83ef3042de
which should always result in an error. NB. Some of the hunks in this commit rely on a later commit which adds `tcx` into `param_env` and modifies `ParameterEnvironment` to implement `Typer`.
547 lines
19 KiB
Rust
547 lines
19 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Trait Resolution. See doc.rs.
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pub use self::SelectionError::*;
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pub use self::FulfillmentErrorCode::*;
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pub use self::Vtable::*;
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pub use self::ObligationCauseCode::*;
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use middle::mem_categorization::Typer;
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use middle::subst;
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use middle::ty::{mod, Ty};
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use middle::infer::InferCtxt;
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use std::slice::Iter;
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use std::rc::Rc;
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use syntax::ast;
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use syntax::codemap::{Span, DUMMY_SP};
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use util::ppaux::{Repr, UserString};
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pub use self::error_reporting::report_fulfillment_errors;
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pub use self::error_reporting::suggest_new_overflow_limit;
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pub use self::coherence::orphan_check;
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pub use self::coherence::OrphanCheckErr;
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pub use self::fulfill::{FulfillmentContext, RegionObligation};
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pub use self::project::MismatchedProjectionTypes;
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pub use self::project::normalize;
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pub use self::project::Normalized;
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pub use self::object_safety::is_object_safe;
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pub use self::object_safety::object_safety_violations;
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pub use self::object_safety::ObjectSafetyViolation;
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pub use self::object_safety::MethodViolationCode;
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pub use self::select::SelectionContext;
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pub use self::select::SelectionCache;
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pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
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pub use self::select::{MethodMatchedData}; // intentionally don't export variants
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pub use self::util::elaborate_predicates;
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pub use self::util::get_vtable_index_of_object_method;
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pub use self::util::trait_ref_for_builtin_bound;
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pub use self::util::supertraits;
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pub use self::util::Supertraits;
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pub use self::util::transitive_bounds;
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pub use self::util::upcast;
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mod coherence;
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mod error_reporting;
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mod fulfill;
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mod project;
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mod object_safety;
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mod select;
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mod util;
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/// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
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/// which the vtable must be found. The process of finding a vtable is
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/// called "resolving" the `Obligation`. This process consists of
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/// either identifying an `impl` (e.g., `impl Eq for int`) that
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/// provides the required vtable, or else finding a bound that is in
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/// scope. The eventual result is usually a `Selection` (defined below).
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#[deriving(Clone)]
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pub struct Obligation<'tcx, T> {
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pub cause: ObligationCause<'tcx>,
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pub recursion_depth: uint,
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pub predicate: T,
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}
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pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
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pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
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/// Why did we incur this obligation? Used for error reporting.
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#[deriving(Clone)]
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pub struct ObligationCause<'tcx> {
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pub span: Span,
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// The id of the fn body that triggered this obligation. This is
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// used for region obligations to determine the precise
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// environment in which the region obligation should be evaluated
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// (in particular, closures can add new assumptions). See the
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// field `region_obligations` of the `FulfillmentContext` for more
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// information.
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pub body_id: ast::NodeId,
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pub code: ObligationCauseCode<'tcx>
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}
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#[deriving(Clone)]
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pub enum ObligationCauseCode<'tcx> {
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/// Not well classified or should be obvious from span.
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MiscObligation,
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/// In an impl of trait X for type Y, type Y must
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/// also implement all supertraits of X.
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ItemObligation(ast::DefId),
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/// Obligation incurred due to an object cast.
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ObjectCastObligation(/* Object type */ Ty<'tcx>),
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/// Various cases where expressions must be sized/copy/etc:
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AssignmentLhsSized, // L = X implies that L is Sized
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StructInitializerSized, // S { ... } must be Sized
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VariableType(ast::NodeId), // Type of each variable must be Sized
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ReturnType, // Return type must be Sized
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RepeatVec, // [T,..n] --> T must be Copy
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// Captures of variable the given id by a closure (span is the
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// span of the closure)
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ClosureCapture(ast::NodeId, Span, ty::BuiltinBound),
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// Types of fields (other than the last) in a struct must be sized.
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FieldSized,
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// Only Sized types can be made into objects
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ObjectSized,
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// static items must have `Sync` type
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SharedStatic,
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BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
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ImplDerivedObligation(DerivedObligationCause<'tcx>),
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}
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#[deriving(Clone)]
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pub struct DerivedObligationCause<'tcx> {
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/// The trait reference of the parent obligation that led to the
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/// current obligation. Note that only trait obligations lead to
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/// derived obligations, so we just store the trait reference here
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/// directly.
