Let the editor answer reference timestamps for the incremental builder

[xperiandri]

With the background compiler, every request re-reads the last-write time of each non-framework reference of the project to decide whether its imports are stale. FSharpChecker.SetReferenceStampProvider (internal) lets a host that already watches those files answer instead.

Details

• The provider is asked both when a builder is created and when it checks for staleness, so a host view that lags the disk cannot recreate a builder on every request.
• Project references keep their in-memory logical stamps. A checker nobody gave a provider stats as before.
• Internal, so no surface-area change. Visual Studio will set it from the tracker in Cache reference timestamps behind an IVsAsyncFileChangeEx2 watcher for snapshot reuse #20457 once both are in.

🤖 Generated with Claude Code

[github-actions]

✅ Release-note check exempted

The NO_RELEASE_NOTES label or localization-bot authorship exempts this pull request.

[Copilot]

🟡 Changes recommended

The new optional callback representation conflicts with the compiler’s required voption convention and needs a thread-safe multi-file adjustment.

1 open finding

• Use voption with safe atomic publication for optional callback · New

What changed in this PR

Adds an internal host-provided reference timestamp source to reduce repeated filesystem access during incremental checking.

Changes:

• Routes the provider through FSharpChecker and background compilers.
• Uses host stamps for non-framework references while preserving project-reference stamps.
• Adds integration tests and release notes.

File	Description
ReferenceStampProviderTests.fs	Tests provider behavior and invalidation.
FSharp.Compiler.Service.Tests.fsproj	Includes the new tests.
TransparentCompiler.fs	Forwards provider configuration.
service.fsi	Declares and documents the internal API.
service.fs	Exposes the checker method.
IncrementalBuild.fsi	Extends builder creation parameters.
IncrementalBuild.fs	Applies host-provided reference stamps.
BackgroundCompiler.fsi	Declares provider plumbing.
BackgroundCompiler.fs	Stores and forwards the provider.
11.0.200.md	Documents the addition.

🧠 Review effort: Balanced

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[T-Gro]

🤖 🕵️ LGTM

[T-Gro]

The diff is still way too big - apply the NoBloat instructions and CodeCompaction skill.

Especially the massive code comments would benefit not just with drastic reduction, but ideally with well named functions/arguments/bindings/types making the intention clear.

If a well named piece of code just tells what the comment says - delete the comment.

• Excluding 7 public API documentation lines, this diff still adds 16 implementation and test comment lines and 1513 comment chars.
• Comments bypass the type system and become stale maintenance state. Keep only durable public contracts; express implementation intent through names, functions, active patterns, discriminated unions, and types.

[xperiandri]

Addressed the NoBloat / CodeCompaction review in 6d4d94eb79 (plus a merge of main before it, no rebase):

• The change now adds 3 comment lines, down from 23: the two-line doc of SetReferenceStampProvider, which states what a host has to provide, and the license header of the new test file. The doc on the IBackgroundCompiler member, the notes on the option field and on the stamper, and the narration inside the tests are gone. The stamper is one binding, stampReferencedAssembly, used both when the builder is created and when it checks for staleness, which is what the removed note said.
• The four tests keep their behavior-named titles and share withFixture, recording and legacyChecker for setup.
• The release note is removed: the API is internal and the PR carries NO_RELEASE_NOTES.

ReferenceStampProviderTests, SurfaceAreaTest, IncrementalBuilderRaceTests and MultiProjectAnalysisTests pass (19 tests).

[T-Gro]

🤖🕵️ LGTM ✅

Dimensions covered (expand)

• Delta scope, feedback resolution, and pinned-map exclusions (Grok 4.7 High)