Make sure to add screen row to block decoration nodes

spec/text-editor-component-spec.js

@@ -3540,6 +3540,37 @@ describe('TextEditorComponent', function () {
       })
     })
 
+    describe('when the mousewheel event\'s target is a block decoration', function () {
+      it('keeps it on the DOM if it is scrolled off-screen', async function () {
+        wrapperNode.style.height = 4.5 * lineHeightInPixels + 'px'
+        wrapperNode.style.width = 20 * charWidth + 'px'
+        component.measureDimensions()
+        await nextViewUpdatePromise()
+
+        let item = document.createElement("div")
+        item.style.width = "30px"
+        item.style.height = "30px"
+        item.className = "decoration-1"
+        editor.addBlockDecorationForScreenRow(0, item)
+
+        await nextViewUpdatePromise()
+
+        let wheelEvent = new WheelEvent('mousewheel', {
+          wheelDeltaX: 0,
+          wheelDeltaY: -500
+        })
+        Object.defineProperty(wheelEvent, 'target', {
+          get: function () {
+            return item
+          }
+        })
+        componentNode.dispatchEvent(wheelEvent)
+        await nextAnimationFramePromise()
+
+        expect(component.getTopmostDOMNode().contains(item)).toBe(true)
+      })
+    })
+
     it('only prevents the default action of the mousewheel event if it actually lead to scrolling', async function () {
       spyOn(WheelEvent.prototype, 'preventDefault').andCallThrough()
       wrapperNode.style.height = 4.5 * lineHeightInPixels + 'px'

src/block-decorations-component.coffee

@@ -31,10 +31,9 @@ class BlockDecorationsComponent
       if @oldState.blockDecorations.hasOwnProperty(id)
         @updateBlockDecorationNode(id)
       else
+        @oldState.blockDecorations[id] = {}
         @createAndAppendBlockDecorationNode(id)
 
-      @oldState.blockDecorations[id] = cloneObject(blockDecorationState)
-
   measureBlockDecorations: ->
     for decorationId, blockDecorationNode of @blockDecorationNodesById
       decoration = @newState.blockDecorations[decorationId].decoration
@@ -48,18 +47,20 @@ class BlockDecorationsComponent
     blockDecorationState = @newState.blockDecorations[id]
     blockDecorationNode = @views.getView(blockDecorationState.decoration.getProperties().item)
     blockDecorationNode.id = "atom--block-decoration-#{id}"
-    unless blockDecorationState.isVisible
-      blockDecorationNode.classList.add("atom--invisible-block-decoration")
-
     @container.appendChild(blockDecorationNode)
-
     @blockDecorationNodesById[id] = blockDecorationNode
+    @updateBlockDecorationNode(id)
 
   updateBlockDecorationNode: (id) ->
     newBlockDecorationState = @newState.blockDecorations[id]
+    oldBlockDecorationState = @oldState.blockDecorations[id]
     blockDecorationNode = @blockDecorationNodesById[id]
 
     if newBlockDecorationState.isVisible
       blockDecorationNode.classList.remove("atom--invisible-block-decoration")
     else
       blockDecorationNode.classList.add("atom--invisible-block-decoration")
+
+    if oldBlockDecorationState.screenRow isnt newBlockDecorationState.screenRow
+      blockDecorationNode.dataset.screenRow = newBlockDecorationState.screenRow
+      oldBlockDecorationState.screenRow = newBlockDecorationState.screenRow