Need support for a "--headless-hosted-plugin-inspect" backend cmdline argument

[jcortell68]

Bug Description:

We need support for a --headless-hosted-plugin-inspect (or similar name) backend cmdline argument that will tell the headless plugin-host to listen on that port for a debug attachment. Today, both plugin hosts seem to be affected by the traditional --hosted-plugin-inspect argument, but clearly only one can listen on that port. So the first plugin-host to run gets the port and the other plugin-host becomes un-debuggable. As the headless plugin host always runs first, that's the winner.

Note: the notion of headless plugins was introduced in Theia 1.46.0.

Additional Info
Today I tried debugging a headless plugin using VS Code but in an environment focused on just the plugin developer instead of a Theia app developer that is also developing a plugin. Additionally, the plugin package being developed contributes both a standard plugin (runs in Node.js but interacts with app's frontend) and a headless plugin (runs in Node.js but interacts with app's backend).

Under the covers, there is a plugin-host process for the standard plugins (one for each connected frontend), and a single plugin-host process for all the headless plugins

The way you historically use VSCode to debug a plugin in this plugin-centric type of environment is to launch the app's backend using --hosted-plugin-inspect=<port>, then use a launch config in VS Code like this

{
    "type": "node",
    "request": "attach",
    "name": "Attach to Plugin Host",
    "port": <port>,
    ...
}

But as described earlier, only one of the two plugin-host processes will get to use the port specified via --hosted-plugin-inspect--the first plugin-host to run.

We should have a switch specifically for the headless plugin-host, reserving the current one for the standard plugin host.

Steps to Reproduce:

git clone -b std_and_headless_plugins https://github.com/jcortell68/theiasandbox
cd theiasandbox
yarn
yarn start:electron --hosted-plugin-inspect=9339

1. In VS Code, launch the Attach to Plugin Host launch configuration.
2. Set a breakpoint on the "heartbeat" lines of

• myext\src\extension-headless.ts
• myext\src\extension.ts

3. Notice that only the extension-headless.ts breakpoint resolves and is hit

To prove that both plugin-hosts competed for the debug port, remove these lines from package.json

  "theiaPlugin": {
    "headless": "./dist/extension-headless.js"
  },

That will make the plugin-package have just a standard plugin. You'll see that its breakpoint is now hit.

As further proof, the log/console has this:

2024-03-14T13:10:04.417Z root ERROR [hosted-plugin: 15948] Starting inspector on 127.0.0.1:9339 failed: address already in use

Additional Information

• Operating System: Windows
• Theia Version: 1.47.1

[jcortell68]

Some pointers to the Theia code:

hosted-instance-manager.ts

hosted-plugin-preferences.ts

hosted-plugin-process.ts

[jcortell68]

@cdamus FYI

[jcortell68]

Update: we moved our product to the latest Theia yesterday. I updated our vscode launch configs to make use of this new argument. Debugging of both standard and headless plugins now works. Thanks!