1292 lines
51 KiB
Rust
1292 lines
51 KiB
Rust
use crate::infer::error_reporting::{note_and_explain_free_region, note_and_explain_region};
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use crate::infer::{self, InferCtxt, InferOk, TypeVariableOrigin, TypeVariableOriginKind};
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use crate::middle::region;
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use crate::traits::{self, PredicateObligation};
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use crate::ty::fold::{BottomUpFolder, TypeFoldable, TypeFolder, TypeVisitor};
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use crate::ty::free_region_map::FreeRegionRelations;
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use crate::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef};
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use crate::ty::{self, GenericParamDefKind, Ty, TyCtxt};
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use errors::{struct_span_err, DiagnosticBuilder};
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use rustc::session::config::nightly_options;
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use rustc_data_structures::fx::FxHashMap;
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use rustc_data_structures::sync::Lrc;
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use rustc_hir as hir;
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use rustc_hir::def_id::{DefId, DefIdMap};
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use rustc_hir::Node;
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use rustc_span::Span;
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use rustc_error_codes::*;
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pub type OpaqueTypeMap<'tcx> = DefIdMap<OpaqueTypeDecl<'tcx>>;
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/// Information about the opaque types whose values we
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/// are inferring in this function (these are the `impl Trait` that
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/// appear in the return type).
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#[derive(Copy, Clone, Debug)]
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pub struct OpaqueTypeDecl<'tcx> {
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/// The opaque type (`ty::Opaque`) for this declaration.
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pub opaque_type: Ty<'tcx>,
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/// The substitutions that we apply to the opaque type that this
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/// `impl Trait` desugars to. e.g., if:
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///
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/// fn foo<'a, 'b, T>() -> impl Trait<'a>
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///
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/// winds up desugared to:
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///
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/// type Foo<'x, X> = impl Trait<'x>
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/// fn foo<'a, 'b, T>() -> Foo<'a, T>
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///
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/// then `substs` would be `['a, T]`.
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pub substs: SubstsRef<'tcx>,
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/// The span of this particular definition of the opaque type. So
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/// for example:
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///
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/// ```
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/// type Foo = impl Baz;
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/// fn bar() -> Foo {
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/// ^^^ This is the span we are looking for!
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/// ```
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///
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/// In cases where the fn returns `(impl Trait, impl Trait)` or
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/// other such combinations, the result is currently
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/// over-approximated, but better than nothing.
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pub definition_span: Span,
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/// The type variable that represents the value of the opaque type
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/// that we require. In other words, after we compile this function,
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/// we will be created a constraint like:
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///
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/// Foo<'a, T> = ?C
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///
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/// where `?C` is the value of this type variable. =) It may
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/// naturally refer to the type and lifetime parameters in scope
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/// in this function, though ultimately it should only reference
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/// those that are arguments to `Foo` in the constraint above. (In
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/// other words, `?C` should not include `'b`, even though it's a
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/// lifetime parameter on `foo`.)
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pub concrete_ty: Ty<'tcx>,
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/// Returns `true` if the `impl Trait` bounds include region bounds.
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/// For example, this would be true for:
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///
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/// fn foo<'a, 'b, 'c>() -> impl Trait<'c> + 'a + 'b
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///
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/// but false for:
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///
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/// fn foo<'c>() -> impl Trait<'c>
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///
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/// unless `Trait` was declared like:
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///
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/// trait Trait<'c>: 'c
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///
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/// in which case it would be true.
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///
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/// This is used during regionck to decide whether we need to
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/// impose any additional constraints to ensure that region
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/// variables in `concrete_ty` wind up being constrained to
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/// something from `substs` (or, at minimum, things that outlive
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/// the fn body). (Ultimately, writeback is responsible for this
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/// check.)
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pub has_required_region_bounds: bool,
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/// The origin of the opaque type.
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pub origin: hir::OpaqueTyOrigin,
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}
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impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
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/// Replaces all opaque types in `value` with fresh inference variables
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/// and creates appropriate obligations. For example, given the input:
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///
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/// impl Iterator<Item = impl Debug>
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///
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/// this method would create two type variables, `?0` and `?1`. It would
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/// return the type `?0` but also the obligations:
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///
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/// ?0: Iterator<Item = ?1>
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/// ?1: Debug
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///
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/// Moreover, it returns a `OpaqueTypeMap` that would map `?0` to
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/// info about the `impl Iterator<..>` type and `?1` to info about
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/// the `impl Debug` type.
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///
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/// # Parameters
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///
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/// - `parent_def_id` -- the `DefId` of the function in which the opaque type
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/// is defined
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/// - `body_id` -- the body-id with which the resulting obligations should
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/// be associated
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/// - `param_env` -- the in-scope parameter environment to be used for
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/// obligations
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/// - `value` -- the value within which we are instantiating opaque types
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/// - `value_span` -- the span where the value came from, used in error reporting
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pub fn instantiate_opaque_types<T: TypeFoldable<'tcx>>(
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&self,
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parent_def_id: DefId,
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body_id: hir::HirId,
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param_env: ty::ParamEnv<'tcx>,
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value: &T,
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value_span: Span,
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) -> InferOk<'tcx, (T, OpaqueTypeMap<'tcx>)> {
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debug!(
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"instantiate_opaque_types(value={:?}, parent_def_id={:?}, body_id={:?}, \
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param_env={:?}, value_span={:?})",
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value, parent_def_id, body_id, param_env, value_span,
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);
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let mut instantiator = Instantiator {
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infcx: self,
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parent_def_id,
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body_id,
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param_env,
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value_span,
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opaque_types: Default::default(),
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obligations: vec![],
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};
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let value = instantiator.instantiate_opaque_types_in_map(value);
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InferOk { value: (value, instantiator.opaque_types), obligations: instantiator.obligations }
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}
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/// Given the map `opaque_types` containing the opaque
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/// `impl Trait` types whose underlying, hidden types are being
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/// inferred, this method adds constraints to the regions
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/// appearing in those underlying hidden types to ensure that they
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/// at least do not refer to random scopes within the current
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/// function. These constraints are not (quite) sufficient to
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/// guarantee that the regions are actually legal values; that
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/// final condition is imposed after region inference is done.
