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Use subtyping for UnsafeFnPointer coercion, too #129288

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Aug 26, 2024
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Use subtyping for UnsafeFnPointer coercion, too #129288

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4 changes: 2 additions & 2 deletions compiler/rustc_borrowck/src/type_check/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2043,9 +2043,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {

let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(fn_sig);

if let Err(terr) = self.eq_types(
*ty,
if let Err(terr) = self.sub_types(
ty_fn_ptr_from,
*ty,
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can you flip the args and check whether there's an existing test which goes from fail to pass to make sure we check for that potential unsoundness?

r=me after that

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Yes, tests/ui/nll/mir_check_cast_unsafe_fn.rs checks this, which was added 7 years ago:

#![allow(dead_code)]

fn bar<'a>(input: &'a u32, f: fn(&'a u32) -> &'a u32) -> &'static u32 {
    // Here the NLL checker must relate the types in `f` to the types
    // in `g`. These are related via the `UnsafeFnPointer` cast.
    let g: unsafe fn(_) -> _ = f;
    unsafe { g(input) }
    //~^ ERROR lifetime may not live long enough
}

fn main() {}

location.to_locations(),
ConstraintCategory::Cast { unsize_to: None },
) {
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14 changes: 14 additions & 0 deletions tests/ui/coercion/cast-higher-ranked-unsafe-fn-ptr.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
//@ check-pass

fn higher_ranked_fndef(ctx: &mut ()) {}

fn test(higher_ranked_fnptr: fn(&mut ())) {
fn as_unsafe<T>(_: unsafe fn(T)) {}

// Make sure that we can cast higher-ranked fn items and pointers to
// a non-higher-ranked target.
as_unsafe(higher_ranked_fndef);
as_unsafe(higher_ranked_fnptr);
}

fn main() {}
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