If a command fails but does not have stderr/stdout, bootstrap shows no context for what failed

[jieyouxu]

E.g. #144995 (comment)

If we have neither command stdout nor stderr, then

rust/src/bootstrap/src/utils/exec.rs

Lines 748 to 769 in dc0bae1

	fn fail(&self, message: &str, output: CommandOutput) -> ! {
	if self.is_verbose() {
	println!("{message}");
	} else {
	let (stdout, stderr) = (output.stdout_if_present(), output.stderr_if_present());
	// If the command captures output, the user would not see any indication that
	// it has failed. In this case, print a more verbose error, since to provide more
	// context.
	if stdout.is_some() || stderr.is_some() {
	if let Some(stdout) = output.stdout_if_present().take_if(|s| !s.trim().is_empty()) {
	println!("STDOUT:\n{stdout}\n");
	}
	if let Some(stderr) = output.stderr_if_present().take_if(|s| !s.trim().is_empty()) {
	println!("STDERR:\n{stderr}\n");
	}
	println!("Command has failed. Rerun with -v to see more details.");
	} else {
	println!("Command has failed. Rerun with -v to see more details.");
	}
	}
	exit!(1);
	}

we only get the message

Command has failed. Rerun with -v to see more details.

which especially in CI, there's no indication as to what actually failed.

cc @Shourya742 (in case you're interested)

[Kobzol]

Hmm, I remember that we dealt with a similar issue, we made it more verbose, and then someone was complaining that it is too verbose, or something =D But maybe the previous behavior was slightly different and it got lost in the refactoring.

We have like 4 different branches that decide what should the error message look like, and then we throw away the full message unless verbose mode is enabled, hmm. I think that the main problem is that the debug output of the executed command is too long and it's hard to understand what it was doing. But we have the short command description now, so maybe that could be useful.

So, I would suggest:

• Unify the four branches in finish_process, so that we always write the status code, created and executed location, and stdout/stderr, if present.
• If verbose mode is enabled, use the full debug representation of the Command, rather than the short format description.
• Always print this message when failing, even if verbose mode is not enabled.
• If verbose mode is not enabled, add a line that says to use -v to see more information about the command.