rustc_hir_typeck/method/confirm.rs
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use std::ops::Deref;
use rustc_hir as hir;
use rustc_hir::GenericArg;
use rustc_hir::def_id::DefId;
use rustc_hir_analysis::hir_ty_lowering::generics::{
check_generic_arg_count_for_call, lower_generic_args,
};
use rustc_hir_analysis::hir_ty_lowering::{
FeedConstTy, GenericArgsLowerer, HirTyLowerer, IsMethodCall, RegionInferReason,
};
use rustc_infer::infer::{self, DefineOpaqueTypes, InferOk};
use rustc_middle::traits::{ObligationCauseCode, UnifyReceiverContext};
use rustc_middle::ty::adjustment::{
Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability, PointerCoercion,
};
use rustc_middle::ty::fold::TypeFoldable;
use rustc_middle::ty::{
self, GenericArgs, GenericArgsRef, GenericParamDefKind, Ty, TyCtxt, TypeVisitableExt, UserArgs,
UserType,
};
use rustc_middle::{bug, span_bug};
use rustc_span::{DUMMY_SP, Span};
use rustc_trait_selection::traits;
use tracing::debug;
use super::{MethodCallee, probe};
use crate::{FnCtxt, callee};
struct ConfirmContext<'a, 'tcx> {
fcx: &'a FnCtxt<'a, 'tcx>,
span: Span,
self_expr: &'tcx hir::Expr<'tcx>,
call_expr: &'tcx hir::Expr<'tcx>,
skip_record_for_diagnostics: bool,
}
impl<'a, 'tcx> Deref for ConfirmContext<'a, 'tcx> {
type Target = FnCtxt<'a, 'tcx>;
fn deref(&self) -> &Self::Target {
self.fcx
}
}
#[derive(Debug)]
pub(crate) struct ConfirmResult<'tcx> {
pub callee: MethodCallee<'tcx>,
pub illegal_sized_bound: Option<Span>,
}
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
pub(crate) fn confirm_method(
&self,
span: Span,
self_expr: &'tcx hir::Expr<'tcx>,
call_expr: &'tcx hir::Expr<'tcx>,
unadjusted_self_ty: Ty<'tcx>,
pick: &probe::Pick<'tcx>,
segment: &'tcx hir::PathSegment<'tcx>,
) -> ConfirmResult<'tcx> {
debug!(
"confirm(unadjusted_self_ty={:?}, pick={:?}, generic_args={:?})",
unadjusted_self_ty, pick, segment.args,
);
let mut confirm_cx = ConfirmContext::new(self, span, self_expr, call_expr);
confirm_cx.confirm(unadjusted_self_ty, pick, segment)
}
pub(crate) fn confirm_method_for_diagnostic(
&self,
span: Span,
self_expr: &'tcx hir::Expr<'tcx>,
call_expr: &'tcx hir::Expr<'tcx>,
unadjusted_self_ty: Ty<'tcx>,
pick: &probe::Pick<'tcx>,
segment: &hir::PathSegment<'tcx>,
) -> ConfirmResult<'tcx> {
let mut confirm_cx = ConfirmContext::new(self, span, self_expr, call_expr);
confirm_cx.skip_record_for_diagnostics = true;
confirm_cx.confirm(unadjusted_self_ty, pick, segment)
}
}
impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
fn new(
fcx: &'a FnCtxt<'a, 'tcx>,
span: Span,
self_expr: &'tcx hir::Expr<'tcx>,
call_expr: &'tcx hir::Expr<'tcx>,
) -> ConfirmContext<'a, 'tcx> {
ConfirmContext { fcx, span, self_expr, call_expr, skip_record_for_diagnostics: false }
}
fn confirm(
&mut self,
unadjusted_self_ty: Ty<'tcx>,
pick: &probe::Pick<'tcx>,
segment: &hir::PathSegment<'tcx>,
) -> ConfirmResult<'tcx> {
// Adjust the self expression the user provided and obtain the adjusted type.
let self_ty = self.adjust_self_ty(unadjusted_self_ty, pick);
// Create generic args for the method's type parameters.
let rcvr_args = self.fresh_receiver_args(self_ty, pick);
let all_args = self.instantiate_method_args(pick, segment, rcvr_args);
debug!("rcvr_args={rcvr_args:?}, all_args={all_args:?}");
// Create the final signature for the method, replacing late-bound regions.
let (method_sig, method_predicates) = self.instantiate_method_sig(pick, all_args);
// If there is a `Self: Sized` bound and `Self` is a trait object, it is possible that
// something which derefs to `Self` actually implements the trait and the caller
// wanted to make a static dispatch on it but forgot to import the trait.
