"exceeding bitshifts" lint does not always work in debug mode on playground

[RalfJung]

I tried this code:

#![crate_type = "lib"]
pub fn foo(x: i32) -> i32 {
    x << 33
}

I am building in debug mode on the playground.

I expected to see this happen: it should warn about the exceeding bitshift (like it does in release mode).

Instead, this happened: there is no warning,

Meta

Possibly related to #69021

[RalfJung]

I am quite puzzled why this does not get caught by this test which I added specifically to catch cases like this. Isn't the "noopt" revision equivalent to debug mode?

// revisions: noopt opt opt_with_overflow_checks
//[noopt]compile-flags: -C opt-level=0
//[opt]compile-flags: -O
//[opt_with_overflow_checks]compile-flags: -C overflow-checks=on -O

[RalfJung]

Oh, well that is strange... when I locally just run rustc on the same code (with no flags), I get the expected warning.

@shepmaster what is the exact invocation that playground uses with "Debug" mode to build the code?

[RalfJung]

Oh lol, I only checked stable Rust; this got fixed by one of my PRs from February and those are not on stable yet... d'oh.

[RalfJung]

Also, we have to make sure that there always is some ICE we can trigger in rustc, because that's a good way to get the actual compiler flags. ;)

[shepmaster]

there always is some ICE we can trigger in rustc

Isn’t that what break rust is for?

fn main() {
    break rust;
}

error: internal compiler error: It looks like you're trying to break rust; would you like some ICE?

note: the compiler expectedly panicked. this is a feature.

note: we would appreciate a joke overview: https://github.com/rust-lang/rust/issues/43162#issuecomment-320764675

[RalfJung]

@shepmaster yeah but see #70661