| //! Inference of closure parameter types based on the closure's expected type. |
| |
| pub(crate) mod analysis; |
| |
| use std::ops::ControlFlow; |
| use std::{iter, mem}; |
| |
| use hir_def::{ |
| TraitId, |
| hir::{ClosureKind, ExprId, PatId}, |
| lang_item::LangItem, |
| type_ref::TypeRefId, |
| }; |
| use rustc_type_ir::{ |
| ClosureArgs, ClosureArgsParts, CoroutineArgs, CoroutineArgsParts, Interner, TypeSuperVisitable, |
| TypeVisitable, TypeVisitableExt, TypeVisitor, |
| inherent::{BoundExistentialPredicates, GenericArgs as _, IntoKind, SliceLike, Ty as _}, |
| }; |
| use tracing::debug; |
| |
| use crate::traits::FnTrait; |
| use crate::{ |
| FnAbi, |
| db::{InternedClosure, InternedCoroutine}, |
| infer::{BreakableKind, Diverges, coerce::CoerceMany}, |
| next_solver::{ |
| AliasTy, Binder, ClauseKind, DbInterner, ErrorGuaranteed, FnSig, GenericArgs, PolyFnSig, |
| PolyProjectionPredicate, Predicate, PredicateKind, SolverDefId, Ty, TyKind, |
| abi::Safety, |
| infer::{ |
| BoundRegionConversionTime, DefineOpaqueTypes, InferOk, InferResult, |
| traits::{ObligationCause, PredicateObligations}, |
| }, |
| mapping::{ChalkToNextSolver, NextSolverToChalk}, |
| util::explicit_item_bounds, |
| }, |
| }; |
| |
| use super::{Expectation, InferenceContext}; |
| |
| #[derive(Debug)] |
| struct ClosureSignatures<'tcx> { |
| /// The signature users of the closure see. |
| bound_sig: 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: FnSig<'tcx>, |
| } |
| |
| impl<'db> InferenceContext<'db> { |
| pub(super) fn infer_closure( |
| &mut self, |
| body: ExprId, |
| args: &[PatId], |
| ret_type: Option<TypeRefId>, |
| arg_types: &[Option<TypeRefId>], |
| closure_kind: ClosureKind, |
| tgt_expr: ExprId, |
| expected: &Expectation, |
| ) -> crate::Ty { |
| assert_eq!(args.len(), arg_types.len()); |
| |
| let interner = self.table.interner; |
| let (expected_sig, expected_kind) = match expected.to_option(&mut self.table) { |
| Some(expected_ty) => { |
| self.deduce_closure_signature(expected_ty.to_nextsolver(interner), closure_kind) |
| } |
| None => (None, None), |
| }; |
| |
| let ClosureSignatures { bound_sig, liberated_sig } = |
| self.sig_of_closure(arg_types, ret_type, expected_sig); |
| let body_ret_ty = bound_sig.output().skip_binder(); |
| let sig_ty = Ty::new_fn_ptr(interner, bound_sig); |
| |
| let parent_args = GenericArgs::identity_for_item(interner, self.generic_def.into()); |
| let (id, ty, resume_yield_tys) = match closure_kind { |
| ClosureKind::Coroutine(_) => { |
| let yield_ty = self.table.next_ty_var(); |
| let resume_ty = liberated_sig |
| .inputs() |
| .get(0) |
| .unwrap_or(self.result.standard_types.unit.to_nextsolver(interner)); |
| |
| // FIXME: Infer the upvars later. |
| let parts = CoroutineArgsParts { |
| parent_args, |
| kind_ty: Ty::new_unit(interner), |
| resume_ty, |
| yield_ty, |
| return_ty: body_ret_ty, |
| tupled_upvars_ty: Ty::new_unit(interner), |
| }; |
| |
| let coroutine_id = |
| self.db.intern_coroutine(InternedCoroutine(self.owner, tgt_expr)).into(); |
| let coroutine_ty = Ty::new_coroutine( |
| interner, |
| coroutine_id, |
| CoroutineArgs::new(interner, parts).args, |
| ); |
| |
| ( |
| None, |
| coroutine_ty, |
| Some((resume_ty.to_chalk(interner), yield_ty.to_chalk(interner))), |
| ) |
| } |
| // FIXME(next-solver): `ClosureKind::Async` should really be a separate arm that creates a `CoroutineClosure`. |
| // But for now we treat it as a closure. |
| ClosureKind::Closure | ClosureKind::Async => { |
