.cpp

@@ -1309,9 +1309,6 @@ PresShell::Destroy()
     // to us. To avoid the pres context having a dangling reference, set its
     // pres shell to nullptr
     mPresContext->DetachShell();
-
-    // Clear the link handler (weak reference) as well
-    mPresContext->SetLinkHandler(nullptr);
   }
 
   mHaveShutDown = true;

layout/generic/nsImageFrame.cpp

@@ -2046,7 +2046,7 @@ nsImageFrame::HandleEvent(nsPresContext* aPresContext,
             *aEventStatus = nsEventStatus_eConsumeDoDefault;
             clicked = true;
           }
-          nsContentUtils::TriggerLink(anchorNode, aPresContext, uri, target,
+          nsContentUtils::TriggerLink(anchorNode, uri, target,
                                       clicked, true, true);
         }
       }