Move cargo-clippy into cargo

[Manishearth]

See rust-lang/cargo#6664 (comment) for some context.

Currently cargo clippy is a thin wrapper script around Cargo that invokes cargo check with a RUSTC_WRAPPER: https://github.com/rust-lang/rust-clippy/blob/8dfabdf11c6cdaffd7c6e6552a6ead8d52c49b10/src/main.rs

It does some additional hacks to support the clippy dogfood test and passing down arguments.

We should move this into cargo proper, like rustc: Ideally it's just a copy of cargo check that sets a different rustc executable (temporarily can be done by overriding RUSTC_WRAPPER, but the better solution probably involves modifying config.rustc() https://github.com/rust-lang/cargo/blob/716b02cb4c7b75ce435eb06defa25bc2d725909c/src/cargo/util/config.rs#L194-L215

Steps:

• Add cargo clippy-preview to cargo Cargo clippy cargo#6759
• Make it work with dogfood tests Update dogfood tests to use cargo clippy-preview #4050
• Improve cargo integration, especially with cargo fix call clippy-driver directly rather than as a rustc_wrapper cargo#7006
• add better help Better help support in clippy-driver #4173
• Make cargo-clippy shell out to clippy-preview?
• Perhaps make -Wlintname work as a shortcut for -Wclippy::lintname
• rename and stabilize cargo clippy-preview

[Manishearth]

I think as a first step we should write a very basic cargo clippy-preview (nightly only?) subcommand for cargo that just is a copy of cargo check with rustc_wrapper set. We can also clean it up to make this part of the config.

We can then do the back and forth of testing it with clippy to ensure it works, and eventually rename and ship it. We should probably continue to ship cargo-clippy for a couple releases since in some cases you use a cargo from an older release.

Once we have this there are a bunch of nice changes we can make: e.g. we can modify the argument parsing so that you can just do cargo clippy -Wclippy::foo instead of needing the pesky --.

This also helps integration with cargo fix, since that can now be wholly solved on the cargo side.

[Manishearth]

One implementation issue is that rustup currently does not export a clippy-driver binary, we should change it to do this.

[Manishearth]

This could also be handled by using the current exe path I guess.

[Manishearth]

Filed rust-lang/rustup#1678

I do have concerns as to how this will work for non-rustup users.

[Manishearth]

@yaahallo is looking into implementing this

[Manishearth]

Shouldn't have been closed