Add a foldable indicator for multi-line comments

spec/fixtures/sample-with-comments.js

@@ -15,6 +15,6 @@ var quicksort = function () {
     }
     return sort(left).concat(pivot).concat(sort(right));
   };
-
+  // this is a single-line comment
   return sort(Array.apply(this, arguments));
 };

spec/language-mode-spec.coffee

@@ -106,7 +106,6 @@ describe "LanguageMode", ->
           range = languageMode.rowRangeForParagraphAtBufferRow(15)
           expect(range).toEqual [[15,0], [15,26]]
 
-
   describe "coffeescript", ->
     beforeEach ->
       atom.packages.activatePackage('language-coffee-script', sync: true)
@@ -297,6 +296,14 @@ describe "LanguageMode", ->
           languageMode.unfoldBufferRow(1)
           expect(editor.lineForScreenRow(1).fold).toBeUndefined()
 
+    describe ".isFoldableAtBufferRow(bufferRow)", ->
+      it "returns true if the line starts a foldable row range", ->
+        expect(languageMode.isFoldableAtBufferRow(0)).toBe true
+        expect(languageMode.isFoldableAtBufferRow(1)).toBe true
+        expect(languageMode.isFoldableAtBufferRow(2)).toBe false
+        expect(languageMode.isFoldableAtBufferRow(3)).toBe false
+        expect(languageMode.isFoldableAtBufferRow(4)).toBe true
+
   describe "folding with comments", ->
     beforeEach ->
       atom.packages.activatePackage('language-javascript', sync: true)
@@ -350,6 +357,12 @@ describe "LanguageMode", ->
         fold2 = editor.lineForScreenRow(5).fold
         expect(fold2).toBeFalsy()
 
+    describe ".isFoldableAtBufferRow(bufferRow)", ->
+      it "returns true if the line starts a multi-line comment", ->
+        expect(languageMode.isFoldableAtBufferRow(1)).toBe true
+        expect(languageMode.isFoldableAtBufferRow(6)).toBe true
+        expect(languageMode.isFoldableAtBufferRow(17)).toBe false
+
   describe "css", ->
     beforeEach ->
       atom.packages.activatePackage('language-source', sync: true)

src/language-mode.coffee

@@ -178,22 +178,40 @@ class LanguageMode
 
     [bufferRow, foldEndRow]
 
+  # Public: Returns a {Boolean} indicating whether the given buffer row starts a
+  # foldable row range. Rows that are "foldable" have a fold icon next to their
+  # icon in the gutter in the default configuration.
   isFoldableAtBufferRow: (bufferRow) ->
+    @isFoldableCodeAtBufferRow(bufferRow) or @isFoldableCommentAtBufferRow(bufferRow)
+
+  # Private: Returns a {Boolean} indicating whether the given buffer row starts
+  # a a foldable row range due to the code's indentation patterns.
+  isFoldableCodeAtBufferRow: (bufferRow) ->
     return false if @editor.isBufferRowBlank(bufferRow)
     nextNonEmptyRow = @editor.nextNonBlankBufferRow(bufferRow)
     return false unless nextNonEmptyRow?
     @editor.indentationForBufferRow(nextNonEmptyRow) > @editor.indentationForBufferRow(bufferRow)
 
+  # Private: Returns a {Boolean} indicating whether the given buffer row starts
+  # a foldable row range due to a being the start of a multi-line comment.
+  isFoldableCommentAtBufferRow: (bufferRow) ->
+    @isLineCommentedAtBufferRow(bufferRow) and
+      @isLineCommentedAtBufferRow(bufferRow + 1) and
+        not @isLineCommentedAtBufferRow(bufferRow - 1)
+
+  # Private: Returns a {Boolean} indicating whether the line at the given buffer
+  # row is a comment.
+  isLineCommentedAtBufferRow: (bufferRow) ->
+    return false unless 0 <= bufferRow <= @editor.getLastBufferRow()
+    @editor.displayBuffer.tokenizedBuffer.lineForScreenRow(bufferRow).isComment()
+
   # Find a row range for a 'paragraph' around specified bufferRow.
   # Right now, a paragraph is a block of text bounded by and empty line or a
   # block of text that is not the same type (comments next to source code).
   rowRangeForParagraphAtBufferRow: (bufferRow) ->
     return unless /\w/.test(@editor.lineForBufferRow(bufferRow))
 
-    isRowComment = (row) =>
-      @editor.displayBuffer.tokenizedBuffer.lineForScreenRow(row).isComment()
-
-    if isRowComment(bufferRow)
+    if @isLineCommentedAtBufferRow(bufferRow)
       isOriginalRowComment = true
       range = @rowRangeForCommentAtBufferRow(bufferRow)
       [firstRow, lastRow] = range or [bufferRow, bufferRow]
@@ -203,14 +221,14 @@ class LanguageMode
 
     startRow = bufferRow
     while startRow > firstRow
-      break if isRowComment(startRow - 1) != isOriginalRowComment
+      break if @isLineCommentedAtBufferRow(startRow - 1) != isOriginalRowComment
       break unless /\w/.test(@editor.lineForBufferRow(startRow - 1))
       startRow--
 
     endRow = bufferRow
     lastRow = @editor.getLastBufferRow()
     while endRow < lastRow
-      break if isRowComment(endRow + 1) != isOriginalRowComment
+      break if @isLineCommentedAtBufferRow(endRow + 1) != isOriginalRowComment
       break unless /\w/.test(@editor.lineForBufferRow(endRow + 1))
       endRow++