rust/compiler/rustc_ty_utils/src/instance.rs
2020-11-19 21:57:29 +01:00

285 lines
12 KiB
Rust

use rustc_errors::ErrorReported;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::{self, Instance, TyCtxt, TypeFoldable};
use rustc_span::{sym, DUMMY_SP};
use rustc_target::spec::abi::Abi;
use rustc_trait_selection::traits;
use traits::{translate_substs, Reveal};
use tracing::debug;
fn resolve_instance<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
) -> Result<Option<Instance<'tcx>>, ErrorReported> {
let (param_env, (did, substs)) = key.into_parts();
if let Some(did) = did.as_local() {
if let Some(param_did) = tcx.opt_const_param_of(did) {
return tcx.resolve_instance_of_const_arg(param_env.and((did, param_did, substs)));
}
}
inner_resolve_instance(tcx, param_env.and((ty::WithOptConstParam::unknown(did), substs)))
}
fn resolve_instance_of_const_arg<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, (LocalDefId, DefId, SubstsRef<'tcx>)>,
) -> Result<Option<Instance<'tcx>>, ErrorReported> {
let (param_env, (did, const_param_did, substs)) = key.into_parts();
inner_resolve_instance(
tcx,
param_env.and((
ty::WithOptConstParam { did: did.to_def_id(), const_param_did: Some(const_param_did) },
substs,
)),
)
}
fn inner_resolve_instance<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, (ty::WithOptConstParam<DefId>, SubstsRef<'tcx>)>,
) -> Result<Option<Instance<'tcx>>, ErrorReported> {
let (param_env, (def, substs)) = key.into_parts();
debug!("resolve(def={:?}, substs={:?})", def.did, substs);
let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
let item = tcx.associated_item(def.did);
resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
} else {
let ty = tcx.type_of(def.def_id_for_type_of());
let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, ty);
let def = match *item_type.kind() {
ty::FnDef(..)
if {
let f = item_type.fn_sig(tcx);
f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
} =>
{
debug!(" => intrinsic");
ty::InstanceDef::Intrinsic(def.did)
}
ty::FnDef(def_id, substs) if Some(def_id) == tcx.lang_items().drop_in_place_fn() => {
let ty = substs.type_at(0);
if ty.needs_drop(tcx, param_env) {
debug!(" => nontrivial drop glue");
match *ty.kind() {
ty::Closure(..)
| ty::Generator(..)
| ty::Tuple(..)
| ty::Adt(..)
| ty::Dynamic(..)
| ty::Array(..)
| ty::Slice(..) => {}
// Drop shims can only be built from ADTs.
_ => return Ok(None),
}
ty::InstanceDef::DropGlue(def_id, Some(ty))
} else {
debug!(" => trivial drop glue");
ty::InstanceDef::DropGlue(def_id, None)
}
}
_ => {
debug!(" => free item");
ty::InstanceDef::Item(def)
}
};
Ok(Some(Instance { def, substs }))
};
debug!("resolve(def.did={:?}, substs={:?}) = {:?}", def.did, substs, result);
result
}
fn resolve_associated_item<'tcx>(
tcx: TyCtxt<'tcx>,
trait_item: &ty::AssocItem,
param_env: ty::ParamEnv<'tcx>,
trait_id: DefId,
rcvr_substs: SubstsRef<'tcx>,
) -> Result<Option<Instance<'tcx>>, ErrorReported> {
let def_id = trait_item.def_id;
debug!(
"resolve_associated_item(trait_item={:?}, \
param_env={:?}, \
trait_id={:?}, \
rcvr_substs={:?})",
def_id, param_env, trait_id, rcvr_substs
);
let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)))?;
// Now that we know which impl is being used, we can dispatch to
// the actual function:
Ok(match vtbl {
traits::ImplSource::UserDefined(impl_data) => {
debug!(
"resolving ImplSource::UserDefined: {:?}, {:?}, {:?}, {:?}",
param_env, trait_item, rcvr_substs, impl_data
);
assert!(!rcvr_substs.needs_infer());
assert!(!trait_ref.needs_infer());
let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
let trait_def = tcx.trait_def(trait_def_id);
let leaf_def = trait_def
.ancestors(tcx, impl_data.impl_def_id)?
.leaf_def(tcx, trait_item.ident, trait_item.kind)
.unwrap_or_else(|| {
bug!("{:?} not found in {:?}", trait_item, impl_data.impl_def_id);
});
let substs = tcx.infer_ctxt().enter(|infcx| {
let param_env = param_env.with_reveal_all_normalized(tcx);
let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
let substs = translate_substs(
&infcx,
param_env,
impl_data.impl_def_id,
substs,
leaf_def.defining_node,
);
infcx.tcx.erase_regions(substs)
});
// Since this is a trait item, we need to see if the item is either a trait default item
// or a specialization because we can't resolve those unless we can `Reveal::All`.
