827 lines
32 KiB
Rust
827 lines
32 KiB
Rust
//! Code for type-checking closure expressions.
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use super::{check_fn, Expectation, FnCtxt, GeneratorTypes};
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use crate::astconv::AstConv;
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use hir::def::DefKind;
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use rustc_hir as hir;
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use rustc_hir::def_id::DefId;
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use rustc_hir::lang_items::LangItem;
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use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
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use rustc_infer::infer::LateBoundRegionConversionTime;
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use rustc_infer::infer::{InferOk, InferResult};
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use rustc_middle::ty::subst::InternalSubsts;
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use rustc_middle::ty::visit::TypeVisitable;
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use rustc_middle::ty::{self, Ty};
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use rustc_span::source_map::Span;
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use rustc_target::spec::abi::Abi;
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use rustc_trait_selection::traits::error_reporting::ArgKind;
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use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
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use std::cmp;
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use std::iter;
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/// What signature do we *expect* the closure to have from context?
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#[derive(Debug)]
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struct ExpectedSig<'tcx> {
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/// Span that gave us this expectation, if we know that.
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cause_span: Option<Span>,
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sig: ty::PolyFnSig<'tcx>,
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}
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struct ClosureSignatures<'tcx> {
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/// The signature users of the closure see.
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bound_sig: ty::PolyFnSig<'tcx>,
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/// The signature within the function body.
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/// This mostly differs in the sense that lifetimes are now early bound and any
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/// opaque types from the signature expectation are overriden in case there are
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/// explicit hidden types written by the user in the closure signature.
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liberated_sig: ty::FnSig<'tcx>,
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}
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impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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#[instrument(skip(self, expr, _capture, decl, body_id), level = "debug")]
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pub fn check_expr_closure(
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&self,
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expr: &hir::Expr<'_>,
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_capture: hir::CaptureBy,
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decl: &'tcx hir::FnDecl<'tcx>,
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body_id: hir::BodyId,
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gen: Option<hir::Movability>,
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expected: Expectation<'tcx>,
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) -> Ty<'tcx> {
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trace!("decl = {:#?}", decl);
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trace!("expr = {:#?}", expr);
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// It's always helpful for inference if we know the kind of
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// closure sooner rather than later, so first examine the expected
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// type, and see if can glean a closure kind from there.
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let (expected_sig, expected_kind) = match expected.to_option(self) {
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Some(ty) => self.deduce_expectations_from_expected_type(ty),
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None => (None, None),
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};
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let body = self.tcx.hir().body(body_id);
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self.check_closure(expr, expected_kind, decl, body, gen, expected_sig)
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}
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#[instrument(skip(self, expr, body, decl), level = "debug", ret)]
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fn check_closure(
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&self,
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expr: &hir::Expr<'_>,
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opt_kind: Option<ty::ClosureKind>,
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decl: &'tcx hir::FnDecl<'tcx>,
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body: &'tcx hir::Body<'tcx>,
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gen: Option<hir::Movability>,
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expected_sig: Option<ExpectedSig<'tcx>>,
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) -> Ty<'tcx> {
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trace!("decl = {:#?}", decl);
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let expr_def_id = self.tcx.hir().local_def_id(expr.hir_id);
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debug!(?expr_def_id);
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let ClosureSignatures { bound_sig, liberated_sig } =
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self.sig_of_closure(expr.hir_id, expr_def_id.to_def_id(), decl, body, expected_sig);
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debug!(?bound_sig, ?liberated_sig);
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let return_type_pre_known = !liberated_sig.output().is_ty_infer();
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let generator_types = check_fn(
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self,
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self.param_env.without_const(),
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liberated_sig,
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decl,
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expr.hir_id,
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body,
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gen,
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return_type_pre_known,
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)
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.1;
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let parent_substs = InternalSubsts::identity_for_item(
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self.tcx,
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self.tcx.typeck_root_def_id(expr_def_id.to_def_id()),
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);
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let tupled_upvars_ty = self.next_ty_var(TypeVariableOrigin {
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kind: TypeVariableOriginKind::ClosureSynthetic,
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span: self.tcx.hir().span(expr.hir_id),
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});
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if let Some(GeneratorTypes { resume_ty, yield_ty, interior, movability }) = generator_types
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{
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let generator_substs = ty::GeneratorSubsts::new(
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self.tcx,
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ty::GeneratorSubstsParts {
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parent_substs,
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resume_ty,
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yield_ty,
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return_ty: liberated_sig.output(),
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witness: interior,
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tupled_upvars_ty,
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},
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);
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return self.tcx.mk_generator(
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expr_def_id.to_def_id(),
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generator_substs.substs,
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movability,
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);
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}
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// Tuple up the arguments and insert the resulting function type into
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// the `closures` table.
