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pub mod inspect;
use std::fmt;
use std::hash::Hash;
use derive_where::derive_where;
#[cfg(feature = "nightly")]
use rustc_macros::{HashStable_NoContext, TyDecodable, TyEncodable};
use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
use crate::{self as ty, Canonical, CanonicalVarValues, Interner, Upcast};
/// Depending on the stage of compilation, we want projection to be
/// more or less conservative.
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
pub enum Reveal {
/// At type-checking time, we refuse to project any associated
/// type that is marked `default`. Non-`default` ("final") types
/// are always projected. This is necessary in general for
/// soundness of specialization. However, we *could* allow
/// projections in fully-monomorphic cases. We choose not to,
/// because we prefer for `default type` to force the type
/// definition to be treated abstractly by any consumers of the
/// impl. Concretely, that means that the following example will
/// fail to compile:
///
/// ```compile_fail,E0308
/// #![feature(specialization)]
/// trait Assoc {
/// type Output;
/// }
///
/// impl<T> Assoc for T {
/// default type Output = bool;
/// }
///
/// fn main() {
/// let x: <() as Assoc>::Output = true;
/// }
/// ```
///
/// We also do not reveal the hidden type of opaque types during
/// type-checking.
UserFacing,
/// At codegen time, all monomorphic projections will succeed.
/// Also, `impl Trait` is normalized to the concrete type,
/// which has to be already collected by type-checking.
///
/// NOTE: as `impl Trait`'s concrete type should *never*
/// be observable directly by the user, `Reveal::All`
/// should not be used by checks which may expose
/// type equality or type contents to the user.
/// There are some exceptions, e.g., around auto traits and
/// transmute-checking, which expose some details, but
/// not the whole concrete type of the `impl Trait`.
All,
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SolverMode {
/// Ordinary trait solving, using everywhere except for coherence.
Normal,
/// Trait solving during coherence. There are a few notable differences
/// between coherence and ordinary trait solving.
///
/// Most importantly, trait solving during coherence must not be incomplete,
/// i.e. return `Err(NoSolution)` for goals for which a solution exists.
/// This means that we must not make any guesses or arbitrary choices.
Coherence,
}
pub type CanonicalInput<I, T = <I as Interner>::Predicate> = Canonical<I, QueryInput<I, T>>;
pub type CanonicalResponse<I> = Canonical<I, Response<I>>;
/// The result of evaluating a canonical query.
///
/// FIXME: We use a different type than the existing canonical queries. This is because
/// we need to add a `Certainty` for `overflow` and may want to restructure this code without
/// having to worry about changes to currently used code. Once we've made progress on this
/// solver, merge the two responses again.
pub type QueryResult<I> = Result<CanonicalResponse<I>, NoSolution>;
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
pub struct NoSolution;
/// A goal is a statement, i.e. `predicate`, we want to prove
/// given some assumptions, i.e. `param_env`.
///
/// Most of the time the `param_env` contains the `where`-bounds of the function
/// we're currently typechecking while the `predicate` is some trait bound.
#[derive_where(Clone; I: Interner, P: Clone)]
#[derive_where(Copy; I: Interner, P: Copy)]
#[derive_where(Hash; I: Interner, P: Hash)]
#[derive_where(PartialEq; I: Interner, P: PartialEq)]
#[derive_where(Eq; I: Interner, P: Eq)]
#[derive_where(Debug; I: Interner, P: fmt::Debug)]
#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
pub struct Goal<I: Interner, P> {
pub param_env: I::ParamEnv,
pub predicate: P,
}
impl<I: Interner, P> Goal<I, P> {
pub fn new(cx: I, param_env: I::ParamEnv, predicate: impl Upcast<I, P>) -> Goal<I, P> {
Goal { param_env, predicate: predicate.upcast(cx) }
}
/// Updates the goal to one with a different `predicate` but the same `param_env`.
pub fn with<Q>(self, cx: I, predicate: impl Upcast<I, Q>) -> Goal<I, Q> {
Goal { param_env: self.param_env, predicate: predicate.upcast(cx) }
}
}
/// Why a specific goal has to be proven.
///
/// This is necessary as we treat nested goals different depending on
/// their source.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
pub enum GoalSource {
Misc,
/// We're proving a where-bound of an impl.
///
/// FIXME(-Znext-solver=coinductive): Explain how and why this
/// changes whether cycles are coinductive.
///
/// This also impacts whether we erase constraints on overflow.
/// Erasing constraints is generally very useful for perf and also
/// results in better error messages by avoiding spurious errors.
/// We do not erase overflow constraints in `normalizes-to` goals unless
/// they are from an impl where-clause. This is necessary due to
/// backwards compatibility, cc trait-system-refactor-initiatitive#70.
ImplWhereBound,
/// Instantiating a higher-ranked goal and re-proving it.
InstantiateHigherRanked,
}
#[derive_where(Clone; I: Interner, Goal<I, P>: Clone)]
#[derive_where(Copy; I: Interner, Goal<I, P>: Copy)]
#[derive_where(Hash; I: Interner, Goal<I, P>: Hash)]
#[derive_where(PartialEq; I: Interner, Goal<I, P>: PartialEq)]
#[derive_where(Eq; I: Interner, Goal<I, P>: Eq)]
#[derive_where(Debug; I: Interner, Goal<I, P>: fmt::Debug)]
#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
pub struct QueryInput<I: Interner, P> {
pub goal: Goal<I, P>,
pub predefined_opaques_in_body: I::PredefinedOpaques,
}
/// Opaques that are defined in the inference context before a query is called.
