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use crate::FnCtxt;
use rustc_errors::{
struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan,
};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::Expr;
use rustc_hir_analysis::astconv::AstConv;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_infer::infer::{Coercion, InferOk, InferResult};
use rustc_infer::traits::Obligation;
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::adjustment::{
Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability, PointerCast,
};
use rustc_middle::ty::error::TypeError;
use rustc_middle::ty::relate::RelateResult;
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::visit::TypeVisitable;
use rustc_middle::ty::{self, Ty, TypeAndMut};
use rustc_session::parse::feature_err;
use rustc_span::symbol::sym;
use rustc_span::{self, BytePos, DesugaringKind, Span};
use rustc_target::spec::abi::Abi;
use rustc_trait_selection::infer::InferCtxtExt as _;
use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
use rustc_trait_selection::traits::{
self, NormalizeExt, ObligationCause, ObligationCauseCode, ObligationCtxt,
};
use smallvec::{smallvec, SmallVec};
use std::ops::Deref;
struct Coerce<'a, 'tcx> {
fcx: &'a FnCtxt<'a, 'tcx>,
cause: ObligationCause<'tcx>,
use_lub: bool,
allow_two_phase: AllowTwoPhase,
}
impl<'a, 'tcx> Deref for Coerce<'a, 'tcx> {
type Target = FnCtxt<'a, 'tcx>;
fn deref(&self) -> &Self::Target {
&self.fcx
}
}
type CoerceResult<'tcx> = InferResult<'tcx, (Vec<Adjustment<'tcx>>, Ty<'tcx>)>;
struct CollectRetsVisitor<'tcx> {
ret_exprs: Vec<&'tcx hir::Expr<'tcx>>,
}
impl<'tcx> Visitor<'tcx> for CollectRetsVisitor<'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
if let hir::ExprKind::Ret(_) = expr.kind {
self.ret_exprs.push(expr);
}
intravisit::walk_expr(self, expr);
}
}
fn coerce_mutbls<'tcx>(
from_mutbl: hir::Mutability,
to_mutbl: hir::Mutability,
) -> RelateResult<'tcx, ()> {
if from_mutbl >= to_mutbl { Ok(()) } else { Err(TypeError::Mutability) }
}
fn identity(_: Ty<'_>) -> Vec<Adjustment<'_>> {
vec![]
}
fn simple<'tcx>(kind: Adjust<'tcx>) -> impl FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>> {
move |target| vec![Adjustment { kind, target }]
}
fn success<'tcx>(
adj: Vec<Adjustment<'tcx>>,
target: Ty<'tcx>,
obligations: traits::PredicateObligations<'tcx>,
) -> CoerceResult<'tcx> {
Ok(InferOk { value: (adj, target), obligations })
}
impl<'f, 'tcx> Coerce<'f, 'tcx> {
fn new(
fcx: &'f FnCtxt<'f, 'tcx>,
cause: ObligationCause<'tcx>,
allow_two_phase: AllowTwoPhase,
) -> Self {
Coerce { fcx, cause, allow_two_phase, use_lub: false }
}
fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
debug!("unify(a: {:?}, b: {:?}, use_lub: {})", a, b, self.use_lub);
self.commit_if_ok(|_| {
if self.use_lub {
self.at(&self.cause, self.fcx.param_env).lub(b, a)
} else {
self.at(&self.cause, self.fcx.param_env)
.sup(b, a)
.map(|InferOk { value: (), obligations }| InferOk { value: a, obligations })
}
})
}
fn unify_and<F>(&self, a: Ty<'tcx>, b: Ty<'tcx>, f: F) -> CoerceResult<'tcx>
where
F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
{
self.unify(a, b)
.and_then(|InferOk { value: ty, obligations }| success(f(ty), ty, obligations))
}
#[instrument(skip(self))]
fn coerce(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
let a = self.shallow_resolve(a);
let b = self.shallow_resolve(b);
debug!("Coerce.tys({:?} => {:?})", a, b);
if a.references_error() || b.references_error() {
return success(vec![], self.fcx.tcx.ty_error(), vec![]);
}
if a.is_never() {
return success(simple(Adjust::NeverToAny)(b), b, vec![]);
}
if a.is_ty_var() {
return self.coerce_from_inference_variable(a, b, identity);
}
let unsize = self.commit_if_ok(|_| self.coerce_unsized(a, b));
match unsize {
Ok(_) => {
debug!("coerce: unsize successful");
return unsize;
}
Err(error) => {
debug!(?error, "coerce: unsize failed");
}
}
match *b.kind() {
ty::RawPtr(mt_b) => {
return self.coerce_unsafe_ptr(a, b, mt_b.mutbl);
}
ty::Ref(r_b, _, mutbl_b) => {
return self.coerce_borrowed_pointer(a, b, r_b, mutbl_b);
}
ty::Dynamic(predicates, region, ty::DynStar) if self.tcx.features().dyn_star => {
return self.coerce_dyn_star(a, b, predicates, region);
}
_ => {}
}
match *a.kind() {
ty::FnDef(..) => {
self.coerce_from_fn_item(a, b)
}
ty::FnPtr(a_f) => {
self.coerce_from_fn_pointer(a, a_f, b)
}
ty::Closure(closure_def_id_a, substs_a) => {
self.coerce_closure_to_fn(a, closure_def_id_a, substs_a, b)
}
_ => {
self.unify_and(a, b, identity)
}
}
}
fn coerce_from_inference_variable(
