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//! Code for type-checking closure expressions.
use super::{check_fn, Expectation, FnCtxt, GeneratorTypes};
use rustc_errors::ErrorGuaranteed;
use rustc_hir as hir;
use rustc_hir::lang_items::LangItem;
use rustc_hir_analysis::astconv::AstConv;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_infer::infer::{DefineOpaqueTypes, LateBoundRegionConversionTime};
use rustc_infer::infer::{InferOk, InferResult};
use rustc_macros::{TypeFoldable, TypeVisitable};
use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt};
use rustc_middle::ty::GenericArgs;
use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor};
use rustc_span::def_id::LocalDefId;
use rustc_span::source_map::Span;
use rustc_span::sym;
use rustc_target::spec::abi::Abi;
use rustc_trait_selection::traits;
use rustc_trait_selection::traits::error_reporting::ArgKind;
use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
use std::cmp;
use std::iter;
use std::ops::ControlFlow;
/// What signature do we *expect* the closure to have from context?
#[derive(Debug, Clone, TypeFoldable, TypeVisitable)]
struct ExpectedSig<'tcx> {
/// Span that gave us this expectation, if we know that.
cause_span: Option<Span>,
sig: ty::PolyFnSig<'tcx>,
}
struct ClosureSignatures<'tcx> {
/// The signature users of the closure see.
bound_sig: ty::PolyFnSig<'tcx>,
/// The signature within the function body.
/// This mostly differs in the sense that lifetimes are now early bound and any
/// opaque types from the signature expectation are overridden in case there are
/// explicit hidden types written by the user in the closure signature.
liberated_sig: ty::FnSig<'tcx>,
}
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
#[instrument(skip(self, closure), level = "debug")]
pub fn check_expr_closure(
&self,
closure: &hir::Closure<'tcx>,
expr_span: Span,
expected: Expectation<'tcx>,
) -> Ty<'tcx> {
trace!("decl = {:#?}", closure.fn_decl);
// It's always helpful for inference if we know the kind of
// closure sooner rather than later, so first examine the expected
// type, and see if can glean a closure kind from there.
let (expected_sig, expected_kind) = match expected.to_option(self) {
Some(ty) => self.deduce_closure_signature(ty),
None => (None, None),
};
let body = self.tcx.hir().body(closure.body);
self.check_closure(closure, expr_span, expected_kind, body, expected_sig)
}
#[instrument(skip(self, closure, body), level = "debug", ret)]
fn check_closure(
&self,
closure: &hir::Closure<'tcx>,
expr_span: Span,
opt_kind: Option<ty::ClosureKind>,
body: &'tcx hir::Body<'tcx>,
expected_sig: Option<ExpectedSig<'tcx>>,
) -> Ty<'tcx> {
trace!("decl = {:#?}", closure.fn_decl);
let expr_def_id = closure.def_id;
debug!(?expr_def_id);
let ClosureSignatures { bound_sig, liberated_sig } =
self.sig_of_closure(expr_def_id, closure.fn_decl, body, expected_sig);
debug!(?bound_sig, ?liberated_sig);
let mut fcx = FnCtxt::new(self, self.param_env, closure.def_id);
let generator_types = check_fn(
&mut fcx,
liberated_sig,
closure.fn_decl,
expr_def_id,
body,
closure.movability,
// Closure "rust-call" ABI doesn't support unsized params
false,
);
let parent_args = GenericArgs::identity_for_item(
self.tcx,
self.tcx.typeck_root_def_id(expr_def_id.to_def_id()),
);
let tupled_upvars_ty = self.next_root_ty_var(TypeVariableOrigin {
kind: TypeVariableOriginKind::ClosureSynthetic,
span: self.tcx.def_span(expr_def_id),
});
if let Some(GeneratorTypes { resume_ty, yield_ty, interior, movability }) = generator_types
{
let generator_args = ty::GeneratorArgs::new(
self.tcx,
ty::GeneratorArgsParts {
parent_args,
resume_ty,
yield_ty,
return_ty: liberated_sig.output(),
witness: interior,
tupled_upvars_ty,
},
);
return Ty::new_generator(
self.tcx,
expr_def_id.to_def_id(),
generator_args.args,
movability,
);
}
// Tuple up the arguments and insert the resulting function type into
// the `closures` table.