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parent_trait_ref: ty::PolyTraitRef<'tcx>,
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/// The parent trait had this cause
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parent_code: Rc<ObligationCauseCode<'tcx>>
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}
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pub type Obligations<'tcx, O> = subst::VecPerParamSpace<Obligation<'tcx, O>>;
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pub type PredicateObligations<'tcx> = subst::VecPerParamSpace<PredicateObligation<'tcx>>;
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pub type TraitObligations<'tcx> = subst::VecPerParamSpace<TraitObligation<'tcx>>;
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pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
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#[deriving(Clone,Show)]
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pub enum SelectionError<'tcx> {
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Unimplemented,
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Overflow,
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OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
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ty::PolyTraitRef<'tcx>,
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ty::type_err<'tcx>),
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}
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pub struct FulfillmentError<'tcx> {
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pub obligation: PredicateObligation<'tcx>,
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pub code: FulfillmentErrorCode<'tcx>
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}
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#[deriving(Clone)]
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pub enum FulfillmentErrorCode<'tcx> {
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CodeSelectionError(SelectionError<'tcx>),
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CodeProjectionError(MismatchedProjectionTypes<'tcx>),
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CodeAmbiguity,
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}
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/// When performing resolution, it is typically the case that there
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/// can be one of three outcomes:
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///
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/// - `Ok(Some(r))`: success occurred with result `r`
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/// - `Ok(None)`: could not definitely determine anything, usually due
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/// to inconclusive type inference.
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/// - `Err(e)`: error `e` occurred
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pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
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/// Given the successful resolution of an obligation, the `Vtable`
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/// indicates where the vtable comes from. Note that while we call this
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/// a "vtable", it does not necessarily indicate dynamic dispatch at
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/// runtime. `Vtable` instances just tell the compiler where to find
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/// methods, but in generic code those methods are typically statically
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/// dispatched -- only when an object is constructed is a `Vtable`
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/// instance reified into an actual vtable.
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///
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/// For example, the vtable may be tied to a specific impl (case A),
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/// or it may be relative to some bound that is in scope (case B).
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///
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///
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/// ```
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/// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
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/// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
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/// impl Clone for int { ... } // Impl_3
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///
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/// fn foo<T:Clone>(concrete: Option<Box<int>>,
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/// param: T,
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/// mixed: Option<T>) {
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///
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/// // Case A: Vtable points at a specific impl. Only possible when
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/// // type is concretely known. If the impl itself has bounded
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/// // type parameters, Vtable will carry resolutions for those as well:
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/// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
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///
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/// // Case B: Vtable must be provided by caller. This applies when
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/// // type is a type parameter.
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/// param.clone(); // VtableParam
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///
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/// // Case C: A mix of cases A and B.
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/// mixed.clone(); // Vtable(Impl_1, [VtableParam])
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/// }
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/// ```
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///
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/// ### The type parameter `N`
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///
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/// See explanation on `VtableImplData`.
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#[deriving(Show,Clone)]
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pub enum Vtable<'tcx, N> {
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/// Vtable identifying a particular impl.
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VtableImpl(VtableImplData<'tcx, N>),
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/// Successful resolution to an obligation provided by the caller
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/// for some type parameter.
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VtableParam,
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/// Virtual calls through an object
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VtableObject(VtableObjectData<'tcx>),
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/// Successful resolution for a builtin trait.
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VtableBuiltin(VtableBuiltinData<N>),
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/// Vtable automatically generated for an unboxed closure. The def
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/// ID is the ID of the closure expression. This is a `VtableImpl`
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/// in spirit, but the impl is generated by the compiler and does
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/// not appear in the source.
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VtableUnboxedClosure(ast::DefId, subst::Substs<'tcx>),
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/// Same as above, but for a fn pointer type with the given signature.
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VtableFnPointer(ty::Ty<'tcx>),
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}
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/// Identifies a particular impl in the source, along with a set of
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/// substitutions from the impl's type/lifetime parameters. The
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/// `nested` vector corresponds to the nested obligations attached to
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/// the impl's type parameters.
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///
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/// The type parameter `N` indicates the type used for "nested
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/// obligations" that are required by the impl. During type check, this
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/// is `Obligation`, as one might expect. During trans, however, this
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/// is `()`, because trans only requires a shallow resolution of an
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/// impl, and nested obligations are satisfied later.
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#[deriving(Clone)]
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pub struct VtableImplData<'tcx, N> {
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pub impl_def_id: ast::DefId,
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pub substs: subst::Substs<'tcx>,
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pub nested: subst::VecPerParamSpace<N>
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}
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#[deriving(Show,Clone)]
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pub struct VtableBuiltinData<N> {
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pub nested: subst::VecPerParamSpace<N>
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}
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/// A vtable for some object-safe trait `Foo` automatically derived
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/// for the object type `Foo`.
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#[deriving(PartialEq,Eq,Clone)]
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pub struct VtableObjectData<'tcx> {
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pub object_ty: Ty<'tcx>,
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}
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/// True if there exist types that satisfy both of the two given impls.