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///
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/// # The Problem
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///
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/// Let's work through an example to explain how it works. Assume
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/// the current function is as follows:
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///
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/// ```text
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/// fn foo<'a, 'b>(..) -> (impl Bar<'a>, impl Bar<'b>)
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/// ```
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///
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/// Here, we have two `impl Trait` types whose values are being
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/// inferred (the `impl Bar<'a>` and the `impl
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/// Bar<'b>`). Conceptually, this is sugar for a setup where we
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/// define underlying opaque types (`Foo1`, `Foo2`) and then, in
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/// the return type of `foo`, we *reference* those definitions:
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///
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/// ```text
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/// type Foo1<'x> = impl Bar<'x>;
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/// type Foo2<'x> = impl Bar<'x>;
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/// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. }
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/// // ^^^^ ^^
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/// // | |
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/// // | substs
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/// // def_id
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/// ```
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///
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/// As indicating in the comments above, each of those references
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/// is (in the compiler) basically a substitution (`substs`)
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/// applied to the type of a suitable `def_id` (which identifies
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/// `Foo1` or `Foo2`).
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///
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/// Now, at this point in compilation, what we have done is to
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/// replace each of the references (`Foo1<'a>`, `Foo2<'b>`) with
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/// fresh inference variables C1 and C2. We wish to use the values
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/// of these variables to infer the underlying types of `Foo1` and
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/// `Foo2`. That is, this gives rise to higher-order (pattern) unification
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/// constraints like:
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///
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/// ```text
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/// for<'a> (Foo1<'a> = C1)
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/// for<'b> (Foo1<'b> = C2)
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/// ```
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///
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/// For these equation to be satisfiable, the types `C1` and `C2`
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/// can only refer to a limited set of regions. For example, `C1`
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/// can only refer to `'static` and `'a`, and `C2` can only refer
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/// to `'static` and `'b`. The job of this function is to impose that
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/// constraint.
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///
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/// Up to this point, C1 and C2 are basically just random type
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/// inference variables, and hence they may contain arbitrary
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/// regions. In fact, it is fairly likely that they do! Consider
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/// this possible definition of `foo`:
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///
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/// ```text
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/// fn foo<'a, 'b>(x: &'a i32, y: &'b i32) -> (impl Bar<'a>, impl Bar<'b>) {
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/// (&*x, &*y)
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/// }
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/// ```
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///
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/// Here, the values for the concrete types of the two impl
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/// traits will include inference variables:
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///
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/// ```text
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/// &'0 i32
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/// &'1 i32
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/// ```
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///
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/// Ordinarily, the subtyping rules would ensure that these are
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/// sufficiently large. But since `impl Bar<'a>` isn't a specific
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/// type per se, we don't get such constraints by default. This
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/// is where this function comes into play. It adds extra
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/// constraints to ensure that all the regions which appear in the
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/// inferred type are regions that could validly appear.
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///
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/// This is actually a bit of a tricky constraint in general. We
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/// want to say that each variable (e.g., `'0`) can only take on
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/// values that were supplied as arguments to the opaque type
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/// (e.g., `'a` for `Foo1<'a>`) or `'static`, which is always in
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/// scope. We don't have a constraint quite of this kind in the current
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/// region checker.
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///
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/// # The Solution
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///
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/// We generally prefer to make `<=` constraints, since they
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/// integrate best into the region solver. To do that, we find the
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/// "minimum" of all the arguments that appear in the substs: that
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/// is, some region which is less than all the others. In the case
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/// of `Foo1<'a>`, that would be `'a` (it's the only choice, after
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/// all). Then we apply that as a least bound to the variables
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/// (e.g., `'a <= '0`).
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///
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/// In some cases, there is no minimum. Consider this example:
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///
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/// ```text
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/// fn baz<'a, 'b>() -> impl Trait<'a, 'b> { ... }
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/// ```
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///
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/// Here we would report a more complex "in constraint", like `'r
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/// in ['a, 'b, 'static]` (where `'r` is some regon appearing in
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/// the hidden type).
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///
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/// # Constrain regions, not the hidden concrete type
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///
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/// Note that generating constraints on each region `Rc` is *not*
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/// the same as generating an outlives constraint on `Tc` iself.
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/// For example, if we had a function like this:
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///
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/// ```rust
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/// fn foo<'a, T>(x: &'a u32, y: T) -> impl Foo<'a> {
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/// (x, y)
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/// }
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///
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/// // Equivalent to:
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/// type FooReturn<'a, T> = impl Foo<'a>;
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/// fn foo<'a, T>(..) -> FooReturn<'a, T> { .. }
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/// ```
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///
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/// then the hidden type `Tc` would be `(&'0 u32, T)` (where `'0`
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/// is an inference variable). If we generated a constraint that
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/// `Tc: 'a`, then this would incorrectly require that `T: 'a` --
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/// but this is not necessary, because the opaque type we
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/// create will be allowed to reference `T`. So we only generate a
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/// constraint that `'0: 'a`.
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///
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/// # The `free_region_relations` parameter
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///
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/// The `free_region_relations` argument is used to find the
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/// "minimum" of the regions supplied to a given opaque type.
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/// It must be a relation that can answer whether `'a <= 'b`,
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/// where `'a` and `'b` are regions that appear in the "substs"
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/// for the opaque type references (the `<'a>` in `Foo1<'a>`).
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///
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/// Note that we do not impose the constraints based on the
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/// generic regions from the `Foo1` definition (e.g., `'x`). This
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/// is because the constraints we are imposing here is basically
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/// the concern of the one generating the constraining type C1,
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/// which is the current function. It also means that we can
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/// take "implied bounds" into account in some cases:
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///
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/// ```text
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/// trait SomeTrait<'a, 'b> { }
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/// fn foo<'a, 'b>(_: &'a &'b u32) -> impl SomeTrait<'a, 'b> { .. }
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/// ```
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///
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/// Here, the fact that `'b: 'a` is known only because of the
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/// implied bounds from the `&'a &'b u32` parameter, and is not
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/// "inherent" to the opaque type definition.
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///
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/// # Parameters
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///
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/// - `opaque_types` -- the map produced by `instantiate_opaque_types`
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/// - `free_region_relations` -- something that can be used to relate
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/// the free regions (`'a`) that appear in the impl trait.
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pub fn constrain_opaque_types<FRR: FreeRegionRelations<'tcx>>(
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&self,
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opaque_types: &OpaqueTypeMap<'tcx>,
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free_region_relations: &FRR,
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) {
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debug!("constrain_opaque_types()");
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for (&def_id, opaque_defn) in opaque_types {
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self.constrain_opaque_type(def_id, opaque_defn, free_region_relations);
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}
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}
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/// See `constrain_opaque_types` for documentation.
