Bug 454059 - Generate hyperlinks in PDF output for HTML link elements. r=mstange,mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D114208

layout/generic/nsIFrame.cpp

@@ -3991,6 +3991,20 @@ void nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,
     return;
   }
 
+  // If we're generating a display list for printing, include Link items for
+  // frames that correspond to HTML link elements so that we can have active
+  // links in saved PDF output. Note that the state of "within a link" is
+  // set on the display-list builder, such that all descendants of the link
+  // element will generate display-list links.
+  // TODO: we should be able to optimize this so as to avoid creating links
+  // for the same destination that entirely overlap each other, which adds
+  // nothing useful to the final PDF.
+  Maybe<nsDisplayListBuilder::Linkifier> linkifier;
+  if (aBuilder->IsForPrinting()) {
+    linkifier.emplace(aBuilder, aChild);
+    linkifier->MaybeAppendLink(aBuilder, aChild, aLists.Content());
+  }
+
   nsIFrame* child = aChild;
   auto* placeholder = child->IsPlaceholderFrame()
                           ? static_cast<nsPlaceholderFrame*>(child)

layout/painting/nsDisplayList.cpp

@@ -554,6 +554,47 @@ nsRect nsDisplayListBuilder::OutOfFlowDisplayData::ComputeVisibleRectForFrame(
   return visible;
 }
 
+nsDisplayListBuilder::Linkifier::Linkifier(nsDisplayListBuilder* aBuilder,
+                                           nsIFrame* aFrame) {
+  // Links don't nest, so if the builder already has a destination, no need to
+  // check for a link element here.
+  if (!aBuilder->mLinkSpec.IsEmpty()) {
+    return;
+  }
+
+  // Find the element that we need to check for link-ness, bailing out if
+  // we can't find one.
+  Element* elem = Element::FromNodeOrNull(aFrame->GetContent());
+  if (!elem) {
+    return;
+  }
+
+  // Check if we have actually found a link and it has a usable spec.
+  nsCOMPtr<nsIURI> linkURI;
+  if (!elem->IsLink(getter_AddRefs(linkURI))) {
+    return;
+  }
+  if (NS_FAILED(linkURI->GetSpec(aBuilder->mLinkSpec)) ||
+      aBuilder->mLinkSpec.IsEmpty()) {
+    return;
+  }
+
+  // Record that we need to reset the builder's state on destruction.
+  mBuilderToReset = aBuilder;
+}
+
+void nsDisplayListBuilder::Linkifier::MaybeAppendLink(
+    nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsDisplayList* aList) {
+  // Note that we may generate a link here even if the constructor bailed out
+  // without updating aBuilder->LinkSpec(), because it may have been set by
+  // an ancestor that was associated with a link element.
+  if (!aBuilder->mLinkSpec.IsEmpty()) {
+    auto* link = MakeDisplayItem<nsDisplayLink>(
+        aBuilder, aFrame, aBuilder->mLinkSpec.get(), aFrame->GetRect());
+    aList->AppendToTop(link);
+  }
+}
+
 nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
                                            nsDisplayListBuilderMode aMode,
                                            bool aBuildCaret,

layout/painting/nsDisplayList.h

@@ -1824,6 +1824,25 @@ class nsDisplayListBuilder {
   void AddScrollFrameToNotify(nsIScrollableFrame* aScrollFrame);
   void NotifyAndClearScrollFrames();
 
+  // Helper class to find what link spec (if any) to associate with a frame,
+  // recording it in the builder, and generate the corresponding DisplayItem.
+  class Linkifier {
+   public:
+    Linkifier(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame);
+
+    ~Linkifier() {
+      if (mBuilderToReset) {
+        mBuilderToReset->mLinkSpec.Truncate(0);
+      }
+    }
+
+    void MaybeAppendLink(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                         nsDisplayList* aList);
+
+   private:
+    nsDisplayListBuilder* mBuilderToReset = nullptr;
+  };
+
  private:
   bool MarkOutOfFlowFrameForDisplay(nsIFrame* aDirtyFrame, nsIFrame* aFrame,
                                     const nsRect& aVisibleRect,
@@ -2002,6 +2021,7 @@ class nsDisplayListBuilder {
   // filter. Otherwise nullptr.
   const ActiveScrolledRoot* mFilterASR;
   std::unordered_set<nsIScrollableFrame*> mScrollFramesToNotify;
+  nsCString mLinkSpec;  // Destination of link currently being emitted, if any.
   bool mContainsBlendMode;
   bool mIsBuildingScrollbar;
   bool mCurrentScrollbarWillHaveLayer;