Fix SourceLink go-to-definition failure when .NET 10 is used on Linux

[serefarikan]

Summary

Fix SourceLink go-to-definition failure on .NET 10 for FSharp.Core symbols (e.g., List.map).

Problem

Go-to-definition fails for FSharp.Core symbols on .NET 10 with error MissingSourceFile, while working correctly on .NET 9.

Root cause: FSharp.Core 10.x is built on Linux (was Windows for 9.x), so PDB paths use forward slashes. On Linux, Path.GetFileName correctly strips the directory, leaving just the basename (list.fs), which then fails to match the full PDB document path (/__w/1/s/.../list.fs).

Changes

1. ParseAndCheckResults.fs (getFileName): Keep the full FCS path instead of calling Path.GetFileName on non-Windows. Just normalize backslashes to forward slashes.
2. Sourcelink.fs (compareRepoPath): Use suffix matching - the PDB document should be a suffix of (or equal to) the FCS path, to handle workspace prefixes FCS may add.

Tests

• .NET 10 devcontainer (mcr.microsoft.com/dotnet/sdk:10.0.100-noble-aot) - go-to-definition on List.map now works
• .NET 9 devcontainer (mcr.microsoft.com/devcontainers/dotnet:1-9.0) - no regression

Details

This PR aims to solve the issue described here: ionide/ionide-vscode-fsharp#2115

This has been a very interesting experience because I used claude code to track down the problem, then understand the root cause and implement a fix. I left the comments claude added in the code, because they clarify the context, though for the maintainers of this repo they may be just redundant.

I also tried to track down the changes to how fsharp core libraries are built, which took place with the .NET 10 release, but it is hard to find a single document that explains it. Overall, it looks like the sourcelink document metadata in fsharp dlls have changed. I added some debug statements to trace the document paths FCS returns and I can see that .net 9 and .net 10 environments have different values for the same entry:

• FSharp.Core 9.x → PDB contains paths such as D:\a\_work\1\s\src\FSharp.Core\list.fs
• FSharp.Core 10.x → PDB contains paths such as /__w/1/s/src/fsharp/src/FSharp.Core/list.fs

[TheAngryByrd]

Thanks for investigating! This seems to have broken Windows sourcelink lookups. Would you mind investigating those?

[serefarikan]

That's interesting. I should not have assumed it'd work with Windows. I'll investigate.

[serefarikan]

@TheAngryByrd I had to make a one line change. I tested the results and I can confirm the .net 10 build I've created in my local devcontainer env is working with both ubuntu (devcontainer) and native windows 10 instances of vs code in my local dev setup.