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pub fn constrain_opaque_type<FRR: FreeRegionRelations<'tcx>>(
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&self,
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def_id: DefId,
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opaque_defn: &OpaqueTypeDecl<'tcx>,
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free_region_relations: &FRR,
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) {
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debug!("constrain_opaque_type()");
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debug!("constrain_opaque_type: def_id={:?}", def_id);
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debug!("constrain_opaque_type: opaque_defn={:#?}", opaque_defn);
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let tcx = self.tcx;
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let concrete_ty = self.resolve_vars_if_possible(&opaque_defn.concrete_ty);
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debug!("constrain_opaque_type: concrete_ty={:?}", concrete_ty);
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let opaque_type_generics = tcx.generics_of(def_id);
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let span = tcx.def_span(def_id);
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// If there are required region bounds, we can use them.
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if opaque_defn.has_required_region_bounds {
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let predicates_of = tcx.predicates_of(def_id);
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debug!("constrain_opaque_type: predicates: {:#?}", predicates_of,);
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let bounds = predicates_of.instantiate(tcx, opaque_defn.substs);
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debug!("constrain_opaque_type: bounds={:#?}", bounds);
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let opaque_type = tcx.mk_opaque(def_id, opaque_defn.substs);
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let required_region_bounds =
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required_region_bounds(tcx, opaque_type, bounds.predicates);
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debug_assert!(!required_region_bounds.is_empty());
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for required_region in required_region_bounds {
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concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
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tcx: self.tcx,
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op: |r| self.sub_regions(infer::CallReturn(span), required_region, r),
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});
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}
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return;
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}
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// There were no `required_region_bounds`,
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// so we have to search for a `least_region`.
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// Go through all the regions used as arguments to the
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// opaque type. These are the parameters to the opaque
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// type; so in our example above, `substs` would contain
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// `['a]` for the first impl trait and `'b` for the
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// second.
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let mut least_region = None;
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for param in &opaque_type_generics.params {
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match param.kind {
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GenericParamDefKind::Lifetime => {}
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_ => continue,
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}
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// Get the value supplied for this region from the substs.
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let subst_arg = opaque_defn.substs.region_at(param.index as usize);
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// Compute the least upper bound of it with the other regions.
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debug!("constrain_opaque_types: least_region={:?}", least_region);
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debug!("constrain_opaque_types: subst_arg={:?}", subst_arg);
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match least_region {
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None => least_region = Some(subst_arg),
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Some(lr) => {
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if free_region_relations.sub_free_regions(lr, subst_arg) {
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// keep the current least region
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} else if free_region_relations.sub_free_regions(subst_arg, lr) {
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// switch to `subst_arg`
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least_region = Some(subst_arg);
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} else {
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// There are two regions (`lr` and
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// `subst_arg`) which are not relatable. We
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// can't find a best choice. Therefore,
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// instead of creating a single bound like
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// `'r: 'a` (which is our preferred choice),
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// we will create a "in bound" like `'r in
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// ['a, 'b, 'c]`, where `'a..'c` are the
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// regions that appear in the impl trait.
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return self.generate_member_constraint(
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concrete_ty,
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opaque_type_generics,
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opaque_defn,
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def_id,
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lr,
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subst_arg,
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);
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}
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}
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}
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|
}
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let least_region = least_region.unwrap_or(tcx.lifetimes.re_static);
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debug!("constrain_opaque_types: least_region={:?}", least_region);
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concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
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tcx: self.tcx,
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op: |r| self.sub_regions(infer::CallReturn(span), least_region, r),
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});
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}
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|
|
/// As a fallback, we sometimes generate an "in constraint". For
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/// a case like `impl Foo<'a, 'b>`, where `'a` and `'b` cannot be
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/// related, we would generate a constraint `'r in ['a, 'b,
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/// 'static]` for each region `'r` that appears in the hidden type
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/// (i.e., it must be equal to `'a`, `'b`, or `'static`).
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///
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/// `conflict1` and `conflict2` are the two region bounds that we
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/// detected which were unrelated. They are used for diagnostics.
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|
fn generate_member_constraint(
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&self,
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concrete_ty: Ty<'tcx>,
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opaque_type_generics: &ty::Generics,
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|
opaque_defn: &OpaqueTypeDecl<'tcx>,
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|
opaque_type_def_id: DefId,
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conflict1: ty::Region<'tcx>,
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|
conflict2: ty::Region<'tcx>,
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) {
|
|
// For now, enforce a feature gate outside of async functions.
|
|
if self.member_constraint_feature_gate(
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opaque_defn,
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opaque_type_def_id,
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conflict1,
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conflict2,
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|
) {
|
|
return;
|
|
}
|
|
|
|
// Create the set of choice regions: each region in the hidden
|
|
// type can be equal to any of the region parameters of the
|
|
// opaque type definition.
|
|
let choice_regions: Lrc<Vec<ty::Region<'tcx>>> = Lrc::new(
|
|
opaque_type_generics
|
|
.params
|
|
.iter()
|
|
.filter(|param| match param.kind {
|
|
GenericParamDefKind::Lifetime => true,
|
|
GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => false,
|
|
})
|
|
.map(|param| opaque_defn.substs.region_at(param.index as usize))
|
|
.chain(std::iter::once(self.tcx.lifetimes.re_static))
|
|
.collect(),
|
|
);
|
|
|
|
concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
|
|
tcx: self.tcx,
|
|
op: |r| {
|
|
self.member_constraint(
|
|
opaque_type_def_id,
|
|
opaque_defn.definition_span,
|
|
concrete_ty,
|
|
r,
|
|
&choice_regions,
|
|
)
|
|
},
|
|
});
|
|
}
|
|
|
|
/// Member constraints are presently feature-gated except for
|
|
/// async-await. We expect to lift this once we've had a bit more
|
|
/// time.
|
|
fn member_constraint_feature_gate(
|
|
&self,
|
|
opaque_defn: &OpaqueTypeDecl<'tcx>,
|
|
opaque_type_def_id: DefId,
|
|
conflict1: ty::Region<'tcx>,
|
|
conflict2: ty::Region<'tcx>,
|
|
) -> bool {
|
|
// If we have `#![feature(member_constraints)]`, no problems.
|
|
if self.tcx.features().member_constraints {
|
|
return false;
|
|
}
|
|
|
|
let span = self.tcx.def_span(opaque_type_def_id);
|
|
|
|
// Without a feature-gate, we only generate member-constraints for async-await.
