Let FSharpProjectSnapshot.FromOptions take reference stamps from the host

[xperiandri]

Description

FSharpProjectSnapshot.FromOptions stats every -r: reference (FileSystem.GetLastWriteTimeShim) each time a snapshot is built from options. Under the transparent compiler in Visual Studio that is the from-scratch path for every new Roslyn Project instance whose options are not reusable — after every options recompute, since FSharpProjectOptions.AreSameForChecking compares only the Stamp — so a project with a few hundred references pays a few hundred stats per typecheck request.

This adds an optional getReferenceStamp: string -> DateTime to FromOptions. A host that already tracks the last-write times of its references (#20457 keeps them behind an IVsAsyncFileChangeEx2 watcher) supplies them; everyone else gets the same FileSystem.GetLastWriteTimeShim as before. The callback is threaded through the recursive call for FSharpReferencedProject.FSharpReference, so referenced projects' snapshots use it too.

No behaviour change for existing callers; the surface-area baseline gains the new optional parameter on the existing overload.

Checklist

• Test cases added — FSharpChecker/ProjectSnapshot.fs: the stamps of both the project and its referenced F# project come from the callback.
• Performance benchmarks added in case of performance changes — none; the change removes a stat per reference only when a host opts in, the default path is unchanged.
• Release notes entry updated — docs/release-notes/.FSharp.Compiler.Service/11.0.100.md.

[github-actions]

✅ Release notes checked

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
`src/Compiler`	docs/release-notes/.FSharp.Compiler.Service/11.0.200.md

[T-Gro]

🤖🕵️ Keep the existing public FromOptions CLR method. Put shared logic in a private implementation and expose a distinctly named internal host entry point for the editor.

[xperiandri]

@xperiandri but arguments are optional

[T-Gro]

@xperiandri TODO - I think this hasnt been addressed

[xperiandri]

I wonder if this really required, if added parameter is optional

[xperiandri]

I wonder if this really required, if added parameter is optional

[xperiandri]

Addressed now, in ab9604d250. You were right and my "the arguments are optional" was not: an optional parameter is part of the CLR signature, so adding one replaced the existing FromOptions instead of extending it, and a consumer built against the old one would have hit a MissingMethodException.

The shape is the one you asked for — a private SnapshotOfOptions does the work, the three FromOptions overloads are byte-for-byte what main has, and the host entry point is the separately named FromOptionsWithReferenceStamps(options, getFileSnapshot, getReferenceStamp, ?snapshotAccumulator).

It is public rather than internal: FSharp.Compiler.Service grants InternalsVisibleTo to fsc, fsi, VisualFSharp.Salsa, VisualFSharp.UnitTests and the two test projects, and not to FSharp.Editor, which is the host that would pass the stamps. Happy to make it internal and add that IVT instead if you prefer to keep it off the public surface.

[github-actions]

🔍 Tooling Safety Check — Affects-Design-Time
Affects-Design-Time: Changes project snapshots consumed by design-time hosts.

Generated by PR Tooling Safety Check · gpt56 3.1M · ◷

[Copilot]

Copilot review overview

🟡 Changes recommended

Preserve the existing FromOptions overload to avoid breaking already-built consumers.

Review effort: Lite
Findings: 1

Open (1)

• Preserve the existing 3-argument CLR overload for binary compatibility · New

What changed in this PR

Adds host-provided reference timestamp callbacks to FSharpProjectSnapshot.FromOptions, including recursive referenced projects.

Changes:

• Adds callback-based reference stamping with filesystem fallback.
• Adds tests for project and referenced-project stamps.
• Updates the API baseline and release notes.

File	Summary
src/​Compiler/​Service/​FSharpProjectSnapshot.fs	Implements callback-based stamping; retain the existing 3-argument overload for binary compatibility.
tests/​FSharp.Compiler.ComponentTests/​FSharpChecker/​ProjectSnapshot.fs	Tests callback propagation.
tests/​FSharp.Compiler.Service.Tests/​FSharp.Compiler.Service.SurfaceArea.netstandard20.bsl	Updates the public API baseline.
docs/​release-notes/​.FSharp.Compiler.Service/​11.0.100.md	Documents the API enhancement.

[xperiandri]

Both of you are right, and my "but the argument is optional" was wrong: F# compiles an optional parameter into the CLR signature, so the 3-argument method was replaced rather than extended, and a consumer built against it would have found no such method.

Fixed in ab9604d250, the way @T-Gro asked for it: the work moved to a private SnapshotOfOptions, the three FromOptions overloads are back exactly as they were on main, and a host that already tracks its references calls the new FromOptionsWithReferenceStamps(options, getFileSnapshot, getReferenceStamp, ?snapshotAccumulator).

One deviation from your wording, @T-Gro: the new entry point is public rather than internal. FSharp.Compiler.Service has InternalsVisibleTo for fsc, fsi, VisualFSharp.Salsa, VisualFSharp.UnitTests and the two test projects, but not for FSharp.Editor, which is the host meant to pass the stamps — internal would need a new IVT entry for it. Say the word if you would rather have the IVT than a public name.

The surface-area baseline now has the three original lines untouched plus one for the new member (regenerated with TEST_UPDATE_BSL=1, and the test passes on a re-run). The component test calls the new name and passes.