Allow to suppress --inspect hint

[segrey]

When started with inspector protocol, node emits messages relevant for debugging in Chrome DevTools:

node --inspect=48235 --debug-brk test.js
Debugger listening on port 48235.
Warning: This is an experimental feature and could change at any time.
To start debugging, open the following URL in Chrome:
    chrome-devtools://devtools/bundled/inspector.html?experiments=true&v8only=true&ws=127.0.0.1:48235/c80523d4-0bd2-4e43-8af0-8dc75f12eeb3

However, these messages are not relevant when debugging using a tool (e.g. IDE) that connects to the debug port immediately.
It would be nice if it would be possible to suppress the hint. Possible ways:

1. Check some environment variable (not great, but possible)
2. Or print the hint text only if no connections within 1-2 seconds (that should be enough time for a tool to connect).

• Version: 7.9.0
• Platform: Linux segrey-desktop 3.19.0-32-generic 37~14.04.1-Ubuntu SMP Thu Oct 22 09:41:40 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
• Subsystem: debugger

[segrey]

Currently, tools can analyze stderr stream and chop off the messages. Since messages format is not strictly defined, it looks like a guessing on tools' side. E.g. hint text format is going to be changed in #11207.

[Fishrock123]

I think you can --debug-brk and then send a SIGUSR1 signal?

[cjihrig]

On current master, it looks like --debug and --debug-brk no longer exist. I think there is some ongoing discussion about those flags, but right now I'm getting "bad option"

[segrey]

@cjihrig Correct, on current master no --debug-brk. The issue can be reproduced without --debug-brk as well.

[cjihrig]

Right. @Fishrock123 was proposing an existing solution to the problem.

[segrey]

@cjihrig Thank you for looking into it and the PR! What do you think about postponing printing the hint text for some time to let tools connect the the port? Seems there is already a logic that prints the hint when a client disconnects.

[cjihrig]

If you mean adding an arbitrary timeout before printing, I'm -1 on that idea. It's difficult to add testing for, and can be affected by the machine (as we've seen in our own CI).

[segrey]

Might be helpful for VSCode /cc @roblourens

[roblourens]

Yeah, currently VS Code snips out the message from the output stream. I probably wouldn't use --inspect-silent at least for awhile, because of edge cases in determining whether we are launching a version of node that supports it (same issues from #12364).

[segrey]

Right, makes sense.

[segrey]

@Fishrock123 IIUC, passing --debug-brk (and signaling a process with SIGUSR1) will enable old protocol. Here inspector protocol is targeted.

[Trott]

This is still an issue, right? No canonical way to squelch the output? Or should this be closed?

[cjihrig]

I closed #12671 without merging because we couldn't really decide how this should be implemented. I'm happy to reopen it if we come up with a plan first.