|
|
let context_name = match opaque_defn.origin {
|
|
// No feature-gate required for `async fn`.
|
|
hir::OpaqueTyOrigin::AsyncFn => return false,
|
|
|
|
// Otherwise, generate the label we'll use in the error message.
|
|
hir::OpaqueTyOrigin::TypeAlias => "impl Trait",
|
|
hir::OpaqueTyOrigin::FnReturn => "impl Trait",
|
|
};
|
|
let msg = format!("ambiguous lifetime bound in `{}`", context_name);
|
|
let mut err = self.tcx.sess.struct_span_err(span, &msg);
|
|
|
|
let conflict1_name = conflict1.to_string();
|
|
let conflict2_name = conflict2.to_string();
|
|
let label_owned;
|
|
let label = match (&*conflict1_name, &*conflict2_name) {
|
|
("'_", "'_") => "the elided lifetimes here do not outlive one another",
|
|
_ => {
|
|
label_owned = format!(
|
|
"neither `{}` nor `{}` outlives the other",
|
|
conflict1_name, conflict2_name,
|
|
);
|
|
&label_owned
|
|
}
|
|
};
|
|
err.span_label(span, label);
|
|
|
|
if nightly_options::is_nightly_build() {
|
|
err.help("add #![feature(member_constraints)] to the crate attributes to enable");
|
|
}
|
|
|
|
err.emit();
|
|
true
|
|
}
|
|
|
|
/// Given the fully resolved, instantiated type for an opaque
|
|
/// type, i.e., the value of an inference variable like C1 or C2
|
|
/// (*), computes the "definition type" for an opaque type
|
|
/// definition -- that is, the inferred value of `Foo1<'x>` or
|
|
/// `Foo2<'x>` that we would conceptually use in its definition:
|
|
///
|
|
/// type Foo1<'x> = impl Bar<'x> = AAA; <-- this type AAA
|
|
/// type Foo2<'x> = impl Bar<'x> = BBB; <-- or this type BBB
|
|
/// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. }
|
|
///
|
|
/// Note that these values are defined in terms of a distinct set of
|
|
/// generic parameters (`'x` instead of `'a`) from C1 or C2. The main
|
|
/// purpose of this function is to do that translation.
|
|
///
|
|
/// (*) C1 and C2 were introduced in the comments on
|
|
/// `constrain_opaque_types`. Read that comment for more context.
|
|
///
|
|
/// # Parameters
|
|
///
|
|
/// - `def_id`, the `impl Trait` type
|
|
/// - `opaque_defn`, the opaque definition created in `instantiate_opaque_types`
|
|
/// - `instantiated_ty`, the inferred type C1 -- fully resolved, lifted version of
|
|
/// `opaque_defn.concrete_ty`
|
|
pub fn infer_opaque_definition_from_instantiation(
|
|
&self,
|
|
def_id: DefId,
|
|
opaque_defn: &OpaqueTypeDecl<'tcx>,
|
|
instantiated_ty: Ty<'tcx>,
|
|
span: Span,
|
|
) -> Ty<'tcx> {
|
|
debug!(
|
|
"infer_opaque_definition_from_instantiation(def_id={:?}, instantiated_ty={:?})",
|
|
def_id, instantiated_ty
|
|
);
|
|
|
|
// Use substs to build up a reverse map from regions to their
|
|
// identity mappings. This is necessary because of `impl
|
|
// Trait` lifetimes are computed by replacing existing
|
|
// lifetimes with 'static and remapping only those used in the
|
|
// `impl Trait` return type, resulting in the parameters
|
|
// shifting.
|
|
let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id);
|
|
let map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>> = opaque_defn
|
|
.substs
|
|
.iter()
|
|
.enumerate()
|
|
.map(|(index, subst)| (*subst, id_substs[index]))
|
|
.collect();
|
|
|
|
// Convert the type from the function into a type valid outside
|
|
// the function, by replacing invalid regions with 'static,
|
|
// after producing an error for each of them.
|
|
let definition_ty = instantiated_ty.fold_with(&mut ReverseMapper::new(
|
|
self.tcx,
|
|
self.is_tainted_by_errors(),
|
|
def_id,
|
|
map,
|
|
instantiated_ty,
|
|
span,
|
|
));
|
|
debug!("infer_opaque_definition_from_instantiation: definition_ty={:?}", definition_ty);
|
|
|
|
definition_ty
|
|
}
|
|
}
|
|
|
|
pub fn unexpected_hidden_region_diagnostic(
|
|
tcx: TyCtxt<'tcx>,
|
|
region_scope_tree: Option<®ion::ScopeTree>,
|
|
opaque_type_def_id: DefId,
|
|
hidden_ty: Ty<'tcx>,
|
|
hidden_region: ty::Region<'tcx>,
|
|
) -> DiagnosticBuilder<'tcx> {
|
|
let span = tcx.def_span(opaque_type_def_id);
|
|
let mut err = struct_span_err!(
|
|
tcx.sess,
|
|
span,
|
|
E0700,
|
|
"hidden type for `impl Trait` captures lifetime that does not appear in bounds",
|
|
);
|
|
|
|
// Explain the region we are capturing.
|
|
if let ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic | ty::ReEmpty = hidden_region {
|
|
// Assuming regionck succeeded (*), we ought to always be
|
|
// capturing *some* region from the fn header, and hence it
|
|
// ought to be free. So under normal circumstances, we will go
|
|
// down this path which gives a decent human readable
|
|
// explanation.
|
|
//
|
|
// (*) if not, the `tainted_by_errors` flag would be set to
|
|
// true in any case, so we wouldn't be here at all.
|
|
note_and_explain_free_region(
|
|
tcx,
|
|
&mut err,
|
|
&format!("hidden type `{}` captures ", hidden_ty),
|
|
hidden_region,
|
|
"",
|
|
);
|
|
} else {
|
|
// Ugh. This is a painful case: the hidden region is not one
|
|
// that we can easily summarize or explain. This can happen
|
|
// in a case like
|
|
// `src/test/ui/multiple-lifetimes/ordinary-bounds-unsuited.rs`:
|
|
//
|
|
// ```
|
|
// fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b> {
|
|
// if condition() { a } else { b }
|
|
// }
|
|
// ```
|
|
//
|
|
// Here the captured lifetime is the intersection of `'a` and
|
|
// `'b`, which we can't quite express.
|
|
|
|
if let Some(region_scope_tree) = region_scope_tree {
|
|
// If the `region_scope_tree` is available, this is being
|
|
// invoked from the "region inferencer error". We can at
|
|
// least report a really cryptic error for now.
