Bug 532998. Cache the offset of the next newline character in preformatted text. r=smontagu

content/base/src/nsGkAtomList.h

@@ -573,6 +573,7 @@ GK_ATOM(NaN, "NaN")
 GK_ATOM(negate, "negate")
 GK_ATOM(never, "never")
 GK_ATOM(_new, "new")
+GK_ATOM(newline, "newline")
 GK_ATOM(nextBidi, "NextBidi")
 GK_ATOM(no, "no")
 GK_ATOM(noautohide, "noautohide")

layout/generic/nsTextFrameThebes.cpp

@@ -3408,6 +3408,11 @@ nsTextFrame::Init(nsIContent*      aContent,
   NS_ASSERTION(!aPrevInFlow, "Can't be a continuation!");
   NS_PRECONDITION(aContent->IsNodeOfType(nsINode::eTEXT),
                   "Bogus content!");
+
+  // Remove any NewlineOffsetProperty since it might be invalid
+  // if the content was modified while there was no frame
+  aContent->DeleteProperty(nsGkAtoms::newline);
+
   // Since our content has a frame now, this flag is no longer needed.
   aContent->UnsetFlags(NS_CREATE_FRAME_IF_NON_WHITESPACE);
   // We're not a continuing frame.
@@ -3781,6 +3786,8 @@ nsTextFrame::ClearTextRun()
 NS_IMETHODIMP
 nsTextFrame::CharacterDataChanged(CharacterDataChangeInfo* aInfo)
 {
+  mContent->DeleteProperty(nsGkAtoms::newline);
+
   // Find the first frame whose text has changed. Frames that are entirely
   // before the text change are completely unaffected.
   nsTextFrame* next;
@@ -6032,6 +6039,18 @@ nsTextFrame::IsFloatingFirstLetterChild()
   return frame->GetStyleDisplay()->IsFloating();
 }
 
+struct NewlineProperty {
+  PRInt32 mStartOffset;
+  // The offset of the first \n after mStartOffset, or -1 if there is none
+  PRInt32 mNewlineOffset;
+
+  static void Destroy(void* aObject, nsIAtom* aPropertyName,
+                      void* aPropertyValue, void* aData)
+  {
+    delete static_cast<NewlineProperty*>(aPropertyValue);
+  }
+};
+
 NS_IMETHODIMP
 nsTextFrame::Reflow(nsPresContext*           aPresContext,
                     nsHTMLReflowMetrics&     aMetrics,
@@ -6106,8 +6125,18 @@ nsTextFrame::Reflow(nsPresContext*           aPresContext,
 
   // Restrict preformatted text to the nearest newline
   PRInt32 newLineOffset = -1; // this will be -1 or a content offset
+  // Pointer to the nsGkAtoms::newline set on this frame's element
+  NewlineProperty* cachedNewlineOffset;
   if (textStyle->NewlineIsSignificant()) {
-    newLineOffset = FindChar(frag, offset, length, '\n');
+    cachedNewlineOffset =
+      static_cast<NewlineProperty*>(mContent->GetProperty(nsGkAtoms::newline));
+    if (cachedNewlineOffset && cachedNewlineOffset->mStartOffset <= offset &&
+        (cachedNewlineOffset->mNewlineOffset == -1 ||
+         cachedNewlineOffset->mNewlineOffset >= offset)) {
+      newLineOffset = cachedNewlineOffset->mNewlineOffset;
+    } else {
+      newLineOffset = FindChar(frag, offset, length, '\n');
+    }
     if (newLineOffset >= 0) {
       length = newLineOffset + 1 - offset;
     }
@@ -6451,6 +6480,28 @@ nsTextFrame::Reflow(nsPresContext*           aPresContext,
     aStatus |= NS_INLINE_BREAK_FIRST_LETTER_COMPLETE;
   }
 
+  // Updated the cached NewlineProperty, or delete it.
+  if (contentLength < maxContentLength &&
+      textStyle->NewlineIsSignificant() &&
+      (newLineOffset < 0 || mContentOffset + contentLength <= newLineOffset)) {
+    if (!cachedNewlineOffset) {
+      cachedNewlineOffset = new NewlineProperty;
+      if (cachedNewlineOffset) {
+        if (NS_FAILED(mContent->SetProperty(nsGkAtoms::newline, cachedNewlineOffset,
+                                            NewlineProperty::Destroy))) {
+          delete cachedNewlineOffset;
+          cachedNewlineOffset = nsnull;
+        }
+      }
+    }
+    if (cachedNewlineOffset) {
+      cachedNewlineOffset->mStartOffset = offset;
+      cachedNewlineOffset->mNewlineOffset = newLineOffset;
+    }
+  } else if (cachedNewlineOffset) {
+    mContent->DeleteProperty(nsGkAtoms::newline);
+  }
+
   // Compute space and letter counts for justification, if required
   if (!textStyle->WhiteSpaceIsSignificant() &&
       lineContainer->GetStyleText()->mTextAlign == NS_STYLE_TEXT_ALIGN_JUSTIFY) {