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Auto merge of #107728 - RalfJung:miri-dyn-star, r=RalfJung,oli-obk

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Miri: basic dyn* support

As usual I am very unsure about the dynamic dispatch stuff, but it passes even the `Pin<&mut dyn* Trait>` test so that is something.

TBH I think it was a mistake to make `dyn Trait` and `dyn* Trait` part of the same `TyKind` variant. Almost everywhere in Miri this lead to the wrong default behavior, resulting in strange ICEs instead of nice "unimplemented" messages. The two types describe pretty different runtime data layout after all.

Strangely I did not need to do the equivalent of [this diff](https://github.com/rust-lang/rust/pull/106532#discussion_r1087095963) in Miri. Maybe that is because the unsizing logic matches on `ty::Dynamic(.., ty::Dyn)` already? In `unsized_info` I don't think the `target_dyn_kind` can be `DynStar`, since then it wouldn't be unsized!

r? `@oli-obk` Cc `@eholk` (dyn-star) https://github.com/rust-lang/rust/issues/102425
This commit is contained in:
bors 2023-02-21 04:22:23 +00:00
commit f715e430aa
18 changed files with 320 additions and 85 deletions
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107
compiler/rustc_const_eval/src/interpret/terminator.rs
View file

@ -547,7 +547,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
let receiver_place = loop {
match receiver.layout.ty.kind() {
ty::Ref(..) | ty::RawPtr(..) => break self.deref_operand(&receiver)?,
ty::Dynamic(..) => break receiver.assert_mem_place(), // no immediate unsized values
ty::Dynamic(.., ty::Dyn) => break receiver.assert_mem_place(), // no immediate unsized values
ty::Dynamic(.., ty::DynStar) => {
// Not clear how to handle this, so far we assume the receiver is always a pointer.
span_bug!(
self.cur_span(),
"by-value calls on a `dyn*`... are those a thing?"
);
}
_ => {
// Not there yet, search for the only non-ZST field.
let mut non_zst_field = None;
@ -573,39 +580,59 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
}
}
};
// Obtain the underlying trait we are working on.
let receiver_tail = self
.tcx
.struct_tail_erasing_lifetimes(receiver_place.layout.ty, self.param_env);
let ty::Dynamic(data, ..) = receiver_tail.kind() else {
span_bug!(self.cur_span(), "dynamic call on non-`dyn` type {}", receiver_tail)
};
// Get the required information from the vtable.
let vptr = receiver_place.meta.unwrap_meta().to_pointer(self)?;
let (dyn_ty, dyn_trait) = self.get_ptr_vtable(vptr)?;
if dyn_trait != data.principal() {
throw_ub_format!(
"`dyn` call on a pointer whose vtable does not match its type"
);
}
// Obtain the underlying trait we are working on, and the adjusted receiver argument.
let (vptr, dyn_ty, adjusted_receiver) = if let ty::Dynamic(data, _, ty::DynStar) =
receiver_place.layout.ty.kind()
{
let (recv, vptr) = self.unpack_dyn_star(&receiver_place.into())?;
let (dyn_ty, dyn_trait) = self.get_ptr_vtable(vptr)?;
if dyn_trait != data.principal() {
throw_ub_format!(
"`dyn*` call on a pointer whose vtable does not match its type"
);
}
let recv = recv.assert_mem_place(); // we passed an MPlaceTy to `unpack_dyn_star` so we definitely still have one
(vptr, dyn_ty, recv.ptr)
} else {
// Doesn't have to be a `dyn Trait`, but the unsized tail must be `dyn Trait`.
// (For that reason we also cannot use `unpack_dyn_trait`.)
let receiver_tail = self
.tcx
.struct_tail_erasing_lifetimes(receiver_place.layout.ty, self.param_env);
let ty::Dynamic(data, _, ty::Dyn) = receiver_tail.kind() else {
span_bug!(self.cur_span(), "dynamic call on non-`dyn` type {}", receiver_tail)
};
assert!(receiver_place.layout.is_unsized());
// Get the required information from the vtable.
let vptr = receiver_place.meta.unwrap_meta().to_pointer(self)?;
let (dyn_ty, dyn_trait) = self.get_ptr_vtable(vptr)?;
if dyn_trait != data.principal() {
throw_ub_format!(
"`dyn` call on a pointer whose vtable does not match its type"
);
}
// It might be surprising that we use a pointer as the receiver even if this
// is a by-val case; this works because by-val passing of an unsized `dyn
// Trait` to a function is actually desugared to a pointer.
(vptr, dyn_ty, receiver_place.ptr)
};
// Now determine the actual method to call. We can do that in two different ways and
// compare them to ensure everything fits.
let Some(ty::VtblEntry::Method(fn_inst)) = self.get_vtable_entries(vptr)?.get(idx).copied() else {
throw_ub_format!("`dyn` call trying to call something that is not a method")
};
trace!("Virtual call dispatches to {fn_inst:#?}");
if cfg!(debug_assertions) {
let tcx = *self.tcx;
let trait_def_id = tcx.trait_of_item(def_id).unwrap();
let virtual_trait_ref =
ty::TraitRef::from_method(tcx, trait_def_id, instance.substs);
assert_eq!(
receiver_tail,
virtual_trait_ref.self_ty(),
"mismatch in underlying dyn trait computation within Miri and MIR building",
);
let existential_trait_ref =
ty::ExistentialTraitRef::erase_self_ty(tcx, virtual_trait_ref);
let concrete_trait_ref = existential_trait_ref.with_self_ty(tcx, dyn_ty);
@ -620,17 +647,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
assert_eq!(fn_inst, concrete_method);
}
// `*mut receiver_place.layout.ty` is almost the layout that we
// want for args[0]: We have to project to field 0 because we want
// a thin pointer.
assert!(receiver_place.layout.is_unsized());
let receiver_ptr_ty = self.tcx.mk_mut_ptr(receiver_place.layout.ty);
let this_receiver_ptr = self.layout_of(receiver_ptr_ty)?.field(self, 0);
// Adjust receiver argument.
args[0] = OpTy::from(ImmTy::from_immediate(
Scalar::from_maybe_pointer(receiver_place.ptr, self).into(),
this_receiver_ptr,
));
// Adjust receiver argument. Layout can be any (thin) ptr.
args[0] = ImmTy::from_immediate(
Scalar::from_maybe_pointer(adjusted_receiver, self).into(),
self.layout_of(self.tcx.mk_mut_ptr(dyn_ty))?,
)
.into();
trace!("Patched receiver operand to {:#?}", args[0]);
// recurse with concrete function
self.eval_fn_call(
@ -659,15 +681,24 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// implementation fail -- a problem shared by rustc.
let place = self.force_allocation(place)?;
let (instance, place) = match place.layout.ty.kind() {
ty::Dynamic(..) => {
let place = match place.layout.ty.kind() {
ty::Dynamic(_, _, ty::Dyn) => {
// Dropping a trait object. Need to find actual drop fn.
let place = self.unpack_dyn_trait(&place)?;
let instance = ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
(instance, place)
self.unpack_dyn_trait(&place)?.0
}
ty::Dynamic(_, _, ty::DynStar) => {
// Dropping a `dyn*`. Need to find actual drop fn.
self.unpack_dyn_star(&place.into())?.0.assert_mem_place()
}
_ => {
debug_assert_eq!(
instance,
ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty)
);
place
}
_ => (instance, place),
};
let instance = ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
let arg = ImmTy::from_immediate(