let sig = bound_sig.map_bound(|sig| {
self.tcx.mk_fn_sig(
[Ty::new_tup(self.tcx, sig.inputs())],
sig.output(),
sig.c_variadic,
sig.unsafety,
sig.abi,
)
});
debug!(?sig, ?opt_kind);
let closure_kind_ty = match opt_kind {
Some(kind) => kind.to_ty(self.tcx),
// Create a type variable (for now) to represent the closure kind.
// It will be unified during the upvar inference phase (`upvar.rs`)
None => self.next_root_ty_var(TypeVariableOrigin {
// FIXME(eddyb) distinguish closure kind inference variables from the rest.
kind: TypeVariableOriginKind::ClosureSynthetic,
span: expr_span,
}),
};
let closure_args = ty::ClosureArgs::new(
self.tcx,
ty::ClosureArgsParts {
parent_args,
closure_kind_ty,
closure_sig_as_fn_ptr_ty: Ty::new_fn_ptr(self.tcx, sig),
tupled_upvars_ty,
},
);
Ty::new_closure(self.tcx, expr_def_id.to_def_id(), closure_args.args)
}
/// Given the expected type, figures out what it can about this closure we
/// are about to type check:
#[instrument(skip(self), level = "debug")]
fn deduce_closure_signature(
&self,
expected_ty: Ty<'tcx>,
) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
match *expected_ty.kind() {
ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => self
.deduce_closure_signature_from_predicates(
expected_ty,
self.tcx
.explicit_item_bounds(def_id)
.iter_instantiated_copied(self.tcx, args)
.map(|(c, s)| (c.as_predicate(), s)),
),
ty::Dynamic(ref object_type, ..) => {
let sig = object_type.projection_bounds().find_map(|pb| {
let pb = pb.with_self_ty(self.tcx, self.tcx.types.trait_object_dummy_self);
self.deduce_sig_from_projection(None, pb)
});
let kind = object_type
.principal_def_id()
.and_then(|did| self.tcx.fn_trait_kind_from_def_id(did));
(sig, kind)
}
ty::Infer(ty::TyVar(vid)) => self.deduce_closure_signature_from_predicates(
Ty::new_var(self.tcx, self.root_var(vid)),
self.obligations_for_self_ty(vid).map(|obl| (obl.predicate, obl.cause.span)),
),
ty::FnPtr(sig) => {
let expected_sig = ExpectedSig { cause_span: None, sig };
(Some(expected_sig), Some(ty::ClosureKind::Fn))
}
_ => (None, None),
}
}
fn deduce_closure_signature_from_predicates(
&self,
expected_ty: Ty<'tcx>,
predicates: impl DoubleEndedIterator<Item = (ty::Predicate<'tcx>, Span)>,
) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
let mut expected_sig = None;
let mut expected_kind = None;
for (pred, span) in traits::elaborate(
self.tcx,
// Reverse the obligations here, since `elaborate_*` uses a stack,
// and we want to keep inference generally in the same order of
// the registered obligations.
predicates.rev(),
)
// We only care about self bounds
.filter_only_self()
{
debug!(?pred);
let bound_predicate = pred.kind();
// Given a Projection predicate, we can potentially infer
// the complete signature.
if expected_sig.is_none()
&& let ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj_predicate)) = bound_predicate.skip_binder()
{
let inferred_sig = self.normalize(
span,
self.deduce_sig_from_projection(
Some(span),
bound_predicate.rebind(proj_predicate),
),
);
// Make sure that we didn't infer a signature that mentions itself.
