Bug in IDE checking using VIsualFSharp.sln on main

[dsyme]

"main" has a bug where opening VIsualFSharp.sln (after installing into RoslynDev ) reveals an error:

There are many other errors later in the solution as well, e.g. here in range.fs

It's a very strange problem, I will try to determine the source of the issue now.

Repro

1. Build "main"

   .\build -c Release -deploy
   

2. Open VisualFSharp.sln

   devenv VisualFSharp.sln /RootSuffix RoslynDev
   

3. Open "lib.fs" and "range.fs" and see if the above errors occur (they shouldn't)

[dsyme]

I'm going to do a binary chop on the commit history to determine where this bug crept in

Starting with 178ec2f as a random point in time

[auduchinok]

@dsyme This is what I see in Rider with an FCS build based on 718d3c4:

[dsyme]

Binary chop

• 89ad371 (4 days ago) - not ok
• aaafa3d - tbd
• 98f344f - not ok
• f820847 - tbd
• 612c65d ( 7 days ago) - ok
• 178ec2f (18 days ago) - ok

Since 612c65d is just a README change this means my cleanup PR #11151 is responsible. I'll look for the problem

https://github.com/dotnet/fsharp/pull/11151/files?diff=unified&w=1#diff-4cf589945def81188bed84b5466d6c2c6eca933e91427e54ed059f018fb9cec9L120 looks suspicious. EmptyParsedInput will fill in a different value for this field.