Autoscroll vertically when click-dragging the line number gutter

spec/text-editor-component-spec.js

@@ -1144,6 +1144,65 @@ describe('TextEditorComponent', () => {
           [[2, 0], [4, 4]]
         ])
       })
+
+      it('autoscrolls the content when dragging near the edge of the screen', async () => {
+        const {component, editor} = buildComponent({width: 200, height: 200})
+        const {scroller} = component.refs
+        spyOn(component, 'handleMouseDragUntilMouseUp')
+
+        let previousScrollTop = 0
+        let previousScrollLeft = 0
+        function assertScrolledDown () {
+          expect(scroller.scrollTop).toBeGreaterThan(previousScrollTop)
+          previousScrollTop = scroller.scrollTop
+          expect(scroller.scrollLeft).toBe(previousScrollLeft)
+          previousScrollLeft = scroller.scrollLeft
+        }
+
+        function assertScrolledUp () {
+          expect(scroller.scrollTop).toBeLessThan(previousScrollTop)
+          previousScrollTop = scroller.scrollTop
+          expect(scroller.scrollLeft).toBe(previousScrollLeft)
+          previousScrollLeft = scroller.scrollLeft
+        }
+
+        component.didMouseDownOnLineNumberGutter({detail: 1, button: 0, clientX: 0, clientY: 100})
+        const {didDrag, didStopDragging} = component.handleMouseDragUntilMouseUp.argsForCall[0][0]
+        didDrag({clientX: 199, clientY: 199})
+        assertScrolledDown()
+        didDrag({clientX: 199, clientY: 199})
+        assertScrolledDown()
+        didDrag({clientX: 199, clientY: 199})
+        assertScrolledDown()
+        didDrag({clientX: component.getGutterContainerWidth() + 1, clientY: 1})
+        assertScrolledUp()
+        didDrag({clientX: component.getGutterContainerWidth() + 1, clientY: 1})
+        assertScrolledUp()
+        didDrag({clientX: component.getGutterContainerWidth() + 1, clientY: 1})
+        assertScrolledUp()
+
+        // Don't artificially update scroll measurements beyond the minimum or
+        // maximum possible scroll positions
+        expect(scroller.scrollTop).toBe(0)
+        expect(scroller.scrollLeft).toBe(0)
+        didDrag({clientX: component.getGutterContainerWidth() + 1, clientY: 1})
+        expect(component.measurements.scrollTop).toBe(0)
+        expect(scroller.scrollTop).toBe(0)
+        expect(component.measurements.scrollLeft).toBe(0)
+        expect(scroller.scrollLeft).toBe(0)
+
+        const maxScrollTop = scroller.scrollHeight - scroller.clientHeight
+        const maxScrollLeft = scroller.scrollWidth - scroller.clientWidth
+        scroller.scrollTop = maxScrollTop
+        scroller.scrollLeft = maxScrollLeft
+        await component.getNextUpdatePromise()
+
+        didDrag({clientX: 199, clientY: 199})
+        didDrag({clientX: 199, clientY: 199})
+        didDrag({clientX: 199, clientY: 199})
+        expect(component.measurements.scrollTop).toBe(maxScrollTop)
+        expect(component.measurements.scrollLeft).toBe(maxScrollLeft)
+      })
     })
   })
 })

src/text-editor-component.js

@@ -849,6 +849,7 @@ class TextEditorComponent {
     const initialScreenRange = model.screenRangeForBufferRange(initialBufferRange)
     this.handleMouseDragUntilMouseUp({
       didDrag: (event) => {
+        this.autoscrollOnMouseDrag(event, true)
         const dragRow = this.screenPositionForMouseEvent(event).row
         const draggedLineScreenRange = Range(Point(dragRow, 0), Point(dragRow + 1, 0))
         model.getLastSelection().setScreenRange(draggedLineScreenRange.union(initialScreenRange), {
@@ -899,7 +900,7 @@ class TextEditorComponent {
     window.addEventListener('mouseup', didMouseUp)
   }
 
-  autoscrollOnMouseDrag ({clientX, clientY}) {
+  autoscrollOnMouseDrag ({clientX, clientY}, verticalOnly = false) {
     let {top, bottom, left, right} = this.refs.scroller.getBoundingClientRect()
     top += MOUSE_DRAG_AUTOSCROLL_MARGIN
     bottom -= MOUSE_DRAG_AUTOSCROLL_MARGIN
@@ -935,7 +936,7 @@ class TextEditorComponent {
       }
     }
 
-    if (xDelta != null) {
+    if (!verticalOnly && xDelta != null) {
       const scaledDelta = scaleMouseDragAutoscrollDelta(xDelta) * xDirection
       const newScrollLeft = this.constrainScrollLeft(this.measurements.scrollLeft + scaledDelta)
       if (newScrollLeft !== this.measurements.scrollLeft) {