// This can happen when we elaborate certain supertrait bounds that
// mention projections containing the `Self` type. See #105401.
struct MentionsTy<'tcx> {
expected_ty: Ty<'tcx>,
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MentionsTy<'tcx> {
type BreakTy = ();
fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
if t == self.expected_ty {
ControlFlow::Break(())
} else {
t.super_visit_with(self)
}
}
}
if inferred_sig.visit_with(&mut MentionsTy { expected_ty }).is_continue() {
expected_sig = inferred_sig;
}
}
// Even if we can't infer the full signature, we may be able to
// infer the kind. This can occur when we elaborate a predicate
// like `F : Fn<A>`. Note that due to subtyping we could encounter
// many viable options, so pick the most restrictive.
let trait_def_id = match bound_predicate.skip_binder() {
ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) => {
Some(data.projection_ty.trait_def_id(self.tcx))
}
ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) => Some(data.def_id()),
_ => None,
};
if let Some(closure_kind) =
trait_def_id.and_then(|def_id| self.tcx.fn_trait_kind_from_def_id(def_id))
{
expected_kind = Some(
expected_kind
.map_or_else(|| closure_kind, |current| cmp::min(current, closure_kind)),
);
}
}
(expected_sig, expected_kind)
}
/// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
/// everything we need to know about a closure or generator.
///
/// The `cause_span` should be the span that caused us to
/// have this expected signature, or `None` if we can't readily
/// know that.
#[instrument(level = "debug", skip(self, cause_span), ret)]
fn deduce_sig_from_projection(
&self,
cause_span: Option<Span>,
projection: ty::PolyProjectionPredicate<'tcx>,
) -> Option<ExpectedSig<'tcx>> {
let tcx = self.tcx;
let trait_def_id = projection.trait_def_id(tcx);
let is_fn = tcx.is_fn_trait(trait_def_id);
let gen_trait = tcx.lang_items().gen_trait();
let is_gen = gen_trait == Some(trait_def_id);
if !is_fn && !is_gen {
debug!("not fn or generator");
return None;
}
// Check that we deduce the signature from the `<_ as std::ops::Generator>::Return`
// associated item and not yield.
if is_gen && self.tcx.associated_item(projection.projection_def_id()).name != sym::Return {
debug!("not `Return` assoc item of `Generator`");
return None;
}
let input_tys = if is_fn {
let arg_param_ty = projection.skip_binder().projection_ty.args.type_at(1);
let arg_param_ty = self.resolve_vars_if_possible(arg_param_ty);
debug!(?arg_param_ty);
match arg_param_ty.kind() {
&ty::Tuple(tys) => tys,
_ => return None,
}
} else {
// Generators with a `()` resume type may be defined with 0 or 1 explicit arguments,
// else they must have exactly 1 argument. For now though, just give up in this case.
return None;
};
// Since this is a return parameter type it is safe to unwrap.
let ret_param_ty = projection.skip_binder().term.ty().unwrap();
let ret_param_ty = self.resolve_vars_if_possible(ret_param_ty);
debug!(?ret_param_ty);
let sig = projection.rebind(self.tcx.mk_fn_sig(
input_tys,
ret_param_ty,
false,
hir::Unsafety::Normal,
Abi::Rust,
));
Some(ExpectedSig { cause_span, sig })
}
fn sig_of_closure(
&self,
expr_def_id: LocalDefId,
decl: &hir::FnDecl<'_>,
body: &hir::Body<'_>,
expected_sig: Option<ExpectedSig<'tcx>>,
) -> ClosureSignatures<'tcx> {
if let Some(e) = expected_sig {
self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
} else {
self.sig_of_closure_no_expectation(expr_def_id, decl, body)
}
}
/// If there is no expected signature, then we will convert the
/// types that the user gave into a signature.
