General better support for signature files in tooling

[baronfel]

Right now we have some gaps in our support for signature files:

• Tooltips don't always resolve the xml docs on signature declarations when inside the same project (Tooltip oddity with signatures/quick info #739)
• Go-To Definition/Declaration doesn't know how to find definitions in signature files
• Find References doesn't know how to cover signature files
• Project Tree/results views may not show signatures correctly/may want to logically group the signature and its implementation file

All of these have a common logical operation that we need to be able to do:

• for a 'find declaration' operation, we need to be able to say if we want to implementation or the declaration
• some use cases will always prefer declaration (tooltips/go to declaration), while some may prefer implementation, or even both ranges
• if the declaration is requested, but the given symbol range is in an implementation file,
• try to find the declaration in a signature file of the same name and proceed from there

The Visual Studio integration for concepts like go-to-def can serve as a good scaffolding for how we can tackle this.

The primary motivation for this work is an increased amount of tooling support for deriving performance benefits when signature files are present, which I think will naturally lead to an increased usage of them in the ecosystem.

[github-actions]

🤖 This is an automated response from Repo Assist.

This is a great tracking issue for signature file tooling gaps. Here's a status check and some notes that may help whoever picks this up:

Current gaps summary

Gap	Status
Tooltips in .fsi don't always resolve XML docs from the same project (#739)	Open
Go-To Definition/Declaration for .fsi symbols	Partial — textDocument/definition works but doesn't navigate to/from signature
Find References not covering .fsi files	Open
Go-To Implementation (.fsi → .fs)	Open — filed as #1473

Implementation notes

The core operation is: given a symbol position in a .fsi file, find the corresponding .fs file (or vice versa). The key facts are:

1. .fsi and .fs files share a name and appear together in the project file. The FSharpProjectOptions.SourceFiles array includes both; a .fsi is "paired" with its .fs sibling.

2. FCS provides FSharpCheckFileResults.GetSymbolUseAtLocation to get the symbol at a position, and FSharpCheckProjectResults.GetAllUsesOfAllSymbols to find all sites. These are the building blocks for cross-file navigation.

3. Go-To Implementation (textDocument/implementation) is not yet registered in IFSharpLspServer.fsi — it needs to be added. The .fsi → .fs case is simpler: find the paired .fs file and navigate to the same symbol by position/name.

4. Find References across .fsi: the current FindAllReferences in AdaptiveFSharpLspServer.fs may already be close — worth checking whether it covers .fsi symbol uses.

Related issue

Issue #1473 (recently filed by @Krzysztof-Cieslak) specifically tracks the "go-to implementation" feature. I left an implementation sketch there.

Where to start

A good first step would be IFSharpLspServer.fsi (add textDocument/implementation stub) → AdaptiveFSharpLspServer.fs (implement handler) → handle the .fsi↔.fs pairing logic. The Visual Studio integration code linked in the issue description is a solid reference.

Generated by Repo Assist

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@afb00b92a9514fee9a14c583f059a03d05738f70