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let sig = bound_sig.map_bound(|sig| {
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self.tcx.mk_fn_sig(
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iter::once(self.tcx.intern_tup(sig.inputs())),
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sig.output(),
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sig.c_variadic,
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sig.unsafety,
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sig.abi,
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)
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});
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debug!(?sig, ?opt_kind);
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let closure_kind_ty = match opt_kind {
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Some(kind) => kind.to_ty(self.tcx),
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// Create a type variable (for now) to represent the closure kind.
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// It will be unified during the upvar inference phase (`upvar.rs`)
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None => self.next_ty_var(TypeVariableOrigin {
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// FIXME(eddyb) distinguish closure kind inference variables from the rest.
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kind: TypeVariableOriginKind::ClosureSynthetic,
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span: expr.span,
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}),
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};
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let closure_substs = ty::ClosureSubsts::new(
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self.tcx,
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ty::ClosureSubstsParts {
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parent_substs,
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closure_kind_ty,
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closure_sig_as_fn_ptr_ty: self.tcx.mk_fn_ptr(sig),
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tupled_upvars_ty,
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},
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);
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self.tcx.mk_closure(expr_def_id.to_def_id(), closure_substs.substs)
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}
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/// Given the expected type, figures out what it can about this closure we
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/// are about to type check:
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#[instrument(skip(self), level = "debug")]
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fn deduce_expectations_from_expected_type(
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&self,
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expected_ty: Ty<'tcx>,
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) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
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match *expected_ty.kind() {
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ty::Opaque(def_id, substs) => {
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let bounds = self.tcx.bound_explicit_item_bounds(def_id);
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let sig = bounds
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.transpose_iter()
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.map(|e| e.map_bound(|e| *e).transpose_tuple2())
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.find_map(|(pred, span)| match pred.0.kind().skip_binder() {
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ty::PredicateKind::Projection(proj_predicate) => self
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.deduce_sig_from_projection(
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Some(span.0),
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pred.0
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.kind()
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.rebind(pred.rebind(proj_predicate).subst(self.tcx, substs)),
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),
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_ => None,
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});
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let kind = bounds
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.transpose_iter()
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.map(|e| e.map_bound(|e| *e).transpose_tuple2())
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.filter_map(|(pred, _)| match pred.0.kind().skip_binder() {
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ty::PredicateKind::Trait(tp) => {
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self.tcx.fn_trait_kind_from_lang_item(tp.def_id())
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}
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_ => None,
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})
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.fold(None, |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
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trace!(?sig, ?kind);
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(sig, kind)
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}
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ty::Dynamic(ref object_type, ..) => {
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let sig = object_type.projection_bounds().find_map(|pb| {
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let pb = pb.with_self_ty(self.tcx, self.tcx.types.trait_object_dummy_self);
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self.deduce_sig_from_projection(None, pb)
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});
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let kind = object_type
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.principal_def_id()
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.and_then(|did| self.tcx.fn_trait_kind_from_lang_item(did));
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(sig, kind)
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}
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ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
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ty::FnPtr(sig) => {
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let expected_sig = ExpectedSig { cause_span: None, sig };
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(Some(expected_sig), Some(ty::ClosureKind::Fn))
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}
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_ => (None, None),
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}
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}
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fn deduce_expectations_from_obligations(
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&self,
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expected_vid: ty::TyVid,
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) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
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let expected_sig =
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self.obligations_for_self_ty(expected_vid).find_map(|(_, obligation)| {
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debug!(?obligation.predicate);
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let bound_predicate = obligation.predicate.kind();
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if let ty::PredicateKind::Projection(proj_predicate) =
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obligation.predicate.kind().skip_binder()
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{
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// Given a Projection predicate, we can potentially infer
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// the complete signature.
