Supporting Closed-File Diagnostics in VS Code

Core Problem

Project-wide diagnostics are a highly requested feature for VS Code's JavaScript/TypeScript support, but the TS server's single-threaded nature poses a significant challenge. This limitation can interrupt normal user operations like code completions, hindering effective project-wide error reporting.

Solution & Analysis

To overcome this limitation, we've explored various solutions, including using tasks to run diagnostics in separate processes. However, this approach is not widely adopted due to its complexity and overhead. Instead, we've introduced a new setting that spins up a dedicated TS Server for diagnostics, as demonstrated by the commit f0942786b4ee338f02449e2e5751091e028eb898. This setup enables project-wide error reporting without relying on tasks or the compileOnSave feature.

API: Inverse Dependencies

To improve performance and scalability, we're introducing an API that returns a list of inverse dependencies for a given file. Specifically, this API will provide a list of files that need to be rechecked after changes to the original file. We believe this API is similar to compileOnSaveAffectedFileList, but with some key differences.

The proposed API will allow users to retrieve the list of affected files without relying on the compileOnSave feature, enabling project-wide error reporting even when compileOnSave is disabled.

Code Example

// ts-diagnostics.ts

interface InverseDependencies {
  [filePath: string]: string[];
}

async function getInverseDependencies(filePath: string): Promise<InverseDependencies> {
  const tsServerUrl = getTServerUrl();
  const response = await fetch(`${tsServerUrl}/diagnostics/inverse-dependencies`, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ filePath }),
  });

  if (!response.ok) {
    throw new Error(`Failed to retrieve inverse dependencies for ${filePath}`);
  }

  const data = await response.json();
  return data.inverseDependencies;
}

// ts-diagnostics.ts (continued)

Using the API

To use this API, simply call the getInverseDependencies function and pass the file path as an argument. The function will return a promise that resolves to an object containing the list of inverse dependencies for the given file.

const filePath = 'path/to/file.ts';
getInverseDependencies(filePath)
  .then((inverseDependencies) => {
    console.log(inverseDependencies); // Output: { file1.ts: ['file2.ts', 'file3.ts'] }
  })
  .catch((error) => {
    console.error(error);
  });

Conclusion

By introducing an API that returns inverse dependencies for a given file, we're providing a more efficient and scalable solution for project-wide diagnostics in VS Code. This API allows users to retrieve the list of affected files without relying on tasks or the compileOnSave feature, enabling effective project-wide error reporting even when these features are disabled.

Reference

• Source