From c626836b2e1b195d2974c7e97ca9934e83b7ae66 Mon Sep 17 00:00:00 2001
From: Nathan Sobo <nathan@github.com>
Date: Wed, 16 Aug 2017 11:28:58 -0600
Subject: [PATCH] Only clear linesToMeasure when we have actually measured

Previously, as soon as we decided to render linesToMeasure, we would
clear them out. However, if a second update interleaved with the update
that initially requested measurement, it could cause the requested lines
to not be present when the measurement phase from the first update
occurred. Now, any additional updates will only add to the set of lines
that need to be measured until the measurement phase actually happens.

Signed-off-by: Antonio Scandurra <as-cii@github.com>
---
 spec/text-editor-component-spec.js | 16 ++++++++++++++++
 src/text-editor-component.js       |  6 +++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/spec/text-editor-component-spec.js b/spec/text-editor-component-spec.js
index 916ecd0ed..91727f2f1 100644
--- a/spec/text-editor-component-spec.js
+++ b/spec/text-editor-component-spec.js
@@ -117,6 +117,22 @@ describe('TextEditorComponent', () => {
         )
         expect(actualWidth).toBe(expectedWidth + 'px')
       }
+
+      {
+        // Make sure we do not throw an error if a synchronous update is
+        // triggered before measuring the longest line from a
+        // previously-scheduled update.
+        editor.getBuffer().insert(Point(12, Infinity), 'x'.repeat(100))
+        expect(editor.getLongestScreenRow()).toBe(12)
+
+        TextEditorComponent.getScheduler().readDocument(() => {
+          // This will happen before the measurement phase of the update
+          // triggered above.
+          component.pixelPositionForScreenPosition(Point(11, Infinity))
+        })
+
+        await component.getNextUpdatePromise()
+      }
     })
 
     it('re-renders lines when their height changes', async () => {
diff --git a/src/text-editor-component.js b/src/text-editor-component.js
index 8af4f4a9e..6dcfd128e 100644
--- a/src/text-editor-component.js
+++ b/src/text-editor-component.js
@@ -32,6 +32,10 @@ class TextEditorComponent {
     etch.setScheduler(scheduler)
   }
 
+  static getScheduler () {
+    return etch.getScheduler()
+  }
+
   static didUpdateStyles () {
     if (this.attachedComponents) {
       this.attachedComponents.forEach((component) => {
@@ -389,6 +393,7 @@ class TextEditorComponent {
       this.pendingAutoscroll = null
     }
 
+    this.linesToMeasure.clear()
     this.measuredContent = true
   }
 
@@ -848,7 +853,6 @@ class TextEditorComponent {
         this.extraRenderedScreenLines.set(row, screenLine)
       }
     })
-    this.linesToMeasure.clear()
   }
 
   queryLineNumbersToRender () {