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pub fn overlapping_impls(infcx: &InferCtxt,
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impl1_def_id: ast::DefId,
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impl2_def_id: ast::DefId)
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-> bool
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{
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coherence::impl_can_satisfy(infcx, impl1_def_id, impl2_def_id) &&
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coherence::impl_can_satisfy(infcx, impl2_def_id, impl1_def_id)
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}
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/// Creates predicate obligations from the generic bounds.
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pub fn predicates_for_generics<'tcx>(tcx: &ty::ctxt<'tcx>,
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cause: ObligationCause<'tcx>,
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generic_bounds: &ty::GenericBounds<'tcx>)
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-> PredicateObligations<'tcx>
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{
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util::predicates_for_generics(tcx, cause, 0, generic_bounds)
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}
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/// Determines whether the type `ty` is known to meet `bound` and
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/// returns true if so. Returns false if `ty` either does not meet
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/// `bound` or is not known to meet bound (note that this is
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/// conservative towards *no impl*, which is the opposite of the
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/// `evaluate` methods).
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pub fn evaluate_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
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typer: &ty::UnboxedClosureTyper<'tcx>,
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ty: Ty<'tcx>,
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bound: ty::BuiltinBound,
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span: Span)
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-> SelectionResult<'tcx, ()>
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{
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debug!("type_known_to_meet_builtin_bound(ty={}, bound={})",
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ty.repr(infcx.tcx),
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bound);
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let mut fulfill_cx = FulfillmentContext::new();
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// We can use a dummy node-id here because we won't pay any mind
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// to region obligations that arise (there shouldn't really be any
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// anyhow).
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let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
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fulfill_cx.register_builtin_bound(infcx, ty, bound, cause);
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// Note: we only assume something is `Copy` if we can
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// *definitively* show that it implements `Copy`. Otherwise,
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// assume it is move; linear is always ok.
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let result = match fulfill_cx.select_all_or_error(infcx, typer) {
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Ok(()) => Ok(Some(())), // Success, we know it implements Copy.
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Err(errors) => {
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// Check if overflow occurred anywhere and propagate that.
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if errors.iter().any(
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|err| match err.code { CodeSelectionError(Overflow) => true, _ => false })
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{
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return Err(Overflow);
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}
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// Otherwise, if there were any hard errors, propagate an
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// arbitrary one of those. If no hard errors at all,
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// report ambiguity.
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let sel_error =
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errors.iter()
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.filter_map(|err| {
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match err.code {
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CodeAmbiguity => None,
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CodeSelectionError(ref e) => Some(e.clone()),
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CodeProjectionError(_) => {
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infcx.tcx.sess.span_bug(
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span,
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"projection error while selecting?")
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}
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}
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})
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.next();
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match sel_error {
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None => { Ok(None) }
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Some(e) => { Err(e) }
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}
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}
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};
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debug!("type_known_to_meet_builtin_bound: ty={} bound={} result={}",
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ty.repr(infcx.tcx),
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bound,
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result);
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result
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}
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pub fn type_known_to_meet_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
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typer: &ty::UnboxedClosureTyper<'tcx>,
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ty: Ty<'tcx>,
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bound: ty::BuiltinBound,
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span: Span)
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-> bool
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{
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match evaluate_builtin_bound(infcx, typer, ty, bound, span) {
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Ok(Some(())) => {
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// definitely impl'd
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true
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}
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Ok(None) => {
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// ambiguous: if coherence check was successful, shouldn't
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// happen, but we might have reported an error and been
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// soldering on, so just treat this like not implemented
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false
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}
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Err(Overflow) => {
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infcx.tcx.sess.span_err(
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span,
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format!("overflow evaluating whether `{}` is `{}`",
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ty.user_string(infcx.tcx),
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bound.user_string(infcx.tcx))[]);
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suggest_new_overflow_limit(infcx.tcx, span);
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false
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}
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Err(_) => {
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// other errors: not implemented.
