From 2548891b99fdd8ae6a7bfaa6ea34a77fc9793897 Mon Sep 17 00:00:00 2001
From: Nathan Sobo <nathan@github.com>
Date: Sat, 31 May 2014 18:36:59 +0900
Subject: [PATCH] Clear the mousewheelScreenRow even if the event does not
 cause scrolling

If a mousewheel event is triggered when the editor can't be scrolled,
we still want to clear the mouseWheelScreenRow. This is typically done
when we stop scrolling, but if we never start scrolling it will never
happen. This commit adds another timeout to cover that case.
---
 spec/editor-component-spec.coffee | 16 ++++++++++++++++
 src/editor-component.coffee       | 10 ++++++++++
 2 files changed, 26 insertions(+)

diff --git a/spec/editor-component-spec.coffee b/spec/editor-component-spec.coffee
index 271ea856a..e01fbb853 100644
--- a/spec/editor-component-spec.coffee
+++ b/spec/editor-component-spec.coffee
@@ -790,6 +790,22 @@ describe "EditorComponent", ->
 
         expect(component.mouseWheelScreenRow).toBe null
 
+      it "clears the mouseWheelScreenRow after a delay even if the event does not cause scrolling", ->
+        spyOn(_._, 'now').andCallFake -> window.now # Ensure _.debounce is based on our fake spec timeline
+
+        expect(editor.getScrollTop()).toBe 0
+
+        lineNode = node.querySelector('.line')
+        wheelEvent = new WheelEvent('mousewheel', wheelDeltaX: 0, wheelDeltaY: 10)
+        Object.defineProperty(wheelEvent, 'target', get: -> lineNode)
+        node.dispatchEvent(wheelEvent)
+
+        expect(editor.getScrollTop()).toBe 0
+
+        expect(component.mouseWheelScreenRow).toBe 0
+        advanceClock(component.mouseWheelScreenRowClearDelay)
+        expect(component.mouseWheelScreenRow).toBe null
+
       it "does not preserve the line if it is on screen", ->
         expect(node.querySelectorAll('.line-number').length).toBe 14 # dummy line
         lineNodes = node.querySelectorAll('.line')
diff --git a/src/editor-component.coffee b/src/editor-component.coffee
index de2e40ddb..ede23e203 100644
--- a/src/editor-component.coffee
+++ b/src/editor-component.coffee
@@ -29,6 +29,7 @@ EditorComponent = React.createClass
   pendingVerticalScrollDelta: 0
   pendingHorizontalScrollDelta: 0
   mouseWheelScreenRow: null
+  mouseWheelScreenRowClearDelay: 150
 
   render: ->
     {focused, fontSize, lineHeight, fontFamily, showIndentGuide, showInvisibles, visible} = @state
@@ -370,6 +371,8 @@ EditorComponent = React.createClass
       # Scrolling vertically
       @pendingVerticalScrollDelta -= wheelDeltaY
       @mouseWheelScreenRow = @screenRowForNode(event.target)
+      @clearMouseWheelScreenRowAfterDelay ?= debounce(@clearMouseWheelScreenRow, @mouseWheelScreenRowClearDelay)
+      @clearMouseWheelScreenRowAfterDelay()
 
     unless animationFramePending
       requestAnimationFrame =>
@@ -379,6 +382,13 @@ EditorComponent = React.createClass
         @pendingVerticalScrollDelta = 0
         @pendingHorizontalScrollDelta = 0
 
+  clearMouseWheelScreenRow: ->
+    if @mouseWheelScreenRow?
+      @mouseWheelScreenRow = null
+      @requestUpdate()
+
+  clearMouseWheelScreenRowAfterDelay: null # created lazily
+
   screenRowForNode: (node) ->
     while node isnt document
       if screenRow = node.dataset.screenRow