TSServer Plugins with sub-packages/paths are not loaded #57047

🔎 Search Terms

"language server", "because only package name is allowed plugin name", "language server plugins"

🕗 Version & Regression Information

This behaviour must be going back to 4.2.2 as per #43124.

⏯ Playground Link

No response

💻 Code

tsconfig.json

{
  "compilerOptions": {
    "plugins": [
      {
        "name": "package/lsp"
      }
    ]
  }
}

🙁 Actual behavior

TypeScript rejects sub-path package plugins, as per:

• TypeScript/src/server/editorServices.ts

  Lines 4490 to 4493 in 23faef9

  	if (!pluginConfigEntry.name || parsePackageName(pluginConfigEntry.name).rest) {
  	this.logger.info(`Skipped loading plugin ${pluginConfigEntry.name || JSON.stringify(pluginConfigEntry)} because only package name is allowed plugin name`);
  	return;
  	}

• and;

  TypeScript/src/compiler/moduleNameResolver.ts

  Lines 2525 to 2531 in 23faef9

  	export function parsePackageName(moduleName: string): { packageName: string; rest: string; } {
  	let idx = moduleName.indexOf(directorySeparator);
  	if (moduleName[0] === "@") {
  	idx = moduleName.indexOf(directorySeparator, idx + 1);
  	}
  	return idx === -1 ? { packageName: moduleName, rest: "" } : { packageName: moduleName.slice(0, idx), rest: moduleName.slice(idx + 1) };
  	}

tsserver log

Info 11   [15:52:00.931] Enabling plugin package/subpath from candidate paths: [...]node_modules/typescript/lib/tsserver.js/../../..
Info 12   [15:52:00.931] Skipped loading plugin package/lsp because only package name is allowed plugin name

🙂 Expected behavior

Plugins are loaded as per either package.json:exports with subfolders specified, or via package/sub-path/package.json or package/sub-path/index.js.

Additional information about the issue

Related issues: #42688 and #42688.

If my understanding is correct, TypeScript only wants to allow packages that:

• have been installed via a package manager, so that opening VSCode without installing doesn't immediately run unauthorised code
• are not relative paths or local code that's checked into a repository

Neither applies to sub-packages. The use-case here is to publish packages that both provide code and an LSP package in one, without splitting this into two packages because of the assertion in TypeScript.