Preserve line numbers in presenter based on ::mouseWheelScreenRow

spec/text-editor-presenter-spec.coffee

@@ -1258,6 +1258,28 @@ describe "TextEditorPresenter", ->
           expectValues lineNumberStateForScreenRow(presenter, 7), {bufferRow: 7}
           expect(lineNumberStateForScreenRow(presenter, 8)).toBeUndefined()
 
+        it "does not remove out-of-view line numbers corresponding to ::mouseWheelScreenRow until ::stoppedScrollingDelay elapses", ->
+          presenter = new TextEditorPresenter(model: editor, clientHeight: 25, scrollTop: 0, lineHeight: 10, lineOverdrawMargin: 1, stoppedScrollingDelay: 200)
+
+          expect(lineNumberStateForScreenRow(presenter, 0)).toBeDefined()
+          expect(lineNumberStateForScreenRow(presenter, 4)).toBeDefined()
+          expect(lineNumberStateForScreenRow(presenter, 5)).toBeUndefined()
+
+          presenter.setMouseWheelScreenRow(0)
+          expectStateUpdate presenter, -> presenter.setScrollTop(35)
+
+          expect(lineNumberStateForScreenRow(presenter, 0)).toBeDefined()
+          expect(lineNumberStateForScreenRow(presenter, 1)).toBeUndefined()
+          expect(lineNumberStateForScreenRow(presenter, 7)).toBeDefined()
+          expect(lineNumberStateForScreenRow(presenter, 8)).toBeUndefined()
+
+          expectStateUpdate presenter, -> advanceClock(200)
+
+          expect(lineNumberStateForScreenRow(presenter, 0)).toBeUndefined()
+          expect(lineNumberStateForScreenRow(presenter, 1)).toBeUndefined()
+          expect(lineNumberStateForScreenRow(presenter, 7)).toBeDefined()
+          expect(lineNumberStateForScreenRow(presenter, 8)).toBeUndefined()
+
         describe ".decorationClasses", ->
           it "adds decoration classes to the relevant line number state objects, both initially and when decorations change", ->
             marker1 = editor.markBufferRange([[4, 0], [6, 2]], invalidate: 'touch')

src/text-editor-presenter.coffee

@@ -233,6 +233,13 @@ class TextEditorPresenter
       @state.gutter.lineNumbers[id] = {screenRow, bufferRow, softWrapped, top, decorationClasses, foldable}
       visibleLineNumberIds[id] = true
 
+    if @getMouseWheelScreenRow()? and not startRow <= @getMouseWheelScreenRow() < endRow
+      screenRow = @getMouseWheelScreenRow()
+      top = screenRow * @getLineHeight()
+      bufferRow = @model.bufferRowForScreenRow(screenRow)
+      @state.gutter.lineNumbers[id] = {screenRow, bufferRow, top}
+      visibleLineNumberIds[bufferRow] = true
+
     for id of @state.gutter.lineNumbers
       delete @state.gutter.lineNumbers[id] unless visibleLineNumberIds[id]
 
@@ -372,6 +379,7 @@ class TextEditorPresenter
     if @getMouseWheelScreenRow()?
       @mouseWheelScreenRow = null
       @updateLinesState()
+      @updateLineNumbersState()
     else
       @emitter.emit 'did-update-state'