Open Radar

 
Summary:
Attached is a video showing the problem.
Attached is the project file.

TL;DR - I outdented some incorrect code,  and indented it back.  The line of code with a legitimate error had a red-error-sigil courtesy of Live Issues.  After outdenting and indenting, the error sigil turned disabled-gray, and then disappeared, making me think that my incorrect code suddenly is correct now.

I outdent code (with command-[) before copying it into our Big Nerd Ranch course materials  because the extra level of indentation of the average swift function isn't useful in print - just four wasted columns that we can otherwise use.

So I shifted-over this code:

```
    @IBAction func startObserving() {
        guard progress == nil else {
            // disallow multiple concurrent progress objects
            return
        }
        
        progress = Progress(totalUnitCount: 30)
        swift.watchProgress(progress)
    }
```

'swift.watchProgress(_: Progress)` doesn't exist yet. So this is erroneous code.

In the process of outdenting it, copying it, and re-indenting. I noticed the error sigil disappearing.  It happened reliably enough (about 9 times out of 10) I started up screen flow to catch evidence of the editor losings its mind.  The video shows a successful identification of the error, and then a disappearance of the error signs.

Steps to Reproduce:
It's one of those "have to use Xcode for a while before it loses its mind" things. Quitting Xcode and re-running it doesn't show the problem, so there's something deep in the editor stuff that's going wrong, as witnessed by the evidence here.

Expected Results:


Actual Results:


Version:
Version 8.0 beta 2 (8S162m)
10.11.5 (15F34)


Notes:
It's really not that big a deal - just scratch your head and restart Xcode, but
when these kinds of things happen day-in, day-out, it's just another heavy-sigh
death-of-a-thousand-cuts that makes using Xcode unpleasant.


Configuration:


Attachments:
'bizarre-error-disappearance.mp4' and 'ObjCInterop.zip' were successfully uploaded.