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false
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}
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}
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}
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impl<'tcx,O> Obligation<'tcx,O> {
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pub fn new(cause: ObligationCause<'tcx>,
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trait_ref: O)
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-> Obligation<'tcx, O>
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{
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Obligation { cause: cause,
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recursion_depth: 0,
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predicate: trait_ref }
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}
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fn with_depth(cause: ObligationCause<'tcx>,
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recursion_depth: uint,
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trait_ref: O)
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-> Obligation<'tcx, O>
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{
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Obligation { cause: cause,
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recursion_depth: recursion_depth,
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predicate: trait_ref }
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}
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pub fn misc(span: Span, body_id: ast::NodeId, trait_ref: O) -> Obligation<'tcx, O> {
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Obligation::new(ObligationCause::misc(span, body_id), trait_ref)
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}
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pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
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Obligation { cause: self.cause.clone(),
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recursion_depth: self.recursion_depth,
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predicate: value }
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}
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}
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impl<'tcx> ObligationCause<'tcx> {
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pub fn new(span: Span,
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body_id: ast::NodeId,
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code: ObligationCauseCode<'tcx>)
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-> ObligationCause<'tcx> {
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ObligationCause { span: span, body_id: body_id, code: code }
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}
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pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
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ObligationCause { span: span, body_id: body_id, code: MiscObligation }
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}
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pub fn dummy() -> ObligationCause<'tcx> {
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ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
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}
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}
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impl<'tcx, N> Vtable<'tcx, N> {
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pub fn iter_nested(&self) -> Iter<N> {
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match *self {
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VtableImpl(ref i) => i.iter_nested(),
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VtableFnPointer(..) => (&[]).iter(),
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VtableUnboxedClosure(..) => (&[]).iter(),
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VtableParam => (&[]).iter(),
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VtableObject(_) => (&[]).iter(),
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VtableBuiltin(ref i) => i.iter_nested(),
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}
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}
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pub fn map_nested<M, F>(&self, op: F) -> Vtable<'tcx, M> where F: FnMut(&N) -> M {
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match *self {
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VtableImpl(ref i) => VtableImpl(i.map_nested(op)),
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VtableFnPointer(ref sig) => VtableFnPointer((*sig).clone()),
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VtableUnboxedClosure(d, ref s) => VtableUnboxedClosure(d, s.clone()),
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VtableParam => VtableParam,
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VtableObject(ref p) => VtableObject(p.clone()),
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VtableBuiltin(ref b) => VtableBuiltin(b.map_nested(op)),
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}
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}
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pub fn map_move_nested<M, F>(self, op: F) -> Vtable<'tcx, M> where
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F: FnMut(N) -> M,
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{
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match self {
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VtableImpl(i) => VtableImpl(i.map_move_nested(op)),
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|
VtableFnPointer(sig) => VtableFnPointer(sig),
|
|
VtableUnboxedClosure(d, s) => VtableUnboxedClosure(d, s),
|
|
VtableParam => VtableParam,
|
|
VtableObject(p) => VtableObject(p),
|
|
VtableBuiltin(no) => VtableBuiltin(no.map_move_nested(op)),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'tcx, N> VtableImplData<'tcx, N> {
|
|
pub fn iter_nested(&self) -> Iter<N> {
|
|
self.nested.iter()
|
|
}
|
|
|
|
pub fn map_nested<M, F>(&self, op: F) -> VtableImplData<'tcx, M> where
|
|
F: FnMut(&N) -> M,
|
|
{
|
|
VtableImplData {
|
|
impl_def_id: self.impl_def_id,
|
|
substs: self.substs.clone(),
|
|
nested: self.nested.map(op)
|
|
}
|
|
}
|
|
|
|
pub fn map_move_nested<M, F>(self, op: F) -> VtableImplData<'tcx, M> where
|
|
F: FnMut(N) -> M,
|
|
{
|
|
let VtableImplData { impl_def_id, substs, nested } = self;
|
|
VtableImplData {
|
|
impl_def_id: impl_def_id,
|
|
substs: substs,
|
|
nested: nested.map_move(op)
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<N> VtableBuiltinData<N> {
|
|
pub fn iter_nested(&self) -> Iter<N> {
|
|
self.nested.iter()
|
|
}
|
|
|
|
pub fn map_nested<M, F>(&self, op: F) -> VtableBuiltinData<M> where F: FnMut(&N) -> M {
|
|
VtableBuiltinData {
|
|
nested: self.nested.map(op)
|
|
}
|
|
}
|
|
|
|
pub fn map_move_nested<M, F>(self, op: F) -> VtableBuiltinData<M> where
|
|
F: FnMut(N) -> M,
|
|
{
|
|
VtableBuiltinData {
|
|
nested: self.nested.map_move(op)
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'tcx> FulfillmentError<'tcx> {
|
|
fn new(obligation: PredicateObligation<'tcx>,
|
|
code: FulfillmentErrorCode<'tcx>)
|
|
-> FulfillmentError<'tcx>
|
|
{
|
|
FulfillmentError { obligation: obligation, code: code }
|
|
}
|
|
|
|
pub fn is_overflow(&self) -> bool {
|
|
match self.code {
|
|
CodeAmbiguity => false,
|
|
CodeSelectionError(Overflow) => true,
|
|
CodeSelectionError(_) => false,
|
|
CodeProjectionError(_) => false,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'tcx> TraitObligation<'tcx> {
|
|
fn self_ty(&self) -> Ty<'tcx> {
|
|
self.predicate.0.self_ty()
|
|
}
|
|
}
|