#[instrument(skip(self, expr_def_id, decl, body), level = "debug")]
fn sig_of_closure_no_expectation(
&self,
expr_def_id: LocalDefId,
decl: &hir::FnDecl<'_>,
body: &hir::Body<'_>,
) -> ClosureSignatures<'tcx> {
let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
self.closure_sigs(expr_def_id, body, bound_sig)
}
/// Invoked to compute the signature of a closure expression. This
/// combines any user-provided type annotations (e.g., `|x: u32|
/// -> u32 { .. }`) with the expected signature.
///
/// The approach is as follows:
///
/// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
/// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
/// - If we have no expectation `E`, then the signature of the closure is `S`.
/// - Otherwise, the signature of the closure is E. Moreover:
/// - Skolemize the late-bound regions in `E`, yielding `E'`.
/// - Instantiate all the late-bound regions bound in the closure within `S`
/// with fresh (existential) variables, yielding `S'`
/// - Require that `E' = S'`
/// - We could use some kind of subtyping relationship here,
/// I imagine, but equality is easier and works fine for
/// our purposes.
///
/// The key intuition here is that the user's types must be valid
/// from "the inside" of the closure, but the expectation
/// ultimately drives the overall signature.
///
/// # Examples
///
/// ```ignore (illustrative)
/// fn with_closure<F>(_: F)
/// where F: Fn(&u32) -> &u32 { .. }
///
/// with_closure(|x: &u32| { ... })
/// ```
///
/// Here:
/// - E would be `fn(&u32) -> &u32`.
/// - S would be `fn(&u32) -> ?T`
/// - E' is `&'!0 u32 -> &'!0 u32`
/// - S' is `&'?0 u32 -> ?T`
///
/// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
///
/// # Arguments
///
/// - `expr_def_id`: the `LocalDefId` of the closure expression
/// - `decl`: the HIR declaration of the closure
/// - `body`: the body of the closure
/// - `expected_sig`: the expected signature (if any). Note that
/// this is missing a binder: that is, there may be late-bound
/// regions with depth 1, which are bound then by the closure.
#[instrument(skip(self, expr_def_id, decl, body), level = "debug")]
fn sig_of_closure_with_expectation(
&self,
expr_def_id: LocalDefId,
decl: &hir::FnDecl<'_>,
body: &hir::Body<'_>,
expected_sig: ExpectedSig<'tcx>,
) -> ClosureSignatures<'tcx> {
// Watch out for some surprises and just ignore the
// expectation if things don't see to match up with what we
// expect.
if expected_sig.sig.c_variadic() != decl.c_variadic {
return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
} else if expected_sig.sig.skip_binder().inputs_and_output.len() != decl.inputs.len() + 1 {
return self.sig_of_closure_with_mismatched_number_of_arguments(
expr_def_id,
decl,
body,
expected_sig,
);
}
// Create a `PolyFnSig`. Note the oddity that late bound
// regions appearing free in `expected_sig` are now bound up
// in this binder we are creating.
assert!(!expected_sig.sig.skip_binder().has_vars_bound_above(ty::INNERMOST));
let bound_sig = expected_sig.sig.map_bound(|sig| {
self.tcx.mk_fn_sig(
sig.inputs().iter().cloned(),
sig.output(),
sig.c_variadic,
hir::Unsafety::Normal,
Abi::RustCall,
)
});
// `deduce_expectations_from_expected_type` introduces
// late-bound lifetimes defined elsewhere, which we now
// anonymize away, so as not to confuse the user.
let bound_sig = self.tcx.anonymize_bound_vars(bound_sig);
let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
// Up till this point, we have ignored the annotations that the user
// gave. This function will check that they unify successfully.