&self,
a: Ty<'tcx>,
b: Ty<'tcx>,
make_adjustments: impl FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
) -> CoerceResult<'tcx> {
debug!("coerce_from_inference_variable(a={:?}, b={:?})", a, b);
assert!(a.is_ty_var() && self.shallow_resolve(a) == a);
assert!(self.shallow_resolve(b) == b);
if b.is_ty_var() {
let target_ty = if self.use_lub {
self.next_ty_var(TypeVariableOrigin {
kind: TypeVariableOriginKind::LatticeVariable,
span: self.cause.span,
})
} else {
b
};
let mut obligations = Vec::with_capacity(2);
for &source_ty in &[a, b] {
if source_ty != target_ty {
obligations.push(Obligation::new(
self.tcx(),
self.cause.clone(),
self.param_env,
ty::Binder::dummy(ty::PredicateKind::Coerce(ty::CoercePredicate {
a: source_ty,
b: target_ty,
})),
));
}
}
debug!(
"coerce_from_inference_variable: two inference variables, target_ty={:?}, obligations={:?}",
target_ty, obligations
);
let adjustments = make_adjustments(target_ty);
InferResult::Ok(InferOk { value: (adjustments, target_ty), obligations })
} else {
self.unify_and(a, b, make_adjustments)
}
}
fn coerce_borrowed_pointer(
&self,
a: Ty<'tcx>,
b: Ty<'tcx>,
r_b: ty::Region<'tcx>,
mutbl_b: hir::Mutability,
) -> CoerceResult<'tcx> {
debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b);
let (r_a, mt_a) = match *a.kind() {
ty::Ref(r_a, ty, mutbl) => {
let mt_a = ty::TypeAndMut { ty, mutbl };
coerce_mutbls(mt_a.mutbl, mutbl_b)?;
(r_a, mt_a)
}
_ => return self.unify_and(a, b, identity),
};
let span = self.cause.span;
let mut first_error = None;
let mut r_borrow_var = None;
let mut autoderef = self.autoderef(span, a);
let mut found = None;
for (referent_ty, autoderefs) in autoderef.by_ref() {
if autoderefs == 0 {
continue;
}
let r = if !self.use_lub {
r_b } else if autoderefs == 1 {
r_a } else {
if r_borrow_var.is_none() {
let coercion = Coercion(span);
let r = self.next_region_var(coercion);
r_borrow_var = Some(r); }
r_borrow_var.unwrap()
};
let derefd_ty_a = self.tcx.mk_ref(
r,
TypeAndMut {
ty: referent_ty,
mutbl: mutbl_b, },
);
match self.unify(derefd_ty_a, b) {
Ok(ok) => {
found = Some(ok);
break;
}
Err(err) => {
if first_error.is_none() {
first_error = Some(err);
}
}
}
}
let Some(InferOk { value: ty, mut obligations }) = found else {
let err = first_error.expect("coerce_borrowed_pointer had no error");
debug!("coerce_borrowed_pointer: failed with err = {:?}", err);
return Err(err);
};
if ty == a && mt_a.mutbl.is_not() && autoderef.step_count() == 1 {
assert!(mutbl_b.is_not()); return success(vec![], ty, obligations);
}
let InferOk { value: mut adjustments, obligations: o } =
self.adjust_steps_as_infer_ok(&autoderef);
obligations.extend(o);
obligations.extend(autoderef.into_obligations());
let ty::Ref(r_borrow, _, _) = ty.kind() else {
span_bug!(span, "expected a ref type, got {:?}", ty);
};
let mutbl = AutoBorrowMutability::new(mutbl_b, self.allow_two_phase);
adjustments.push(Adjustment {
kind: Adjust::Borrow(AutoBorrow::Ref(*r_borrow, mutbl)),
target: ty,
});
debug!("coerce_borrowed_pointer: succeeded ty={:?} adjustments={:?}", ty, adjustments);
success(adjustments, ty, obligations)
}
#[instrument(skip(self), level = "debug")]
fn coerce_unsized(&self, mut source: Ty<'tcx>, mut target: Ty<'tcx>) -> CoerceResult<'tcx> {
source = self.shallow_resolve(source);
target = self.shallow_resolve(target);
debug!(?source, ?target);
if source.is_ty_var() {
debug!("coerce_unsized: source is a TyVar, bailing out");
return Err(TypeError::Mismatch);
}
if target.is_ty_var() {
debug!("coerce_unsized: target is a TyVar, bailing out");
return Err(TypeError::Mismatch);
}
let traits =
(self.tcx.lang_items().unsize_trait(), self.tcx.lang_items().coerce_unsized_trait());
let (Some(unsize_did), Some(coerce_unsized_did)) = traits else {
debug!("missing Unsize or CoerceUnsized traits");
return Err(TypeError::Mismatch);
};
let reborrow = match (source.kind(), target.kind()) {
(&ty::Ref(_, ty_a, mutbl_a), &ty::Ref(_, _, mutbl_b)) => {
coerce_mutbls(mutbl_a, mutbl_b)?;
let coercion = Coercion(self.cause.span);
let r_borrow = self.next_region_var(coercion);
let mutbl = AutoBorrowMutability::new(mutbl_b, AllowTwoPhase::No);
Some((
Adjustment { kind: Adjust::Deref(None), target: ty_a },
Adjustment {
kind: Adjust::Borrow(AutoBorrow::Ref(r_borrow, mutbl)),
target: self
.tcx
.mk_ref(r_borrow, ty::TypeAndMut { mutbl: mutbl_b, ty: ty_a }),
},
))
}
(&ty::Ref(_, ty_a, mt_a), &ty::RawPtr(ty::TypeAndMut { mutbl: mt_b, .. })) => {
coerce_mutbls(mt_a, mt_b)?;
Some((
Adjustment { kind: Adjust::Deref(None), target: ty_a },