| let closure_id = self.db.intern_closure(InternedClosure(self.owner, tgt_expr)); |
| match expected_kind { |
| Some(kind) => { |
| self.result.closure_info.insert( |
| closure_id.into(), |
| ( |
| Vec::new(), |
| match kind { |
| rustc_type_ir::ClosureKind::Fn => FnTrait::Fn, |
| rustc_type_ir::ClosureKind::FnMut => FnTrait::FnMut, |
| rustc_type_ir::ClosureKind::FnOnce => FnTrait::FnOnce, |
| }, |
| ), |
| ); |
| } |
| None => {} |
| }; |
| // FIXME: Infer the kind and the upvars later when needed. |
| let parts = ClosureArgsParts { |
| parent_args, |
| closure_kind_ty: Ty::from_closure_kind( |
| interner, |
| expected_kind.unwrap_or(rustc_type_ir::ClosureKind::Fn), |
| ), |
| closure_sig_as_fn_ptr_ty: sig_ty, |
| tupled_upvars_ty: Ty::new_unit(interner), |
| }; |
| let closure_ty = Ty::new_closure( |
| interner, |
| closure_id.into(), |
| ClosureArgs::new(interner, parts).args, |
| ); |
| self.deferred_closures.entry(closure_id).or_default(); |
| self.add_current_closure_dependency(closure_id); |
| (Some(closure_id), closure_ty, None) |
| } |
| }; |
| |
| // Now go through the argument patterns |
| for (arg_pat, arg_ty) in args.iter().zip(bound_sig.skip_binder().inputs()) { |
| self.infer_top_pat(*arg_pat, &arg_ty.to_chalk(interner), None); |
| } |
| |
| // FIXME: lift these out into a struct |
| let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe); |
| let prev_closure = mem::replace(&mut self.current_closure, id); |
| let prev_ret_ty = mem::replace(&mut self.return_ty, body_ret_ty.to_chalk(interner)); |
| let prev_ret_coercion = self.return_coercion.replace(CoerceMany::new(body_ret_ty)); |
| let prev_resume_yield_tys = mem::replace(&mut self.resume_yield_tys, resume_yield_tys); |
| |
| self.with_breakable_ctx(BreakableKind::Border, None, None, |this| { |
| this.infer_return(body); |
| }); |
| |
| self.diverges = prev_diverges; |
| self.return_ty = prev_ret_ty; |
| self.return_coercion = prev_ret_coercion; |
| self.current_closure = prev_closure; |
| self.resume_yield_tys = prev_resume_yield_tys; |
| |
| ty.to_chalk(interner) |
| } |
| |
| fn fn_trait_kind_from_def_id(&self, trait_id: TraitId) -> Option<rustc_type_ir::ClosureKind> { |
| let lang_item = self.db.lang_attr(trait_id.into())?; |
| match lang_item { |
| LangItem::Fn => Some(rustc_type_ir::ClosureKind::Fn), |
| LangItem::FnMut => Some(rustc_type_ir::ClosureKind::FnMut), |
| LangItem::FnOnce => Some(rustc_type_ir::ClosureKind::FnOnce), |
| _ => None, |
| } |
| } |
| |
| fn async_fn_trait_kind_from_def_id( |
| &self, |
| trait_id: TraitId, |
| ) -> Option<rustc_type_ir::ClosureKind> { |
| let lang_item = self.db.lang_attr(trait_id.into())?; |
| match lang_item { |
| LangItem::AsyncFn => Some(rustc_type_ir::ClosureKind::Fn), |
| LangItem::AsyncFnMut => Some(rustc_type_ir::ClosureKind::FnMut), |
| LangItem::AsyncFnOnce => Some(rustc_type_ir::ClosureKind::FnOnce), |
| _ => None, |
| } |
| } |
| |
| /// Given the expected type, figures out what it can about this closure we |
| /// are about to type check: |
| fn deduce_closure_signature( |
| &mut self, |
| expected_ty: Ty<'db>, |
| closure_kind: ClosureKind, |
| ) -> (Option<PolyFnSig<'db>>, Option<rustc_type_ir::ClosureKind>) { |
| match expected_ty.kind() { |
| TyKind::Alias(rustc_type_ir::Opaque, AliasTy { def_id, args, .. }) => self |
| .deduce_closure_signature_from_predicates( |
| expected_ty, |
| closure_kind, |
| explicit_item_bounds(self.table.interner, def_id) |
| .iter_instantiated(self.table.interner, args) |