// See test `tests/ui/issue-35976.rs`.
//
// In that case, we'll error anyway, but we'll also re-run the search with all traits
// in scope, and if we find another method which can be used, we'll output an
// appropriate hint suggesting to import the trait.
let filler_args = rcvr_args
.extend_to(self.tcx, pick.item.def_id, |def, _| self.tcx.mk_param_from_def(def));
let illegal_sized_bound = self.predicates_require_illegal_sized_bound(
self.tcx.predicates_of(pick.item.def_id).instantiate(self.tcx, filler_args),
);
// Unify the (adjusted) self type with what the method expects.
//
// SUBTLE: if we want good error messages, because of "guessing" while matching
// traits, no trait system method can be called before this point because they
// could alter our Self-type, except for normalizing the receiver from the
// signature (which is also done during probing).
let method_sig_rcvr = self.normalize(self.span, method_sig.inputs()[0]);
debug!(
"confirm: self_ty={:?} method_sig_rcvr={:?} method_sig={:?} method_predicates={:?}",
self_ty, method_sig_rcvr, method_sig, method_predicates
);
self.unify_receivers(self_ty, method_sig_rcvr, pick, all_args);
let (method_sig, method_predicates) =
self.normalize(self.span, (method_sig, method_predicates));
let method_sig = ty::Binder::dummy(method_sig);
// Make sure nobody calls `drop()` explicitly.
self.enforce_illegal_method_limitations(pick);
// Add any trait/regions obligations specified on the method's type parameters.
// We won't add these if we encountered an illegal sized bound, so that we can use
// a custom error in that case.
if illegal_sized_bound.is_none() {
self.add_obligations(
Ty::new_fn_ptr(self.tcx, method_sig),
all_args,
method_predicates,
pick.item.def_id,
);
}
// Create the final `MethodCallee`.
let callee = MethodCallee {
def_id: pick.item.def_id,
args: all_args,
sig: method_sig.skip_binder(),
};
ConfirmResult { callee, illegal_sized_bound }
}
///////////////////////////////////////////////////////////////////////////
// ADJUSTMENTS
fn adjust_self_ty(
&mut self,
unadjusted_self_ty: Ty<'tcx>,
pick: &probe::Pick<'tcx>,
) -> Ty<'tcx> {
// Commit the autoderefs by calling `autoderef` again, but this
// time writing the results into the various typeck results.
let mut autoderef = self.autoderef(self.call_expr.span, unadjusted_self_ty);
let Some((ty, n)) = autoderef.nth(pick.autoderefs) else {
return Ty::new_error_with_message(
self.tcx,
DUMMY_SP,
format!("failed autoderef {}", pick.autoderefs),
);
};
assert_eq!(n, pick.autoderefs);
let mut adjustments = self.adjust_steps(&autoderef);
let mut target = self.structurally_resolve_type(autoderef.span(), ty);
match pick.autoref_or_ptr_adjustment {
Some(probe::AutorefOrPtrAdjustment::Autoref { mutbl, unsize }) => {
let region = self.next_region_var(infer::Autoref(self.span));
// Type we're wrapping in a reference, used later for unsizing
let base_ty = target;
target = Ty::new_ref(self.tcx, region, target, mutbl);
// Method call receivers are the primary use case
// for two-phase borrows.