Adjustment {
kind: Adjust::Borrow(AutoBorrow::RawPtr(mt_b)),
target: self.tcx.mk_ptr(ty::TypeAndMut { mutbl: mt_b, ty: ty_a }),
},
))
}
_ => None,
};
let coerce_source = reborrow.as_ref().map_or(source, |(_, r)| r.target);
let origin = TypeVariableOrigin {
kind: TypeVariableOriginKind::MiscVariable,
span: self.cause.span,
};
let coerce_target = self.next_ty_var(origin);
let mut coercion = self.unify_and(coerce_target, target, |target| {
let unsize = Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), target };
match reborrow {
None => vec![unsize],
Some((ref deref, ref autoref)) => vec![deref.clone(), autoref.clone(), unsize],
}
})?;
let mut selcx = traits::SelectionContext::new(self);
let cause = ObligationCause::new(
self.cause.span,
self.body_id,
ObligationCauseCode::Coercion { source, target },
);
let mut queue: SmallVec<[_; 4]> = smallvec![traits::predicate_for_trait_def(
self.tcx,
self.fcx.param_env,
cause,
coerce_unsized_did,
0,
[coerce_source, coerce_target]
)];
let mut has_unsized_tuple_coercion = false;
let mut has_trait_upcasting_coercion = None;
let traits = [coerce_unsized_did, unsize_did];
while !queue.is_empty() {
let obligation = queue.remove(0);
debug!("coerce_unsized resolve step: {:?}", obligation);
let bound_predicate = obligation.predicate.kind();
let trait_pred = match bound_predicate.skip_binder() {
ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred))
if traits.contains(&trait_pred.def_id()) =>
{
if unsize_did == trait_pred.def_id() {
let self_ty = trait_pred.self_ty();
let unsize_ty = trait_pred.trait_ref.substs[1].expect_ty();
if let (ty::Dynamic(ref data_a, ..), ty::Dynamic(ref data_b, ..)) =
(self_ty.kind(), unsize_ty.kind())
&& data_a.principal_def_id() != data_b.principal_def_id()
{
debug!("coerce_unsized: found trait upcasting coercion");
has_trait_upcasting_coercion = Some((self_ty, unsize_ty));
}
if let ty::Tuple(..) = unsize_ty.kind() {
debug!("coerce_unsized: found unsized tuple coercion");
has_unsized_tuple_coercion = true;
}
}
bound_predicate.rebind(trait_pred)
}
_ => {
coercion.obligations.push(obligation);
continue;
}
};
match selcx.select(&obligation.with(selcx.tcx(), trait_pred)) {
Ok(None) => {
if trait_pred.def_id() == unsize_did {
let trait_pred = self.resolve_vars_if_possible(trait_pred);
let self_ty = trait_pred.skip_binder().self_ty();
let unsize_ty = trait_pred.skip_binder().trait_ref.substs[1].expect_ty();
debug!("coerce_unsized: ambiguous unsize case for {:?}", trait_pred);
match (&self_ty.kind(), &unsize_ty.kind()) {
(ty::Infer(ty::TyVar(v)), ty::Dynamic(..))
if self.type_var_is_sized(*v) =>
{
debug!("coerce_unsized: have sized infer {:?}", v);
coercion.obligations.push(obligation);
}
_ => {
debug!("coerce_unsized: ambiguous unsize");
return Err(TypeError::Mismatch);
}
}
} else {
debug!("coerce_unsized: early return - ambiguous");
return Err(TypeError::Mismatch);
}
}
Err(traits::Unimplemented) => {
debug!("coerce_unsized: early return - can't prove obligation");
return Err(TypeError::Mismatch);
}
Err(err) => {
self.err_ctxt().report_selection_error(obligation.clone(), &obligation, &err);
}
Ok(Some(impl_source)) => queue.extend(impl_source.nested_obligations()),
}
}
if has_unsized_tuple_coercion && !self.tcx.features().unsized_tuple_coercion {
feature_err(
&self.tcx.sess.parse_sess,
sym::unsized_tuple_coercion,
self.cause.span,
"unsized tuple coercion is not stable enough for use and is subject to change",
)
.emit();
}
if let Some((sub, sup)) = has_trait_upcasting_coercion
&& !self.tcx().features().trait_upcasting
{
let (sub, sup) = self.tcx.erase_regions((sub, sup));
let mut err = feature_err(
&self.tcx.sess.parse_sess,
sym::trait_upcasting,
self.cause.span,
&format!("cannot cast `{sub}` to `{sup}`, trait upcasting coercion is experimental"),
);
err.note(&format!("required when coercing `{source}` into `{target}`"));
err.emit();
}
Ok(coercion)
}
fn coerce_dyn_star(
&self,
a: Ty<'tcx>,
b: Ty<'tcx>,
predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
b_region: ty::Region<'tcx>,
) -> CoerceResult<'tcx> {
if !self.tcx.features().dyn_star {
return Err(TypeError::Mismatch);
}
if let ty::Dynamic(a_data, _, _) = a.kind()
&& let ty::Dynamic(b_data, _, _) = b.kind()
&& a_data.principal_def_id() == b_data.principal_def_id()
{
return self.unify_and(a, b, |_| vec![]);
}
let mut obligations: Vec<_> = predicates
.iter()
.map(|predicate| {
let predicate = predicate.with_self_ty(self.tcx, a);
Obligation::new(self.tcx, self.cause.clone(), self.param_env, predicate)
})
.chain([
Obligation::new(
