rust/src/vtable.rs

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use rustc::hir::def_id::DefId;
use rustc::traits::{self, Reveal, SelectionContext};
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use rustc::ty::subst::Substs;
use rustc::ty;
use error::EvalResult;
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use eval_context::EvalContext;
use memory::Pointer;
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use terminator::{get_impl_method, ImplMethod};
impl<'a, 'tcx> EvalContext<'a, 'tcx> {
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/// Creates a dynamic vtable for the given type and vtable origin. This is used only for
/// objects.
///
/// The `trait_ref` encodes the erased self type. Hence if we are
/// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
/// `trait_ref` would map `T:Trait`.
pub fn get_vtable(&mut self, trait_ref: ty::PolyTraitRef<'tcx>) -> EvalResult<'tcx, Pointer> {
let tcx = self.tcx;
debug!("get_vtable(trait_ref={:?})", trait_ref);
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let methods: Vec<_> = traits::supertraits(tcx, trait_ref).flat_map(|trait_ref| {
match self.fulfill_obligation(trait_ref) {
// Should default trait error here?
traits::VtableDefaultImpl(_) |
traits::VtableBuiltin(_) => {
Vec::new().into_iter()
}
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traits::VtableImpl(traits::VtableImplData { impl_def_id: id, substs, .. }) => {
self.get_vtable_methods(id, substs)
.into_iter()
.map(|opt_mth| opt_mth.map(|mth| {
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let fn_ty = self.tcx.item_type(mth.method.def_id);
let fn_ty = match fn_ty.sty {
ty::TyFnDef(_, _, fn_ty) => fn_ty,
_ => bug!("bad function type: {}", fn_ty),
};
let fn_ty = self.tcx.erase_regions(&fn_ty);
self.memory.create_fn_ptr(self.tcx, mth.method.def_id, mth.substs, fn_ty)
}))
.collect::<Vec<_>>()
.into_iter()
}
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traits::VtableClosure(
traits::VtableClosureData {
closure_def_id,
substs,
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..
}
) => {
let closure_type = self.tcx.closure_type(closure_def_id, substs);
vec![Some(self.memory.create_closure_ptr(self.tcx, closure_def_id, substs, closure_type))].into_iter()
}
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// turn a function definition into a Fn trait object
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traits::VtableFnPointer(traits::VtableFnPointerData { fn_ty, .. }) => {
match fn_ty.sty {
ty::TyFnDef(did, substs, bare_fn_ty) => {
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vec![Some(self.memory.create_fn_as_trait_glue(self.tcx, did, substs, bare_fn_ty))].into_iter()
},
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ty::TyFnPtr(bare_fn_ty) => {
vec![Some(self.memory.create_fn_ptr_as_trait_glue(bare_fn_ty))].into_iter()
},
_ => bug!("bad VtableFnPointer fn_ty: {:#?}", fn_ty.sty),
}
}
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traits::VtableObject(ref data) => {
// this would imply that the Self type being erased is
// an object type; this cannot happen because we
// cannot cast an unsized type into a trait object
bug!("cannot get vtable for an object type: {:?}",
data);
}
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vtable @ traits::VtableParam(..) => {
bug!("resolved vtable for {:?} to bad vtable {:?} in trans",
trait_ref,
vtable);
}
}
}).collect();
let size = self.type_size(trait_ref.self_ty())?.expect("can't create a vtable for an unsized type");
let align = self.type_align(trait_ref.self_ty())?;
let ptr_size = self.memory.pointer_size();
let vtable = self.memory.allocate(ptr_size * (3 + methods.len() as u64), ptr_size)?;
// in case there is no drop function to be called, this still needs to be initialized
self.memory.write_usize(vtable, 0)?;
if let ty::TyAdt(adt_def, substs) = trait_ref.self_ty().sty {
if let Some(drop_def_id) = adt_def.destructor() {
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let fn_ty = match self.tcx.item_type(drop_def_id).sty {
ty::TyFnDef(_, _, fn_ty) => self.tcx.erase_regions(&fn_ty),
_ => bug!("drop method is not a TyFnDef"),
};
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let fn_ptr = self.memory.create_drop_glue(self.tcx, drop_def_id, substs, fn_ty);
self.memory.write_ptr(vtable, fn_ptr)?;
}
}
self.memory.write_usize(vtable.offset(ptr_size), size)?;
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self.memory.write_usize(vtable.offset(ptr_size * 2), align)?;
for (i, method) in methods.into_iter().enumerate() {
if let Some(method) = method {
self.memory.write_ptr(vtable.offset(ptr_size * (3 + i as u64)), method)?;
}
}
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self.memory.freeze(vtable.alloc_id)?;
Ok(vtable)
}
fn get_vtable_methods(&mut self, impl_id: DefId, substs: &'tcx Substs<'tcx>) -> Vec<Option<ImplMethod<'tcx>>> {
debug!("get_vtable_methods(impl_id={:?}, substs={:?}", impl_id, substs);
let trait_id = match self.tcx.impl_trait_ref(impl_id) {
Some(t_id) => t_id.def_id,
None => bug!("make_impl_vtable: don't know how to \
make a vtable for a type impl!")
