Fix rendering artifacts when resizing with soft wraps

Previously, we were accidentally depending on the state of the display
layer when forcing it to update its index. This caused us to not index
enough content to cover the visibile area, which meant we weren't
querying enough lines to fill the screen in some situations.

spec/text-editor-component-spec.js

@@ -457,6 +457,17 @@ describe('TextEditorComponent', () => {
       expect(editor.lineLengthForScreenRow(0)).toBe(20)
     })
 
+    it('correctly forces the display layer to index visible rows when resizing (regression)', async () => {
+      const text = 'a'.repeat(30) + '\n' + 'b'.repeat(1000)
+      const {component, element, editor} = buildComponent({height: 300, width: 800, attach: false, text})
+      editor.setSoftWrapped(true)
+      jasmine.attachToDOM(element)
+
+      element.style.width = 200 + 'px'
+      await component.getNextUpdatePromise()
+      expect(element.querySelectorAll('.line:not(.dummy)').length).toBe(24)
+    })
+
     it('decorates the line numbers of folded lines', async () => {
       const {component, element, editor} = buildComponent()
       editor.foldBufferRow(1)

src/text-editor-component.js

@@ -236,7 +236,6 @@ class TextEditorComponent {
     this.measureBlockDecorations()
 
     this.measuredContent = false
-    this.updateModelSoftWrapColumn()
     this.updateSyncBeforeMeasuringContent()
     if (useScheduler === true) {
       const scheduler = etch.getScheduler()
@@ -321,6 +320,7 @@ class TextEditorComponent {
 
   updateSyncBeforeMeasuringContent () {
     this.derivedDimensionsCache = {}
+    this.updateModelSoftWrapColumn()
     if (this.pendingAutoscroll) {
       const {screenRange, options} = this.pendingAutoscroll
       this.autoscrollVertically(screenRange, options)
@@ -2668,8 +2668,10 @@ class TextEditorComponent {
   // Ensure the spatial index is populated with rows that are currently
   // visible so we *at least* get the longest row in the visible range.
   populateVisibleRowRange () {
-    const endRow = this.getRenderedStartRow() + this.getVisibleTileCount() * this.getRowsPerTile()
-    this.props.model.displayLayer.populateSpatialIndexIfNeeded(Infinity, endRow)
+    const lastPossibleVisibleRow = this.rowForPixelPosition(this.getScrollBottom())
+    const maxPossibleVisibleTileCount = Math.floor((lastPossibleVisibleRow - this.getFirstVisibleRow()) / this.getRowsPerTile()) + 2
+    const lastPossibleRenderedRow = this.getRenderedStartRow() + maxPossibleVisibleTileCount * this.getRowsPerTile()
+    this.props.model.displayLayer.populateSpatialIndexIfNeeded(Infinity, lastPossibleRenderedRow)
   }
 
   getNextUpdatePromise () {