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self.deduce_sig_from_projection(
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Some(obligation.cause.span),
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bound_predicate.rebind(proj_predicate),
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)
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} else {
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None
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}
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});
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// Even if we can't infer the full signature, we may be able to
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// infer the kind. This can occur when we elaborate a predicate
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// like `F : Fn<A>`. Note that due to subtyping we could encounter
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// many viable options, so pick the most restrictive.
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let expected_kind = self
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.obligations_for_self_ty(expected_vid)
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.filter_map(|(tr, _)| self.tcx.fn_trait_kind_from_lang_item(tr.def_id()))
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.fold(None, |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
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(expected_sig, expected_kind)
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}
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/// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
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/// everything we need to know about a closure or generator.
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///
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/// The `cause_span` should be the span that caused us to
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/// have this expected signature, or `None` if we can't readily
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/// know that.
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#[instrument(level = "debug", skip(self, cause_span), ret)]
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fn deduce_sig_from_projection(
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&self,
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cause_span: Option<Span>,
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projection: ty::PolyProjectionPredicate<'tcx>,
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) -> Option<ExpectedSig<'tcx>> {
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let tcx = self.tcx;
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let trait_def_id = projection.trait_def_id(tcx);
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let is_fn = tcx.fn_trait_kind_from_lang_item(trait_def_id).is_some();
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let gen_trait = tcx.require_lang_item(LangItem::Generator, cause_span);
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let is_gen = gen_trait == trait_def_id;
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if !is_fn && !is_gen {
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debug!("not fn or generator");
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return None;
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}
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if is_gen {
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// Check that we deduce the signature from the `<_ as std::ops::Generator>::Return`
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// associated item and not yield.
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let return_assoc_item = self.tcx.associated_item_def_ids(gen_trait)[1];
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if return_assoc_item != projection.projection_def_id() {
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debug!("not return assoc item of generator");
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return None;
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}
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}
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let input_tys = if is_fn {
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let arg_param_ty = projection.skip_binder().projection_ty.substs.type_at(1);
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let arg_param_ty = self.resolve_vars_if_possible(arg_param_ty);
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debug!(?arg_param_ty);
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match arg_param_ty.kind() {
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&ty::Tuple(tys) => tys,
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_ => return None,
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}
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} else {
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// Generators with a `()` resume type may be defined with 0 or 1 explicit arguments,
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// else they must have exactly 1 argument. For now though, just give up in this case.
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return None;
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};
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// Since this is a return parameter type it is safe to unwrap.
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let ret_param_ty = projection.skip_binder().term.ty().unwrap();
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let ret_param_ty = self.resolve_vars_if_possible(ret_param_ty);
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debug!(?ret_param_ty);
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let sig = projection.rebind(self.tcx.mk_fn_sig(
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input_tys.iter(),
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ret_param_ty,
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false,
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hir::Unsafety::Normal,
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Abi::Rust,
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));
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Some(ExpectedSig { cause_span, sig })
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}
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fn sig_of_closure(
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&self,
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hir_id: hir::HirId,
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expr_def_id: DefId,
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decl: &hir::FnDecl<'_>,
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body: &hir::Body<'_>,
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expected_sig: Option<ExpectedSig<'tcx>>,
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) -> ClosureSignatures<'tcx> {
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if let Some(e) = expected_sig {
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self.sig_of_closure_with_expectation(hir_id, expr_def_id, decl, body, e)
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} else {
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self.sig_of_closure_no_expectation(hir_id, expr_def_id, decl, body)
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}
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}
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/// If there is no expected signature, then we will convert the
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/// types that the user gave into a signature.
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#[instrument(skip(self, hir_id, expr_def_id, decl, body), level = "debug")]
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fn sig_of_closure_no_expectation(
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&self,
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hir_id: hir::HirId,
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expr_def_id: DefId,
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decl: &hir::FnDecl<'_>,
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body: &hir::Body<'_>,
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) -> ClosureSignatures<'tcx> {
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let bound_sig = self.supplied_sig_of_closure(hir_id, expr_def_id, decl, body);
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self.closure_sigs(expr_def_id, body, bound_sig)
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}
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/// Invoked to compute the signature of a closure expression. This
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/// combines any user-provided type annotations (e.g., `|x: u32|
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/// -> u32 { .. }`) with the expected signature.
