--- /dev/null
+//! Code for type-checking closure expressions.
+
+use super::{check_fn, Expectation, FnCtxt, GeneratorTypes};
+
+use hir::def::DefKind;
+use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
+use rustc_hir::lang_items::LangItem;
+use rustc_hir_analysis::astconv::AstConv;
+use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use rustc_infer::infer::LateBoundRegionConversionTime;
+use rustc_infer::infer::{InferOk, InferResult};
+use rustc_middle::ty::subst::InternalSubsts;
+use rustc_middle::ty::visit::TypeVisitable;
+use rustc_middle::ty::{self, Ty};
+use rustc_span::source_map::Span;
+use rustc_target::spec::abi::Abi;
+use rustc_trait_selection::traits::error_reporting::ArgKind;
+use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
+use std::cmp;
+use std::iter;
+
+/// What signature do we *expect* the closure to have from context?
+#[derive(Debug)]
+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 overriden 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, expr, _capture, decl, body_id), level = "debug")]
+ pub fn check_expr_closure(
+ &self,
+ expr: &hir::Expr<'_>,
+ _capture: hir::CaptureBy,
+ decl: &'tcx hir::FnDecl<'tcx>,
+ body_id: hir::BodyId,
+ gen: Option<hir::Movability>,
+ expected: Expectation<'tcx>,
+ ) -> Ty<'tcx> {
+ trace!("decl = {:#?}", decl);
+ trace!("expr = {:#?}", expr);
+
+ // 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_expectations_from_expected_type(ty),
+ None => (None, None),
+ };
+ let body = self.tcx.hir().body(body_id);
+ self.check_closure(expr, expected_kind, decl, body, gen, expected_sig)
+ }
+
+ #[instrument(skip(self, expr, body, decl), level = "debug", ret)]
+ fn check_closure(
+ &self,
+ expr: &hir::Expr<'_>,
+ opt_kind: Option<ty::ClosureKind>,
+ decl: &'tcx hir::FnDecl<'tcx>,
+ body: &'tcx hir::Body<'tcx>,
+ gen: Option<hir::Movability>,
+ expected_sig: Option<ExpectedSig<'tcx>>,
+ ) -> Ty<'tcx> {
+ trace!("decl = {:#?}", decl);
+ let expr_def_id = self.tcx.hir().local_def_id(expr.hir_id);
+ debug!(?expr_def_id);
+
+ let ClosureSignatures { bound_sig, liberated_sig } =
+ self.sig_of_closure(expr.hir_id, expr_def_id.to_def_id(), decl, body, expected_sig);
+
+ debug!(?bound_sig, ?liberated_sig);
+
+ let return_type_pre_known = !liberated_sig.output().is_ty_infer();
+
+ let generator_types = check_fn(
+ self,
+ self.param_env.without_const(),
+ liberated_sig,
+ decl,
+ expr.hir_id,
+ body,
+ gen,
+ return_type_pre_known,
+ )
+ .1;
+
+ let parent_substs = InternalSubsts::identity_for_item(
+ self.tcx,
+ self.tcx.typeck_root_def_id(expr_def_id.to_def_id()),
+ );
+
+ let tupled_upvars_ty = self.next_ty_var(TypeVariableOrigin {
+ kind: TypeVariableOriginKind::ClosureSynthetic,
+ span: self.tcx.hir().span(expr.hir_id),
+ });
+
+ if let Some(GeneratorTypes { resume_ty, yield_ty, interior, movability }) = generator_types
+ {
+ let generator_substs = ty::GeneratorSubsts::new(
+ self.tcx,
+ ty::GeneratorSubstsParts {
+ parent_substs,
+ resume_ty,
+ yield_ty,
+ return_ty: liberated_sig.output(),
+ witness: interior,
+ tupled_upvars_ty,
+ },
+ );
+
+ return self.tcx.mk_generator(
+ expr_def_id.to_def_id(),
+ generator_substs.substs,
+ 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(
+ iter::once(self.tcx.intern_tup(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_ty_var(TypeVariableOrigin {
+ // FIXME(eddyb) distinguish closure kind inference variables from the rest.
