use rustc_errors::ErrorGuaranteed;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::query::Providers;
use rustc_middle::traits::{BuiltinImplSource, CodegenObligationError};
use rustc_middle::ty::GenericArgsRef;
use rustc_middle::ty::{self, Instance, TyCtxt, TypeVisitableExt};
use rustc_span::sym;
use rustc_trait_selection::traits;
use traits::{translate_args, Reveal};
use crate::errors::UnexpectedFnPtrAssociatedItem;
fn resolve_instance<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, (DefId, GenericArgsRef<'tcx>)>,
) -> Result>, ErrorGuaranteed> {
let (param_env, (def_id, args)) = key.into_parts();
let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
resolve_associated_item(
tcx,
def_id,
param_env,
trait_def_id,
tcx.normalize_erasing_regions(param_env, args),
)
} else {
let def = if matches!(tcx.def_kind(def_id), DefKind::Fn) && tcx.is_intrinsic(def_id) {
debug!(" => intrinsic");
ty::InstanceDef::Intrinsic(def_id)
} else if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
let ty = args.type_at(0);
if ty.needs_drop(tcx, param_env) {
debug!(" => nontrivial drop glue");
match *ty.kind() {
ty::Closure(..)
| ty::Coroutine(..)
| 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)
}
} else {
debug!(" => free item");
// FIXME(effects): we may want to erase the effect param if that is present on this item.
ty::InstanceDef::Item(def_id)
};
Ok(Some(Instance { def, args }))
};
debug!("resolve_instance: result={:?}", result);
result
}
fn resolve_associated_item<'tcx>(
tcx: TyCtxt<'tcx>,
trait_item_id: DefId,
param_env: ty::ParamEnv<'tcx>,
trait_id: DefId,
rcvr_args: GenericArgsRef<'tcx>,
) -> Result >, ErrorGuaranteed> {
debug!(?trait_item_id, ?param_env, ?trait_id, ?rcvr_args, "resolve_associated_item");
let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_args);
let vtbl = match tcx.codegen_select_candidate((param_env, trait_ref)) {
Ok(vtbl) => vtbl,
Err(CodegenObligationError::Ambiguity) => {
let reported = tcx.sess.span_delayed_bug(
tcx.def_span(trait_item_id),
format!(
"encountered ambiguity selecting `{trait_ref:?}` during codegen, presuming due to \
overflow or prior type error",
),
);
return Err(reported);
}
Err(CodegenObligationError::Unimplemented) => return Ok(None),
Err(CodegenObligationError::FulfillmentError) => return Ok(None),
};
// 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_id, rcvr_args, impl_data
);
assert!(!rcvr_args.has_infer());
assert!(!trait_ref.has_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_id)
.unwrap_or_else(|| {
bug!("{:?} not found in {:?}", trait_item_id, impl_data.impl_def_id);
});
let infcx = tcx.infer_ctxt().build();
let param_env = param_env.with_reveal_all_normalized(tcx);
let args = rcvr_args.rebase_onto(tcx, trait_def_id, impl_data.args);
let args = translate_args(
&infcx,
param_env,
impl_data.impl_def_id,
args,
leaf_def.defining_node,
);
let args = infcx.tcx.erase_regions(args);
// 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);
}
// HACK: We may have overlapping `dyn Trait` built-in impls and
// user-provided blanket impls. Detect that case here, and return
// ambiguity.
//
// This should not affect totally monomorphized contexts, only
// resolve calls that happen polymorphically, such as the mir-inliner
// and const-prop (and also some lints).
let self_ty = rcvr_args.type_at(0);
if !self_ty.is_known_rigid() {
let predicates = tcx
.predicates_of(impl_data.impl_def_id)
.instantiate(tcx, impl_data.args)
.predicates;
let sized_def_id = tcx.lang_items().sized_trait();
// If we find a `Self: Sized` bound on the item, then we know
// that `dyn Trait` can certainly never apply here.
if !predicates.into_iter().filter_map(ty::Clause::as_trait_clause).any(|clause| {
Some(clause.def_id()) == sized_def_id
&& clause.skip_binder().self_ty() == self_ty
}) {
return Ok(None);
}
}
// Any final impl is required to define all associated items.
if !leaf_def.item.defaultness(tcx).has_value() {
let guard = tcx.sess.span_delayed_bug(
tcx.def_span(leaf_def.item.def_id),
"missing value for assoc item in impl",
);
return Err(guard);
}
let args = tcx.erase_regions(args);
// 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).
if leaf_def.item.kind == ty::AssocKind::Const
&& trait_item_id != leaf_def.item.def_id
&& let Some(leaf_def_item) = leaf_def.item.def_id.as_local()
{
tcx.compare_impl_const((leaf_def_item, trait_item_id))?;
}
Some(ty::Instance::new(leaf_def.item.def_id, args))
}
traits::ImplSource::Builtin(BuiltinImplSource::Object { vtable_base }, _) => {
traits::get_vtable_index_of_object_method(tcx, *vtable_base, trait_item_id).map(
|index| Instance {
def: ty::InstanceDef::Virtual(trait_item_id, index),
args: rcvr_args,
},
)
}
traits::ImplSource::Builtin(BuiltinImplSource::Misc, _) => {
let lang_items = tcx.lang_items();
if Some(trait_ref.def_id) == lang_items.clone_trait() {
// FIXME(eddyb) use lang items for methods instead of names.
let name = tcx.item_name(trait_item_id);
if name == sym::clone {
let self_ty = trait_ref.self_ty();
let is_copy = self_ty.is_copy_modulo_regions(tcx, param_env);
match self_ty.kind() {
_ if is_copy => (),
ty::Coroutine(..)
