TSPerf Type Lens

TSPerf Type Lens is an MIT-licensed VS Code extension for inspecting TypeScript type-checker latency and structural type complexity at the cursor.

It is built for the Algora TSPerf challenge: build a VS Code plugin that shows the complexity and time to load of a TypeScript type.

Features

• TSPerf: Inspect Type at Cursor measures the selected node with the TypeScript compiler API.
• Inline editor decoration shows TSPerf <ms> | score <n> next to the inspected symbol.
• Output channel reports file, node kind, type text, program build time, type resolution time, cache state, and score factors.
• TSPerf: Benchmark Current File walks representative identifiers in the active file and reports average, p95, and max type resolution time.
• TSPerf: Clear Measurement Cache resets warm measurements.

How It Works

The extension finds the nearest tsconfig.json for the active file and builds a TypeScript Program. If no config exists, it creates a single-file program with strict defaults. It then maps the VS Code cursor position to a TypeScript AST node, calls checker.getTypeAtLocation, and scores the returned type from:

flowchart LR
  A[VS Code cursor] --> B[Nearest TypeScript AST node]
  B --> C[tsconfig-aware Program]
  C --> D[TypeChecker getTypeAtLocation]
  D --> E[Latency measurement]
  D --> F[Structural complexity score]
  E --> G[Inline editor lens]
  F --> G
  E --> H[Output channel benchmark report]
  F --> H
  G --> I[Cold and warm cache comparison]
  H --> I

Loading

• union and intersection breadth
• property count
• call and construct signatures
• generic type arguments
• recursive child-type depth
• rendered type length

Measurements are cached by file URI, document version, cursor offset, and TypeScript compiler option signature so repeated inspections distinguish cold and warm paths.

Development

npm install
npm run check
npm run build
npm run package
npm run verify:package

Install the generated .vsix with:

code --install-extension tsperf-type-lens-0.1.2.vsix

Challenge Submission Evidence

This repository includes:

• source for a functional VS Code extension
• MIT license
• architecture visual and Mermaid flow for fast reviewer orientation
• benchmark fixture under fixtures/pathological-types.ts
• TypeScript build configuration
• VSIX packaging script
• package verification that rejects dependency folders, source folders, and macOS AppleDouble metadata from the generated VSIX