Avoid requesting horizontal measurement when auto-scrolling vertically

This was leaving a measurement request in the map that was getting
picked up on the next frame. In some cases, the requested measurement
row was not present, causing an exception.

spec/text-editor-component-spec.js

@@ -826,9 +826,9 @@ describe('TextEditorComponent', () => {
     })
 
     it('accounts for the presence of horizontal scrollbars that appear during the same frame as the autoscroll', async () => {
-      const {component, element, editor} = buildComponent()
+      const {component, element, editor} = buildComponent({autoHeight: false})
       const {scrollContainer} = component.refs
-      element.style.height = component.getScrollHeight() + 'px'
+      element.style.height = component.getContentHeight() / 2 + 'px'
       element.style.width = component.getScrollWidth() + 'px'
       await component.getNextUpdatePromise()
 
@@ -838,6 +838,13 @@ describe('TextEditorComponent', () => {
 
       expect(component.getScrollTop()).toBe(component.getScrollHeight() - component.getScrollContainerClientHeight())
       expect(component.getScrollLeft()).toBe(component.getScrollWidth() - component.getScrollContainerClientWidth())
+
+      // Scrolling to the top should not throw an error. This failed
+      // previously due to horizontalPositionsToMeasure not being empty after
+      // autoscrolling vertically to account for the horizontal scrollbar.
+      spyOn(window, 'onerror')
+      await setScrollTop(component, 0)
+      expect(window.onerror).not.toHaveBeenCalled()
     })
   })
 

src/text-editor-component.js

@@ -311,7 +311,12 @@ class TextEditorComponent {
 
   updateSyncBeforeMeasuringContent () {
     this.derivedDimensionsCache = {}
-    if (this.pendingAutoscroll) this.autoscrollVertically()
+    if (this.pendingAutoscroll) {
+      const {screenRange, options} = this.pendingAutoscroll
+      this.autoscrollVertically(screenRange, options)
+      this.requestHorizontalMeasurement(screenRange.start.row, screenRange.start.column)
+      this.requestHorizontalMeasurement(screenRange.end.row, screenRange.end.column)
+    }
     this.populateVisibleRowRange()
     this.queryScreenLinesToRender()
     this.queryLineNumbersToRender()
@@ -339,9 +344,10 @@ class TextEditorComponent {
 
     if (this.pendingAutoscroll) {
       this.derivedDimensionsCache = {}
-      this.autoscrollHorizontally()
+      const {screenRange, options} = this.pendingAutoscroll
+      this.autoscrollHorizontally(screenRange, options)
       if (!wasHorizontalScrollbarVisible && this.isHorizontalScrollbarVisible()) {
-        this.autoscrollVertically()
+        this.autoscrollVertically(screenRange, options)
       }
       this.pendingAutoscroll = null
     }
@@ -1860,16 +1866,11 @@ class TextEditorComponent {
     }
   }
 
-  autoscrollVertically () {
-    const {screenRange, options} = this.pendingAutoscroll
-
+  autoscrollVertically (screenRange, options) {
     const screenRangeTop = this.pixelPositionAfterBlocksForRow(screenRange.start.row)
     const screenRangeBottom = this.pixelPositionAfterBlocksForRow(screenRange.end.row) + this.getLineHeight()
     const verticalScrollMargin = this.getVerticalAutoscrollMargin()
 
-    this.requestHorizontalMeasurement(screenRange.start.row, screenRange.start.column)
-    this.requestHorizontalMeasurement(screenRange.end.row, screenRange.end.column)
-
     let desiredScrollTop, desiredScrollBottom
     if (options && options.center) {
       const desiredScrollCenter = (screenRangeTop + screenRangeBottom) / 2
@@ -1901,10 +1902,9 @@ class TextEditorComponent {
     return false
   }
 
-  autoscrollHorizontally () {
+  autoscrollHorizontally (screenRange, options) {
     const horizontalScrollMargin = this.getHorizontalAutoscrollMargin()
 
-    const {screenRange, options} = this.pendingAutoscroll
     const gutterContainerWidth = this.getGutterContainerWidth()
     let left = this.pixelLeftForRowAndColumn(screenRange.start.row, screenRange.start.column) + gutterContainerWidth
     let right = this.pixelLeftForRowAndColumn(screenRange.end.row, screenRange.end.column) + gutterContainerWidth