Guard against IndexSizeError when measuring lines

Refs #7464 #7465 #5997

This will ask the user for the content of the offending line, but only
once so as not to be annoying. Hopefully this and the other data we’re
collecting will help us solve the problem.

Signed-off-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

src/lines-tile-component.coffee

@@ -346,17 +346,44 @@ class LinesTileComponent
             rangeForMeasurement ?= document.createRange()
             iterator =  document.createNodeIterator(lineNode, NodeFilter.SHOW_TEXT, AcceptFilter)
             textNode = iterator.nextNode()
+            textNodeLength = textNode.length
             textNodeIndex = 0
             nextTextNodeIndex = textNode.textContent.length
 
           while nextTextNodeIndex <= charIndex
             textNode = iterator.nextNode()
+            textNodeLength = textNode.length
             textNodeIndex = nextTextNodeIndex
             nextTextNodeIndex = textNodeIndex + textNode.textContent.length
 
           i = charIndex - textNodeIndex
           rangeForMeasurement.setStart(textNode, i)
-          rangeForMeasurement.setEnd(textNode, i + charLength)
+
+          if i + charLength <= textNodeLength
+            rangeForMeasurement.setEnd(textNode, i + charLength)
+          else
+            rangeForMeasurement.setEnd(textNode, textNodeLength)
+            atom.assert false, "Expected index to be less than the length of text node while measuring", (error) =>
+              editor = @presenter.model
+              screenRow = tokenizedLine.screenRow
+              bufferRow = editor.bufferRowForScreenRow(screenRow)
+
+              error.metadata = {
+                grammarScopeName: editor.getGrammar().scopeName
+                screenRow: screenRow
+                bufferRow: bufferRow
+                softWrapped: editor.isSoftWrapped()
+                softTabs: editor.getSoftTabs()
+                i: i
+                charLength: charLength
+                textNodeLength: textNode.length
+              }
+              error.privateMetadataDescription = "The contents of line #{bufferRow + 1}."
+              error.privateMetadata = {
+                lineText: editor.lineTextForBufferRow(bufferRow)
+              }
+              error.privateMetadataRequestName = "measured-line-text"
+
           charWidth = rangeForMeasurement.getBoundingClientRect().width
           @presenter.setScopedCharacterWidth(scopes, char, charWidth)