Line folder handles folds starting and ending on same line.

spec/atom/line-folder-spec.coffee

@@ -11,10 +11,44 @@ describe "LineFolder", ->
     highlighter = new Higlighter(buffer)
     folder = new LineFolder(highlighter)
 
-  describe ".screenLinesForRows(startRow, endRow)", ->
+  describe "when there is a single fold spanning multiple lines", ->
     it "renders a placeholder on the first line of a fold, and skips subsequent lines", ->
       folder.createFold(new Range([4, 29], [7, 4]))
       [line4, line5] = folder.screenLinesForRows(4, 5)
+
       expect(line4.text).toBe '    while(items.length > 0) {...}'
       expect(line5.text).toBe '    return sort(left).concat(pivot).concat(sort(right));'
 
+  describe "when there is a single fold contained on a single line", ->
+    it "renders a placeholder for the folded region, but does not skip any lines", ->
+      folder.createFold(new Range([2, 8], [2, 25]))
+      [line2, line3] = folder.screenLinesForRows(2, 3)
+
+      expect(line2.text).toBe '    if (...) return items;'
+      expect(line3.text).toBe '    var pivot = items.shift(), current, left = [], right = [];'
+
+  describe "when there is a nested fold on the last line of another fold", ->
+    it "does not render a placeholder for the nested fold because it is inside of the other fold", ->
+      folder.createFold(new Range([8, 5], [8, 10]))
+      folder.createFold(new Range([4, 29], [8, 36]))
+      [line4, line5] = folder.screenLinesForRows(4, 5)
+
+      expect(line4.text).toBe '    while(items.length > 0) {...concat(sort(right));'
+      expect(line5.text).toBe '  };'
+
+  describe "when another fold begins on the last line of a fold", ->
+    describe "when the second fold is created before the first fold", ->
+      it "renders a placeholder for both folds on the first line of the first fold", ->
+        folder.createFold(new Range([7, 5], [8, 36]))
+        folder.createFold(new Range([4, 29], [7, 4]))
+        [line4, line5] = folder.screenLinesForRows(4, 5)
+
+        expect(line4.text).toBe  '    while(items.length > 0) {...}...concat(sort(right));'
+
+    describe "when the second fold is created after the first fold", ->
+      it "renders a placeholder for both folds on the first line of the first fold", ->
+        folder.createFold(new Range([4, 29], [7, 4]))
+        folder.createFold(new Range([7, 5], [8, 36]))
+        [line4, line5] = folder.screenLinesForRows(4, 5)
+
+        expect(line4.text).toBe  '    while(items.length > 0) {...}...concat(sort(right));'

src/atom/line-folder.coffee

@@ -17,17 +17,32 @@ class LineFolder
     @index.sliceBySpan(startRow, endRow).values
 
   foldRows: (startRow, endRow) ->
-    @index.replace(startRow, 1, @buildScreenLineForBufferRow(startRow))
-    @index.updateSpans(startRow + 1, endRow, 0)
+    @refreshScreenRow(@screenRowForBufferRow(startRow))
+    if endRow > startRow
+      @index.updateSpans(startRow + 1, endRow, 0)
 
-  buildScreenLineForBufferRow: (bufferRow) ->
-    if fold = @activeFolds[bufferRow]
+  refreshScreenRow: (screenRow) ->
+    bufferRow = @bufferRowForScreenRow(screenRow)
+    @index.replace(bufferRow, 1, @buildScreenLineForBufferRow(bufferRow))
+
+  buildScreenLineForBufferRow: (bufferRow, startColumn=0) ->
+    screenLine = @highlighter.screenLineForRow(bufferRow)
+    screenLine = screenLine.splitAt(startColumn)[1] if startColumn
+
+    fold = @activeFolds[bufferRow]
+    if fold and fold.range.start.column >= startColumn
       { start, end } = fold.range
-      endRow = fold.range.end.row
-      prefix = @highlighter.screenLineForRow(start.row).splitAt(start.column)[0]
-      suffix = @highlighter.screenLineForRow(end.row).splitAt(end.column)[1]
+      prefix = screenLine.splitAt(start.column - startColumn)[0]
+      suffix = @buildScreenLineForBufferRow(end.row, end.column)
       prefix.pushToken(type: 'placeholder', value: '...')
-      prefix.concat(suffix)
+      return prefix.concat(suffix)
+    screenLine
+
+  screenRowForBufferRow: (bufferRow) ->
+    @index.spanForIndex(bufferRow) - 1
+
+  bufferRowForScreenRow: (screenRow) ->
+    @index.indexForSpan(screenRow).index
 
 class Fold
   constructor: (@lineFolder, @range) ->