// Along the way, it also writes out entries for types that the user
// wrote into our typeck results, which are then later used by the privacy
// check.
match self.merge_supplied_sig_with_expectation(expr_def_id, decl, body, closure_sigs) {
Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
Err(_) => self.sig_of_closure_no_expectation(expr_def_id, decl, body),
}
}
fn sig_of_closure_with_mismatched_number_of_arguments(
&self,
expr_def_id: LocalDefId,
decl: &hir::FnDecl<'_>,
body: &hir::Body<'_>,
expected_sig: ExpectedSig<'tcx>,
) -> ClosureSignatures<'tcx> {
let hir = self.tcx.hir();
let expr_map_node = hir.get_by_def_id(expr_def_id);
let expected_args: Vec<_> = expected_sig
.sig
.skip_binder()
.inputs()
.iter()
.map(|ty| ArgKind::from_expected_ty(*ty, None))
.collect();
let (closure_span, closure_arg_span, found_args) =
match self.get_fn_like_arguments(expr_map_node) {
Some((sp, arg_sp, args)) => (Some(sp), arg_sp, args),
None => (None, None, Vec::new()),
};
let expected_span =
expected_sig.cause_span.unwrap_or_else(|| self.tcx.def_span(expr_def_id));
let guar = self
.report_arg_count_mismatch(
expected_span,
closure_span,
expected_args,
found_args,
true,
closure_arg_span,
)
.emit();
let error_sig = self.error_sig_of_closure(decl, guar);
self.closure_sigs(expr_def_id, body, error_sig)
}
/// Enforce the user's types against the expectation. See
/// `sig_of_closure_with_expectation` for details on the overall
/// strategy.
#[instrument(level = "debug", skip(self, expr_def_id, decl, body, expected_sigs))]
fn merge_supplied_sig_with_expectation(
&self,
expr_def_id: LocalDefId,
decl: &hir::FnDecl<'_>,
body: &hir::Body<'_>,
mut expected_sigs: ClosureSignatures<'tcx>,
) -> InferResult<'tcx, ClosureSignatures<'tcx>> {
// Get the signature S that the user gave.
//
// (See comment on `sig_of_closure_with_expectation` for the
// meaning of these letters.)
let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
debug!(?supplied_sig);
// FIXME(#45727): As discussed in [this comment][c1], naively
// forcing equality here actually results in suboptimal error
// messages in some cases. For now, if there would have been
// an obvious error, we fallback to declaring the type of the
// closure to be the one the user gave, which allows other
// error message code to trigger.
//
// However, I think [there is potential to do even better
// here][c2], since in *this* code we have the precise span of
// the type parameter in question in hand when we report the
// error.
//
// [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
// [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
self.commit_if_ok(|_| {
let mut all_obligations = vec![];
let inputs: Vec<_> = iter::zip(
decl.inputs,
supplied_sig.inputs().skip_binder(), // binder moved to (*) below
)
.map(|(hir_ty, &supplied_ty)| {
// Instantiate (this part of..) S to S', i.e., with fresh variables.
self.instantiate_binder_with_fresh_vars(
hir_ty.span,
LateBoundRegionConversionTime::FnCall,
// (*) binder moved to here
supplied_sig.inputs().rebind(supplied_ty),
)
})
.collect();
// The liberated version of this signature should be a subtype
// of the liberated form of the expectation.
for ((hir_ty, &supplied_ty), expected_ty) in iter::zip(
iter::zip(decl.inputs, &inputs),
expected_sigs.liberated_sig.inputs(), // `liberated_sig` is E'.
) {
// Check that E' = S'.
let cause = self.misc(hir_ty.span);
let InferOk { value: (), obligations } = self.at(&cause, self.param_env).eq(
DefineOpaqueTypes::Yes,
*expected_ty,
supplied_ty,
)?;
all_obligations.extend(obligations);
}
let supplied_output_ty = self.instantiate_binder_with_fresh_vars(
decl.output.span(),
LateBoundRegionConversionTime::FnCall,
supplied_sig.output(),
);
let cause = &self.misc(decl.output.span());
let InferOk { value: (), obligations } = self.at(cause, self.param_env).eq(
DefineOpaqueTypes::Yes,
expected_sigs.liberated_sig.output(),
supplied_output_ty,
)?;
all_obligations.extend(obligations);
let inputs = inputs.into_iter().map(|ty| self.resolve_vars_if_possible(ty));
expected_sigs.liberated_sig = self.tcx.mk_fn_sig(
inputs,
supplied_output_ty,
expected_sigs.liberated_sig.c_variadic,
hir::Unsafety::Normal,
Abi::RustCall,
);
Ok(InferOk { value: expected_sigs, obligations: all_obligations })
})
}
/// If there is no expected signature, then we will convert the
/// types that the user gave into a signature.
