Bug 400813. Lines with actual content that just happens to be zero-width should be treated as non-empty. r+sr=dbaron

layout/generic/nsLineLayout.cpp

@@ -395,6 +395,7 @@ nsLineLayout::NewPerSpanData(PerSpanData** aResult)
   psd->mLastFrame = nsnull;
   psd->mContainsFloat = PR_FALSE;
   psd->mZeroEffectiveSpanBox = PR_FALSE;
+  psd->mHasNonemptyContent = PR_FALSE;
 
 #ifdef DEBUG
   mSpansAllocated++;
@@ -887,11 +888,11 @@ nsLineLayout::ReflowFrame(nsIFrame* aFrame,
     else if (nsGkAtoms::textFrame == frameType) {
       // Note non-empty text-frames for inline frame compatibility hackery
       pfd->SetFlag(PFD_ISTEXTFRAME, PR_TRUE);
-      // XXX An empty text frame at the end of the line seems not
-      // to have zero width.
-      if (metrics.width) {
+      nsTextFrame* textFrame = static_cast<nsTextFrame*>(pfd->mFrame);
+      if (textFrame->HasNoncollapsedCharacters()) {
+        psd->mHasNonemptyContent = PR_TRUE;
         pfd->SetFlag(PFD_ISNONEMPTYTEXTFRAME, PR_TRUE);
-        nsIContent* content = pfd->mFrame->GetContent();
+        nsIContent* content = textFrame->GetContent();
 
         const nsTextFragment* frag = content->GetText();
         if (frag) {
@@ -921,6 +922,13 @@ nsLineLayout::ReflowFrame(nsIFrame* aFrame,
     }
     else if (nsGkAtoms::brFrame == frameType) {
       pfd->SetFlag(PFD_SKIPWHENTRIMMINGWHITESPACE, PR_TRUE);
+      psd->mHasNonemptyContent = PR_TRUE;
+    } else if (pfd->mSpan) {
+      if (pfd->mSpan->mHasNonemptyContent || !pfd->mFrame->IsSelfEmpty()) {
+        psd->mHasNonemptyContent = PR_TRUE;
+      }
+    } else {
+      psd->mHasNonemptyContent = PR_TRUE;
     }
   }
 
@@ -1304,7 +1312,9 @@ nsLineLayout::PlaceFrame(PerFrameData* pfd, nsHTMLReflowMetrics& aMetrics)
   // Count the number of non-empty frames on the line...
   if (!emptyFrame) {
     mTotalPlacedFrames++;
+    NS_ASSERTION(psd->mHasNonemptyContent, "We should have detected this nonempty content");
   }
+  // XXX roc why not just check !emptyFrame again here?
   if (psd->mX != psd->mLeftEdge || pfd->mBounds.x != psd->mLeftEdge) {
     // As soon as a frame placed on the line advances an X coordinate
     // of any span we can no longer place a float on the line.
@@ -2057,7 +2067,7 @@ nsLineLayout::VerticalAlignFrames(PerSpanData* psd)
       }
     }
     if (applyMinLH) {
-      if ((psd->mX != psd->mLeftEdge) || preMode || foundLI) {
+      if (psd->mHasNonemptyContent || preMode || foundLI) {
 #ifdef NOISY_VERTICAL_ALIGN
         printf("  [span]==> adjusting min/maxY: currentValues: %d,%d", minY, maxY);
 #endif

layout/generic/nsLineLayout.h

@@ -468,6 +468,7 @@ protected:
     PRPackedBool mChangedFrameDirection;
     PRPackedBool mZeroEffectiveSpanBox;
     PRPackedBool mContainsFloat;
+    PRPackedBool mHasNonemptyContent;
 
     nscoord mLeftEdge;
     nscoord mX;

layout/generic/nsTextFrame.h

@@ -58,6 +58,10 @@
 class nsTextPaintStyle;
 class PropertyProvider;
 
+// This state bit is set on frames that have some non-collapsed characters after
+// reflow
+#define TEXT_HAS_NONCOLLAPSED_CHARACTERS 0x02000000
+
 class nsTextFrame : public nsFrame {
 public:
   friend class nsContinuingTextFrame;
@@ -189,6 +193,14 @@ public:
    */
   PRBool IsAtEndOfLine() const;
   
+  /**
+   * Call this only after reflow the frame. Returns true if non-collapsed
+   * characters are present.
+   */
+  PRBool HasNoncollapsedCharacters() const {
+    return (GetStateBits() & TEXT_HAS_NONCOLLAPSED_CHARACTERS) != 0;
+  }
+  
 #ifdef ACCESSIBILITY
   NS_IMETHOD GetAccessible(nsIAccessible** aAccessible);
 #endif

layout/generic/nsTextFrameThebes.cpp

@@ -145,7 +145,10 @@
 
 #define TEXT_REFLOW_FLAGS    \
   (TEXT_FIRST_LETTER|TEXT_START_OF_LINE|TEXT_END_OF_LINE|TEXT_HYPHEN_BREAK| \
-   TEXT_TRIMMED_TRAILING_WHITESPACE)
+   TEXT_TRIMMED_TRAILING_WHITESPACE|TEXT_HAS_NONCOLLAPSED_CHARACTERS)
+
+// defined in nsTextFrame.h
+// #define TEXT_HAS_NONCOLLAPSED_CHARACTERS 0x02000000
 
 // Cache bits for IsEmpty().
 // Set this bit if the textframe is known to be only collapsible whitespace.
@@ -5513,6 +5516,7 @@ nsTextFrame::Reflow(nsPresContext*           aPresContext,
   // frame to accumulate with trimmable width from this frame.)
   if (transformedCharsFit > 0) {
     lineLayout.SetTrimmableWidth(NSToCoordFloor(trimmableWidth));
+    AddStateBits(TEXT_HAS_NONCOLLAPSED_CHARACTERS);
   }
   if (charsFit > 0 && charsFit == length &&
       HasSoftHyphenBefore(frag, mTextRun, offset, end)) {
@@ -5860,7 +5864,7 @@ nsIAtom*
 nsTextFrame::GetType() const
 {
   return nsGkAtoms::textFrame;
-} 
+}
 
 /* virtual */ PRBool
 nsTextFrame::IsEmpty()

layout/reftests/bugs/398144-1-ref.html

@@ -2,7 +2,8 @@
 <html>
 <body>
 <div style="height:100px; background-color:blue;"></div>
-<div style="height:200px;"></div>
+<div style="padding:100px 0; opacity:0;">blank line</div>
 <div style="height:100px; background-color:blue;"></div>
 </body>
 </html>
+

layout/reftests/line-breaking/non-breakable-1-ref.html

@@ -1,3 +1,4 @@
+<!DOCTYPE HTML>
 <html>
 <head>
 <style type="text/css"> p { margin: 5px 1em; width: 0; white-space: nowrap; } p > span { background-color: silver; } </style>

layout/reftests/line-breaking/non-breakable-1.html

@@ -1,3 +1,4 @@
+<!DOCTYPE HTML>
 <html>
 <head>
 <style type="text/css"> p { margin: 5px 1em; width: 0; } p > span { background-color: silver; } </style>