Prevent dependency cycle with -Zthir-unsafeck

[FabianWolff]

Fixes #87414.

r? @LeSeulArtichaut

[LeSeulArtichaut]

AFAICT this PR introduces a correctness hole:

unsafe fn unsf() {}
fn bad<T>() -> Box<dyn Iterator<Item = [(); { unsafe { || { unsf() } }; 4 }]>> { todo!() }
//                                                          ^^^^^^ shouldn't error, but does with this PR

I think the issue in #87414 is rather that the closure tries to run unsafeck for bad instead of bad::{constant#0}, which means that this is incorrect:

rust/compiler/rustc_mir_build/src/check_unsafety.rs

Line 602 in 08095fc

let owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;

This works for closures in functions but apparently misbehaves in constants. The proper fix is probably changing this to use enclosing_body_owner.

@rustbot author

[rustbot]

@FabianWolff

[FabianWolff]

Good point; this should be fixed now (I've also expanded the test case with your example).

@rustbot ready

[rustbot]

@LeSeulArtichaut

[LeSeulArtichaut]

Sorry if I explained badly, I was wondering if using enclosing_body_owner instead of the HirId owner hack was enough to fix the issue, without having special casing on AnonConsts. Can you try that?

[FabianWolff]

Superseded by #87645.