let mutbl = AutoBorrowMutability::new(mutbl, AllowTwoPhase::Yes);
adjustments
.push(Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(mutbl)), target });
if unsize {
let unsized_ty = if let ty::Array(elem_ty, _) = base_ty.kind() {
Ty::new_slice(self.tcx, *elem_ty)
} else {
bug!(
"AutorefOrPtrAdjustment's unsize flag should only be set for array ty, found {}",
base_ty
)
};
target = Ty::new_ref(self.tcx, region, unsized_ty, mutbl.into());
adjustments.push(Adjustment {
kind: Adjust::Pointer(PointerCoercion::Unsize),
target,
});
}
}
Some(probe::AutorefOrPtrAdjustment::ToConstPtr) => {
target = match target.kind() {
&ty::RawPtr(ty, mutbl) => {
assert!(mutbl.is_mut());
Ty::new_imm_ptr(self.tcx, ty)
}
other => panic!("Cannot adjust receiver type {other:?} to const ptr"),
};
adjustments.push(Adjustment {
kind: Adjust::Pointer(PointerCoercion::MutToConstPointer),
target,
});
}
Some(probe::AutorefOrPtrAdjustment::ReborrowPin(mutbl)) => {
let region = self.next_region_var(infer::Autoref(self.span));
target = match target.kind() {
ty::Adt(pin, args) if self.tcx.is_lang_item(pin.did(), hir::LangItem::Pin) => {
let inner_ty = match args[0].expect_ty().kind() {
ty::Ref(_, ty, _) => *ty,
_ => bug!("Expected a reference type for argument to Pin"),
};
Ty::new_pinned_ref(self.tcx, region, inner_ty, mutbl)
}
_ => bug!("Cannot adjust receiver type for reborrowing pin of {target:?}"),
};
adjustments.push(Adjustment { kind: Adjust::ReborrowPin(mutbl), target });
}
None => {}
}
self.register_predicates(autoderef.into_obligations());
// Write out the final adjustments.
if !self.skip_record_for_diagnostics {
self.apply_adjustments(self.self_expr, adjustments);
}
target
}
/// Returns a set of generic parameters for the method *receiver* where all type and region
/// parameters are instantiated with fresh variables. This generic parameters does not include any
/// parameters declared on the method itself.
///
/// Note that this generic parameters may include late-bound regions from the impl level. If so,
/// these are instantiated later in the `instantiate_method_sig` routine.
fn fresh_receiver_args(
&mut self,
self_ty: Ty<'tcx>,
pick: &probe::Pick<'tcx>,
) -> GenericArgsRef<'tcx> {
match pick.kind {
probe::InherentImplPick => {
let impl_def_id = pick.item.container_id(self.tcx);
assert!(
self.tcx.impl_trait_ref(impl_def_id).is_none(),
"impl {impl_def_id:?} is not an inherent impl"
);
self.fresh_args_for_item(self.span, impl_def_id)
}
probe::ObjectPick => {
let trait_def_id = pick.item.container_id(self.tcx);
// This shouldn't happen for non-region error kinds, but may occur
// when we have error regions. Specifically, since we canonicalize
// during method steps, we may successfully deref when we assemble
// the pick, but fail to deref when we try to extract the object
// type from the pick during confirmation. This is fine, we're basically
// already doomed by this point.
if self_ty.references_error() {
return ty::GenericArgs::extend_with_error(self.tcx, trait_def_id, &[]);
}
self.extract_existential_trait_ref(self_ty, |this, object_ty, principal| {
// The object data has no entry for the Self
// Type. For the purposes of this method call, we
// instantiate the object type itself. This
// wouldn't be a sound instantiation in all cases,
// since each instance of the object type is a
// different existential and hence could match
// distinct types (e.g., if `Self` appeared as an
// argument type), but those cases have already
// been ruled out when we deemed the trait to be
// "dyn-compatible".