| .map(|clause| clause.as_predicate()), |
| ), |
| TyKind::Dynamic(object_type, ..) => { |
| let sig = object_type.projection_bounds().into_iter().find_map(|pb| { |
| let pb = |
| pb.with_self_ty(self.table.interner, Ty::new_unit(self.table.interner)); |
| self.deduce_sig_from_projection(closure_kind, pb) |
| }); |
| let kind = object_type |
| .principal_def_id() |
| .and_then(|did| self.fn_trait_kind_from_def_id(did.0)); |
| (sig, kind) |
| } |
| TyKind::Infer(rustc_type_ir::TyVar(vid)) => self |
| .deduce_closure_signature_from_predicates( |
| Ty::new_var(self.table.interner, self.table.infer_ctxt.root_var(vid)), |
| closure_kind, |
| self.table.obligations_for_self_ty(vid).into_iter().map(|obl| obl.predicate), |
| ), |
| TyKind::FnPtr(sig_tys, hdr) => match closure_kind { |
| ClosureKind::Closure => { |
| let expected_sig = sig_tys.with(hdr); |
| (Some(expected_sig), Some(rustc_type_ir::ClosureKind::Fn)) |
| } |
| ClosureKind::Coroutine(_) | ClosureKind::Async => (None, None), |
| }, |
| _ => (None, None), |
| } |
| } |
| |
| fn deduce_closure_signature_from_predicates( |
| &mut self, |
| expected_ty: Ty<'db>, |
| closure_kind: ClosureKind, |
| predicates: impl DoubleEndedIterator<Item = Predicate<'db>>, |
| ) -> (Option<PolyFnSig<'db>>, Option<rustc_type_ir::ClosureKind>) { |
| let mut expected_sig = None; |
| let mut expected_kind = None; |
| |
| for pred in rustc_type_ir::elaborate::elaborate( |
| self.table.interner, |
| // 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 PredicateKind::Clause(ClauseKind::Projection(proj_predicate)) = |
| bound_predicate.skip_binder() |
| { |
| let inferred_sig = self.deduce_sig_from_projection( |
| closure_kind, |
| 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<'db> { |
| expected_ty: Ty<'db>, |
| } |
| impl<'db> TypeVisitor<DbInterner<'db>> for MentionsTy<'db> { |
| type Result = ControlFlow<()>; |
| |
| fn visit_ty(&mut self, t: Ty<'db>) -> Self::Result { |
| if t == self.expected_ty { |
| ControlFlow::Break(()) |
| } else { |
| t.super_visit_with(self) |
| } |
| } |
| } |
| |
| // Don't infer a closure signature from a goal that names the closure type as this will |
| // (almost always) lead to occurs check errors later in type checking. |
| if let Some(inferred_sig) = inferred_sig { |
| // In the new solver it is difficult to explicitly normalize the inferred signature as we |
| // would have to manually handle universes and rewriting bound vars and placeholders back |
| // and forth. |
| // |
| // Instead we take advantage of the fact that we relating an inference variable with an alias |
| // will only instantiate the variable if the alias is rigid(*not quite). Concretely we: |
| // - Create some new variable `?sig` |
| // - Equate `?sig` with the unnormalized signature, e.g. `fn(<Foo<?x> as Trait>::Assoc)` |
| // - Depending on whether `<Foo<?x> as Trait>::Assoc` is rigid, ambiguous or normalizeable, |
| // we will either wind up with `?sig=<Foo<?x> as Trait>::Assoc/?y/ConcreteTy` respectively. |
| // |
| // *: In cases where there are ambiguous aliases in the signature that make use of bound vars |
| // they will wind up present in `?sig` even though they are non-rigid. |
| // |
| // This is a bit weird and means we may wind up discarding the goal due to it naming `expected_ty` |
| // even though the normalized form may not name `expected_ty`. However, this matches the existing |
| // behaviour of the old solver and would be technically a breaking change to fix. |
| let generalized_fnptr_sig = self.table.next_ty_var(); |