self.tcx,
self.cause.clone(),
self.param_env,
ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::TypeOutlives(
ty::OutlivesPredicate(a, b_region),
))),
),
])
.collect();
obligations.push(Obligation::new(
self.tcx,
self.cause.clone(),
self.param_env,
ty::Binder::dummy(
self.tcx.at(self.cause.span).mk_trait_ref(hir::LangItem::PointerSized, [a]),
),
));
Ok(InferOk {
value: (vec![Adjustment { kind: Adjust::DynStar, target: b }], b),
obligations,
})
}
fn coerce_from_safe_fn<F, G>(
&self,
a: Ty<'tcx>,
fn_ty_a: ty::PolyFnSig<'tcx>,
b: Ty<'tcx>,
to_unsafe: F,
normal: G,
) -> CoerceResult<'tcx>
where
F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
G: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
{
self.commit_if_ok(|snapshot| {
let result = if let ty::FnPtr(fn_ty_b) = b.kind()
&& let (hir::Unsafety::Normal, hir::Unsafety::Unsafe) =
(fn_ty_a.unsafety(), fn_ty_b.unsafety())
{
let unsafe_a = self.tcx.safe_to_unsafe_fn_ty(fn_ty_a);
self.unify_and(unsafe_a, b, to_unsafe)
} else {
self.unify_and(a, b, normal)
};
self.leak_check(false, snapshot)?;
result
})
}
fn coerce_from_fn_pointer(
&self,
a: Ty<'tcx>,
fn_ty_a: ty::PolyFnSig<'tcx>,
b: Ty<'tcx>,
) -> CoerceResult<'tcx> {
let b = self.shallow_resolve(b);
debug!("coerce_from_fn_pointer(a={:?}, b={:?})", a, b);
self.coerce_from_safe_fn(
a,
fn_ty_a,
b,
simple(Adjust::Pointer(PointerCast::UnsafeFnPointer)),
identity,
)
}
fn coerce_from_fn_item(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
let b = self.shallow_resolve(b);
let InferOk { value: b, mut obligations } =
self.at(&self.cause, self.param_env).normalize(b);
debug!("coerce_from_fn_item(a={:?}, b={:?})", a, b);
match b.kind() {
ty::FnPtr(b_sig) => {
let a_sig = a.fn_sig(self.tcx);
if let ty::FnDef(def_id, _) = *a.kind() {
if self.tcx.is_intrinsic(def_id) {
return Err(TypeError::IntrinsicCast);
}
if b_sig.unsafety() == hir::Unsafety::Normal
&& !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
{
return Err(TypeError::TargetFeatureCast(def_id));
}
}
let InferOk { value: a_sig, obligations: o1 } =
self.at(&self.cause, self.param_env).normalize(a_sig);
obligations.extend(o1);
let a_fn_pointer = self.tcx.mk_fn_ptr(a_sig);
let InferOk { value, obligations: o2 } = self.coerce_from_safe_fn(
a_fn_pointer,
a_sig,
b,
|unsafe_ty| {
vec![
Adjustment {
kind: Adjust::Pointer(PointerCast::ReifyFnPointer),
target: a_fn_pointer,
},
Adjustment {
kind: Adjust::Pointer(PointerCast::UnsafeFnPointer),
target: unsafe_ty,
},
]
},
simple(Adjust::Pointer(PointerCast::ReifyFnPointer)),
)?;
obligations.extend(o2);
Ok(InferOk { value, obligations })
}
_ => self.unify_and(a, b, identity),
}
}
fn coerce_closure_to_fn(
&self,
a: Ty<'tcx>,
closure_def_id_a: DefId,
substs_a: SubstsRef<'tcx>,
b: Ty<'tcx>,
) -> CoerceResult<'tcx> {
let b = self.shallow_resolve(b);
match b.kind() {
ty::FnPtr(fn_ty)
if self
.tcx
.upvars_mentioned(closure_def_id_a.expect_local())
.map_or(true, |u| u.is_empty()) =>
{
let closure_sig = substs_a.as_closure().sig();
let unsafety = fn_ty.unsafety();
let pointer_ty =
self.tcx.mk_fn_ptr(self.tcx.signature_unclosure(closure_sig, unsafety));
debug!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})", a, b, pointer_ty);
self.unify_and(
pointer_ty,
b,
simple(Adjust::Pointer(PointerCast::ClosureFnPointer(unsafety))),
)
}
_ => self.unify_and(a, b, identity),
}
}
fn coerce_unsafe_ptr(
&self,
a: Ty<'tcx>,
b: Ty<'tcx>,
mutbl_b: hir::Mutability,
) -> CoerceResult<'tcx> {
debug!("coerce_unsafe_ptr(a={:?}, b={:?})", a, b);
let (is_ref, mt_a) = match *a.kind() {
ty::Ref(_, ty, mutbl) => (true, ty::TypeAndMut { ty, mutbl }),
ty::RawPtr(mt) => (false, mt),
_ => return self.unify_and(a, b, identity),
};
coerce_mutbls(mt_a.mutbl, mutbl_b)?;
let a_unsafe = self.tcx.mk_ptr(ty::TypeAndMut { mutbl: mutbl_b, ty: mt_a.ty });
if is_ref {
self.unify_and(a_unsafe, b, |target| {
vec![
Adjustment { kind: Adjust::Deref(None), target: mt_a.ty },
Adjustment { kind: Adjust::Borrow(AutoBorrow::RawPtr(mutbl_b)), target },
]
})
} else if mt_a.mutbl != mutbl_b {
self.unify_and(a_unsafe, b, simple(Adjust::Pointer(PointerCast::MutToConstPointer)))
} else {
self.unify_and(a_unsafe, b, identity)
}
}
}
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
pub fn try_coerce(
&self,
expr: &hir::Expr<'_>,
expr_ty: Ty<'tcx>,
target: Ty<'tcx>,
allow_two_phase: AllowTwoPhase,
cause: Option<ObligationCause<'tcx>>,
) -> RelateResult<'tcx, Ty<'tcx>> {
let source = self.resolve_vars_with_obligations(expr_ty);
debug!("coercion::try({:?}: {:?} -> {:?})", expr, source, target);
