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Check unnormalized signature on pointer cast

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This commit is contained in:
Michael Goulet 2024-08-13 17:38:24 -04:00
parent eb33b43bab
commit e8472e84e3
7 changed files with 127 additions and 13 deletions
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79
compiler/rustc_borrowck/src/type_check/mod.rs
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@ -1979,19 +1979,42 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
match cast_kind {
CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer) => {
let fn_sig = op.ty(body, tcx).fn_sig(tcx);
let src_sig = op.ty(body, tcx).fn_sig(tcx);
// The type that we see in the fcx is like
// `foo::<'a, 'b>`, where `foo` is the path to a
// function definition. When we extract the
// signature, it comes from the `fn_sig` query,
// and hence may contain unnormalized results.
let fn_sig = self.normalize(fn_sig, location);
let ty_fn_ptr_from = Ty::new_fn_ptr(tcx, fn_sig);
// HACK: This shouldn't be necessary... We can remove this when we actually
// get binders with where clauses, then elaborate implied bounds into that
// binder, and implement a higher-ranked subtyping algorithm that actually
// respects these implied bounds.
//
// This protects against the case where we are casting from a higher-ranked
// fn item to a non-higher-ranked fn pointer, where the cast throws away
// implied bounds that would've needed to be checked at the call site. This
// only works when we're casting to a non-higher-ranked fn ptr, since
// placeholders in the target signature could have untracked implied
// bounds, resulting in incorrect errors.
//
// We check that this signature is WF before subtyping the signature with
// the target fn sig.
if src_sig.has_bound_regions()
&& let ty::FnPtr(target_fn_tys, target_hdr) = *ty.kind()
&& let target_sig = target_fn_tys.with(target_hdr)
&& let Some(target_sig) = target_sig.no_bound_vars()
{
let src_sig = self.infcx.instantiate_binder_with_fresh_vars(
span,
BoundRegionConversionTime::HigherRankedType,
src_sig,
);
let src_ty = Ty::new_fn_ptr(self.tcx(), ty::Binder::dummy(src_sig));
self.prove_predicate(
ty::ClauseKind::WellFormed(src_ty.into()),
location.to_locations(),
ConstraintCategory::Cast { unsize_to: None },
);
let src_ty = self.normalize(src_ty, location);
if let Err(terr) = self.sub_types(
ty_fn_ptr_from,
src_ty,
*ty,
location.to_locations(),
ConstraintCategory::Cast { unsize_to: None },
@ -2000,7 +2023,41 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
self,
rvalue,
"equating {:?} with {:?} yields {:?}",
ty_fn_ptr_from,
target_sig,
src_sig,
terr
);
};
}
let src_ty = Ty::new_fn_ptr(tcx, src_sig);
// HACK: We want to assert that the signature of the source fn is
// well-formed, because we don't enforce that via the WF of FnDef
// types normally. This should be removed when we improve the tracking
// of implied bounds of fn signatures.
self.prove_predicate(
ty::ClauseKind::WellFormed(src_ty.into()),
location.to_locations(),
ConstraintCategory::Cast { unsize_to: None },
);
// The type that we see in the fcx is like
// `foo::<'a, 'b>`, where `foo` is the path to a
// function definition. When we extract the
// signature, it comes from the `fn_sig` query,
// and hence may contain unnormalized results.
let src_ty = self.normalize(src_ty, location);
if let Err(terr) = self.sub_types(
src_ty,
*ty,
location.to_locations(),
ConstraintCategory::Cast { unsize_to: None },
) {
span_mirbug!(
self,
rvalue,
"equating {:?} with {:?} yields {:?}",
src_ty,
ty,
terr
);

11
tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance-early-bound.rs Normal file
View File

@ -0,0 +1,11 @@
static UNIT: &'static &'static () = &&();
fn foo<'a: 'a, 'b: 'b, T>(_: &'a &'b (), v: &'b T) -> &'a T { v }
fn bad<'a, T>(x: &'a T) -> &'static T {
let f: fn(_, &'a T) -> &'static T = foo;
//~^ ERROR lifetime may not live long enough
f(UNIT, x)
}
fn main() {}

10
tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance-early-bound.stderr Normal file
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@ -0,0 +1,10 @@
error: lifetime may not live long enough
--> $DIR/implied-bounds-on-nested-references-plus-variance-early-bound.rs:6:12
|
LL | fn bad<'a, T>(x: &'a T) -> &'static T {
| -- lifetime `'a` defined here
LL | let f: fn(_, &'a T) -> &'static T = foo;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
error: aborting due to 1 previous error

17
tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance-unnormalized.rs Normal file
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@ -0,0 +1,17 @@
trait ToArg<T> {
type Arg;
}
impl<T, U> ToArg<T> for U {
type Arg = T;
}
fn extend_inner<'a, 'b>(x: &'a str) -> <&'b &'a () as ToArg<&'b str>>::Arg { x }
fn extend<'a, 'b>(x: &'a str) -> &'b str {
(extend_inner as fn(_) -> _)(x)
//~^ ERROR lifetime may not live long enough
}
fn main() {
let y = extend(&String::from("Hello World"));
println!("{}", y);
}

14
tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance-unnormalized.stderr Normal file
View File

@ -0,0 +1,14 @@
error: lifetime may not live long enough
--> $DIR/implied-bounds-on-nested-references-plus-variance-unnormalized.rs:10:5
|
LL | fn extend<'a, 'b>(x: &'a str) -> &'b str {
| -- -- lifetime `'b` defined here
| |
| lifetime `'a` defined here
LL | (extend_inner as fn(_) -> _)(x)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
|
= help: consider adding the following bound: `'a: 'b`
error: aborting due to 1 previous error

7
tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance.rs
View File

@ -1,15 +1,10 @@
//@ check-pass
//@ known-bug: #25860
// Should fail. The combination of variance and implied bounds for nested
// references allows us to infer a longer lifetime than we can prove.
static UNIT: &'static &'static () = &&();
fn foo<'a, 'b, T>(_: &'a &'b (), v: &'b T) -> &'a T { v }
fn bad<'a, T>(x: &'a T) -> &'static T {
let f: fn(_, &'a T) -> &'static T = foo;
//~^ ERROR lifetime may not live long enough
f(UNIT, x)
}

10
tests/ui/implied-bounds/implied-bounds-on-nested-references-plus-variance.stderr Normal file
View File

@ -0,0 +1,10 @@
error: lifetime may not live long enough
--> $DIR/implied-bounds-on-nested-references-plus-variance.rs:6:12
|
LL | fn bad<'a, T>(x: &'a T) -> &'static T {
| -- lifetime `'a` defined here
LL | let f: fn(_, &'a T) -> &'static T = foo;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
error: aborting due to 1 previous error