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///
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/// The approach is as follows:
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///
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/// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
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/// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
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/// - If we have no expectation `E`, then the signature of the closure is `S`.
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/// - Otherwise, the signature of the closure is E. Moreover:
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/// - Skolemize the late-bound regions in `E`, yielding `E'`.
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/// - Instantiate all the late-bound regions bound in the closure within `S`
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/// with fresh (existential) variables, yielding `S'`
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/// - Require that `E' = S'`
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/// - We could use some kind of subtyping relationship here,
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/// I imagine, but equality is easier and works fine for
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/// our purposes.
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///
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/// The key intuition here is that the user's types must be valid
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/// from "the inside" of the closure, but the expectation
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/// ultimately drives the overall signature.
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///
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/// # Examples
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///
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/// ```ignore (illustrative)
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/// fn with_closure<F>(_: F)
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/// where F: Fn(&u32) -> &u32 { .. }
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///
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/// with_closure(|x: &u32| { ... })
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/// ```
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///
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/// Here:
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/// - E would be `fn(&u32) -> &u32`.
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/// - S would be `fn(&u32) ->
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/// - E' is `&'!0 u32 -> &'!0 u32`
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/// - S' is `&'?0 u32 -> ?T`
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///
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/// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
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///
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/// # Arguments
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///
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/// - `expr_def_id`: the `DefId` of the closure expression
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/// - `decl`: the HIR declaration of the closure
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/// - `body`: the body of the closure
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/// - `expected_sig`: the expected signature (if any). Note that
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/// this is missing a binder: that is, there may be late-bound
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/// regions with depth 1, which are bound then by the closure.
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#[instrument(skip(self, hir_id, expr_def_id, decl, body), level = "debug")]
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fn sig_of_closure_with_expectation(
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&self,
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hir_id: hir::HirId,
|
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expr_def_id: DefId,
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decl: &hir::FnDecl<'_>,
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body: &hir::Body<'_>,
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expected_sig: ExpectedSig<'tcx>,
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) -> ClosureSignatures<'tcx> {
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// Watch out for some surprises and just ignore the
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// expectation if things don't see to match up with what we
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// expect.
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if expected_sig.sig.c_variadic() != decl.c_variadic {
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return self.sig_of_closure_no_expectation(hir_id, expr_def_id, decl, body);
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} else if expected_sig.sig.skip_binder().inputs_and_output.len() != decl.inputs.len() + 1 {
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return self.sig_of_closure_with_mismatched_number_of_arguments(
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expr_def_id,
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decl,
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body,
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expected_sig,
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);
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}
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|
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// Create a `PolyFnSig`. Note the oddity that late bound
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// regions appearing free in `expected_sig` are now bound up
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// in this binder we are creating.
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assert!(!expected_sig.sig.skip_binder().has_vars_bound_above(ty::INNERMOST));
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let bound_sig = expected_sig.sig.map_bound(|sig| {
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self.tcx.mk_fn_sig(
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sig.inputs().iter().cloned(),
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sig.output(),
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sig.c_variadic,
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hir::Unsafety::Normal,
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Abi::RustCall,
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)
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});
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|
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// `deduce_expectations_from_expected_type` introduces
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// late-bound lifetimes defined elsewhere, which we now
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// anonymize away, so as not to confuse the user.
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let bound_sig = self.tcx.anonymize_late_bound_regions(bound_sig);
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|
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let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
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|
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// Up till this point, we have ignored the annotations that the user
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// gave. This function will check that they unify successfully.
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// Along the way, it also writes out entries for types that the user
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// wrote into our typeck results, which are then later used by the privacy
|
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// check.
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match self.merge_supplied_sig_with_expectation(
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hir_id,
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expr_def_id,
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decl,
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body,
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closure_sigs,
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) {
|
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Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
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|
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)
|
|
.transpose_iter()
|
|
.map(|e| e.map_bound(|e| *e).transpose_tuple2())
|
|
.find_map(|(p, s)| get_future_output(p.subst(self.tcx, substs), s.0))?,
|
|
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)
|
|
.transpose_iter()
|
|
.map(|e| e.map_bound(|e| *e).transpose_tuple2())
|
|
.find_map(|(p, s)| get_future_output(p.subst(self.tcx, proj.substs), s.0))?
|
|
}
|
|
_ => 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 }
|
|
}
|
|
}
|