Cargo check fails to detect an error.

[graylikeme]

When running cargo check it fails to output an error that is detected with cargo build
b_reg is u8 and running stable 1.27.1

error: attempt to shift right with overflow
  --> src\cpu\instructions.rs:39:36
   |
39 |             cpu.flags.half_carry = ((b_reg | 0x0F) - 1) >> 31 > 0;
   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[deny(exceeding_bitshifts)] on by default

[graylikeme]

Opened in cargo repo rust-lang/cargo#5747

[graylikeme]

This is the correct place after all

[estebank]

It seems like cargo check doesn't run the lints by default, which it arguably should.

[ehuss]

There are a few things that are not enabled for --emit=rmeta. There is a general issue for this at #49292 that lists some of the things that are not checked.

[RalfJung]

@ehuss specifically for bitshift lints, there have been some fixes fairly recently (see #70660). Could you try with the latest beta?

[RalfJung]

Sorry, pinged the wrong person -- @graylikeme could you test again with the latest beta?

Also it would help if you could distill this into a self-contained example so that we can reproduce the problem on the playground (https://play.rust-lang.org)

[ehuss]

Here is an example, it passes with cargo check, but fails cargo build, latest nightly rustc 1.45.0-nightly (fa51f810e 2020-04-29).

fn main() {
    let a: u8 = 42;
    let b = ((a | 0x0F) - 1) >> 31 > 0;
    println!("{}", b);
}

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=4998a76829fb44657cd8ed814fb2a191

[RalfJung]

Thanks! This looks like we don't run MIR optimizations with cargo check... #70923 has some more concrete plans for this, so I am closing this here in favor of the other one even though that one is newer. I will post your example there.