};
self.tcx.populate_implementations_for_trait_if_necessary(trait_id);
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self.tcx
.associated_items(trait_id)
// Filter out non-method items.
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.filter_map(|trait_method_type| {
if trait_method_type.kind != ty::AssociatedKind::Method {
return None;
}
debug!("get_vtable_methods: trait_method_type={:?}",
trait_method_type);
let name = trait_method_type.name;
// Some methods cannot be called on an object; skip those.
if !self.tcx.is_vtable_safe_method(trait_id, &trait_method_type) {
debug!("get_vtable_methods: not vtable safe");
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return Some(None);
}
debug!("get_vtable_methods: trait_method_type={:?}",
trait_method_type);
// the method may have some early-bound lifetimes, add
// regions for those
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let method_substs = Substs::for_item(self.tcx, trait_method_type.def_id,
|_, _| self.tcx.mk_region(ty::ReErased),
|_, _| self.tcx.types.err);
// The substitutions we have are on the impl, so we grab
// the method type from the impl to substitute into.
let mth = get_impl_method(self.tcx, method_substs, impl_id, substs, name);
debug!("get_vtable_methods: mth={:?}", mth);
// If this is a default method, it's possible that it
// relies on where clauses that do not hold for this
// particular set of type parameters. Note that this
// method could then never be called, so we do not want to
// try and trans it, in that case. Issue #23435.
if mth.is_provided {
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let predicates = self.tcx.item_predicates(trait_method_type.def_id).instantiate_own(self.tcx, mth.substs);
if !self.normalize_and_test_predicates(predicates.predicates) {
debug!("get_vtable_methods: predicates do not hold");
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return Some(None);
}
}
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Some(Some(mth))
})
.collect()
}
/// Normalizes the predicates and checks whether they hold. If this
/// returns false, then either normalize encountered an error or one
/// of the predicates did not hold. Used when creating vtables to
/// check for unsatisfiable methods.
fn normalize_and_test_predicates(&mut self, predicates: Vec<ty::Predicate<'tcx>>) -> bool {
debug!("normalize_and_test_predicates(predicates={:?})",
predicates);
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self.tcx.infer_ctxt((), Reveal::All).enter(|infcx| {
let mut selcx = SelectionContext::new(&infcx);
let mut fulfill_cx = traits::FulfillmentContext::new();
let cause = traits::ObligationCause::dummy();
let traits::Normalized { value: predicates, obligations } =
traits::normalize(&mut selcx, cause.clone(), &predicates);
for obligation in obligations {
fulfill_cx.register_predicate_obligation(&infcx, obligation);
}
for predicate in predicates {
let obligation = traits::Obligation::new(cause.clone(), predicate);
fulfill_cx.register_predicate_obligation(&infcx, obligation);
}
fulfill_cx.select_all_or_error(&infcx).is_ok()
})
}
}