From b4dec8ccbb071a7d4ad3296feb42f53d78177af8 Mon Sep 17 00:00:00 2001
From: Nathan Sobo <nathan@github.com>
Date: Fri, 10 May 2013 12:55:44 -0600
Subject: [PATCH] In Editor.updateRenderedLines, cap renderFrom to the last
 screen row

If we remove a large number of screen lines when we are scrolled down,
the current @firstRenderedScreenRow may end up being larger than the
number of screen rows we now have. Setting renderFrom to the
@firstRenderedScreenRow in this case was causing the renderFrom to be
larger than the renderTo, which was causing problems downstream with
the new mapping code.
---
 spec/app/editor-spec.coffee | 9 +++++++++
 src/app/editor.coffee       | 9 +++++----
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/spec/app/editor-spec.coffee b/spec/app/editor-spec.coffee
index 1b2d4ff11..073cee8c6 100644
--- a/spec/app/editor-spec.coffee
+++ b/spec/app/editor-spec.coffee
@@ -1388,6 +1388,15 @@ describe "Editor", ->
         expect(editor.renderedLines.find('.line').length).toBe 1
         expect(editor.renderedLines.find('.line').text()).toBe buffer.lineForRow(0)
 
+    describe "when folding leaves fewer screen lines than the first rendered screen line (regression)", ->
+      it "clears all screen lines and does not throw any exceptions", ->
+        editor.lineOverdraw = 1
+        editor.attachToDom(heightInLines: 5)
+        editor.scrollToBottom()
+        editor.activeEditSession.foldBufferRow(0)
+        expect(editor.renderedLines.find('.line').length).toBe 1
+        expect(editor.renderedLines.find('.line').text()).toBe buffer.lineForRow(0)
+
     describe "when autoscrolling at the end of the document", ->
       it "renders lines properly", ->
         editor.edit(project.buildEditSession('two-hundred.txt'))
diff --git a/src/app/editor.coffee b/src/app/editor.coffee
index dc512d31b..42888db14 100644
--- a/src/app/editor.coffee
+++ b/src/app/editor.coffee
@@ -1149,13 +1149,14 @@ class Editor extends View
   updateRenderedLines: ->
     firstVisibleScreenRow = @getFirstVisibleScreenRow()
     lastVisibleScreenRow = @getLastVisibleScreenRow()
+    lastScreenRow = @getLastScreenRow()
 
     if @firstRenderedScreenRow? and firstVisibleScreenRow >= @firstRenderedScreenRow and lastVisibleScreenRow <= @lastRenderedScreenRow
-      renderFrom = @firstRenderedScreenRow
-      renderTo = Math.min(@getLastScreenRow(), @lastRenderedScreenRow)
+      renderFrom = Math.min(lastScreenRow, @firstRenderedScreenRow)
+      renderTo = Math.min(lastScreenRow, @lastRenderedScreenRow)
     else
-      renderFrom = Math.max(0, firstVisibleScreenRow - @lineOverdraw)
-      renderTo = Math.min(@getLastScreenRow(), lastVisibleScreenRow + @lineOverdraw)
+      renderFrom = Math.min(lastScreenRow, Math.max(0, firstVisibleScreenRow - @lineOverdraw))
+      renderTo = Math.min(lastScreenRow, lastVisibleScreenRow + @lineOverdraw)
 
     if @pendingChanges.length == 0 and @firstRenderedScreenRow and @firstRenderedScreenRow <= renderFrom and renderTo <= @lastRenderedScreenRow
       return