|
|
note_and_explain_region(
|
|
tcx,
|
|
region_scope_tree,
|
|
&mut err,
|
|
&format!("hidden type `{}` captures ", hidden_ty),
|
|
hidden_region,
|
|
"",
|
|
);
|
|
} else {
|
|
// If the `region_scope_tree` is *unavailable*, this is
|
|
// being invoked by the code that comes *after* region
|
|
// inferencing. This is a bug, as the region inferencer
|
|
// ought to have noticed the failed constraint and invoked
|
|
// error reporting, which in turn should have prevented us
|
|
// from getting trying to infer the hidden type
|
|
// completely.
|
|
tcx.sess.delay_span_bug(
|
|
span,
|
|
&format!(
|
|
"hidden type captures unexpected lifetime `{:?}` \
|
|
but no region inference failure",
|
|
hidden_region,
|
|
),
|
|
);
|
|
}
|
|
}
|
|
|
|
err
|
|
}
|
|
|
|
// Visitor that requires that (almost) all regions in the type visited outlive
|
|
// `least_region`. We cannot use `push_outlives_components` because regions in
|
|
// closure signatures are not included in their outlives components. We need to
|
|
// ensure all regions outlive the given bound so that we don't end up with,
|
|
// say, `ReScope` appearing in a return type and causing ICEs when other
|
|
// functions end up with region constraints involving regions from other
|
|
// functions.
|
|
//
|
|
// We also cannot use `for_each_free_region` because for closures it includes
|
|
// the regions parameters from the enclosing item.
|
|
//
|
|
// We ignore any type parameters because impl trait values are assumed to
|
|
// capture all the in-scope type parameters.
|
|
struct ConstrainOpaqueTypeRegionVisitor<'tcx, OP>
|
|
where
|
|
OP: FnMut(ty::Region<'tcx>),
|
|
{
|
|
tcx: TyCtxt<'tcx>,
|
|
op: OP,
|
|
}
|
|
|
|
impl<'tcx, OP> TypeVisitor<'tcx> for ConstrainOpaqueTypeRegionVisitor<'tcx, OP>
|
|
where
|
|
OP: FnMut(ty::Region<'tcx>),
|
|
{
|
|
fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> bool {
|
|
t.skip_binder().visit_with(self);
|
|
false // keep visiting
|
|
}
|
|
|
|
fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
|
|
match *r {
|
|
// ignore bound regions, keep visiting
|
|
ty::ReLateBound(_, _) => false,
|
|
_ => {
|
|
(self.op)(r);
|
|
false
|
|
}
|
|
}
|
|
}
|
|
|
|
fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
|
|
// We're only interested in types involving regions
|
|
if !ty.flags.intersects(ty::TypeFlags::HAS_FREE_REGIONS) {
|
|
return false; // keep visiting
|
|
}
|
|
|
|
match ty.kind {
|
|
ty::Closure(def_id, ref substs) => {
|
|
// Skip lifetime parameters of the enclosing item(s)
|
|
|
|
for upvar_ty in substs.as_closure().upvar_tys(def_id, self.tcx) {
|
|
upvar_ty.visit_with(self);
|
|
}
|
|
|
|
substs.as_closure().sig_ty(def_id, self.tcx).visit_with(self);
|
|
}
|
|
|
|
ty::Generator(def_id, ref substs, _) => {
|
|
// Skip lifetime parameters of the enclosing item(s)
|
|
// Also skip the witness type, because that has no free regions.
|
|
|
|
for upvar_ty in substs.as_generator().upvar_tys(def_id, self.tcx) {
|
|
upvar_ty.visit_with(self);
|
|
}
|
|
|
|
substs.as_generator().return_ty(def_id, self.tcx).visit_with(self);
|
|
substs.as_generator().yield_ty(def_id, self.tcx).visit_with(self);
|
|
}
|
|
_ => {
|
|
ty.super_visit_with(self);
|
|
}
|
|
}
|
|
|
|
false
|
|
}
|
|
}
|
|
|
|
struct ReverseMapper<'tcx> {
|
|
tcx: TyCtxt<'tcx>,
|
|
|
|
/// If errors have already been reported in this fn, we suppress
|
|
/// our own errors because they are sometimes derivative.
|
|
tainted_by_errors: bool,
|
|
|
|
opaque_type_def_id: DefId,
|
|
map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
|
|
map_missing_regions_to_empty: bool,
|
|
|
|
/// initially `Some`, set to `None` once error has been reported
|
|
hidden_ty: Option<Ty<'tcx>>,
|
|
|
|
/// Span of function being checked.
|
|
span: Span,
|
|
}
|
|
|
|
impl ReverseMapper<'tcx> {
|
|
fn new(
|
|
tcx: TyCtxt<'tcx>,
|
|
tainted_by_errors: bool,
|
|
opaque_type_def_id: DefId,
|
|
map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
|
|
hidden_ty: Ty<'tcx>,
|
|
span: Span,
|
|
) -> Self {
|
|
Self {
|
|
tcx,
|
|
tainted_by_errors,
|
|
opaque_type_def_id,
|
|
map,
|
|
map_missing_regions_to_empty: false,
|
|
hidden_ty: Some(hidden_ty),
|
|
span,
|
|
}
|
|
}
|
|
|
|
fn fold_kind_mapping_missing_regions_to_empty(
|
|
&mut self,
|
|
kind: GenericArg<'tcx>,
|
|
) -> GenericArg<'tcx> {
|
|
assert!(!self.map_missing_regions_to_empty);
|
|
self.map_missing_regions_to_empty = true;
|
|
let kind = kind.fold_with(self);
|
|
self.map_missing_regions_to_empty = false;
|
|
kind
|
|
}
|
|
|
|
fn fold_kind_normally(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> {
|
|
assert!(!self.map_missing_regions_to_empty);
|
|
kind.fold_with(self)
|
|
}
|
|
}
|
|
|
|
impl TypeFolder<'tcx> for ReverseMapper<'tcx> {
|
|
fn tcx(&self) -> TyCtxt<'tcx> {
|
|
self.tcx
|
|
}
|
|
|
|
fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
|
|
match r {
|
|
// ignore bound regions that appear in the type (e.g., this
|
|
// would ignore `'r` in a type like `for<'r> fn(&'r u32)`.