let cause =
cause.unwrap_or_else(|| self.cause(expr.span, ObligationCauseCode::ExprAssignable));
let coerce = Coerce::new(self, cause, allow_two_phase);
let ok = self.commit_if_ok(|_| coerce.coerce(source, target))?;
let (adjustments, _) = self.register_infer_ok_obligations(ok);
self.apply_adjustments(expr, adjustments);
Ok(if expr_ty.references_error() { self.tcx.ty_error() } else { target })
}
pub fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
let source = self.resolve_vars_with_obligations(expr_ty);
debug!("coercion::can_with_predicates({:?} -> {:?})", source, target);
let cause = self.cause(rustc_span::DUMMY_SP, ObligationCauseCode::ExprAssignable);
let coerce = Coerce::new(self, cause, AllowTwoPhase::No);
self.probe(|_| {
let Ok(ok) = coerce.coerce(source, target) else {
return false;
};
let ocx = ObligationCtxt::new_in_snapshot(self);
ocx.register_obligations(ok.obligations);
ocx.select_where_possible().is_empty()
})
}
pub fn deref_steps(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> Option<usize> {
let cause = self.cause(rustc_span::DUMMY_SP, ObligationCauseCode::ExprAssignable);
let coerce = Coerce::new(self, cause, AllowTwoPhase::No);
coerce
.autoderef(rustc_span::DUMMY_SP, expr_ty)
.find_map(|(ty, steps)| self.probe(|_| coerce.unify(ty, target)).ok().map(|_| steps))
}
pub fn deref_once_mutably_for_diagnostic(&self, expr_ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
self.autoderef(rustc_span::DUMMY_SP, expr_ty).nth(1).and_then(|(deref_ty, _)| {
self.infcx
.type_implements_trait(
self.tcx.lang_items().deref_mut_trait()?,
[expr_ty],
self.param_env,
)
.may_apply()
.then(|| deref_ty)
})
}
fn try_find_coercion_lub<E>(
&self,
cause: &ObligationCause<'tcx>,
exprs: &[E],
prev_ty: Ty<'tcx>,
new: &hir::Expr<'_>,
new_ty: Ty<'tcx>,
) -> RelateResult<'tcx, Ty<'tcx>>
where
E: AsCoercionSite,
{
let prev_ty = self.resolve_vars_with_obligations(prev_ty);
let new_ty = self.resolve_vars_with_obligations(new_ty);
debug!(
"coercion::try_find_coercion_lub({:?}, {:?}, exprs={:?} exprs)",
prev_ty,
new_ty,
exprs.len()
);
if prev_ty == new_ty {
return Ok(prev_ty);
}
let (a_sig, b_sig) = {
let is_capturing_closure = |ty: Ty<'tcx>| {
if let &ty::Closure(closure_def_id, _substs) = ty.kind() {
self.tcx.upvars_mentioned(closure_def_id.expect_local()).is_some()
} else {
false
}
};
if is_capturing_closure(prev_ty) || is_capturing_closure(new_ty) {
(None, None)
} else {
match (prev_ty.kind(), new_ty.kind()) {
(ty::FnDef(..), ty::FnDef(..)) => {
match self
.commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
{
Ok(ok) => return Ok(self.register_infer_ok_obligations(ok)),
Err(_) => {
(Some(prev_ty.fn_sig(self.tcx)), Some(new_ty.fn_sig(self.tcx)))
}
}
}
(ty::Closure(_, substs), ty::FnDef(..)) => {
let b_sig = new_ty.fn_sig(self.tcx);
let a_sig = self
.tcx
.signature_unclosure(substs.as_closure().sig(), b_sig.unsafety());
(Some(a_sig), Some(b_sig))
}
(ty::FnDef(..), ty::Closure(_, substs)) => {
let a_sig = prev_ty.fn_sig(self.tcx);
let b_sig = self
.tcx
.signature_unclosure(substs.as_closure().sig(), a_sig.unsafety());
(Some(a_sig), Some(b_sig))
}
(ty::Closure(_, substs_a), ty::Closure(_, substs_b)) => (
Some(self.tcx.signature_unclosure(
substs_a.as_closure().sig(),
hir::Unsafety::Normal,
)),
Some(self.tcx.signature_unclosure(
substs_b.as_closure().sig(),
hir::Unsafety::Normal,
)),
),
_ => (None, None),
}
}
};
if let (Some(a_sig), Some(b_sig)) = (a_sig, b_sig) {
if a_sig.abi() == Abi::RustIntrinsic
|| a_sig.abi() == Abi::PlatformIntrinsic
|| b_sig.abi() == Abi::RustIntrinsic
|| b_sig.abi() == Abi::PlatformIntrinsic
{
return Err(TypeError::IntrinsicCast);
}
let (a_sig, b_sig) = self.normalize(new.span, (a_sig, b_sig));
let sig = self
.at(cause, self.param_env)
.trace(prev_ty, new_ty)
.lub(a_sig, b_sig)
.map(|ok| self.register_infer_ok_obligations(ok))?;
let fn_ptr = self.tcx.mk_fn_ptr(sig);
let prev_adjustment = match prev_ty.kind() {
ty::Closure(..) => Adjust::Pointer(PointerCast::ClosureFnPointer(a_sig.unsafety())),
ty::FnDef(..) => Adjust::Pointer(PointerCast::ReifyFnPointer),
_ => unreachable!(),
};
let next_adjustment = match new_ty.kind() {
ty::Closure(..) => Adjust::Pointer(PointerCast::ClosureFnPointer(b_sig.unsafety())),
ty::FnDef(..) => Adjust::Pointer(PointerCast::ReifyFnPointer),
_ => unreachable!(),
};
for expr in exprs.iter().map(|e| e.as_coercion_site()) {
self.apply_adjustments(
expr,
vec![Adjustment { kind: prev_adjustment.clone(), target: fn_ptr }],
);
}
self.apply_adjustments(new, vec![Adjustment { kind: next_adjustment, target: fn_ptr }]);
