Compiler generates debug symbol document record 'unknown'

[marklam]

Inlining (some complicated) code from another assembly causes the pdb symbols to contain a reference to a file called 'unknown'.
This breaks code coverage tools like coverlet, because it skips the assembly when it can't find an on-disk file called 'unknown'.

Repro steps

1. Create some very complicated code to inline
2. Reference that code from another assembly
3. Check the Documents in the debug metadata

I've created a repo which does these steps and put it in github: https://github.com/marklam/FSharpPdbUnknown
(If a zip is preferred, https://github.com/marklam/FSharpPdbUnknown/archive/master.zip should do it)

Expected behavior

The documents in the PDB (which the referenced project can automatically list) should only contain 'Program.fs'

Actual behavior

The documents include 'Program.fs' and 'unknown'

Known workarounds

Dropping an empty file called 'unknown' in the source directory will make Coverlet happy about producing coverage for the assembly.

Related information

• Operating system Windows 10
• .NET Runtime kind .net core 5
• Editing Tools Visual Studio 16.9

[baronfel]

Worth noting that this file comes from uses of the range0 member (eg from anonymous record codegen), but would likely come from anywhere the rangeStartup or rangeCommandLineArgs members were exposed as well. I'm not sure if there's a reasonable workaround from the compiler's point of view for these cases...

[dsyme]

I checked the repro and it no longer generates unknown using main

The problem may still be around though - looking at the code it's a FeeFee debug point with file name unknown

I'll close this until we get another repro