|
|
ty::ReLateBound(..) |
|
|
|
|
// ignore `'static`, as that can appear anywhere
|
|
ty::ReStatic => return r,
|
|
|
|
_ => { }
|
|
}
|
|
|
|
let generics = self.tcx().generics_of(self.opaque_type_def_id);
|
|
match self.map.get(&r.into()).map(|k| k.unpack()) {
|
|
Some(GenericArgKind::Lifetime(r1)) => r1,
|
|
Some(u) => panic!("region mapped to unexpected kind: {:?}", u),
|
|
None if generics.parent.is_some() => {
|
|
if !self.map_missing_regions_to_empty && !self.tainted_by_errors {
|
|
if let Some(hidden_ty) = self.hidden_ty.take() {
|
|
unexpected_hidden_region_diagnostic(
|
|
self.tcx,
|
|
None,
|
|
self.opaque_type_def_id,
|
|
hidden_ty,
|
|
r,
|
|
)
|
|
.emit();
|
|
}
|
|
}
|
|
self.tcx.lifetimes.re_empty
|
|
}
|
|
None => {
|
|
self.tcx
|
|
.sess
|
|
.struct_span_err(self.span, "non-defining opaque type use in defining scope")
|
|
.span_label(
|
|
self.span,
|
|
format!(
|
|
"lifetime `{}` is part of concrete type but not used in \
|
|
parameter list of the `impl Trait` type alias",
|
|
r
|
|
),
|
|
)
|
|
.emit();
|
|
|
|
self.tcx().mk_region(ty::ReStatic)
|
|
}
|
|
}
|
|
}
|
|
|
|
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
|
|
match ty.kind {
|
|
ty::Closure(def_id, substs) => {
|
|
// I am a horrible monster and I pray for death. When
|
|
// we encounter a closure here, it is always a closure
|
|
// from within the function that we are currently
|
|
// type-checking -- one that is now being encapsulated
|
|
// in an opaque type. Ideally, we would
|
|
// go through the types/lifetimes that it references
|
|
// and treat them just like we would any other type,
|
|
// which means we would error out if we find any
|
|
// reference to a type/region that is not in the
|
|
// "reverse map".
|
|
//
|
|
// **However,** in the case of closures, there is a
|
|
// somewhat subtle (read: hacky) consideration. The
|
|
// problem is that our closure types currently include
|
|
// all the lifetime parameters declared on the
|
|
// enclosing function, even if they are unused by the
|
|
// closure itself. We can't readily filter them out,
|
|
// so here we replace those values with `'empty`. This
|
|
// can't really make a difference to the rest of the
|
|
// compiler; those regions are ignored for the
|
|
// outlives relation, and hence don't affect trait
|
|
// selection or auto traits, and they are erased
|
|
// during codegen.
|
|
|
|
let generics = self.tcx.generics_of(def_id);
|
|
let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, &kind)| {
|
|
if index < generics.parent_count {
|
|
// Accommodate missing regions in the parent kinds...
|
|
self.fold_kind_mapping_missing_regions_to_empty(kind)
|
|
} else {
|
|
// ...but not elsewhere.
|
|
self.fold_kind_normally(kind)
|
|
}
|
|
}));
|
|
|
|
self.tcx.mk_closure(def_id, substs)
|
|
}
|
|
|
|
ty::Generator(def_id, substs, movability) => {
|
|
let generics = self.tcx.generics_of(def_id);
|
|
let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, &kind)| {
|
|
if index < generics.parent_count {
|
|
// Accommodate missing regions in the parent kinds...
|
|
self.fold_kind_mapping_missing_regions_to_empty(kind)
|
|
} else {
|
|
// ...but not elsewhere.
|
|
self.fold_kind_normally(kind)
|
|
}
|
|
}));
|
|
|
|
self.tcx.mk_generator(def_id, substs, movability)
|
|
}
|
|
|
|
ty::Param(..) => {
|
|
// Look it up in the substitution list.
|
|
match self.map.get(&ty.into()).map(|k| k.unpack()) {
|
|
// Found it in the substitution list; replace with the parameter from the
|
|
// opaque type.
|
|
Some(GenericArgKind::Type(t1)) => t1,
|
|
Some(u) => panic!("type mapped to unexpected kind: {:?}", u),
|
|
None => {
|
|
self.tcx
|
|
.sess
|
|
.struct_span_err(
|
|
self.span,
|
|
&format!(
|
|
"type parameter `{}` is part of concrete type but not \
|
|
used in parameter list for the `impl Trait` type alias",
|
|
ty
|
|
),
|
|
)
|
|
.emit();
|
|
|
|
self.tcx().types.err
|
|
}
|
|
}
|
|
}
|
|
|
|
_ => ty.super_fold_with(self),
|
|
}
|
|
}
|
|
|
|
fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
|
|
trace!("checking const {:?}", ct);
|
|
// Find a const parameter
|
|
match ct.val {
|
|
ty::ConstKind::Param(..) => {
|
|
// Look it up in the substitution list.
|
|
match self.map.get(&ct.into()).map(|k| k.unpack()) {
|
|
// Found it in the substitution list, replace with the parameter from the
|
|
// opaque type.
|
|
Some(GenericArgKind::Const(c1)) => c1,
|
|
Some(u) => panic!("const mapped to unexpected kind: {:?}", u),
|
|
None => {
|
|
self.tcx
|
|
.sess
|
|
.struct_span_err(
|
|
self.span,
|
|
&format!(
|
|
"const parameter `{}` is part of concrete type but not \
|
|
used in parameter list for the `impl Trait` type alias",
|
|
ct
|
|
),
|
|
)
|
|
.emit();
|
|
|
|
self.tcx().consts.err
|
|
}
|
|
}
|
|
}
|
|
|
|
_ => ct,
|
|
}
|
|
}
|
|
}
|
|
|
|
struct Instantiator<'a, 'tcx> {
|
|
infcx: &'a InferCtxt<'a, 'tcx>,
|
|
parent_def_id: DefId,
|
|
body_id: hir::HirId,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
value_span: Span,
|
|
opaque_types: OpaqueTypeMap<'tcx>,
|
|
obligations: Vec<PredicateObligation<'tcx>>,
|
|
}
|
|
|
|
impl<'a, 'tcx> Instantiator<'a, 'tcx> {
|
|
fn instantiate_opaque_types_in_map<T: TypeFoldable<'tcx>>(&mut self, value: &T) -> T {
|
|
debug!("instantiate_opaque_types_in_map(value={:?})", value);
|
|
let tcx = self.infcx.tcx;
|
|
value.fold_with(&mut BottomUpFolder {
|
|
tcx,
|
|
ty_op: |ty| {
|
|
if ty.references_error() {
|
|
return tcx.types.err;
|
|
} else if let ty::Opaque(def_id, substs) = ty.kind {
|
|
// Check that this is `impl Trait` type is
|
|
// declared by `parent_def_id` -- i.e., one whose
|
|
// value we are inferring. At present, this is
|
|
// always true during the first phase of
|
|
// type-check, but not always true later on during
|
|
// NLL. Once we support named opaque types more fully,
|
|
// this same scenario will be able to arise during all phases.