return Ok(fn_ptr);
}
let mut coerce = Coerce::new(self, cause.clone(), AllowTwoPhase::No);
coerce.use_lub = true;
let mut first_error = None;
if !self.typeck_results.borrow().adjustments().contains_key(new.hir_id) {
let result = self.commit_if_ok(|_| coerce.coerce(new_ty, prev_ty));
match result {
Ok(ok) => {
let (adjustments, target) = self.register_infer_ok_obligations(ok);
self.apply_adjustments(new, adjustments);
debug!(
"coercion::try_find_coercion_lub: was able to coerce from new type {:?} to previous type {:?} ({:?})",
new_ty, prev_ty, target
);
return Ok(target);
}
Err(e) => first_error = Some(e),
}
}
for expr in exprs {
let expr = expr.as_coercion_site();
let noop = match self.typeck_results.borrow().expr_adjustments(expr) {
&[
Adjustment { kind: Adjust::Deref(_), .. },
Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(_, mutbl_adj)), .. },
] => {
match *self.node_ty(expr.hir_id).kind() {
ty::Ref(_, _, mt_orig) => {
let mutbl_adj: hir::Mutability = mutbl_adj.into();
mutbl_adj == mt_orig
}
_ => false,
}
}
&[Adjustment { kind: Adjust::NeverToAny, .. }] | &[] => true,
_ => false,
};
if !noop {
debug!(
"coercion::try_find_coercion_lub: older expression {:?} had adjustments, requiring LUB",
expr,
);
return self
.commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
.map(|ok| self.register_infer_ok_obligations(ok));
}
}
match self.commit_if_ok(|_| coerce.coerce(prev_ty, new_ty)) {
Err(_) => {
if let Some(e) = first_error {
Err(e)
} else {
self.commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
.map(|ok| self.register_infer_ok_obligations(ok))
}
}
Ok(ok) => {
let (adjustments, target) = self.register_infer_ok_obligations(ok);
for expr in exprs {
let expr = expr.as_coercion_site();
self.apply_adjustments(expr, adjustments.clone());
}
debug!(
"coercion::try_find_coercion_lub: was able to coerce previous type {:?} to new type {:?} ({:?})",
prev_ty, new_ty, target
);
Ok(target)
}
}
}
}
pub struct CoerceMany<'tcx, 'exprs, E: AsCoercionSite> {
expected_ty: Ty<'tcx>,
final_ty: Option<Ty<'tcx>>,
expressions: Expressions<'tcx, 'exprs, E>,
pushed: usize,
}
pub type DynamicCoerceMany<'tcx> = CoerceMany<'tcx, 'tcx, &'tcx hir::Expr<'tcx>>;
enum Expressions<'tcx, 'exprs, E: AsCoercionSite> {
Dynamic(Vec<&'tcx hir::Expr<'tcx>>),
UpFront(&'exprs [E]),
}
impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
pub fn new(expected_ty: Ty<'tcx>) -> Self {
Self::make(expected_ty, Expressions::Dynamic(vec![]))
}
pub fn with_coercion_sites(expected_ty: Ty<'tcx>, coercion_sites: &'exprs [E]) -> Self {
Self::make(expected_ty, Expressions::UpFront(coercion_sites))
}
fn make(expected_ty: Ty<'tcx>, expressions: Expressions<'tcx, 'exprs, E>) -> Self {
CoerceMany { expected_ty, final_ty: None, expressions, pushed: 0 }
}
pub fn expected_ty(&self) -> Ty<'tcx> {
self.expected_ty
}
pub fn merged_ty(&self) -> Ty<'tcx> {
self.final_ty.unwrap_or(self.expected_ty)
}
pub fn coerce<'a>(
&mut self,
fcx: &FnCtxt<'a, 'tcx>,
cause: &ObligationCause<'tcx>,
expression: &'tcx hir::Expr<'tcx>,
expression_ty: Ty<'tcx>,
) {
self.coerce_inner(fcx, cause, Some(expression), expression_ty, None, false)
}
pub fn coerce_forced_unit<'a>(
&mut self,
fcx: &FnCtxt<'a, 'tcx>,
cause: &ObligationCause<'tcx>,
augment_error: &mut dyn FnMut(&mut Diagnostic),
label_unit_as_expected: bool,
) {
self.coerce_inner(
fcx,
cause,
None,
fcx.tcx.mk_unit(),
Some(augment_error),
label_unit_as_expected,
)
}
#[instrument(skip(self, fcx, augment_error, label_expression_as_expected), level = "debug")]
pub(crate) fn coerce_inner<'a>(
&mut self,
fcx: &FnCtxt<'a, 'tcx>,
cause: &ObligationCause<'tcx>,
expression: Option<&'tcx hir::Expr<'tcx>>,
mut expression_ty: Ty<'tcx>,
augment_error: Option<&mut dyn FnMut(&mut Diagnostic)>,
label_expression_as_expected: bool,
) {
if expression_ty.is_ty_var() {
expression_ty = fcx.infcx.shallow_resolve(expression_ty);
}
if expression_ty.references_error() || self.merged_ty().references_error() {
self.final_ty = Some(fcx.tcx.ty_error());
return;
}
let result = if let Some(expression) = expression {
if self.pushed == 0 {
fcx.try_coerce(
expression,
expression_ty,
self.expected_ty,
AllowTwoPhase::No,
Some(cause.clone()),
)
} else {
match self.expressions {
Expressions::Dynamic(ref exprs) => fcx.try_find_coercion_lub(
cause,
exprs,
self.merged_ty(),
expression,
expression_ty,
),
Expressions::UpFront(ref coercion_sites) => fcx.try_find_coercion_lub(
cause,
&coercion_sites[0..self.pushed],
self.merged_ty(),
expression,
expression_ty,
),
