TypeScript 7 VS Code extension: let other extensions send requests to tsc --lsp, like typescript.tsserverRequest

[leonidaz]

VS Code's built-in TypeScript extension lets other extensions send requests to its server with the typescript.tsserverRequest command: built-in requests from a short list, and any request whose name starts with _ (a tsserver plugin can register those). Extensions for content-mapped languages need this, because several commands accept only TypeScript and JavaScript files.

The TypeScript 7 extension has no equivalent. The object its activate returns offers registerContentMappers, onLanguageServerInitialized and initializeAPIConnection (the native API, not the language server's requests), and no command forwards a request to tsc --lsp.

Use cases

From TSRX (.tsrx files, served through a content mapper):

Feature	VS Code's TypeScript (5.9 or 6)	TypeScript 7
Go to Source Definition	TSRX's command sends findSourceDefinition through typescript.tsserverRequest (as a _tsrx: request that its tsserver plugin registers), and it works in .tsrx files	tsc --lsp answers custom/textDocument/sourceDefinition for content-mapped files, but the extension's command accepts only TypeScript and JavaScript language IDs (#64576), and no other extension can send the request
Find File References	same approach possible	not implemented yet (#63806); once it is, TSRX needs a way to ask for it on a .tsrx file

With a way to send requests, an extension could offer these features for its own files without waiting for each command to accept content-mapped languages.

Suggestion

A way for an extension to send a request to tsc --lsp, for example:

• sendRequest(method, params, token) on the API object, or
• a typescript.native-preview.sendRequest command, like typescript.tsserverRequest.

It could be limited to documents of the content mappers that the calling extension registered with registerContentMappers, or to custom/* methods.

Found while adding TypeScript 7 support for .tsrx files (tsrx-org/tsrx#136).