| let inferred_fnptr_sig = Ty::new_fn_ptr(self.table.interner, inferred_sig); |
| // FIXME: Report diagnostics. |
| _ = self |
| .table |
| .infer_ctxt |
| .at(&ObligationCause::new(), self.table.param_env) |
| .eq(DefineOpaqueTypes::Yes, inferred_fnptr_sig, generalized_fnptr_sig) |
| .map(|infer_ok| self.table.register_infer_ok(infer_ok)); |
| |
| let resolved_sig = |
| self.table.infer_ctxt.resolve_vars_if_possible(generalized_fnptr_sig); |
| |
| if resolved_sig.visit_with(&mut MentionsTy { expected_ty }).is_continue() { |
| expected_sig = Some(resolved_sig.fn_sig(self.table.interner)); |
| } |
| } else 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() { |
| PredicateKind::Clause(ClauseKind::Projection(data)) => { |
| Some(data.projection_term.trait_def_id(self.table.interner).0) |
| } |
| PredicateKind::Clause(ClauseKind::Trait(data)) => Some(data.def_id().0), |
| _ => None, |
| }; |
| |
| if let Some(trait_def_id) = trait_def_id { |
| let found_kind = match closure_kind { |
| ClosureKind::Closure => self.fn_trait_kind_from_def_id(trait_def_id), |
| ClosureKind::Async => self |
| .async_fn_trait_kind_from_def_id(trait_def_id) |
| .or_else(|| self.fn_trait_kind_from_def_id(trait_def_id)), |
| _ => None, |
| }; |
| |
| if let Some(found_kind) = found_kind { |
| // always use the closure kind that is more permissive. |
| match (expected_kind, found_kind) { |
| (None, _) => expected_kind = Some(found_kind), |
| ( |
| Some(rustc_type_ir::ClosureKind::FnMut), |
| rustc_type_ir::ClosureKind::Fn, |
| ) => expected_kind = Some(rustc_type_ir::ClosureKind::Fn), |
| ( |
| Some(rustc_type_ir::ClosureKind::FnOnce), |
| rustc_type_ir::ClosureKind::Fn | rustc_type_ir::ClosureKind::FnMut, |
| ) => expected_kind = Some(found_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 coroutine. |
| /// |
| /// The `cause_span` should be the span that caused us to |
| /// have this expected signature, or `None` if we can't readily |
| /// know that. |
| fn deduce_sig_from_projection( |
| &mut self, |
| closure_kind: ClosureKind, |
| projection: PolyProjectionPredicate<'db>, |
| ) -> Option<PolyFnSig<'db>> { |
| let SolverDefId::TypeAliasId(def_id) = projection.item_def_id() else { unreachable!() }; |
| let lang_item = self.db.lang_attr(def_id.into()); |
| |
| // For now, we only do signature deduction based off of the `Fn` and `AsyncFn` traits, |
| // for closures and async closures, respectively. |
| match closure_kind { |
| ClosureKind::Closure if lang_item == Some(LangItem::FnOnceOutput) => { |
| self.extract_sig_from_projection(projection) |
| } |
| ClosureKind::Async if lang_item == Some(LangItem::AsyncFnOnceOutput) => { |
| self.extract_sig_from_projection(projection) |
| } |
| // It's possible we've passed the closure to a (somewhat out-of-fashion) |
| // `F: FnOnce() -> Fut, Fut: Future<Output = T>` style bound. Let's still |
| // guide inference here, since it's beneficial for the user. |
| ClosureKind::Async if lang_item == Some(LangItem::FnOnceOutput) => { |
| self.extract_sig_from_projection_and_future_bound(projection) |
| } |
| _ => None, |
| } |
| } |
| |
| /// Given an `FnOnce::Output` or `AsyncFn::Output` projection, extract the args |
| /// and return type to infer a [`ty::PolyFnSig`] for the closure. |
| fn extract_sig_from_projection( |
| &self, |
| projection: PolyProjectionPredicate<'db>, |
| ) -> Option<PolyFnSig<'db>> { |
| let projection = self.table.infer_ctxt.resolve_vars_if_possible(projection); |
| |
