XnaFiddle: Skill for Claude Code

Architecture

One IntellisenseService singleton (DI, app lifetime) holds an AdhocWorkspace + a single User.cs document. Every JSInvokable call swaps document text via Solution.WithDocumentText(_documentId, ...) + _workspace.TryApplyChanges(...), then drives Roslyn:

• Completion: CompletionService.GetService(document).GetCompletionsAsync(...)
• Hover: SemanticModel.GetDeclaredSymbol / GetSymbolInfo + custom SymbolDisplayFormat
• Signature help: walk syntax tree for enclosing InvocationExpressionSyntax, resolve via SemanticModel.GetSymbolInfo, format manually
• Live diagnostics: Project.GetCompilationAsync().GetDiagnostics()

SignatureHelpService and QuickInfoService are internal in Roslyn 4.14, so hover and sig help bypass them and drive the SemanticModel directly. Metadata references are pulled from CompilationService.GetMetadataReferencesAsync so the completion surface exactly matches the compile surface.

Key files

WASM single-thread constraint (critical)

All Roslyn work runs on the one WASM thread; a long call blocks typing. Three layered mitigations:

1. JS-side tiered debounce in _registerCompletions:
   • . (member access): 50ms
   • Ctrl+Space on empty word: 0ms (fire immediately)
   • Typing with word length >= 3: 400ms
   • Typing with word length < 3: skipped entirely (returns {suggestions: []})
2. Word-start cache (_completionCache, keyed by {sourcePrefix, wordStartOffset}): while the user types inside the same word, Monaco filters client-side against the cached result and no .NET call happens.
3. Per-op CancellationTokenSource in IntellisenseService (_currentCompletionCts, _currentSignatureHelpCts, _currentHoverCts, _currentDiagnosticsCts): a new request on the same channel cancels the prior one mid-flight. Separate CTS per op means sig help and completion don't cancel each other.