From afa6c9a786512561295600cc8bea244c6355de0b Mon Sep 17 00:00:00 2001
From: Nathan Sobo <nathan@github.com>
Date: Thu, 9 Jul 2015 01:20:04 -0500
Subject: [PATCH] Add invariant assertion about line count to see if we can
 find a bug

Does the line count ever get out of whack after an update, or is it
happening in some other way?
---
 src/display-buffer.coffee | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/display-buffer.coffee b/src/display-buffer.coffee
index d7dc236d6..6d3f47bea 100644
--- a/src/display-buffer.coffee
+++ b/src/display-buffer.coffee
@@ -1194,6 +1194,9 @@ class DisplayBuffer extends Model
     screenDelta = screenLines.length - (endScreenRow - startScreenRow)
 
     _.spliceWithArray(@screenLines, startScreenRow, endScreenRow - startScreenRow, screenLines, 10000)
+
+    @checkScreenLinesInvariant()
+
     @rowMap.spliceRegions(startBufferRow, endBufferRow - startBufferRow, regions)
     @findMaxLineLength(startScreenRow, endScreenRow, screenLines, screenDelta)
 
@@ -1313,6 +1316,20 @@ class DisplayBuffer extends Model
     else
       delete @overlayDecorationsById[decoration.id]
 
+  checkScreenLinesInvariant: ->
+    return if @isSoftWrapped()
+    return if _.size(@foldsByMarkerId) > 0
+
+    screenLinesCount = @screenLines.length
+    tokenizedLinesCount = @tokenizedBuffer.getLineCount()
+    bufferLinesCount = @buffer.getLineCount()
+
+    atom.assert screenLinesCount is tokenizedLinesCount, "Display buffer line count out of sync with tokenized buffer", (error) ->
+      error.metadata = {screenLinesCount, tokenizedLinesCount, bufferLinesCount}
+
+    atom.assert screenLinesCount is bufferLinesCount, "Display buffer line count out of sync with buffer", (error) ->
+      error.metadata = {screenLinesCount, tokenizedLinesCount, bufferLinesCount}
+
 if Grim.includeDeprecatedAPIs
   DisplayBuffer.properties
     softWrapped: null