let original_poly_trait_ref = principal.with_self_ty(this.tcx, object_ty);
let upcast_poly_trait_ref = this.upcast(original_poly_trait_ref, trait_def_id);
let upcast_trait_ref =
this.instantiate_binder_with_fresh_vars(upcast_poly_trait_ref);
debug!(
"original_poly_trait_ref={:?} upcast_trait_ref={:?} target_trait={:?}",
original_poly_trait_ref, upcast_trait_ref, trait_def_id
);
upcast_trait_ref.args
})
}
probe::TraitPick => {
let trait_def_id = pick.item.container_id(self.tcx);
// Make a trait reference `$0 : Trait<$1...$n>`
// consisting entirely of type variables. Later on in
// the process we will unify the transformed-self-type
// of the method with the actual type in order to
// unify some of these variables.
self.fresh_args_for_item(self.span, trait_def_id)
}
probe::WhereClausePick(poly_trait_ref) => {
// Where clauses can have bound regions in them. We need to instantiate
// those to convert from a poly-trait-ref to a trait-ref.
self.instantiate_binder_with_fresh_vars(poly_trait_ref).args
}
}
}
fn extract_existential_trait_ref<R, F>(&mut self, self_ty: Ty<'tcx>, mut closure: F) -> R
where
F: FnMut(&mut ConfirmContext<'a, 'tcx>, Ty<'tcx>, ty::PolyExistentialTraitRef<'tcx>) -> R,
{
// If we specified that this is an object method, then the
// self-type ought to be something that can be dereferenced to
// yield an object-type (e.g., `&Object` or `Box<Object>`
// etc).
// FIXME: this feels, like, super dubious
self.fcx
.autoderef(self.span, self_ty)
.include_raw_pointers()
.find_map(|(ty, _)| match ty.kind() {
ty::Dynamic(data, ..) => Some(closure(
self,
ty,
data.principal().unwrap_or_else(|| {
span_bug!(self.span, "calling trait method on empty object?")
}),
)),
_ => None,
})
.unwrap_or_else(|| {
span_bug!(
self.span,
"self-type `{}` for ObjectPick never dereferenced to an object",
self_ty
)
})
}
fn instantiate_method_args(
&mut self,
pick: &probe::Pick<'tcx>,
seg: &hir::PathSegment<'tcx>,
parent_args: GenericArgsRef<'tcx>,
) -> GenericArgsRef<'tcx> {
// Determine the values for the generic parameters of the method.
// If they were not explicitly supplied, just construct fresh
// variables.
let generics = self.tcx.generics_of(pick.item.def_id);
let arg_count_correct = check_generic_arg_count_for_call(
self.fcx,
pick.item.def_id,
generics,
seg,
IsMethodCall::Yes,
);
// Create generic parameters for early-bound lifetime parameters,
// combining parameters from the type and those from the method.
assert_eq!(generics.parent_count, parent_args.len());
struct GenericArgsCtxt<'a, 'tcx> {
cfcx: &'a ConfirmContext<'a, 'tcx>,
pick: &'a probe::Pick<'tcx>,
seg: &'a hir::PathSegment<'tcx>,
}
impl<'a, 'tcx> GenericArgsLowerer<'a, 'tcx> for GenericArgsCtxt<'a, 'tcx> {
fn args_for_def_id(
&mut self,
def_id: DefId,
) -> (Option<&'a hir::GenericArgs<'tcx>>, bool) {
if def_id == self.pick.item.def_id {
if let Some(data) = self.seg.args {
return (Some(data), false);
}
}
(None, false)
}
fn provided_kind(
&mut self,
_preceding_args: &[ty::GenericArg<'tcx>],
param: &ty::GenericParamDef,
arg: &GenericArg<'tcx>,
) -> ty::GenericArg<'tcx> {
match (¶m.kind, arg) {
(GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => self
.cfcx
.fcx
.lowerer()
.lower_lifetime(lt, RegionInferReason::Param(param))
.into(),
(GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
self.cfcx.lower_ty(ty).raw.into()
}
(GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
self.cfcx.lower_const_arg(ct, FeedConstTy::Param(param.def_id)).into()
}
(GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
self.cfcx.ty_infer(Some(param), inf.span).into()
}
(GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
self.cfcx.ct_infer(Some(param), inf.span).into()
}
(kind, arg) => {
bug!("mismatched method arg kind {kind:?} in turbofish: {arg:?}")
}
}
}
fn inferred_kind(
&mut self,
_preceding_args: &[ty::GenericArg<'tcx>],
param: &ty::GenericParamDef,
_infer_args: bool,
) -> ty::GenericArg<'tcx> {
self.cfcx.var_for_def(self.cfcx.span, param)
}
}
let args = lower_generic_args(
self.fcx,
pick.item.def_id,
parent_args,
false,
None,
&arg_count_correct,
&mut GenericArgsCtxt { cfcx: self, pick, seg },
);
// When the method is confirmed, the `args` includes
// parameters from not just the method, but also the impl of
// the method -- in particular, the `Self` type will be fully
// resolved. However, those are not something that the "user
// specified" -- i.e., those types come from the inferred type
// of the receiver, not something the user wrote. So when we
// create the user-args, we want to replace those earlier
// types with just the types that the user actually wrote --
// that is, those that appear on the *method itself*.
