`x clippy` implementation is deeply coupled with the core bootstrap

[onur-ozkan]

It's not possible to run x clippy only on certain paths. When running x clippy $tool, clippy starts giving warnings on the entire compiler and library tree as well. Therefore we are unable to run clippy with different set of rules indivudually for each tool/path.

The root cause of this problem is that bootstrap overrides all the commands before invocations with clippy as seen here:

rust/src/bootstrap/src/core/builder.rs

Lines 1291 to 1300 in df8ac8f

	/// Like `cargo`, but only passes flags that are valid for all commands.
	pub fn bare_cargo(
	&self,
	compiler: Compiler,
	mode: Mode,
	target: TargetSelection,
	cmd: &str,
	) -> Command {
	let mut cargo = if cmd == "clippy" {
	self.cargo_clippy_cmd(compiler)

And that is because clippy is sharing the same logic with x check:

rust/src/bootstrap/src/core/builder.rs

Lines 770 to 783 in df8ac8f

	Kind::Check | Kind::Clippy | Kind::Fix => describe!(
	check::Std,
	check::Rustc,
	check::Rustdoc,
	check::CodegenBackend,
	check::Clippy,
	check::Miri,
	check::CargoMiri,
	check::MiroptTestTools,
	check::Rls,
	check::Rustfmt,
	check::RustAnalyzer,
	check::Bootstrap,
	),

To prevent this problem we can create a new build step for clippy and then remove clippy-specific conditions from the core bootstrap flow.