bootstrap: `--warnings warn` doesn't apply to bootstrap itself

[matthiaskrgr]

Bootstrapping with RUSTFLAGS="-Wsomething that warns ./x.py check --warnings warn does not work; a warning inside bootstrap will still abort the compilation process:

error: trivial numeric cast: `u32` as `u32`
   --> src/bootstrap/lib.rs:156:31
    |
156 |             libc::setpriority(libc::PRIO_PGRP as _, 0, 10);
    |                               ^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D trivial-numeric-casts` implied by `-D warnings`
    = help: cast can be replaced by coercion; this might require a temporary variable

error: aborting due to previous error

error: could not compile `bootstrap`.

EDIT: well, putting --cap-lints warn into RUSTFLAGS works but it seems very unintuitive.

[Mark-Simulacrum]

x.py doesn't check the warnings flag, but you can set deny-warnings in config.toml to false to patch around this.

[jyn514]

Mentoring instructions: Add a --warnings flag to bootstrap.py around

rust/src/bootstrap/bootstrap.py

Lines 833 to 842 in 043c634

	def parse_args():
	"""Parse the command line arguments that the python script needs."""
	parser = argparse.ArgumentParser(add_help=False)
	parser.add_argument('-h', '--help', action='store_true')
	parser.add_argument('--config')
	parser.add_argument('--build-dir')
	parser.add_argument('--build')
	parser.add_argument('--color', choices=['always', 'never', 'auto'])
	parser.add_argument('--clean', action='store_true')
	parser.add_argument('-v', '--verbose', action='count', default=0)

and check it when building bootstrap, around

rust/src/bootstrap/bootstrap.py

Lines 778 to 788 in 043c634

	if self.use_locked_deps:
	args.append("--locked")
	if self.use_vendored_sources:
	args.append("--frozen")
	if self.get_toml("metrics", "build"):
	args.append("--features")
	args.append("build-metrics")
	if color == "always":
	args.append("--color=always")
	elif color == "never":
	args.append("--color=never")