| let arg_param_ty = projection.skip_binder().projection_term.args.type_at(1); |
| debug!(?arg_param_ty); |
| |
| let TyKind::Tuple(input_tys) = arg_param_ty.kind() else { |
| return None; |
| }; |
| |
| // Since this is a return parameter type it is safe to unwrap. |
| let ret_param_ty = projection.skip_binder().term.expect_type(); |
| debug!(?ret_param_ty); |
| |
| let sig = projection.rebind(self.table.interner.mk_fn_sig( |
| input_tys, |
| ret_param_ty, |
| false, |
| Safety::Safe, |
| FnAbi::Rust, |
| )); |
| |
| Some(sig) |
| } |
| |
| /// When an async closure is passed to a function that has a "two-part" `Fn` |
| /// and `Future` trait bound, like: |
| /// |
| /// ```rust |
| /// use std::future::Future; |
| /// |
| /// fn not_exactly_an_async_closure<F, Fut>(_f: F) |
| /// where |
| /// F: FnOnce(String, u32) -> Fut, |
| /// Fut: Future<Output = i32>, |
| /// {} |
| /// ``` |
| /// |
| /// The we want to be able to extract the signature to guide inference in the async |
| /// closure. We will have two projection predicates registered in this case. First, |
| /// we identify the `FnOnce<Args, Output = ?Fut>` bound, and if the output type is |
| /// an inference variable `?Fut`, we check if that is bounded by a `Future<Output = Ty>` |
| /// projection. |
| /// |
| /// This function is actually best-effort with the return type; if we don't find a |
| /// `Future` projection, we still will return arguments that we extracted from the `FnOnce` |
| /// projection, and the output will be an unconstrained type variable instead. |
| fn extract_sig_from_projection_and_future_bound( |
| &mut self, |
| projection: PolyProjectionPredicate<'db>, |
| ) -> Option<PolyFnSig<'db>> { |
| let projection = self.table.infer_ctxt.resolve_vars_if_possible(projection); |
| |
| let arg_param_ty = projection.skip_binder().projection_term.args.type_at(1); |
| debug!(?arg_param_ty); |
| |
| let TyKind::Tuple(input_tys) = arg_param_ty.kind() else { |
| return None; |
| }; |
| |
| // If the return type is a type variable, look for bounds on it. |
| // We could theoretically support other kinds of return types here, |
| // but none of them would be useful, since async closures return |
| // concrete anonymous future types, and their futures are not coerced |
| // into any other type within the body of the async closure. |
| let TyKind::Infer(rustc_type_ir::TyVar(return_vid)) = |
| projection.skip_binder().term.expect_type().kind() |
| else { |
| return None; |
| }; |
| |
| // FIXME: We may want to elaborate here, though I assume this will be exceedingly rare. |
| let mut return_ty = None; |
| for bound in self.table.obligations_for_self_ty(return_vid) { |
| if let PredicateKind::Clause(ClauseKind::Projection(ret_projection)) = |
| bound.predicate.kind().skip_binder() |
| && let ret_projection = bound.predicate.kind().rebind(ret_projection) |
| && let Some(ret_projection) = ret_projection.no_bound_vars() |
| && let SolverDefId::TypeAliasId(assoc_type) = ret_projection.def_id() |
| && self.db.lang_attr(assoc_type.into()) == Some(LangItem::FutureOutput) |
| { |
| return_ty = Some(ret_projection.term.expect_type()); |
| break; |
| } |
| } |
| |
| // SUBTLE: If we didn't find a `Future<Output = ...>` bound for the return |
| // vid, we still want to attempt to provide inference guidance for the async |
| // closure's arguments. Instantiate a new vid to plug into the output type. |
| // |
| // You may be wondering, what if it's higher-ranked? Well, given that we |