+ kind: TypeVariableOriginKind::ClosureSynthetic,
+ span: expr.span,
+ }),
+ };
+
+ let closure_substs = ty::ClosureSubsts::new(
+ self.tcx,
+ ty::ClosureSubstsParts {
+ parent_substs,
+ closure_kind_ty,
+ closure_sig_as_fn_ptr_ty: self.tcx.mk_fn_ptr(sig),
+ tupled_upvars_ty,
+ },
+ );
+
+ self.tcx.mk_closure(expr_def_id.to_def_id(), closure_substs.substs)
+ }
+
+ /// 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_expectations_from_expected_type(
+ &self,
+ expected_ty: Ty<'tcx>,
+ ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
+ match *expected_ty.kind() {
+ ty::Opaque(def_id, substs) => {
+ let bounds = self.tcx.bound_explicit_item_bounds(def_id);
+ let sig =
+ bounds.subst_iter_copied(self.tcx, substs).find_map(|(pred, span)| match pred
+ .kind()
+ .skip_binder()
+ {
+ ty::PredicateKind::Projection(proj_predicate) => self
+ .deduce_sig_from_projection(
+ Some(span),
+ pred.kind().rebind(proj_predicate),
+ ),
+ _ => None,
+ });
+
+ let kind = bounds
+ .0
+ .iter()
+ .filter_map(|(pred, _)| match pred.kind().skip_binder() {
+ ty::PredicateKind::Trait(tp) => {
+ self.tcx.fn_trait_kind_from_lang_item(tp.def_id())
+ }
+ _ => None,
+ })
+ .fold(None, |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
+ trace!(?sig, ?kind);
+ (sig, kind)
+ }
+ 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_lang_item(did));
+ (sig, kind)
+ }
+ ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
+ ty::FnPtr(sig) => {
+ let expected_sig = ExpectedSig { cause_span: None, sig };
+ (Some(expected_sig), Some(ty::ClosureKind::Fn))
+ }
+ _ => (None, None),
+ }
+ }
+
+ fn deduce_expectations_from_obligations(
+ &self,
+ expected_vid: ty::TyVid,
+ ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
+ let expected_sig =
+ self.obligations_for_self_ty(expected_vid).find_map(|(_, obligation)| {
+ debug!(?obligation.predicate);
+
+ let bound_predicate = obligation.predicate.kind();
+ if let ty::PredicateKind::Projection(proj_predicate) =
+ obligation.predicate.kind().skip_binder()
+ {
+ // Given a Projection predicate, we can potentially infer
+ // the complete signature.
+ self.deduce_sig_from_projection(
+ Some(obligation.cause.span),
+ bound_predicate.rebind(proj_predicate),
+ )
+ } else {
+ None
+ }
+ });
+
+ // 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 expected_kind = self
+ .obligations_for_self_ty(expected_vid)
+ .filter_map(|(tr, _)| self.tcx.fn_trait_kind_from_lang_item(tr.def_id()))
+ .fold(None, |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
+
+ (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.fn_trait_kind_from_lang_item(trait_def_id).is_some();
+ let gen_trait = tcx.require_lang_item(LangItem::Generator, cause_span);
+ let is_gen = gen_trait == trait_def_id;
+ if !is_fn && !is_gen {
+ debug!("not fn or generator");
+ return None;
+ }
+
+ if is_gen {
+ // Check that we deduce the signature from the `<_ as std::ops::Generator>::Return`
+ // associated item and not yield.
+ let return_assoc_item = self.tcx.associated_item_def_ids(gen_trait)[1];
+ if return_assoc_item != projection.projection_def_id() {
+ debug!("not return assoc item of generator");
+ return None;
+ }
+ }
+
+ let input_tys = if is_fn {
+ let arg_param_ty = projection.skip_binder().projection_ty.substs.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.iter(),
+ ret_param_ty,
+ false,
+ hir::Unsafety::Normal,
+ Abi::Rust,
+ ));
+
+ Some(ExpectedSig { cause_span, sig })
+ }
+
+ fn sig_of_closure(
+ &self,
+ hir_id: hir::HirId,
+ expr_def_id: DefId,
+ 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(hir_id, expr_def_id, decl, body, e)
+ } else {
+ self.sig_of_closure_no_expectation(hir_id, 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, hir_id, expr_def_id, decl, body), level = "debug")]
+ fn sig_of_closure_no_expectation(
+ &self,
+ hir_id: hir::HirId,
+ expr_def_id: DefId,
+ decl: &hir::FnDecl<'_>,
+ body: &hir::Body<'_>,
+ ) -> ClosureSignatures<'tcx> {
+ let bound_sig = self.supplied_sig_of_closure(hir_id, 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) ->
+ /// - 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 `DefId` 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, hir_id, expr_def_id, decl, body), level = "debug")]
+ fn sig_of_closure_with_expectation(
+ &self,
+ hir_id: hir::HirId,
+ expr_def_id: DefId,
+ 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(hir_id, 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_late_bound_regions(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(
+ hir_id,
+ expr_def_id,
+ decl,
+ body,
+ closure_sigs,
+ ) {
+ Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