// NOTE: This should be kept in sync with the similar code in
// `rustc_trait_selection::traits::project::assemble_candidates_from_impls()`.
let eligible = if leaf_def.is_final() {
// Non-specializable items are always projectable.
true
} else {
// Only reveal a specializable default if we're past type-checking
// and the obligation is monomorphic, otherwise passes such as
// transmute checking and polymorphic MIR optimizations could
// get a result which isn't correct for all monomorphizations.
if param_env.reveal() == Reveal::All {
!trait_ref.still_further_specializable()
} else {
false
}
};
if !eligible {
return Ok(None);
}
let substs = tcx.erase_regions(substs);
// Check if we just resolved an associated `const` declaration from
// a `trait` to an associated `const` definition in an `impl`, where
// the definition in the `impl` has the wrong type (for which an
// error has already been/will be emitted elsewhere).
//
// NB: this may be expensive, we try to skip it in all the cases where
// we know the error would've been caught (e.g. in an upstream crate).
//
// A better approach might be to just introduce a query (returning
// `Result<(), ErrorReported>`) for the check that `rustc_typeck`
// performs (i.e. that the definition's type in the `impl` matches
// the declaration in the `trait`), so that we can cheaply check
// here if it failed, instead of approximating it.
if trait_item.kind == ty::AssocKind::Const
&& trait_item.def_id != leaf_def.item.def_id
&& leaf_def.item.def_id.is_local()
{
let normalized_type_of = |def_id, substs| {
tcx.subst_and_normalize_erasing_regions(substs, param_env, tcx.type_of(def_id))
};
let original_ty = normalized_type_of(trait_item.def_id, rcvr_substs);
let resolved_ty = normalized_type_of(leaf_def.item.def_id, substs);
if original_ty != resolved_ty {
let msg = format!(
"Instance::resolve: inconsistent associated `const` type: \
was `{}: {}` but resolved to `{}: {}`",
tcx.def_path_str_with_substs(trait_item.def_id, rcvr_substs),
original_ty,
tcx.def_path_str_with_substs(leaf_def.item.def_id, substs),
resolved_ty,
);
let span = tcx.def_span(leaf_def.item.def_id);
tcx.sess.delay_span_bug(span, &msg);
return Err(ErrorReported);
}
}
Some(ty::Instance::new(leaf_def.item.def_id, substs))
}
traits::ImplSource::Generator(generator_data) => Some(Instance {
def: ty::InstanceDef::Item(ty::WithOptConstParam::unknown(
generator_data.generator_def_id,
)),
substs: generator_data.substs,
}),
traits::ImplSource::Closure(closure_data) => {
let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
Some(Instance::resolve_closure(
tcx,
closure_data.closure_def_id,
closure_data.substs,
trait_closure_kind,
))
}
traits::ImplSource::FnPointer(ref data) => match data.fn_ty.kind() {
ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
substs: rcvr_substs,
}),
_ => None,
},
traits::ImplSource::Object(ref data) => {
let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
}
traits::ImplSource::Builtin(..) => {
if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {
// FIXME(eddyb) use lang items for methods instead of names.
let name = tcx.item_name(def_id);
if name == sym::clone {
let self_ty = trait_ref.self_ty();
let is_copy = self_ty.is_copy_modulo_regions(tcx.at(DUMMY_SP), param_env);
match self_ty.kind() {
_ if is_copy => (),
ty::Array(..) | ty::Closure(..) | ty::Tuple(..) => {}
_ => return Ok(None),
};
Some(Instance {
def: ty::InstanceDef::CloneShim(def_id, self_ty),
substs: rcvr_substs,
})
} else {
assert_eq!(name, sym::clone_from);
// Use the default `fn clone_from` from `trait Clone`.
let substs = tcx.erase_regions(rcvr_substs);
Some(ty::Instance::new(def_id, substs))
}
} else {
None
}
}
traits::ImplSource::AutoImpl(..)
| traits::ImplSource::Param(..)
| traits::ImplSource::TraitAlias(..)
| traits::ImplSource::DiscriminantKind(..) => None,
})
}
pub fn provide(providers: &mut ty::query::Providers) {
*providers =
ty::query::Providers { resolve_instance, resolve_instance_of_const_arg, ..*providers };
}