LineFolder renders a placeholder in place of a folded region.

spec/atom/line-folder-spec.coffee

@@ -3,7 +3,7 @@ Higlighter = require 'highlighter'
 LineFolder = require 'line-folder'
 Range = require 'range'
 
-fdescribe "LineFolder", ->
+describe "LineFolder", ->
   [buffer, folder] = []
 
   beforeEach ->
@@ -11,13 +11,10 @@ fdescribe "LineFolder", ->
     highlighter = new Higlighter(buffer)
     folder = new LineFolder(highlighter)
 
-  describe ".screenLineForRow(row)", ->
-    beforeEach ->
-      folder.createFold(new Range([4, 29], [7, 4]))
-
+  describe ".screenLinesForRows(startRow, endRow)", ->
     it "renders a placeholder on the first line of a fold, and skips subsequent lines", ->
-      line4 = folder.screenLineForRow(4)
-      line5 = folder.screenLineForRow(5)
+      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));'
 

src/atom/line-folder.coffee

@@ -1,22 +1,35 @@
-LineIndex = require 'line-index'
+SpanIndex = require 'span-index'
 
 module.exports =
 class LineFolder
   constructor: (@highlighter) ->
     @activeFolds = {}
-    @lineIndex = new LineIndex
-    @lineIndex.insertLines(0, 1, @highlighter.allScreenLines())
+    @buildIndex()
+
+  buildIndex: ->
+    @index = new SpanIndex
+    @index.insert 0, 1, @highlighter.screenLines
 
   createFold: (range) ->
     new Fold(this, range)
-    @activeFolds[range.start.row] = { range }
 
-  screenLineForRow: (screenRow) ->
-    
+  screenLinesForRows: (startRow, endRow) ->
+    @index.sliceBySpan(startRow, endRow).values
 
-  collapseRows: (startRow, endRow) ->
-    @lineIndex.updateSpansForRows(startRow, endRow, 0)
+  foldRows: (startRow, endRow) ->
+    @index.replace(startRow, 1, @buildScreenLineForBufferRow(startRow))
+    @index.updateSpans(startRow + 1, endRow, 0)
+
+  buildScreenLineForBufferRow: (bufferRow) ->
+    if fold = @activeFolds[bufferRow]
+      { 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.pushToken(type: 'placeholder', value: '...')
+      prefix.concat(suffix)
 
 class Fold
   constructor: (@lineFolder, @range) ->
-    @lineFolder.collapseRows(@range.start.row, @range.end.row)
+    @lineFolder.activeFolds[@range.start.row] = this
+    @lineFolder.foldRows(@range.start.row, @range.end.row)