Cache .foldable on tokenized lines based on block comments

Still need to handle indentation

spec/tokenized-buffer-spec.coffee

@@ -695,7 +695,7 @@ describe "TokenizedBuffer", ->
       expect(rightToken.firstNonWhitespaceIndex).toBe null
       expect(rightToken.firstTrailingWhitespaceIndex).toBe 5
 
-  describe "indent level", ->
+  describe ".indentLevel on tokenized lines", ->
     beforeEach ->
       buffer = atom.project.bufferForPathSync('sample.js')
       tokenizedBuffer = new TokenizedBuffer({buffer})
@@ -784,3 +784,43 @@ describe "TokenizedBuffer", ->
         expect(tokenizedBuffer.tokenizedLineForRow(8).indentLevel).toBe 2
         expect(tokenizedBuffer.tokenizedLineForRow(9).indentLevel).toBe 2
         expect(tokenizedBuffer.tokenizedLineForRow(10).indentLevel).toBe 2 # }
+
+  describe ".foldable on tokenized lines", ->
+    changes = null
+
+    beforeEach ->
+      changes = []
+      buffer = atom.project.bufferForPathSync('sample.js')
+      buffer.insert [10, 0], "  // multi-line\n  // comment\n  // block\n"
+      buffer.insert [0, 0], "// multi-line\n// comment\n// block\n"
+      tokenizedBuffer = new TokenizedBuffer({buffer})
+      fullyTokenize(tokenizedBuffer)
+      tokenizedBuffer.onDidChange (change) ->
+        delete change.bufferChange
+        changes.push(change)
+
+    it "sets .foldable to true on the first line of multi-line comments", ->
+      expect(tokenizedBuffer.tokenizedLineForRow(0).foldable).toBe true
+      expect(tokenizedBuffer.tokenizedLineForRow(1).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(2).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(3).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(13).foldable).toBe true
+      expect(tokenizedBuffer.tokenizedLineForRow(14).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(15).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(16).foldable).toBe false
+
+      buffer.insert([0, Infinity], '\n')
+      expect(changes).toEqual [{start: 0, end: 1, delta: 1}]
+
+      expect(tokenizedBuffer.tokenizedLineForRow(0).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(1).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(2).foldable).toBe true
+      expect(tokenizedBuffer.tokenizedLineForRow(3).foldable).toBe false
+
+      changes = []
+      buffer.delete([[0, Infinity], [1, 0]])
+      expect(changes).toEqual [{start: 0, end: 2, delta: -1}]
+      expect(tokenizedBuffer.tokenizedLineForRow(0).foldable).toBe true
+      expect(tokenizedBuffer.tokenizedLineForRow(1).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(2).foldable).toBe false
+      expect(tokenizedBuffer.tokenizedLineForRow(3).foldable).toBe false

src/tokenized-buffer.coffee

@@ -167,6 +167,9 @@ class TokenizedBuffer extends Model
 
       @validateRow(endRow)
       @invalidateRow(endRow + 1) unless filledRegion
+
+      @updateFoldableStatus(startRow, endRow)
+
       event = {start: startRow, end: endRow, delta: 0}
       @emit 'changed', event
       @emitter.emit 'did-change', event
@@ -217,6 +220,9 @@ 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 }
     @emit 'changed', event
     @emitter.emit 'did-change', event
@@ -231,6 +237,28 @@ class TokenizedBuffer extends Model
 
     row - increment
 
+  updateFoldableStatus: (startRow, endRow) ->
+    scanEndRow = @buffer.nextNonBlankRow(endRow) ? endRow
+    scanEndRow++ if scanEndRow < @buffer.getLastRow()
+    scanStartRow = startRow
+    while scanStartRow > 0 and @tokenizedLineForRow(scanStartRow).isComment()
+      scanStartRow = @buffer.previousNonBlankRow(scanStartRow) ? 0
+
+    commentLineCount = 0
+    for row in [scanStartRow..scanEndRow] by 1
+      if @tokenizedLineForRow(row).isComment()
+        if row > 0
+          foldable = commentLineCount is 1
+          unless @tokenizedLineForRow(row - 1).foldable is foldable
+            @tokenizedLineForRow(row - 1).foldable = foldable
+            startRow = Math.min(startRow, row - 1)
+            endRow = Math.max(endRow, row - 1)
+        commentLineCount++
+      else
+        commentLineCount = 0
+
+    [startRow, endRow]
+
   buildTokenizedLinesForRows: (startRow, endRow, startingStack) ->
     ruleStack = startingStack
     stopTokenizingAt = startRow + @chunkSize

src/tokenized-line.coffee

@@ -10,6 +10,7 @@ module.exports =
 class TokenizedLine
   endOfLineInvisibles: null
   lineIsWhitespaceOnly: false
+  foldable: false
 
   constructor: ({tokens, @lineEnding, @ruleStack, @startBufferColumn, @fold, @tabLength, @indentLevel, @invisibles}) ->
     @startBufferColumn ?= 0