| // found a type variable for the `FnOnce::Output` projection above, we know |
| // that the output can't mention any of the vars. |
| // |
| // Also note that we use a fresh var here for the signature since the signature |
| // records the output of the *future*, and `return_vid` above is the type |
| // variable of the future, not its output. |
| // |
| // FIXME: We probably should store this signature inference output in a way |
| // that does not misuse a `FnSig` type, but that can be done separately. |
| let return_ty = return_ty.unwrap_or_else(|| self.table.next_ty_var()); |
| |
| let sig = projection.rebind(self.table.interner.mk_fn_sig( |
| input_tys, |
| return_ty, |
| false, |
| Safety::Safe, |
| FnAbi::Rust, |
| )); |
| |
| Some(sig) |
| } |
| |
| fn sig_of_closure( |
| &mut self, |
| decl_inputs: &[Option<TypeRefId>], |
| decl_output: Option<TypeRefId>, |
| expected_sig: Option<PolyFnSig<'db>>, |
| ) -> ClosureSignatures<'db> { |
| if let Some(e) = expected_sig { |
| self.sig_of_closure_with_expectation(decl_inputs, decl_output, e) |
| } else { |
| self.sig_of_closure_no_expectation(decl_inputs, decl_output) |
| } |
| } |
| |
| /// If there is no expected signature, then we will convert the |
| /// types that the user gave into a signature. |
| fn sig_of_closure_no_expectation( |
| &mut self, |
| decl_inputs: &[Option<TypeRefId>], |
| decl_output: Option<TypeRefId>, |
| ) -> ClosureSignatures<'db> { |
| let bound_sig = self.supplied_sig_of_closure(decl_inputs, decl_output); |
| |
| self.closure_sigs(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. |
| fn sig_of_closure_with_expectation( |
| &mut self, |
| decl_inputs: &[Option<TypeRefId>], |
| decl_output: Option<TypeRefId>, |
| expected_sig: PolyFnSig<'db>, |
| ) -> ClosureSignatures<'db> { |
| // 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.c_variadic() { |
| return self.sig_of_closure_no_expectation(decl_inputs, decl_output); |
| } else if expected_sig.skip_binder().inputs_and_output.len() != decl_inputs.len() + 1 { |
| return self |
| .sig_of_closure_with_mismatched_number_of_arguments(decl_inputs, decl_output); |
| } |
| |
| // 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.skip_binder().has_vars_bound_above(rustc_type_ir::INNERMOST)); |
| let bound_sig = expected_sig.map_bound(|sig| { |
| self.table.interner.mk_fn_sig( |
| sig.inputs(), |
| sig.output(), |
| sig.c_variadic, |
| Safety::Safe, |
| FnAbi::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.table.interner.anonymize_bound_vars(bound_sig); |
| |
| let closure_sigs = self.closure_sigs(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(decl_inputs, decl_output, closure_sigs) { |
| Ok(infer_ok) => self.table.register_infer_ok(infer_ok), |
| Err(_) => self.sig_of_closure_no_expectation(decl_inputs, decl_output), |
| } |
| } |
| |
| fn sig_of_closure_with_mismatched_number_of_arguments( |
| &mut self, |
| decl_inputs: &[Option<TypeRefId>], |
| decl_output: Option<TypeRefId>, |
| ) -> ClosureSignatures<'db> { |
| let error_sig = self.error_sig_of_closure(decl_inputs, decl_output); |
| |
| self.closure_sigs(error_sig) |
| } |
| |
| /// Enforce the user's types against the expectation. See |
| /// `sig_of_closure_with_expectation` for details on the overall |
| /// strategy. |
| fn merge_supplied_sig_with_expectation( |
| &mut self, |
| decl_inputs: &[Option<TypeRefId>], |
| decl_output: Option<TypeRefId>, |
| mut expected_sigs: ClosureSignatures<'db>, |
| ) -> InferResult<'db, ClosureSignatures<'db>> { |