|
|
//
|
|
// Here is an example using type alias `impl Trait`
|
|
// that indicates the distinction we are checking for:
|
|
//
|
|
// ```rust
|
|
// mod a {
|
|
// pub type Foo = impl Iterator;
|
|
// pub fn make_foo() -> Foo { .. }
|
|
// }
|
|
//
|
|
// mod b {
|
|
// fn foo() -> a::Foo { a::make_foo() }
|
|
// }
|
|
// ```
|
|
//
|
|
// Here, the return type of `foo` references a
|
|
// `Opaque` indeed, but not one whose value is
|
|
// presently being inferred. You can get into a
|
|
// similar situation with closure return types
|
|
// today:
|
|
//
|
|
// ```rust
|
|
// fn foo() -> impl Iterator { .. }
|
|
// fn bar() {
|
|
// let x = || foo(); // returns the Opaque assoc with `foo`
|
|
// }
|
|
// ```
|
|
if let Some(opaque_hir_id) = tcx.hir().as_local_hir_id(def_id) {
|
|
let parent_def_id = self.parent_def_id;
|
|
let def_scope_default = || {
|
|
let opaque_parent_hir_id = tcx.hir().get_parent_item(opaque_hir_id);
|
|
parent_def_id == tcx.hir().local_def_id(opaque_parent_hir_id)
|
|
};
|
|
let (in_definition_scope, origin) = match tcx.hir().find(opaque_hir_id) {
|
|
Some(Node::Item(item)) => match item.kind {
|
|
// Anonymous `impl Trait`
|
|
hir::ItemKind::OpaqueTy(hir::OpaqueTy {
|
|
impl_trait_fn: Some(parent),
|
|
origin,
|
|
..
|
|
}) => (parent == self.parent_def_id, origin),
|
|
// Named `type Foo = impl Bar;`
|
|
hir::ItemKind::OpaqueTy(hir::OpaqueTy {
|
|
impl_trait_fn: None,
|
|
origin,
|
|
..
|
|
}) => (
|
|
may_define_opaque_type(tcx, self.parent_def_id, opaque_hir_id),
|
|
origin,
|
|
),
|
|
_ => (def_scope_default(), hir::OpaqueTyOrigin::TypeAlias),
|
|
},
|
|
Some(Node::ImplItem(item)) => match item.kind {
|
|
hir::ImplItemKind::OpaqueTy(_) => (
|
|
may_define_opaque_type(tcx, self.parent_def_id, opaque_hir_id),
|
|
hir::OpaqueTyOrigin::TypeAlias,
|
|
),
|
|
_ => (def_scope_default(), hir::OpaqueTyOrigin::TypeAlias),
|
|
},
|
|
_ => bug!(
|
|
"expected (impl) item, found {}",
|
|
tcx.hir().node_to_string(opaque_hir_id),
|
|
),
|
|
};
|
|
if in_definition_scope {
|
|
return self.fold_opaque_ty(ty, def_id, substs, origin);
|
|
}
|
|
|
|
debug!(
|
|
"instantiate_opaque_types_in_map: \
|
|
encountered opaque outside its definition scope \
|
|
def_id={:?}",
|
|
def_id,
|
|
);
|
|
}
|
|
}
|
|
|
|
ty
|
|
},
|
|
lt_op: |lt| lt,
|
|
ct_op: |ct| ct,
|
|
})
|
|
}
|
|
|
|
fn fold_opaque_ty(
|
|
&mut self,
|
|
ty: Ty<'tcx>,
|
|
def_id: DefId,
|
|
substs: SubstsRef<'tcx>,
|
|
origin: hir::OpaqueTyOrigin,
|
|
) -> Ty<'tcx> {
|
|
let infcx = self.infcx;
|
|
let tcx = infcx.tcx;
|
|
|
|
debug!("instantiate_opaque_types: Opaque(def_id={:?}, substs={:?})", def_id, substs);
|
|
|
|
// Use the same type variable if the exact same opaque type appears more
|
|
// than once in the return type (e.g., if it's passed to a type alias).
|
|
if let Some(opaque_defn) = self.opaque_types.get(&def_id) {
|
|
debug!("instantiate_opaque_types: returning concrete ty {:?}", opaque_defn.concrete_ty);
|
|
return opaque_defn.concrete_ty;
|
|
}
|
|
let span = tcx.def_span(def_id);
|
|
debug!("fold_opaque_ty {:?} {:?}", self.value_span, span);
|
|
let ty_var = infcx
|
|
.next_ty_var(TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span });
|
|
|
|
let predicates_of = tcx.predicates_of(def_id);
|
|
debug!("instantiate_opaque_types: predicates={:#?}", predicates_of,);
|
|
let bounds = predicates_of.instantiate(tcx, substs);
|
|
|
|
let param_env = tcx.param_env(def_id);
|
|
let InferOk { value: bounds, obligations } =
|
|
infcx.partially_normalize_associated_types_in(span, self.body_id, param_env, &bounds);
|
|
self.obligations.extend(obligations);
|
|
|
|
debug!("instantiate_opaque_types: bounds={:?}", bounds);
|
|
|
|
let required_region_bounds = required_region_bounds(tcx, ty, bounds.predicates.clone());
|
|
debug!("instantiate_opaque_types: required_region_bounds={:?}", required_region_bounds);
|
|
|
|
// Make sure that we are in fact defining the *entire* type
|
|
// (e.g., `type Foo<T: Bound> = impl Bar;` needs to be
|
|
// defined by a function like `fn foo<T: Bound>() -> Foo<T>`).
|
|
debug!("instantiate_opaque_types: param_env={:#?}", self.param_env,);
|
|
debug!("instantiate_opaque_types: generics={:#?}", tcx.generics_of(def_id),);
|
|
|
|
// Ideally, we'd get the span where *this specific `ty` came
|
|
// from*, but right now we just use the span from the overall
|
|
// value being folded. In simple cases like `-> impl Foo`,
|
|
// these are the same span, but not in cases like `-> (impl
|
|
// Foo, impl Bar)`.
