Add function argument count validation to language service

[Copilot]

• Explore the repository structure and understand the codebase
• Understand language service implementation
• Implement function argument count validation in language service
  • Add ArityInfo interface for tracking function argument min/max
  • Add arityInfo() method to FunctionDetails class to return min/max args
  • Add getDiagnostics() method to LanguageServiceApi interface
  • Implement getDiagnostics() in createLanguageService() that validates function argument counts
  • Export GetDiagnosticsParams and ArityInfo types from language service
• Add tests for the new getDiagnostics functionality (17 new tests)
• Run tests to verify the implementation (all 1194 tests pass)
• Address code review feedback
  • Extract getDiagnostics logic to separate diagnostics.ts file
  • Reduce complexity by extracting helper functions
  • Integrate diagnostics into playground
  • Update documentation on the language service
• Run security scan with CodeQL (no alerts)

Original prompt

The language server should also indicate when a function has not the correct number of arguments (too few or too much).

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[Sander-Toonen]

Move the logic for getDiagnostics to a seperate file and reduce the complexity of teh getDiagnostics function by extracting

[Sander-Toonen]

Ensure that the functionality can be demonstrated in the playground

[Copilot]

Move the logic for getDiagnostics to a seperate file and reduce the complexity of teh getDiagnostics function by extracting

Done in 1c797cc. Extracted the diagnostics logic to a new diagnostics.ts file and reduced complexity by breaking down the argument counting into smaller, focused functions:

• ArgumentCounterState interface for state management
• createArgumentCounterState(), isAtTopLevel(), markArgumentSeen() for state operations
• processParenToken(), processBracketToken(), processBraceToken(), processCommaToken(), processOtherToken() for token handling
• countFunctionArguments() for the main counting logic
• validateFunctionCall(), createTooFewArgumentsDiagnostic(), createTooManyArgumentsDiagnostic() for validation and diagnostic creation

[Copilot]

Ensure that the functionality can be demonstrated in the playground

Done in 7d5a2a8. Integrated diagnostics into the playground:

• Added applyDiagnostics() function in app.js that calls ls.getDiagnostics() and displays error markers in Monaco using setModelMarkers
• Diagnostics are applied on initialization and whenever the expression changes
• Added a "Diagnostics Demo" example that demonstrates the feature with pow(2) (too few args) and random(1, 2, 3) (too many args)

Run npm run playground and click the "Diagnostics Demo" example to see red squiggly underlines on function calls with incorrect argument counts.

[Sander-Toonen]

@copilot Update documentation on the language server

[Copilot]

Pull request overview

Adds function-argument-count diagnostics to the language service API and wires them into the playground sample so incorrect function calls surface as LSP-style errors.

Changes:

• Extend LanguageServiceApi with getDiagnostics(params: GetDiagnosticsParams): Diagnostic[] and plumb this through createLanguageService.
• Introduce ArityInfo and FunctionDetails.arityInfo() plus a new diagnostics.ts module that token-walks expressions, counts arguments (including nested/array/object/variadic/optional cases), and produces LSP diagnostics.
• Integrate diagnostics into the Monaco playground with applyDiagnostics() and a new "Diagnostics Demo" example showcasing incorrect calls to pow and random.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/language-service/language-service.ts	Adds comprehensive tests for getDiagnostics, covering correct/incorrect arity, nested calls, literals as arguments, severity, source, and range, plus a basic API-existence check.
src/language-service/language-service.types.ts	Extends the public language service types with getDiagnostics, GetDiagnosticsParams, and ArityInfo to describe function arity.
src/language-service/language-service.ts	Implements getDiagnostics on the language service by tokenizing the document, building a FunctionDetails map, and delegating to the new diagnostics module; returns it in the public API object.
src/language-service/language-service.models.ts	Enhances FunctionDetails with arityInfo() that derives (min, max) argument counts from built-in docs (including variadic and optional parameters) or JS function arity as a fallback.
src/language-service/diagnostics.ts	New module that walks token spans, counts function-call arguments with nesting/arrays/objects handled, compares against ArityInfo, and emits LSP Diagnostic objects with accurate ranges, messages, severity, and source.
samples/language-service-sample/examples.js	Adds a "Diagnostics Demo" example expression intentionally using wrong argument counts to surface diagnostics in the playground.
samples/language-service-sample/app.js	Adds applyDiagnostics() to convert LSP diagnostics to Monaco markers and invokes it on expression changes to show argument-count errors in the editor.
index.ts	Re-exports new language service types (GetDiagnosticsParams, ArityInfo) from the package root for public consumption.

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[Copilot]

@copilot Update documentation on the language server

Done in 1705043. Updated docs/language-service.md with:

• Added Diagnostics to the Features section with details on argument validation
• Added getDiagnostics() call to the Basic Usage example
• Updated Monaco playground description to mention the "Diagnostics Demo" example
• Added complete ls.getDiagnostics(params) API reference with parameters, return type, and examples
• Added Monaco Editor integration example showing how to display diagnostics using setModelMarkers
• Updated TypeScript Exported Types to include GetDiagnosticsParams and ArityInfo
• Updated LSP Types to include Diagnostic and DiagnosticSeverity