///
/// Also, record this closure signature for later.
#[instrument(skip(self, decl, body), level = "debug", ret)]
fn supplied_sig_of_closure(
&self,
expr_def_id: LocalDefId,
decl: &hir::FnDecl<'_>,
body: &hir::Body<'_>,
) -> ty::PolyFnSig<'tcx> {
let astconv: &dyn AstConv<'_> = self;
trace!("decl = {:#?}", decl);
debug!(?body.generator_kind);
let hir_id = self.tcx.hir().local_def_id_to_hir_id(expr_def_id);
let bound_vars = self.tcx.late_bound_vars(hir_id);
// First, convert the types that the user supplied (if any).
let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
let supplied_return = match decl.output {
hir::FnRetTy::Return(ref output) => astconv.ast_ty_to_ty(&output),
hir::FnRetTy::DefaultReturn(_) => match body.generator_kind {
// In the case of the async block that we create for a function body,
// we expect the return type of the block to match that of the enclosing
// function.
Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn)) => {
debug!("closure is async fn body");
let def_id = self.tcx.hir().body_owner_def_id(body.id());
self.deduce_future_output_from_obligations(expr_def_id, def_id).unwrap_or_else(
|| {
// AFAIK, deducing the future output
// always succeeds *except* in error cases
// like #65159. I'd like to return Error
// here, but I can't because I can't
// easily (and locally) prove that we
// *have* reported an
// error. --nikomatsakis
astconv.ty_infer(None, decl.output.span())
},
)
}
_ => astconv.ty_infer(None, decl.output.span()),
},
};
let result = ty::Binder::bind_with_vars(
self.tcx.mk_fn_sig(
supplied_arguments,
supplied_return,
decl.c_variadic,
hir::Unsafety::Normal,
Abi::RustCall,
),
bound_vars,
);
let c_result = self.inh.infcx.canonicalize_response(result);
self.typeck_results.borrow_mut().user_provided_sigs.insert(expr_def_id, c_result);
// Normalize only after registering in `user_provided_sigs`.
self.normalize(self.tcx.hir().span(hir_id), result)
}
/// Invoked when we are translating the generator that results
/// from desugaring an `async fn`. Returns the "sugared" return
/// type of the `async fn` -- that is, the return type that the
/// user specified. The "desugared" return type is an `impl
/// Future<Output = T>`, so we do this by searching through the
/// obligations to extract the `T`.
#[instrument(skip(self), level = "debug", ret)]
fn deduce_future_output_from_obligations(
&self,
expr_def_id: LocalDefId,
body_def_id: LocalDefId,
) -> Option<Ty<'tcx>> {
let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
span_bug!(self.tcx.def_span(expr_def_id), "async fn generator outside of a fn")
});
let ret_ty = ret_coercion.borrow().expected_ty();
let ret_ty = self.inh.infcx.shallow_resolve(ret_ty);
let get_future_output = |predicate: ty::Predicate<'tcx>, span| {
// Search for a pending obligation like
//
// `<R as Future>::Output = T`
//
// where R is the return type we are expecting. This type `T`
// will be our output.
let bound_predicate = predicate.kind();
if let ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj_predicate)) =
bound_predicate.skip_binder()
{
self.deduce_future_output_from_projection(
span,
bound_predicate.rebind(proj_predicate),
)
} else {
None
}
};
let span = self.tcx.def_span(expr_def_id);
let output_ty = match *ret_ty.kind() {
ty::Infer(ty::TyVar(ret_vid)) => {
self.obligations_for_self_ty(ret_vid).find_map(|obligation| {
get_future_output(obligation.predicate, obligation.cause.span)
})?