| ty::CoroutineWitness(..)
| ty::Closure(..)
| ty::Tuple(..) => {}
_ => return Ok(None),
};
Some(Instance {
def: ty::InstanceDef::CloneShim(trait_item_id, self_ty),
args: rcvr_args,
})
} else {
assert_eq!(name, sym::clone_from);
// Use the default `fn clone_from` from `trait Clone`.
let args = tcx.erase_regions(rcvr_args);
Some(ty::Instance::new(trait_item_id, args))
}
} else if Some(trait_ref.def_id) == lang_items.fn_ptr_trait() {
if lang_items.fn_ptr_addr() == Some(trait_item_id) {
let self_ty = trait_ref.self_ty();
if !matches!(self_ty.kind(), ty::FnPtr(..)) {
return Ok(None);
}
Some(Instance {
def: ty::InstanceDef::FnPtrAddrShim(trait_item_id, self_ty),
args: rcvr_args,
})
} else {
tcx.sess.emit_fatal(UnexpectedFnPtrAssociatedItem {
span: tcx.def_span(trait_item_id),
})
}
} else if Some(trait_ref.def_id) == lang_items.future_trait() {
let ty::Coroutine(coroutine_def_id, args, _) = *rcvr_args.type_at(0).kind() else {
bug!()
};
if Some(trait_item_id) == tcx.lang_items().future_poll_fn() {
// `Future::poll` is generated by the compiler.
Some(Instance { def: ty::InstanceDef::Item(coroutine_def_id), args: args })
} else {
// All other methods are default methods of the `Future` trait.
// (this assumes that `ImplSource::Builtin` is only used for methods on `Future`)
debug_assert!(tcx.defaultness(trait_item_id).has_value());
Some(Instance::new(trait_item_id, rcvr_args))
}
} else if Some(trait_ref.def_id) == lang_items.iterator_trait() {
let ty::Coroutine(coroutine_def_id, args, _) = *rcvr_args.type_at(0).kind() else {
bug!()
};
if Some(trait_item_id) == tcx.lang_items().next_fn() {
// `Iterator::next` is generated by the compiler.
Some(Instance { def: ty::InstanceDef::Item(coroutine_def_id), args })
} else {
// All other methods are default methods of the `Iterator` trait.
// (this assumes that `ImplSource::Builtin` is only used for methods on `Iterator`)
debug_assert!(tcx.defaultness(trait_item_id).has_value());
Some(Instance::new(trait_item_id, rcvr_args))
}
} else if Some(trait_ref.def_id) == lang_items.async_iterator_trait() {
let ty::Coroutine(coroutine_def_id, args, _) = *rcvr_args.type_at(0).kind() else {
bug!()
};
if cfg!(debug_assertions) && tcx.item_name(trait_item_id) != sym::poll_next {
span_bug!(
tcx.def_span(coroutine_def_id),
"no definition for `{trait_ref}::{}` for built-in coroutine type",
tcx.item_name(trait_item_id)
)
}
// `AsyncIterator::poll_next` is generated by the compiler.
Some(Instance { def: ty::InstanceDef::Item(coroutine_def_id), args })
} else if Some(trait_ref.def_id) == lang_items.coroutine_trait() {
let ty::Coroutine(coroutine_def_id, args, _) = *rcvr_args.type_at(0).kind() else {
bug!()
};
if cfg!(debug_assertions) && tcx.item_name(trait_item_id) != sym::resume {
// For compiler developers who'd like to add new items to `Coroutine`,
// you either need to generate a shim body, or perhaps return
// `InstanceDef::Item` pointing to a trait default method body if
// it is given a default implementation by the trait.
span_bug!(
tcx.def_span(coroutine_def_id),
"no definition for `{trait_ref}::{}` for built-in coroutine type",
tcx.item_name(trait_item_id)
)
}
Some(Instance { def: ty::InstanceDef::Item(coroutine_def_id), args })
} else if tcx.fn_trait_kind_from_def_id(trait_ref.def_id).is_some() {
// FIXME: This doesn't check for malformed libcore that defines, e.g.,
// `trait Fn { fn call_once(&self) { .. } }`. This is mostly for extension
// methods.
if cfg!(debug_assertions)
&& ![sym::call, sym::call_mut, sym::call_once]
.contains(&tcx.item_name(trait_item_id))
{
// For compiler developers who'd like to add new items to `Fn`/`FnMut`/`FnOnce`,
// you either need to generate a shim body, or perhaps return
// `InstanceDef::Item` pointing to a trait default method body if
// it is given a default implementation by the trait.
bug!(
"no definition for `{trait_ref}::{}` for built-in callable type",
tcx.item_name(trait_item_id)
)
}
match *rcvr_args.type_at(0).kind() {
ty::Closure(closure_def_id, args) => {
let trait_closure_kind = tcx.fn_trait_kind_from_def_id(trait_id).unwrap();
Instance::resolve_closure(tcx, closure_def_id, args, trait_closure_kind)
}
ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
def: ty::InstanceDef::FnPtrShim(trait_item_id, rcvr_args.type_at(0)),
args: rcvr_args,
}),
_ => bug!(
"no built-in definition for `{trait_ref}::{}` for non-fn type",
tcx.item_name(trait_item_id)
),
}
} else {
None
}
}
traits::ImplSource::Param(..)
| traits::ImplSource::Builtin(BuiltinImplSource::TraitUpcasting { .. }, _)
| traits::ImplSource::Builtin(BuiltinImplSource::TupleUnsizing, _) => None,
})
}
pub(crate) fn provide(providers: &mut Providers) {
*providers = Providers { resolve_instance, ..*providers };
}