Clamp the caret's position so that we always draw within the nearest scrollframe. Not doing this allows the scrollframe to clip the caret, causing it to not show up at all. bug 335560, r+sr=roc

layout/base/nsCaret.cpp

@@ -48,6 +48,7 @@
 #include "nsIServiceManager.h"
 #include "nsFrameSelection.h"
 #include "nsIFrame.h"
+#include "nsIScrollableFrame.h"
 #include "nsIDOMNode.h"
 #include "nsIDOMRange.h"
 #include "nsIFontMetrics.h"
@@ -59,6 +60,7 @@
 #include "nsIRenderingContext.h"
 #include "nsIDeviceContext.h"
 #include "nsIView.h"
+#include "nsIScrollableView.h"
 #include "nsIViewManager.h"
 #include "nsPresContext.h"
 #include "nsILookAndFeel.h"
@@ -1032,6 +1034,34 @@ nsresult nsCaret::UpdateCaretRects(nsIFrame* aFrame, PRInt32 aFrameOffset)
   mCaretRect += framePos;
   mCaretRect.width = mCaretWidth;
 
+  // Clamp our position to be within our scroll frame. If we don't, then it
+  // clips us, and we don't appear at all. See bug 335560.
+  nsIFrame *scrollFrame =
+    nsLayoutUtils::GetClosestFrameOfType(aFrame, nsGkAtoms::scrollFrame);
+  if (scrollFrame)
+  {
+    // First, use the scrollFrame to get at the scrollable view that we're in.
+    nsIScrollableFrame *scrollable;
+    CallQueryInterface(scrollFrame, &scrollable);
+    nsIScrollableView *scrollView = scrollable->GetScrollableView();
+    nsIView *view;
+    scrollView->GetScrolledView(view);
+
+    // Compute the caret's coordinates in the enclosing view's coordinate
+    // space. To do so, we need to correct for both the original frame's
+    // offset from the scrollframe, and the scrollable view's offset from the
+    // scrolled frame's view.
+    nsPoint toScroll = aFrame->GetOffsetTo(scrollFrame) -
+      view->GetOffsetTo(scrollFrame->GetView());
+    nsRect caretInScroll = mCaretRect + toScroll;
+
+    // Now see if thet caret extends beyond the view's bounds. If it does,
+    // then snap it back, put it as close to the edge as it can.
+    nscoord overflow = caretInScroll.XMost() - view->GetBounds().width;
+    if (overflow > 0)
+      mCaretRect.x -= overflow;
+  }
+
   // on RTL frames the right edge of mCaretRect must be equal to framePos
   const nsStyleVisibility* vis = aFrame->GetStyleVisibility();
   if (NS_STYLE_DIRECTION_RTL == vis->mDirection)