Add TokenizedBuffer.prototype.foldableRowsForRowRange

src/display-buffer.coffee

@@ -413,6 +413,9 @@ class DisplayBuffer extends Model
   isFoldedAtScreenRow: (screenRow) ->
     @largestFoldContainingBufferRow(@bufferRowForScreenRow(screenRow))?
 
+  foldableBufferRowsForBufferRowRange: (startRow, endRow) ->
+    @tokenizedBuffer.foldableRowsForRowRange(startRow, endRow)
+
   # Destroys the fold with the given id
   destroyFoldWithId: (id) ->
     @foldsByMarkerId[id]?.destroy()

src/text-editor-presenter.coffee

@@ -599,6 +599,7 @@ class TextEditorPresenter
 
     if endRow > startRow
       bufferRows = @model.bufferRowsForScreenRows(startRow, endRow - 1)
+      foldableBufferRows = @model.foldableBufferRowsForBufferRowRange(bufferRows[0], bufferRows[bufferRows.length - 1])
       for bufferRow, i in bufferRows
         if bufferRow is lastBufferRow
           softWrapped = true
@@ -609,7 +610,7 @@ class TextEditorPresenter
         screenRow = startRow + i
         line = @model.tokenizedLineForScreenRow(screenRow)
         decorationClasses = @lineNumberDecorationClassesForRow(screenRow)
-        foldable = @model.isFoldableAtScreenRow(screenRow)
+        foldable = foldableBufferRows.has(bufferRow)
         blockDecorationsBeforeCurrentScreenRowHeight = @lineTopIndex.pixelPositionAfterBlocksForRow(screenRow) - @lineTopIndex.pixelPositionBeforeBlocksForRow(screenRow)
         blockDecorationsHeight = blockDecorationsBeforeCurrentScreenRowHeight
         if screenRow % @tileSize isnt 0

src/text-editor.coffee

@@ -2940,7 +2940,7 @@ class TextEditor extends Model
   # Returns a {Boolean}.
   isFoldableAtBufferRow: (bufferRow) ->
     # @languageMode.isFoldableAtBufferRow(bufferRow)
-    @displayBuffer.tokenizedBuffer.tokenizedLineForRow(bufferRow)?.foldable ? false
+    @foldableBufferRowsForBufferRowRange(bufferRow, bufferRow).has(bufferRow)
 
   # Extended: Determine whether the given row in screen coordinates is foldable.
   #
@@ -2953,6 +2953,9 @@ class TextEditor extends Model
     bufferRow = @displayBuffer.bufferRowForScreenRow(screenRow)
     @isFoldableAtBufferRow(bufferRow)
 
+  foldableBufferRowsForBufferRowRange: (startRow, endRow) ->
+    @displayBuffer.foldableBufferRowsForBufferRowRange(startRow, endRow)
+
   # Extended: Fold the given buffer row if it isn't currently folded, and unfold
   # it otherwise.
   toggleFoldAtBufferRow: (bufferRow) ->

src/tokenized-buffer.coffee

@@ -210,8 +210,6 @@ class TokenizedBuffer extends Model
       @validateRow(endRow)
       @invalidateRow(endRow + 1) unless filledRegion
 
-      [startRow, endRow] = @updateFoldableStatus(startRow, endRow)
-
       event = {start: startRow, end: endRow, delta: 0}
       @emitter.emit 'did-change', event
 
@@ -271,9 +269,6 @@ class TokenizedBuffer extends Model
     if newEndStack and not _.isEqual(newEndStack, previousEndStack)
       @invalidateRow(end + delta + 1)
 
-    [start, end] = @updateFoldableStatus(start, end + delta)
-    end -= delta
-
     event = {start, end, delta, bufferChange: e}
     @emitter.emit 'did-change', event
 
@@ -287,23 +282,14 @@ class TokenizedBuffer extends Model
 
     row - increment
 
-  updateFoldableStatus: (startRow, endRow) ->
-    return [startRow, endRow]
-    return [startRow, endRow] if @largeFileMode
-
+  foldableRowsForRowRange: (startRow, endRow) ->
     scanStartRow = @buffer.previousNonBlankRow(startRow) ? startRow
     scanStartRow-- while scanStartRow > 0 and @tokenizedLineForRow(scanStartRow).isComment()
     scanEndRow = @buffer.nextNonBlankRow(endRow) ? endRow
-
-    for row in [scanStartRow..scanEndRow] by 1
-      foldable = @isFoldableAtRow(row)
-      line = @tokenizedLineForRow(row)
-      unless line.foldable is foldable
-        line.foldable = foldable
-        startRow = Math.min(startRow, row)
-        endRow = Math.max(endRow, row)
-
-    [startRow, endRow]
+    foldableRows = new Set
+    for row in [scanStartRow..scanEndRow] by 1 when @isFoldableAtRow(row)
+      foldableRows.add(row)
+    foldableRows
 
   isFoldableAtRow: (row) ->
     if @largeFileMode