//
// As an example, if the user wrote something like
// `foo.bar::<u32>(...)` -- the `Self` type here will be the
// type of `foo` (possibly adjusted), but we don't want to
// include that. We want just the `[_, u32]` part.
if !args.is_empty() && !generics.is_own_empty() {
let user_type_annotation = self.probe(|_| {
let user_args = UserArgs {
args: GenericArgs::for_item(self.tcx, pick.item.def_id, |param, _| {
let i = param.index as usize;
if i < generics.parent_count {
self.fcx.var_for_def(DUMMY_SP, param)
} else {
args[i]
}
}),
user_self_ty: None, // not relevant here
};
self.fcx.canonicalize_user_type_annotation(UserType::TypeOf(
pick.item.def_id,
user_args,
))
});
debug!("instantiate_method_args: user_type_annotation={:?}", user_type_annotation);
if !self.skip_record_for_diagnostics {
self.fcx.write_user_type_annotation(self.call_expr.hir_id, user_type_annotation);
}
}
self.normalize(self.span, args)
}
fn unify_receivers(
&mut self,
self_ty: Ty<'tcx>,
method_self_ty: Ty<'tcx>,
pick: &probe::Pick<'tcx>,
args: GenericArgsRef<'tcx>,
) {
debug!(
"unify_receivers: self_ty={:?} method_self_ty={:?} span={:?} pick={:?}",
self_ty, method_self_ty, self.span, pick
);
let cause = self.cause(
self.self_expr.span,
ObligationCauseCode::UnifyReceiver(Box::new(UnifyReceiverContext {
assoc_item: pick.item,
param_env: self.param_env,
args,
})),
);
match self.at(&cause, self.param_env).sup(DefineOpaqueTypes::Yes, method_self_ty, self_ty) {
Ok(InferOk { obligations, value: () }) => {
self.register_predicates(obligations);
}
Err(terr) => {
if self.tcx.features().arbitrary_self_types() {
self.err_ctxt()
.report_mismatched_types(
&cause,
self.param_env,
method_self_ty,
self_ty,
terr,
)
.emit();
} else {
// This has/will have errored in wfcheck, which we cannot depend on from here, as typeck on functions
// may run before wfcheck if the function is used in const eval.
self.dcx().span_delayed_bug(
cause.span,
format!("{self_ty} was a subtype of {method_self_ty} but now is not?"),
);
}
}
}
}
// NOTE: this returns the *unnormalized* predicates and method sig. Because of
// inference guessing, the predicates and method signature can't be normalized
// until we unify the `Self` type.
fn instantiate_method_sig(
&mut self,
pick: &probe::Pick<'tcx>,
all_args: GenericArgsRef<'tcx>,
) -> (ty::FnSig<'tcx>, ty::InstantiatedPredicates<'tcx>) {
debug!("instantiate_method_sig(pick={:?}, all_args={:?})", pick, all_args);
// Instantiate the bounds on the method with the
// type/early-bound-regions instantiations performed. There can
// be no late-bound regions appearing here.