| // 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(decl_inputs, decl_output); |
| |
| 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.table.commit_if_ok(|table| { |
| let mut all_obligations = PredicateObligations::new(); |
| let supplied_sig = table.infer_ctxt.instantiate_binder_with_fresh_vars( |
| BoundRegionConversionTime::FnCall, |
| supplied_sig, |
| ); |
| |
| // The liberated version of this signature should be a subtype |
| // of the liberated form of the expectation. |
| for (supplied_ty, expected_ty) in |
| iter::zip(supplied_sig.inputs(), expected_sigs.liberated_sig.inputs()) |
| { |
| // Check that E' = S'. |
| let cause = ObligationCause::new(); |
| let InferOk { value: (), obligations } = table |
| .infer_ctxt |
| .at(&cause, table.param_env) |
| .eq(DefineOpaqueTypes::Yes, expected_ty, supplied_ty)?; |
| all_obligations.extend(obligations); |
| } |
| |
| let supplied_output_ty = supplied_sig.output(); |
| let cause = ObligationCause::new(); |
| let InferOk { value: (), obligations } = |
| table.infer_ctxt.at(&cause, table.param_env).eq( |
| DefineOpaqueTypes::Yes, |
| expected_sigs.liberated_sig.output(), |
| supplied_output_ty, |
| )?; |
| all_obligations.extend(obligations); |
| |
| let inputs = supplied_sig |
| .inputs() |
| .into_iter() |
| .map(|ty| table.infer_ctxt.resolve_vars_if_possible(ty)); |
| |
| expected_sigs.liberated_sig = table.interner.mk_fn_sig( |
| inputs, |
| supplied_output_ty, |
| expected_sigs.liberated_sig.c_variadic, |
| Safety::Safe, |
| FnAbi::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. |
| fn supplied_sig_of_closure( |
| &mut self, |
| decl_inputs: &[Option<TypeRefId>], |
| decl_output: Option<TypeRefId>, |
| ) -> PolyFnSig<'db> { |
| let interner = self.table.interner; |
| |
| let supplied_return = match decl_output { |
| Some(output) => { |
| let output = self.make_body_ty(output); |
| self.process_user_written_ty(output).to_nextsolver(interner) |
| } |
| None => self.table.next_ty_var(), |
| }; |
| // First, convert the types that the user supplied (if any). |
| let supplied_arguments = decl_inputs.iter().map(|&input| match input { |
| Some(input) => { |
| let input = self.make_body_ty(input); |
| self.process_user_written_ty(input).to_nextsolver(interner) |
| } |
| None => self.table.next_ty_var(), |
| }); |
| |
| Binder::dummy(interner.mk_fn_sig( |
| supplied_arguments, |
| supplied_return, |
| false, |
| Safety::Safe, |
| FnAbi::RustCall, |
| )) |
| } |
| |
| /// 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( |
| &mut self, |
| decl_inputs: &[Option<TypeRefId>], |
| decl_output: Option<TypeRefId>, |
| ) -> PolyFnSig<'db> { |
| let interner = self.table.interner; |
| let err_ty = Ty::new_error(interner, ErrorGuaranteed); |
| |
| if let Some(output) = decl_output { |
| self.make_body_ty(output); |
| } |
| let supplied_arguments = decl_inputs.iter().map(|&input| match input { |
| Some(input) => { |
| self.make_body_ty(input); |
| err_ty |
| } |
| None => err_ty, |
| }); |
| |
| let result = Binder::dummy(interner.mk_fn_sig( |
| supplied_arguments, |
| err_ty, |
| false, |
| Safety::Safe, |
| FnAbi::RustCall, |
| )); |
| |
| debug!("supplied_sig_of_closure: result={:?}", result); |
| |
| result |
| } |
| |
| fn closure_sigs(&self, bound_sig: PolyFnSig<'db>) -> ClosureSignatures<'db> { |
| let liberated_sig = bound_sig.skip_binder(); |
| // FIXME: When we lower HRTB we'll need to actually liberate regions here. |
| ClosureSignatures { bound_sig, liberated_sig } |
| } |
| } |
