Bug 416168. Ensure that the overflow rect for a frame always includes (0,0) even if the frame rect is empty. Also ensures that if the frame rect is empty but has non-zero dimension on one axis, the overflow rect includes that size. A scrolled view for such a frame also includes that size to ensure width:0,height:Npx and width:Npx,height:0 frames are scrollable by that amount. r+sr=dbaron

gfx/public/nsRect.h

@@ -100,12 +100,21 @@ struct NS_GFX nsRect {
   PRBool IntersectRect(const nsRect& aRect1, const nsRect& aRect2);
 
   // Computes the smallest rectangle that contains both aRect1 and aRect2 and
-  // fills 'this' with the result. Returns FALSE and sets 'this' rect to be an
-  // empty rect if both aRect1 and aRect2 are empty
+  // fills 'this' with the result, ignoring empty input rectangles.
+  // Returns FALSE and sets 'this' rect to be an empty rect if both aRect1
+  // and aRect2 are empty.
   //
   // 'this' can be the same object as either aRect1 or aRect2
   PRBool UnionRect(const nsRect& aRect1, const nsRect& aRect2);
 
+  // Computes the smallest rectangle that contains both aRect1 and aRect2,
+  // where empty input rectangles are allowed to affect the result; the
+  // top-left of an empty input rectangle will be inside or on the edge of
+  // the result.
+  //
+  // 'this' can be the same object as either aRect1 or aRect2
+  void UnionRectIncludeEmpty(const nsRect& aRect1, const nsRect& aRect2);
+  
   // Accessors
   void SetRect(nscoord aX, nscoord aY, nscoord aWidth, nscoord aHeight) {
     x = aX; y = aY; width = aWidth; height = aHeight;
@@ -143,6 +152,13 @@ struct NS_GFX nsRect {
     return (PRBool) !operator==(aRect);
   }
 
+  // Useful when we care about the exact x/y/width/height values being
+  // equal (i.e. we care about differences in empty rectangles)
+  PRBool IsExactEqual(const nsRect& aRect) const {
+    return x == aRect.x && y == aRect.y &&
+           width == aRect.width && height == aRect.height;
+  }
+  
   nsRect  operator+(const nsPoint& aPoint) const {
     return nsRect(x + aPoint.x, y + aPoint.y, width, height);
   }

gfx/src/nsRect.cpp

@@ -115,23 +115,28 @@ PRBool nsRect::UnionRect(const nsRect &aRect1, const nsRect &aRect2)
     // aRect2 is empty so set the result to aRect1
     *this = aRect1;
   } else {
-    nscoord xmost1 = aRect1.XMost();
-    nscoord xmost2 = aRect2.XMost();
-    nscoord ymost1 = aRect1.YMost();
-    nscoord ymost2 = aRect2.YMost();
-
-    // Compute the origin
-    x = PR_MIN(aRect1.x, aRect2.x);
-    y = PR_MIN(aRect1.y, aRect2.y);
-
-    // Compute the size
-    width = PR_MAX(xmost1, xmost2) - x;
-    height = PR_MAX(ymost1, ymost2) - y;
+    UnionRectIncludeEmpty(aRect1, aRect2);
   }
 
   return result;
 }
 
+void nsRect::UnionRectIncludeEmpty(const nsRect &aRect1, const nsRect &aRect2)
+{
+  nscoord xmost1 = aRect1.XMost();
+  nscoord xmost2 = aRect2.XMost();
+  nscoord ymost1 = aRect1.YMost();
+  nscoord ymost2 = aRect2.YMost();
+
+  // Compute the origin
+  x = PR_MIN(aRect1.x, aRect2.x);
+  y = PR_MIN(aRect1.y, aRect2.y);
+
+  // Compute the size
+  width = PR_MAX(xmost1, xmost2) - x;
+  height = PR_MAX(ymost1, ymost2) - y;
+}
+
 // Inflate the rect by the specified width and height
 void nsRect::Inflate(nscoord aDx, nscoord aDy)
 {