+ Err(_) => self.sig_of_closure_no_expectation(hir_id, expr_def_id, decl, body),
+ }
+ }
+
+ fn sig_of_closure_with_mismatched_number_of_arguments(
+ &self,
+ expr_def_id: DefId,
+ decl: &hir::FnDecl<'_>,
+ body: &hir::Body<'_>,
+ expected_sig: ExpectedSig<'tcx>,
+ ) -> ClosureSignatures<'tcx> {
+ let hir = self.tcx.hir();
+ let expr_map_node = hir.get_if_local(expr_def_id).unwrap();
+ let expected_args: Vec<_> = expected_sig
+ .sig
+ .skip_binder()
+ .inputs()
+ .iter()
+ .map(|ty| ArgKind::from_expected_ty(*ty, None))
+ .collect();
+ let (closure_span, found_args) = match self.get_fn_like_arguments(expr_map_node) {
+ Some((sp, args)) => (Some(sp), args),
+ None => (None, Vec::new()),
+ };
+ let expected_span =
+ expected_sig.cause_span.unwrap_or_else(|| hir.span_if_local(expr_def_id).unwrap());
+ self.report_arg_count_mismatch(
+ expected_span,
+ closure_span,
+ expected_args,
+ found_args,
+ true,
+ )
+ .emit();
+
+ let error_sig = self.error_sig_of_closure(decl);
+
+ 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, hir_id, expr_def_id, decl, body, expected_sigs))]
+ fn merge_supplied_sig_with_expectation(
+ &self,
+ hir_id: hir::HirId,
+ expr_def_id: DefId,
+ 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(hir_id, 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.replace_bound_vars_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(*expected_ty, supplied_ty)?;
+ all_obligations.extend(obligations);
+ }
+
+ let supplied_output_ty = self.replace_bound_vars_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(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,
+ hir_id: hir::HirId,
+ expr_def_id: DefId,
+ decl: &hir::FnDecl<'_>,
+ body: &hir::Body<'_>,
+ ) -> ty::PolyFnSig<'tcx> {
+ let astconv: &dyn AstConv<'_> = self;
+
+ trace!("decl = {:#?}", decl);
+ debug!(?body.generator_kind);
+
+ 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");
+ self.deduce_future_output_from_obligations(expr_def_id, body.id().hir_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,
+ );
+ // Astconv can't normalize inputs or outputs with escaping bound vars,
+ // so normalize them here, after we've wrapped them in a binder.
+ let result = self.normalize_associated_types_in(self.tcx.hir().span(hir_id), result);
+
+ let c_result = self.inh.infcx.canonicalize_response(result);
+ self.typeck_results.borrow_mut().user_provided_sigs.insert(expr_def_id, c_result);
+
+ 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: DefId,
+ body_id: hir::HirId,
+ ) -> 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::Projection(proj_predicate) = bound_predicate.skip_binder() {
+ self.deduce_future_output_from_projection(
+ span,
+ bound_predicate.rebind(proj_predicate),
+ )
+ } else {
+ None
+ }
+ };
+
+ 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::Opaque(def_id, substs) => self
+ .tcx
+ .bound_explicit_item_bounds(def_id)
+ .subst_iter_copied(self.tcx, substs)
+ .find_map(|(p, s)| get_future_output(p, s))?,
+ ty::Error(_) => return None,
+ ty::Projection(proj)
+ if self.tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder =>
+ {
+ self.tcx
+ .bound_explicit_item_bounds(proj.item_def_id)
+ .subst_iter_copied(self.tcx, proj.substs)
+ .find_map(|(p, s)| get_future_output(p, s))?
+ }
+ _ => span_bug!(
+ self.tcx.def_span(expr_def_id),
+ "async fn generator return type not an inference variable: {ret_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_id,
+ self.tcx.def_span(expr_def_id),
+ 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.item_def_id {
+ span_bug!(
+ cause_span,
+ "projecting associated item `{:?}` from future, which is not Output `{:?}`",
+ predicate.projection_ty.item_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 `TyErr`.
+ fn error_sig_of_closure(&self, decl: &hir::FnDecl<'_>) -> ty::PolyFnSig<'tcx> {
+ let astconv: &dyn AstConv<'_> = self;
+
+ 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);
+ self.tcx.ty_error()
+ });
+
+ 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,
+ self.tcx.ty_error(),
+ decl.c_variadic,
+ hir::Unsafety::Normal,
+ Abi::RustCall,
+ ));
+
+ debug!("supplied_sig_of_closure: result={:?}", result);
+
+ result
+ }
+
+ fn closure_sigs(
+ &self,
+ expr_def_id: DefId,
+ body: &hir::Body<'_>,
+ bound_sig: ty::PolyFnSig<'tcx>,
+ ) -> ClosureSignatures<'tcx> {
+ let liberated_sig = self.tcx().liberate_late_bound_regions(expr_def_id, bound_sig);
+ let liberated_sig = self.inh.normalize_associated_types_in(
+ body.value.span,
+ body.value.hir_id,
+ self.param_env,
+ liberated_sig,
+ );
+ ClosureSignatures { bound_sig, liberated_sig }
+ }
+}
projects / rustc.git / blobdiff