Variables do not show in debugger in top-level program

[albahari]

Repro steps

Create a new F# project in VS2019 that targets .NET Framework 4.6 or .NET Core, and type in the following program:

open System

let x = 2
let y = 3
let z = x + y

Console.WriteLine (z)

Set a breakpoint on the last line, press F5, and go to the "Locals Window".

Expected behavior

You should see three variables: x, y, and z. And in the Watch window, you should be able to type 'y' or 'z' to see the value of y or z.

Actual behavior

Only variable x appears. And if you type 'y' into the Watch window, it says "The name 'y' does not exist in the current context.'

Known workarounds.

If you do same thing in VS2017, x, y, and z are all visible.

Related information

I believe the problem is caused by a bug in the way the PDB file is generated in the newer version of VS/F#. You can verify this by running the following program without attaching the debugger (Ctrl+F5):

let x = 2
let y = 3
let z = x + y
System.Diagnostics.Debugger.Launch()

First, build the program in VS2017, and run with Ctrl+F5. When the just-in-time debugging prompt appears, choose VS2019 as your debugger - the debugger will work perfectly and you'll be able to see variables x, y and z.

Now do the reverse. Build the program in VS2019, and run with Ctrl+F5. When the just-in-time debugging prompt appears, choose VS2017 as your debugger - now you'll only be able to see variable x in the locals window.

Microsoft Windows [Version 10.0.18362.295]
VS2019 Microsoft Visual F# Tools 10.4 for F# 4.6
VS2017: Microsoft Visual F# Tools 10.2 for F# 4.5
Same behavior with .NET Framework 4.5 -> 4.8, and .NET Core 2.2 and 3.0

[albahari]

Any progress on this?

[cartermp]

Sorry for not responding to this one @albahari. This is now tracked as a regression. I'll bring it up in our next team standup for folks to assess.

[cartermp]

@jonsequitur @TIHan @KevinRansom I closed out the VS bug in favor of this one, which is tracked as a regression.