}
}
} else {
assert!(expression_ty.is_unit(), "if let hack without unit type");
fcx.at(cause, fcx.param_env)
.eq_exp(label_expression_as_expected, expression_ty, self.merged_ty())
.map(|infer_ok| {
fcx.register_infer_ok_obligations(infer_ok);
expression_ty
})
};
debug!(?result);
match result {
Ok(v) => {
self.final_ty = Some(v);
if let Some(e) = expression {
match self.expressions {
Expressions::Dynamic(ref mut buffer) => buffer.push(e),
Expressions::UpFront(coercion_sites) => {
assert_eq!(
coercion_sites[self.pushed].as_coercion_site().hir_id,
e.hir_id
);
}
}
self.pushed += 1;
}
}
Err(coercion_error) => {
fcx.set_tainted_by_errors(
fcx.tcx.sess.delay_span_bug(cause.span, "coercion error but no error emitted"),
);
let (expected, found) = if label_expression_as_expected {
(expression_ty, self.merged_ty())
} else {
(self.merged_ty(), expression_ty)
};
let (expected, found) = fcx.resolve_vars_if_possible((expected, found));
let mut err;
let mut unsized_return = false;
let mut visitor = CollectRetsVisitor { ret_exprs: vec![] };
match *cause.code() {
ObligationCauseCode::ReturnNoExpression => {
err = struct_span_err!(
fcx.tcx.sess,
cause.span,
E0069,
"`return;` in a function whose return type is not `()`"
);
err.span_label(cause.span, "return type is not `()`");
}
ObligationCauseCode::BlockTailExpression(blk_id) => {
let parent_id = fcx.tcx.hir().get_parent_node(blk_id);
err = self.report_return_mismatched_types(
cause,
expected,
found,
coercion_error.clone(),
fcx,
parent_id,
expression,
Some(blk_id),
);
if !fcx.tcx.features().unsized_locals {
unsized_return = self.is_return_ty_unsized(fcx, blk_id);
}
if let Some(expression) = expression
&& let hir::ExprKind::Loop(loop_blk, ..) = expression.kind {
intravisit::walk_block(& mut visitor, loop_blk);
}
}
ObligationCauseCode::ReturnValue(id) => {
err = self.report_return_mismatched_types(
cause,
expected,
found,
coercion_error.clone(),
fcx,
id,
expression,
None,
);
if !fcx.tcx.features().unsized_locals {
let id = fcx.tcx.hir().get_parent_node(id);
unsized_return = self.is_return_ty_unsized(fcx, id);
}
}
_ => {
err = fcx.err_ctxt().report_mismatched_types(
cause,
expected,
found,
coercion_error.clone(),
);
}
}
if let Some(augment_error) = augment_error {
augment_error(&mut err);
}
let is_insufficiently_polymorphic =
matches!(coercion_error, TypeError::RegionsInsufficientlyPolymorphic(..));
if !is_insufficiently_polymorphic && let Some(expr) = expression {
fcx.emit_coerce_suggestions(
&mut err,
expr,
found,
expected,
None,
Some(coercion_error),
);
}
if visitor.ret_exprs.len() > 0 && let Some(expr) = expression {
self.note_unreachable_loop_return(&mut err, &expr, &visitor.ret_exprs);
}
let reported = err.emit_unless(unsized_return);
self.final_ty = Some(fcx.tcx.ty_error_with_guaranteed(reported));
}
}
}
fn note_unreachable_loop_return(
&self,
err: &mut Diagnostic,
expr: &hir::Expr<'tcx>,
ret_exprs: &Vec<&'tcx hir::Expr<'tcx>>,
) {
let hir::ExprKind::Loop(_, _, _, loop_span) = expr.kind else { return;};
let mut span: MultiSpan = vec![loop_span].into();
span.push_span_label(loop_span, "this might have zero elements to iterate on");
const MAXITER: usize = 3;
let iter = ret_exprs.iter().take(MAXITER);
for ret_expr in iter {
span.push_span_label(
ret_expr.span,
"if the loop doesn't execute, this value would never get returned",
);
}
err.span_note(
span,
"the function expects a value to always be returned, but loops might run zero times",
);
if MAXITER < ret_exprs.len() {
err.note(&format!(
"if the loop doesn't execute, {} other values would never get returned",
ret_exprs.len() - MAXITER
));
}
err.help(
"return a value for the case when the loop has zero elements to iterate on, or \
consider changing the return type to account for that possibility",
);
}
fn report_return_mismatched_types<'a>(
&self,
cause: &ObligationCause<'tcx>,
expected: Ty<'tcx>,
found: Ty<'tcx>,
ty_err: TypeError<'tcx>,
fcx: &FnCtxt<'a, 'tcx>,
id: hir::HirId,
expression: Option<&'tcx hir::Expr<'tcx>>,
blk_id: Option<hir::HirId>,
) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
let mut err = fcx.err_ctxt().report_mismatched_types(cause, expected, found, ty_err);
let mut pointing_at_return_type = false;
let mut fn_output = None;
let parent_id = fcx.tcx.hir().get_parent_node(id);
let parent = fcx.tcx.hir().get(parent_id);
if let Some(expr) = expression
&& let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(&hir::Closure { body, .. }), .. }) = parent
&& !matches!(fcx.tcx.hir().body(body).value.kind, hir::ExprKind::Block(..))