}
ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => self
.tcx
.explicit_item_bounds(def_id)
.iter_instantiated_copied(self.tcx, args)
.find_map(|(p, s)| get_future_output(p.as_predicate(), s))?,
ty::Error(_) => return None,
_ => span_bug!(
span,
"async fn generator return type not an inference variable: {ret_ty}"
),
};
let output_ty = self.normalize(span, output_ty);
// async fn that have opaque types in their return type need to redo the conversion to inference variables
// as they fetch the still opaque version from the signature.
let InferOk { value: output_ty, obligations } = self
.replace_opaque_types_with_inference_vars(output_ty, body_def_id, span, self.param_env);
self.register_predicates(obligations);
Some(output_ty)
}
/// Given a projection like
///
/// `<X as Future>::Output = T`
///
/// where `X` is some type that has no late-bound regions, returns
/// `Some(T)`. If the projection is for some other trait, returns
/// `None`.
fn deduce_future_output_from_projection(
&self,
cause_span: Span,
predicate: ty::PolyProjectionPredicate<'tcx>,
) -> Option<Ty<'tcx>> {
debug!("deduce_future_output_from_projection(predicate={:?})", predicate);
// We do not expect any bound regions in our predicate, so
// skip past the bound vars.
let Some(predicate) = predicate.no_bound_vars() else {
debug!("deduce_future_output_from_projection: has late-bound regions");
return None;
};
// Check that this is a projection from the `Future` trait.
let trait_def_id = predicate.projection_ty.trait_def_id(self.tcx);
let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(cause_span));
if trait_def_id != future_trait {
debug!("deduce_future_output_from_projection: not a future");
return None;
}
// The `Future` trait has only one associated item, `Output`,
// so check that this is what we see.
let output_assoc_item = self.tcx.associated_item_def_ids(future_trait)[0];
if output_assoc_item != predicate.projection_ty.def_id {
span_bug!(
cause_span,
"projecting associated item `{:?}` from future, which is not Output `{:?}`",
predicate.projection_ty.def_id,
output_assoc_item,
);
}
// Extract the type from the projection. Note that there can
// be no bound variables in this type because the "self type"
// does not have any regions in it.
let output_ty = self.resolve_vars_if_possible(predicate.term);
debug!("deduce_future_output_from_projection: output_ty={:?}", output_ty);
// This is a projection on a Fn trait so will always be a type.
Some(output_ty.ty().unwrap())
}
/// Converts the types that the user supplied, in case that doing
/// so should yield an error, but returns back a signature where
/// all parameters are of type `ty::Error`.
fn error_sig_of_closure(
&self,
decl: &hir::FnDecl<'_>,
guar: ErrorGuaranteed,
) -> ty::PolyFnSig<'tcx> {
let astconv: &dyn AstConv<'_> = self;
let err_ty = Ty::new_error(self.tcx, guar);
let supplied_arguments = decl.inputs.iter().map(|a| {
// Convert the types that the user supplied (if any), but ignore them.
astconv.ast_ty_to_ty(a);
err_ty
});
if let hir::FnRetTy::Return(ref output) = decl.output {
astconv.ast_ty_to_ty(&output);
}
let result = ty::Binder::dummy(self.tcx.mk_fn_sig(
supplied_arguments,
err_ty,
decl.c_variadic,
hir::Unsafety::Normal,
Abi::RustCall,
));
debug!("supplied_sig_of_closure: result={:?}", result);
result
}
fn closure_sigs(
&self,
expr_def_id: LocalDefId,
body: &hir::Body<'_>,
bound_sig: ty::PolyFnSig<'tcx>,
) -> ClosureSignatures<'tcx> {
let liberated_sig =
self.tcx().liberate_late_bound_regions(expr_def_id.to_def_id(), bound_sig);
let liberated_sig = self.normalize(body.value.span, liberated_sig);
ClosureSignatures { bound_sig, liberated_sig }
}
}