Answer the Navigate To search that runs while the solution loads

[xperiandri]

Draft: it cannot build against the Roslyn this repository references yet. dotnet/roslyn#85213, the contract this implements, merged on 2026-09-09, but main still builds against Roslyn 5.12.0-1.26428.6 (2026-08-28), which predates it. It needs the next dependency update from dotnet/roslyn.

Navigate To runs a search of its own while a solution is still loading, and F# contributes nothing to it: that phase is dispatched through IAdvancedNavigateToSearchService, which the F# language service does not implement, so every F# project is reported complete and searched not at all. No full search follows — that is deliberate on the Roslyn side ("Telemetry shows no meaningful change if we do a full search after this point") — so on a large solution Ctrl+T lists nothing F# declares until the user searches again.

The search itself is a parse away and needs no type checking. What it lacked is the project's compilation options, which do not exist yet during load, so the accurate parse entry point raises; the quick one parses with whatever parsing options the project system has already produced, or defaults — a dictionary read, no reactor, no I/O. Those defines can be the wrong ones, and the document's version does not change when the real options arrive, so a cache entry now records whether it was approximate: the accurate path refuses those and reparses, while the loading path takes either, since its contract allows out-of-date results. Otherwise a declaration behind #if could be missed, or reported from a branch that never compiles.

The search follows the shape of the C# and VB service: priority documents and the projects holding them first, results reported per document rather than per project so the first ones appear while the rest are still parsing, and every project's parses taking turns on one throttle that leaves a core free, so a search during load cannot take the cores away from the load itself.

Stacked on #20409, which adds the per-document parse cache this extends; once that merges the diff is two commits — giving the quick parsing options the file they parse, and the change itself.

🤖 Generated with Claude Code

[github-actions]

✅ Release notes checked

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Change path	Release notes path	Description
`src/Compiler`	docs/release-notes/.FSharp.Compiler.Service/11.0.200.md	No current pull request URL (#20492) found, please consider adding it
`vsintegration/src`	docs/release-notes/.VisualStudio/18.vNext.md

[T-Gro]

🤖🕵️ Please shorten the description using this guidance. Focus on the problem and why the change is needed, in simplified technical English. Leave the implementation inventory to the Files tab and retain necessary caveats.

[xperiandri]

Moved out of the PR description per the pr-description guidance — how this was verified, since the branch cannot build in CI yet.

Against a local build of Roslyn containing dotnet/roslyn#85213: NavigateToSearchWhileLoadingTests, three tests — the loading search finds a declaration where the accurate search raises for want of options; a file behind #if FOO read under the wrong defines returns nothing and does not poison the accurate search that follows once --define:FOO arrives; and every project is reported complete exactly once whether or not anything was found in it. With the approximate check removed, the first two fail. With NavigateToSearchServiceTests and CopilotContextProviderTests, 31 pass. The full FSharp.Editor.Tests run: 7219 passed, 2 skipped, 4 failed — fsiShouldTriggerCompletionInFsxFile and three type provider tests, which fail the same way on this branch's base without its commits. FSharp.Editor builds with -p:Optimize=true.

Checked live as well, with that Roslyn build deployed to the experimental hive: on a 26-project mixed C#/F# solution, breaking in the F# implementation gives the stack ProcessOrderedProjectsAsync → NavigateToSearcher.SearchCachedDocumentsAsync → the external access adapter → here, with the active document and priority documents intact, and Ctrl+T lists F# declarations immediately while the solution is still loading.