layout/base/nsPresShell.cpp

@@ -3803,11 +3803,7 @@ UnionRectForClosestScrolledView(nsIFrame* aFrame,
       // We can't use nsRect::UnionRect since it drops empty rects on
       // the floor, and we need to include them.  (Thus we need
       // aHaveRect to know when to drop the initial value on the floor.)
-      nscoord x = PR_MIN(aRect.x, frameBounds.x),
-              y = PR_MIN(aRect.y, frameBounds.y),
-          xmost = PR_MAX(aRect.XMost(), frameBounds.XMost()),
-          ymost = PR_MAX(aRect.YMost(), frameBounds.YMost());
-      aRect.SetRect(x, y, xmost - x, ymost - y);
+      aRect.UnionRectIncludeEmpty(aRect, frameBounds);
     } else {
       aHaveRect = PR_TRUE;
       aRect = frameBounds;

layout/generic/nsFrame.cpp

@@ -5293,6 +5293,11 @@ nsIFrame::FinishAndStoreOverflow(nsRect* aOverflowArea, nsSize aNewSize)
       aOverflowArea->UnionRect(*aOverflowArea, r);
     }
   }
+  
+  // Overflow area must always include the frame's top-left and bottom-right,
+  // even if the frame rect is empty.
+  aOverflowArea->UnionRectIncludeEmpty(*aOverflowArea,
+                                       nsRect(nsPoint(0, 0), aNewSize));
 
   PRBool geometricOverflow =
     aOverflowArea->x < 0 || aOverflowArea->y < 0 ||
@@ -5318,7 +5323,6 @@ nsIFrame::FinishAndStoreOverflow(nsRect* aOverflowArea, nsSize aNewSize)
   }
 
   if (outlineRect != nsRect(nsPoint(0, 0), aNewSize)) {
-    // Throw out any overflow if we're -moz-hidden-unscrollable
     mState |= NS_FRAME_OUTSIDE_CHILDREN;
     nsRect* overflowArea = GetOverflowAreaProperty(PR_TRUE); 
     NS_ASSERTION(overflowArea, "should have created rect");

layout/generic/nsGfxScrollFrame.cpp

@@ -673,8 +673,9 @@ nsHTMLScrollFrame::PlaceScrollArea(const ScrollReflowState& aState)
   scrolledFrame->SetPosition(scrolledView->GetOffsetTo(GetView()));
 
   nsRect scrolledArea;
-  scrolledArea.UnionRect(mInner.GetScrolledRect(aState.mScrollPortRect.Size()),
-                         nsRect(nsPoint(0,0), aState.mScrollPortRect.Size()));
+  // Preserve the width or height of empty rects
+  scrolledArea.UnionRectIncludeEmpty(mInner.GetScrolledRect(aState.mScrollPortRect.Size()),
+                                     nsRect(nsPoint(0,0), aState.mScrollPortRect.Size()));
 
   // Store the new overflow area. Note that this changes where an outline
   // of the scrolled frame would be painted, but scrolled frames can't have

layout/generic/test/Makefile.in

@@ -59,6 +59,7 @@ _TEST_FILES = 	test_bug288789.html \
 		test_bug402380.html \
 		test_bug404872.html \
 		test_bug405178.html \
+		test_bug416168.html \
 		test_character_movement.html \
 		test_word_movement.html \
 		test_backspace_delete.html \

layout/generic/test/test_bug416168.html

@@ -0,0 +1,45 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=416168
+-->
+<head>
+  <title>Test for Bug 416168</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=416168">Mozilla Bug 416168</a>
+<p id="display">
+
+<div id="a" style="overflow: hidden; outline: 1px solid black; height: 0px;">
+  <div style="margin-top: 50px; width:20px; height:20px;"></div>
+</div>
+
+<div id="b" style="overflow: hidden; outline: 1px solid black; width:0px; height: 100px;">
+</div>
+
+<div id="c" style="overflow: hidden; outline: 1px solid black; width:100px; height: 0px;">
+</div>
+
+</p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+var a = document.getElementById("a");
+is(a.scrollHeight, 70, "margin-top included");
+
+var b = document.getElementById("b");
+is(b.scrollHeight, 100, "zero width");
+
+var c = document.getElementById("c");
+is(c.scrollWidth, 100, "zero height");
+
+</script>
+</pre>
+</body>
+</html>

view/src/nsViewManager.cpp

@@ -1662,7 +1662,7 @@ NS_IMETHODIMP nsViewManager::ResizeView(nsIView *aView, const nsRect &aRect, PRB
   nsRect oldDimensions;
 
   view->GetDimensions(oldDimensions);
-  if (oldDimensions != aRect) {
+  if (!oldDimensions.IsExactEqual(aRect)) {
     nsView* parentView = view->GetParent();
     if (parentView == nsnull)
       parentView = view;