Merge pull request #15831 from atom/b3-failing-seed

Handle edits that scroll up due to hiding the horizontal scrollbar

spec/text-editor-component-spec.js

@@ -905,6 +905,46 @@ describe('TextEditorComponent', () => {
       expect(component.getLineNumberGutterWidth()).toBe(originalLineNumberGutterWidth)
     })
 
+    it('gracefully handles edits that change the maxScrollTop by causing the horizontal scrollbar to disappear', async () => {
+      const rowsPerTile = 1
+      const {component, element, editor} = buildComponent({rowsPerTile, autoHeight: false})
+
+      await setEditorHeightInLines(component, 1)
+      await setEditorWidthInCharacters(component, 7)
+
+      // Updating scrollbar styles.
+      const style = document.createElement('style')
+      style.textContent = '::-webkit-scrollbar { height: 17px; width: 10px; }'
+      jasmine.attachToDOM(style)
+      TextEditor.didUpdateScrollbarStyles()
+      await component.getNextUpdatePromise()
+
+      element.focus()
+      component.setScrollTop(component.measurements.lineHeight)
+
+      component.scheduleUpdate()
+      await component.getNextUpdatePromise()
+
+      editor.setSelectedBufferRange([[0, 1], [12, 2]])
+      editor.backspace()
+
+      // component.scheduleUpdate()
+      await component.getNextUpdatePromise()
+
+      expect(component.getScrollTop()).toBe(0)
+
+      const renderedLines = queryOnScreenLineElements(element).sort((a, b) => a.dataset.screenRow - b.dataset.screenRow)
+      const renderedLineNumbers = queryOnScreenLineNumberElements(element).sort((a, b) => a.dataset.screenRow - b.dataset.screenRow)
+      const renderedStartRow = component.getRenderedStartRow()
+      const expectedLines = editor.displayLayer.getScreenLines(renderedStartRow, component.getRenderedEndRow())
+
+      expect(renderedLines.length).toBe(expectedLines.length)
+      expect(renderedLineNumbers.length).toBe(expectedLines.length)
+
+      element.remove()
+      editor.destroy()
+    })
+
     describe('randomized tests', () => {
       let originalTimeout
 
@@ -921,7 +961,7 @@ describe('TextEditorComponent', () => {
         const initialSeed = Date.now()
         for (var i = 0; i < 20; i++) {
           let seed = initialSeed + i
-          // seed = 1507224195357
+          // seed = 1507231571985
           const failureMessage = 'Randomized test failed with seed: ' + seed
           const random = Random(seed)
 
@@ -930,6 +970,7 @@ describe('TextEditorComponent', () => {
           editor.setSoftWrapped(Boolean(random(2)))
           await setEditorWidthInCharacters(component, random(20))
           await setEditorHeightInLines(component, random(10))
+
           element.focus()
 
           for (var j = 0; j < 5; j++) {

src/text-editor-component.js

@@ -266,14 +266,22 @@ class TextEditorComponent {
     if (useScheduler === true) {
       const scheduler = etch.getScheduler()
       scheduler.readDocument(() => {
-        this.measureContentDuringUpdateSync()
+        const restartFrame = this.measureContentDuringUpdateSync()
         scheduler.updateDocument(() => {
-          this.updateSyncAfterMeasuringContent()
+          if (restartFrame) {
+            this.updateSync(true)
+          } else {
+            this.updateSyncAfterMeasuringContent()
+          }
         })
       })
     } else {
-      this.measureContentDuringUpdateSync()
-      this.updateSyncAfterMeasuringContent()
+      const restartFrame = this.measureContentDuringUpdateSync()
+      if (restartFrame) {
+        this.updateSync(false)
+      } else {
+        this.updateSyncAfterMeasuringContent()
+      }
     }
 
     this.updateScheduled = false
@@ -391,15 +399,16 @@ class TextEditorComponent {
     this.measureHorizontalPositions()
     this.updateAbsolutePositionedDecorations()
 
+    const isHorizontalScrollbarVisible = (
+      this.canScrollHorizontally() &&
+      this.getHorizontalScrollbarHeight() > 0
+    )
+
     if (this.pendingAutoscroll) {
       this.derivedDimensionsCache = {}
       const {screenRange, options} = this.pendingAutoscroll
       this.autoscrollHorizontally(screenRange, options)
 
-      const isHorizontalScrollbarVisible = (
-        this.canScrollHorizontally() &&
-        this.getHorizontalScrollbarHeight() > 0
-      )
       if (!wasHorizontalScrollbarVisible && isHorizontalScrollbarVisible) {
         this.autoscrollVertically(screenRange, options)
       }
@@ -408,6 +417,8 @@ class TextEditorComponent {
 
     this.linesToMeasure.clear()
     this.measuredContent = true
+
+    return wasHorizontalScrollbarVisible !== isHorizontalScrollbarVisible
   }
 
   updateSyncAfterMeasuringContent () {