--watch prints messages to stdout, but should print to stderr

[lydell]

Version

v22.12.0

Platform

macOS (but reading the source code of Node.js the issue should be present on any platform)

Subsystem

node/lib/internal/main/watch_mode.js

What steps will reproduce the bug?

echo 'process.stdin.resume()' >index.mjs
node --watch index.mjs 2>/dev/null

In another terminal:

touch index.mjs

How often does it reproduce? Is there a required condition?

Always.

What is the expected behavior? Why is that the expected behavior?

Nothing is printed, since I redirect stderr to /dev/null.

What do you see instead?

Restarting 'index.mjs' is printed (to stdout).

Additional information

How to use stdout and stderr is purely conventional, but the GNU C library says:

stdout: The standard output stream, which is used for normal output from the program.

stderr: The standard error stream, which is used for error messages and diagnostics issued by the program.

I’m making a program that reads input from stdin and writes to stdout. It is a long-lived program: Another program writes to stdin over time, and consumes output from stdout. I use --watch so I can iterate on the sub-program more easily. Unfortunately, --watch writes messages to stdout, causing the consuming program to receive output it does not expect.

I would argue that my program creates the “normal output” while the --watch messages are “diagnostics”.

Here’s one of the places where stdout is used instead of stderr:

node/lib/internal/main/watch_mode.js

Line 139 in 9400eae

process.stdout.write(`${green}Restarting ${kCommandStr}${white}\n`);

Is there a reason for this? Should it be changed to stderr?