let def_id = pick.item.def_id;
let method_predicates = self.tcx.predicates_of(def_id).instantiate(self.tcx, all_args);
debug!("method_predicates after instantitation = {:?}", method_predicates);
let sig = self.tcx.fn_sig(def_id).instantiate(self.tcx, all_args);
debug!("type scheme instantiated, sig={:?}", sig);
let sig = self.instantiate_binder_with_fresh_vars(sig);
debug!("late-bound lifetimes from method instantiated, sig={:?}", sig);
(sig, method_predicates)
}
fn add_obligations(
&mut self,
fty: Ty<'tcx>,
all_args: GenericArgsRef<'tcx>,
method_predicates: ty::InstantiatedPredicates<'tcx>,
def_id: DefId,
) {
debug!(
"add_obligations: fty={:?} all_args={:?} method_predicates={:?} def_id={:?}",
fty, all_args, method_predicates, def_id
);
// FIXME: could replace with the following, but we already calculated `method_predicates`,
// so we just call `predicates_for_generics` directly to avoid redoing work.
// `self.add_required_obligations(self.span, def_id, &all_args);`
for obligation in traits::predicates_for_generics(
|idx, span| {
let code = ObligationCauseCode::WhereClauseInExpr(
def_id,
span,
self.call_expr.hir_id,
idx,
);
traits::ObligationCause::new(self.span, self.body_id, code)
},
self.param_env,
method_predicates,
) {
self.register_predicate(obligation);
}
// this is a projection from a trait reference, so we have to
// make sure that the trait reference inputs are well-formed.
self.add_wf_bounds(all_args, self.call_expr);
// the function type must also be well-formed (this is not
// implied by the args being well-formed because of inherent
// impls and late-bound regions - see issue #28609).
self.register_wf_obligation(fty.into(), self.span, ObligationCauseCode::WellFormed(None));
}
///////////////////////////////////////////////////////////////////////////
// MISCELLANY
fn predicates_require_illegal_sized_bound(
&self,
predicates: ty::InstantiatedPredicates<'tcx>,
) -> Option<Span> {
let sized_def_id = self.tcx.lang_items().sized_trait()?;
traits::elaborate(self.tcx, predicates.predicates.iter().copied())
// We don't care about regions here.
.filter_map(|pred| match pred.kind().skip_binder() {
ty::ClauseKind::Trait(trait_pred) if trait_pred.def_id() == sized_def_id => {
let span = predicates
.iter()
.find_map(|(p, span)| if p == pred { Some(span) } else { None })
.unwrap_or(DUMMY_SP);
Some((trait_pred, span))
}
_ => None,
})
.find_map(|(trait_pred, span)| match trait_pred.self_ty().kind() {
ty::Dynamic(..) => Some(span),
_ => None,
})
}
fn enforce_illegal_method_limitations(&self, pick: &probe::Pick<'_>) {
// Disallow calls to the method `drop` defined in the `Drop` trait.
if let Some(trait_def_id) = pick.item.trait_container(self.tcx) {
if let Err(e) = callee::check_legal_trait_for_method_call(
self.tcx,
self.span,
Some(self.self_expr.span),
self.call_expr.span,
trait_def_id,
self.body_id.to_def_id(),
) {
self.set_tainted_by_errors(e);
}
}
}
fn upcast(
&mut self,
source_trait_ref: ty::PolyTraitRef<'tcx>,
target_trait_def_id: DefId,
) -> ty::PolyTraitRef<'tcx> {
let upcast_trait_refs =
traits::upcast_choices(self.tcx, source_trait_ref, target_trait_def_id);
// must be exactly one trait ref or we'd get an ambig error etc
let [upcast_trait_ref] = upcast_trait_refs.as_slice() else {
span_bug!(
self.span,
"cannot uniquely upcast `{:?}` to `{:?}`: `{:?}`",
source_trait_ref,
target_trait_def_id,
upcast_trait_refs
)
};
*upcast_trait_ref
}
fn instantiate_binder_with_fresh_vars<T>(&self, value: ty::Binder<'tcx, T>) -> T
where
T: TypeFoldable<TyCtxt<'tcx>> + Copy,
{
self.fcx.instantiate_binder_with_fresh_vars(self.span, infer::FnCall, value)
}
}