Resolve Go To Definition targets through the workspace's current solution

[xperiandri]

Description

Go To Definition in an F# file, on a symbol declared in another F# project of the same solution, opened a generated signature (the "F# Metadata" document) instead of the source, and Go To Implementation reported nothing. Reproduced with the in-box tools on Visual Studio 18 Insiders while a large solution (135 project instances) was still loading.

Root cause, measured in the debugger: GoToDefinition.FindDefinitionAtPosition decides that a symbol is external when originDocument.Project.Solution has no document for the file FCS reports. The Document Roslyn hands to the navigation service can come from a snapshot taken before every project finished loading: for the same path, originDocument.Project.Solution.GetDocumentIdsWithFilePath returned 0 documents while Workspace.CurrentSolution.GetDocumentIdsWithFilePath returned 2. Every later lookup in that method (TryGetDocumentFromPath for the signature/implementation counterparts) used the same snapshot, so even a symbol that passed the first check could end in a silent no-op. The same lookup in GetSymbolScope narrowed the scope of Find All References and Rename, and rangeToDocumentSpans could miss declaration spans.

Fix: Document gains TryFindInSolutions, GetSolutionDocumentsWithFilePath, TryGetSolutionDocumentFromPath and TryGetSolutionDocumentFromFSharpRange (CodeAnalysisExtensions.fs). They look in the document's own solution first, which keeps forks carrying unsaved buffer text intact, and in Workspace.CurrentSolution when that has nothing; they normalise the path (the old ContainsDocumentWithFilePath check did not) and prefer the target-framework instance the origin project depends on. All lookups in GoToDefinition.fs, the scope computation in Symbols.fs, the signature/implementation counterpart lookup in SymbolHelpers.fs and rangeToDocumentSpans in FindUsagesService.fs use them. The "caret is already on the declaration" branch of FindDefinitionAtPosition moves into FindCounterpartOfDeclarationAtCaret, and the repeated "declaration in this implementation document → navigable item" sequence into FindNavigableDeclarationIn.

Tests: RoslynTestHelpers can now build a Roslyn solution with several F# projects wired by project references (CreateMultiProjectSolution) and one with several target-framework instances of a single project (CreateMultiTargetSolution); the F# options come from the same SyntheticProject, so FCS gets in-memory project references the way it does in VS. GoToDefinitionServiceTests reproduces the measured condition — the origin document taken from a solution fork that lacks the library document while the workspace has it — and checks that the lookup, FindDefinitionAtPosition and GetSymbolScope all resolve the library, plus a control that a symbol whose file is in no solution is still reported as external.

Checklist

• Test cases added

• Performance benchmarks added in case of performance changes

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
`vsintegration/src`	docs/release-notes/.VisualStudio/18.vNext.md