debug: support "console" property in launch.json (RunInTerminal)

[ramya-rao-a]

From microsoft/vscode-go#843

Please support "console" Property in launch.json, which have "none", "integratedTerminal", "externalTerminal" three Value like python's, and I can debug my go project at outside console and also support standard input.

This feature request has a lot of upvotes microsoft/vscode-go#843, please follow the discussion there for more context and user scenarios where this feature would be relevant

[hyangah]

I managed to prototype this and let vscode launch the headless delve server in the terminal using DAP RunInTerminal request.
I still need to figure out a reliable way to address the race occurred when the debug adapter tries to connect to the headless server. DAP RunInTerminal response sometime arrives before the delve headless server is ready to accept the request. When the connection attempt is made too early, the json-rpc2 seems to be hung silently. Since json-rpc2 is not under active maintenance mode, we may need to consider switching the underlying json rpc package (#113)

cc/ @suzmue @polinasok

[gopherbot]

Change https://golang.org/cl/268461 mentions this issue: src/debugAdapter: implement runInTerminal

[JCzz]

Any progress on this?

[polinasok]

@hyangah

I managed to prototype this and let vscode launch the headless delve server in the terminal using DAP RunInTerminal request. I still need to figure out a reliable way to address the race occurred when the debug adapter tries to connect to the headless server. DAP RunInTerminal response sometime arrives before the delve headless server is ready to accept the request.

What is the sequence of requests/responses here? Something like this?

[from client to DA] Launch request with console set to terminal
[from DA to client] RunInTerminal request with dlv command
   client starts dlv
[from client to DA] RunInTerminal response
   DA tries tries to connect to dlv, but dlv is not yet responsive

Can you not introduce a delay like we do in the regular adapter:

vscode-go/src/debugAdapter/goDebug.ts

Lines 697 to 709 in bc20520

	function connectClient(port: number, host: string) {
	// Add a slight delay to avoid issues on Linux with
	// Delve failing calls made shortly after connection.
	setTimeout(() => {
	const client = Client.$create(port, host);
	client.connectSocket((err, conn) => {
	if (err) {
	return reject(err);
	}
	return resolve(conn);
	});
	client.on('error', reject);
	}, 200);

?

[polinasok]

The integratedTerminal and externalTerminal modes are powered by RunInTerminal request. This is advertised as the mechanism for debugging applications that "read from an interactive terminal and/or need to control their output on the terminal" (source, source).

For a high level summary, here are the use cases mentioned by the users in relationship to the request for console=*Terminal feature:

1. debugging with interactive stdin
   Examples: Please support "console" Property in launch.json microsoft/vscode-go#843 (comment), Cannot debug programs which read from STDIN microsoft/vscode-go#219
   Stdin cannot be entered into the Debug console. Hence, there is a need for an interactive terminal where it can be entered instead. Plain dlv makes this possible, but the user must start a dlv --headless server in one terminal (this is where stdin will go) and a client with dlv connect in another terminal (this is where debug commands will go). Hence, the workaround (mentioned at Please support "console" Property in launch.json microsoft/vscode-go#843 (comment) and Please support "console" Property in launch.json microsoft/vscode-go#843 (comment)) is to launch a headless dlv server in a terminal manually and then use remote attach in vscode to connect to it.
2. debugging interactive applications
   Examples: Please support "console" Property in launch.json microsoft/vscode-go#843 (comment), Simple ui debugging - not working #863, Unable to debug terminal user interface microsoft/vscode-go#2151
   A workaround (mentioned in Please support "console" Property in launch.json microsoft/vscode-go#843 (comment)) involves starting the application in a terminal and then using local attach.
3. redirecting output
   Examples: Debugger output and application stdout have to be splitted microsoft/vscode-go#2204
   In case of launch or local attach, dlv is started from the debug adapter, so its output is mixed with the logging and error messages from the adapter in Debug Console. Similarly to 1, a workaround to separate these is to start dlv manually in a separate terminal and then connect to it with remote attach from vscode. In that case dlv's and launched program output would end up in the terminal and not in Debug Console.
4. running delve with root priviledges
   Examples: debug: abiltiy to debug with root privileges #558, debug the golang project use root privilege microsoft/vscode-go#2889

Of course, the workarounds do not offer a great user experience. But in the absence of the console option, the users are asking if we could offer some shortcuts for these workarounds via the extra extension settings and features. In the meantime, dlv added new options that look related --allow-non-terminal-interactive, --tty, -r (https://github.com/go-delve/delve/blob/master/Documentation/usage/dlv_redirect.md).