Don't require a normal tool build of clippy/rustfmt when running their test steps

[jieyouxu]

This is redundant and wasteful.

Noticed in #147372 (comment).

[rustbot]

r? @Zalathar

rustbot has assigned @Zalathar.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[jieyouxu]

Sure. I agree the current wording is confusing, let me reword it.

[jieyouxu]

Reworded PR title/commit message as suggested.

[Zalathar]

Historical note: For rustfmt, this redundancy seems to date all the way back to the introduction of its test step, which at that time was a “check” step:

• Add Rustfmt #44533

So at the time it was probably motivated by wanting to “test” as much as possible in CI in one step. Nowadays we would prefer the test step to only invoke cargo test; if building the tool normally fails then some other step will catch that.

[Zalathar]

I'm not very familiar with compiler staging of these tools, so hopefully you've done your homework. 😅

Let's also consult a try job that runs tests in stage 1, to augment PR CI:

@bors try jobs=x86_64-gnu-llvm-20-3

[jieyouxu]

I'm not very familiar with compiler staging of these tools, so hopefully you've done your homework.

These should still be right, because they (rustfmt/clippy both being rustc_private tools) now use the RustcPrivateCompilers helper type which captures the {build_compiler,target_compiler} distinctions (where 2 compilers are involved!)

rust/src/bootstrap/src/core/build_steps/tool.rs

Lines 1324 to 1342 in 83e49b7

	/// Represents which compilers are involved in the compilation of a tool
	/// that depends on compiler internals (`rustc_private`).
	/// Their compilation looks like this:
	///
	/// - `build_compiler` (stage N-1) builds `target_compiler` (stage N) to produce .rlibs
	/// - These .rlibs are copied into the sysroot of `build_compiler`
	/// - `build_compiler` (stage N-1) builds `<tool>` (stage N)
	/// - `<tool>` links to .rlibs from `target_compiler`
	///
	/// Eventually, this could also be used for .rmetas and check builds, but so far we only deal with
	/// normal builds here.
	#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
	pub struct RustcPrivateCompilers {
	/// Compiler that builds the tool and that builds `target_compiler`.
	build_compiler: Compiler,
	/// Compiler to which .rlib artifacts the tool links to.
	/// The host target of this compiler corresponds to the target of the tool.
	target_compiler: Compiler,
	}

[Zalathar]

r=me when PR+try is green.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 981a0d1 (981a0d1725813fff9e47ad07e66b18ceaec26af5, parent: 83e49b75e7daf827e4390ae0ccbcb0d0e2c96493)

[jieyouxu]

Both PR+try are green.

@bors r=Zalathar rollup

[jieyouxu]

Both PR+try are green.

@bors r=Zalathar rollup

[bors]

📌 Commit 4d21e76 has been approved by Zalathar

It is now in the queue for this repository.

[bors]

📌 Commit 4d21e76 has been approved by Zalathar

It is now in the queue for this repository.