|
|
let definition_span = self.value_span;
|
|
|
|
self.opaque_types.insert(
|
|
def_id,
|
|
OpaqueTypeDecl {
|
|
opaque_type: ty,
|
|
substs,
|
|
definition_span,
|
|
concrete_ty: ty_var,
|
|
has_required_region_bounds: !required_region_bounds.is_empty(),
|
|
origin,
|
|
},
|
|
);
|
|
debug!("instantiate_opaque_types: ty_var={:?}", ty_var);
|
|
|
|
for predicate in &bounds.predicates {
|
|
if let ty::Predicate::Projection(projection) = &predicate {
|
|
if projection.skip_binder().ty.references_error() {
|
|
// No point on adding these obligations since there's a type error involved.
|
|
return ty_var;
|
|
}
|
|
}
|
|
}
|
|
|
|
self.obligations.reserve(bounds.predicates.len());
|
|
for predicate in bounds.predicates {
|
|
// Change the predicate to refer to the type variable,
|
|
// which will be the concrete type instead of the opaque type.
|
|
// This also instantiates nested instances of `impl Trait`.
|
|
let predicate = self.instantiate_opaque_types_in_map(&predicate);
|
|
|
|
let cause = traits::ObligationCause::new(span, self.body_id, traits::SizedReturnType);
|
|
|
|
// Require that the predicate holds for the concrete type.
|
|
debug!("instantiate_opaque_types: predicate={:?}", predicate);
|
|
self.obligations.push(traits::Obligation::new(cause, self.param_env, predicate));
|
|
}
|
|
|
|
ty_var
|
|
}
|
|
}
|
|
|
|
/// Returns `true` if `opaque_hir_id` is a sibling or a child of a sibling of `def_id`.
|
|
///
|
|
/// Example:
|
|
/// ```rust
|
|
/// pub mod foo {
|
|
/// pub mod bar {
|
|
/// pub trait Bar { .. }
|
|
///
|
|
/// pub type Baz = impl Bar;
|
|
///
|
|
/// fn f1() -> Baz { .. }
|
|
/// }
|
|
///
|
|
/// fn f2() -> bar::Baz { .. }
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// Here, `def_id` is the `DefId` of the defining use of the opaque type (e.g., `f1` or `f2`),
|
|
/// and `opaque_hir_id` is the `HirId` of the definition of the opaque type `Baz`.
|
|
/// For the above example, this function returns `true` for `f1` and `false` for `f2`.
|
|
pub fn may_define_opaque_type(tcx: TyCtxt<'_>, def_id: DefId, opaque_hir_id: hir::HirId) -> bool {
|
|
let mut hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
|
|
|
|
// Named opaque types can be defined by any siblings or children of siblings.
|
|
let scope = tcx.hir().get_defining_scope(opaque_hir_id);
|
|
// We walk up the node tree until we hit the root or the scope of the opaque type.
|
|
while hir_id != scope && hir_id != hir::CRATE_HIR_ID {
|
|
hir_id = tcx.hir().get_parent_item(hir_id);
|
|
}
|
|
// Syntactically, we are allowed to define the concrete type if:
|
|
let res = hir_id == scope;
|
|
trace!(
|
|
"may_define_opaque_type(def={:?}, opaque_node={:?}) = {}",
|
|
tcx.hir().get(hir_id),
|
|
tcx.hir().get(opaque_hir_id),
|
|
res
|
|
);
|
|
res
|
|
}
|
|
|
|
/// Given a set of predicates that apply to an object type, returns
|
|
/// the region bounds that the (erased) `Self` type must
|
|
/// outlive. Precisely *because* the `Self` type is erased, the
|
|
/// parameter `erased_self_ty` must be supplied to indicate what type
|
|
/// has been used to represent `Self` in the predicates
|
|
/// themselves. This should really be a unique type; `FreshTy(0)` is a
|
|
/// popular choice.
|
|
///
|
|
/// N.B., in some cases, particularly around higher-ranked bounds,
|
|
/// this function returns a kind of conservative approximation.
|
|
/// That is, all regions returned by this function are definitely
|
|
/// required, but there may be other region bounds that are not
|
|
/// returned, as well as requirements like `for<'a> T: 'a`.
|
|
///
|
|
/// Requires that trait definitions have been processed so that we can
|
|
/// elaborate predicates and walk supertraits.
|
|
//
|
|
// FIXME: callers may only have a `&[Predicate]`, not a `Vec`, so that's
|
|
// what this code should accept.
|
|
crate fn required_region_bounds(
|
|
tcx: TyCtxt<'tcx>,
|
|
erased_self_ty: Ty<'tcx>,
|
|
predicates: Vec<ty::Predicate<'tcx>>,
|
|
) -> Vec<ty::Region<'tcx>> {
|
|
debug!(
|
|
"required_region_bounds(erased_self_ty={:?}, predicates={:?})",
|
|
erased_self_ty, predicates
|
|
);
|
|
|
|
assert!(!erased_self_ty.has_escaping_bound_vars());
|
|
|
|
traits::elaborate_predicates(tcx, predicates)
|
|
.filter_map(|predicate| {
|
|
match predicate {
|
|
ty::Predicate::Projection(..)
|
|
| ty::Predicate::Trait(..)
|
|
| ty::Predicate::Subtype(..)
|
|
| ty::Predicate::WellFormed(..)
|
|
| ty::Predicate::ObjectSafe(..)
|
|
| ty::Predicate::ClosureKind(..)
|
|
| ty::Predicate::RegionOutlives(..)
|
|
| ty::Predicate::ConstEvaluatable(..) => None,
|
|
ty::Predicate::TypeOutlives(predicate) => {
|
|
// Search for a bound of the form `erased_self_ty
|
|
// : 'a`, but be wary of something like `for<'a>
|
|
// erased_self_ty : 'a` (we interpret a
|
|
// higher-ranked bound like that as 'static,
|
|
// though at present the code in `fulfill.rs`
|
|
// considers such bounds to be unsatisfiable, so
|
|
// it's kind of a moot point since you could never
|
|
// construct such an object, but this seems
|
|
// correct even if that code changes).
|
|
let ty::OutlivesPredicate(ref t, ref r) = predicate.skip_binder();
|
|
if t == &erased_self_ty && !r.has_escaping_bound_vars() {
|
|
Some(*r)
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
}
|
|
})
|
|
.collect()
|
|
}
|