{
fcx.suggest_missing_semicolon(&mut err, expr, expected, true);
}
let fn_decl = if let (Some(expr), Some(blk_id)) = (expression, blk_id) {
pointing_at_return_type =
fcx.suggest_mismatched_types_on_tail(&mut err, expr, expected, found, blk_id);
if let (Some(cond_expr), true, false) = (
fcx.tcx.hir().get_if_cause(expr.hir_id),
expected.is_unit(),
pointing_at_return_type,
)
&& matches!(
cond_expr.span.desugaring_kind(),
None | Some(DesugaringKind::WhileLoop)
) && !in_external_macro(fcx.tcx.sess, cond_expr.span)
&& !matches!(
cond_expr.kind,
hir::ExprKind::Match(.., hir::MatchSource::TryDesugar)
)
{
err.span_label(cond_expr.span, "expected this to be `()`");
if expr.can_have_side_effects() {
fcx.suggest_semicolon_at_end(cond_expr.span, &mut err);
}
}
fcx.get_node_fn_decl(parent).map(|(fn_decl, _, is_main)| (fn_decl, is_main))
} else {
fcx.get_fn_decl(parent_id)
};
if let Some((fn_decl, can_suggest)) = fn_decl {
if blk_id.is_none() {
pointing_at_return_type |= fcx.suggest_missing_return_type(
&mut err,
&fn_decl,
expected,
found,
can_suggest,
fcx.tcx.hir().get_parent_item(id).into(),
);
}
if !pointing_at_return_type {
fn_output = Some(&fn_decl.output); }
}
let parent_id = fcx.tcx.hir().get_parent_item(id);
let parent_item = fcx.tcx.hir().get_by_def_id(parent_id.def_id);
if let (Some(expr), Some(_), Some((fn_decl, _, _))) =
(expression, blk_id, fcx.get_node_fn_decl(parent_item))
{
fcx.suggest_missing_break_or_return_expr(
&mut err,
expr,
fn_decl,
expected,
found,
id,
parent_id.into(),
);
}
let ret_coercion_span = fcx.ret_coercion_span.get();
if let Some(sp) = ret_coercion_span
&& let Some(fn_sig) = fcx.body_fn_sig()
&& fn_sig.output().is_ty_var()
{
err.span_note(
sp,
&format!(
"return type inferred to be `{}` here",
expected
),
);
}
if let (Some(sp), Some(fn_output)) = (ret_coercion_span, fn_output) {
self.add_impl_trait_explanation(&mut err, cause, fcx, expected, sp, fn_output);
}
err
}
fn add_impl_trait_explanation<'a>(
&self,
err: &mut Diagnostic,
cause: &ObligationCause<'tcx>,
fcx: &FnCtxt<'a, 'tcx>,
expected: Ty<'tcx>,
sp: Span,
fn_output: &hir::FnRetTy<'_>,
) {
let return_sp = fn_output.span();
err.span_label(return_sp, "expected because this return type...");
err.span_label(
sp,
format!("...is found to be `{}` here", fcx.resolve_vars_with_obligations(expected)),
);
let impl_trait_msg = "for information on `impl Trait`, see \
<https://doc.rust-lang.org/book/ch10-02-traits.html\
#returning-types-that-implement-traits>";
let trait_obj_msg = "for information on trait objects, see \
<https://doc.rust-lang.org/book/ch17-02-trait-objects.html\
#using-trait-objects-that-allow-for-values-of-different-types>";
err.note("to return `impl Trait`, all returned values must be of the same type");
err.note(impl_trait_msg);
let snippet = fcx
.tcx
.sess
.source_map()
.span_to_snippet(return_sp)
.unwrap_or_else(|_| "dyn Trait".to_string());
let mut snippet_iter = snippet.split_whitespace();
let has_impl = snippet_iter.next().map_or(false, |s| s == "impl");
let mut is_object_safe = false;
if let hir::FnRetTy::Return(ty) = fn_output
&& let hir::TyKind::OpaqueDef(..) = ty.kind
{
let ty = <dyn AstConv<'_>>::ast_ty_to_ty(fcx, ty);
if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) = ty.kind()
&& let hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, .. }) =
fcx.tcx.hir().expect_item(def_id.expect_local()).kind
{
is_object_safe = bounds.iter().all(|bound| {
bound
.trait_ref()
.and_then(|t| t.trait_def_id())
.map_or(false, |def_id| {
fcx.tcx.object_safety_violations(def_id).is_empty()
})
})
}
};
if has_impl {
if is_object_safe {
err.multipart_suggestion(
"you could change the return type to be a boxed trait object",
vec![
(return_sp.with_hi(return_sp.lo() + BytePos(4)), "Box<dyn".to_string()),
(return_sp.shrink_to_hi(), ">".to_string()),
],
Applicability::MachineApplicable,
);
let sugg = [sp, cause.span]
.into_iter()
.flat_map(|sp| {
[
(sp.shrink_to_lo(), "Box::new(".to_string()),
(sp.shrink_to_hi(), ")".to_string()),
]
.into_iter()
})
.collect::<Vec<_>>();
err.multipart_suggestion(
"if you change the return type to expect trait objects, box the returned \
expressions",
sugg,
Applicability::MaybeIncorrect,
);
} else {
err.help(&format!(
"if the trait `{}` were object safe, you could return a boxed trait object",
&snippet[5..]
));
}
err.note(trait_obj_msg);
}
err.help("you could instead create a new `enum` with a variant for each returned type");
}
fn is_return_ty_unsized<'a>(&self, fcx: &FnCtxt<'a, 'tcx>, blk_id: hir::HirId) -> bool {
if let Some((fn_decl, _)) = fcx.get_fn_decl(blk_id)
&& let hir::FnRetTy::Return(ty) = fn_decl.output
&& let ty = <dyn AstConv<'_>>::ast_ty_to_ty(fcx, ty)
&& let ty::Dynamic(..) = ty.kind()
{
return true;
}
false
}
pub fn complete<'a>(self, fcx: &FnCtxt<'a, 'tcx>) -> Ty<'tcx> {
if let Some(final_ty) = self.final_ty {
final_ty
} else {
assert_eq!(self.pushed, 0);
fcx.tcx.types.never
}
}
}
pub trait AsCoercionSite {
fn as_coercion_site(&self) -> &hir::Expr<'_>;
}
impl AsCoercionSite for hir::Expr<'_> {
fn as_coercion_site(&self) -> &hir::Expr<'_> {
self
}
}
impl<'a, T> AsCoercionSite for &'a T
where
T: AsCoercionSite,
{
fn as_coercion_site(&self) -> &hir::Expr<'_> {
(**self).as_coercion_site()
}
}
impl AsCoercionSite for ! {
fn as_coercion_site(&self) -> &hir::Expr<'_> {
unreachable!()
}
}
impl AsCoercionSite for hir::Arm<'_> {
fn as_coercion_site(&self) -> &hir::Expr<'_> {
&self.body
}
}