#[derive_where(Clone, Hash, PartialEq, Eq, Debug, Default; I: Interner)]
#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
pub struct PredefinedOpaquesData<I: Interner> {
pub opaque_types: Vec<(ty::OpaqueTypeKey<I>, I::Ty)>,
}
/// Possible ways the given goal can be proven.
#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
pub enum CandidateSource<I: Interner> {
/// A user written impl.
///
/// ## Examples
///
/// ```rust
/// fn main() {
/// let x: Vec<u32> = Vec::new();
/// // This uses the impl from the standard library to prove `Vec<T>: Clone`.
/// let y = x.clone();
/// }
/// ```
Impl(I::DefId),
/// A builtin impl generated by the compiler. When adding a new special
/// trait, try to use actual impls whenever possible. Builtin impls should
/// only be used in cases where the impl cannot be manually be written.
///
/// Notable examples are auto traits, `Sized`, and `DiscriminantKind`.
/// For a list of all traits with builtin impls, check out the
/// `EvalCtxt::assemble_builtin_impl_candidates` method.
BuiltinImpl(BuiltinImplSource),
/// An assumption from the environment.
///
/// More precisely we've used the `n-th` assumption in the `param_env`.
///
/// ## Examples
///
/// ```rust
/// fn is_clone<T: Clone>(x: T) -> (T, T) {
/// // This uses the assumption `T: Clone` from the `where`-bounds
/// // to prove `T: Clone`.
/// (x.clone(), x)
/// }
/// ```
ParamEnv(usize),
/// If the self type is an alias type, e.g. an opaque type or a projection,
/// we know the bounds on that alias to hold even without knowing its concrete
/// underlying type.
///
/// More precisely this candidate is using the `n-th` bound in the `item_bounds` of
/// the self type.
///
/// ## Examples
///
/// ```rust
/// trait Trait {
/// type Assoc: Clone;
/// }
///
/// fn foo<T: Trait>(x: <T as Trait>::Assoc) {
/// // We prove `<T as Trait>::Assoc` by looking at the bounds on `Assoc` in
/// // in the trait definition.
/// let _y = x.clone();
/// }
/// ```
AliasBound,
/// A candidate that is registered only during coherence to represent some
/// yet-unknown impl that could be produced downstream without violating orphan
/// rules.
// FIXME: Merge this with the forced ambiguity candidates, so those don't use `Misc`.
CoherenceUnknowable,
}
#[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext, TyEncodable, TyDecodable))]
pub enum BuiltinImplSource {
/// Some built-in impl we don't need to differentiate. This should be used
/// unless more specific information is necessary.
Misc,
/// A built-in impl for trait objects. The index is only used in winnowing.
Object(usize),
/// A built-in implementation of `Upcast` for trait objects to other trait objects.
///
/// This can be removed when `feature(dyn_upcasting)` is stabilized, since we only
/// use it to detect when upcasting traits in hir typeck.
TraitUpcasting,
/// Unsizing a tuple like `(A, B, ..., X)` to `(A, B, ..., Y)` if `X` unsizes to `Y`.
///
/// This can be removed when `feature(tuple_unsizing)` is stabilized, since we only
/// use it to detect when unsizing tuples in hir typeck.
TupleUnsizing,
}
#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
pub struct Response<I: Interner> {
pub certainty: Certainty,
pub var_values: CanonicalVarValues<I>,
/// Additional constraints returned by this query.
pub external_constraints: I::ExternalConstraints,
}
/// Additional constraints returned on success.
#[derive_where(Clone, Hash, PartialEq, Eq, Debug, Default; I: Interner)]
#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
pub struct ExternalConstraintsData<I: Interner> {
pub region_constraints: Vec<ty::OutlivesPredicate<I, I::GenericArg>>,
pub opaque_types: Vec<(ty::OpaqueTypeKey<I>, I::Ty)>,
pub normalization_nested_goals: NestedNormalizationGoals<I>,
}
#[derive_where(Clone, Hash, PartialEq, Eq, Debug, Default; I: Interner)]
#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
pub struct NestedNormalizationGoals<I: Interner>(pub Vec<(GoalSource, Goal<I, I::Predicate>)>);
impl<I: Interner> NestedNormalizationGoals<I> {
pub fn empty() -> Self {
NestedNormalizationGoals(vec![])
}
pub fn is_empty(&self) -> bool {
self.0.is_empty()
}
}
#[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
pub enum Certainty {
Yes,
Maybe(MaybeCause),
}
impl Certainty {
pub const AMBIGUOUS: Certainty = Certainty::Maybe(MaybeCause::Ambiguity);
/// Use this function to merge the certainty of multiple nested subgoals.
///
/// Given an impl like `impl<T: Foo + Bar> Baz for T {}`, we have 2 nested
/// subgoals whenever we use the impl as a candidate: `T: Foo` and `T: Bar`.
/// If evaluating `T: Foo` results in ambiguity and `T: Bar` results in
/// success, we merge these two responses. This results in ambiguity.
///
/// If we unify ambiguity with overflow, we return overflow. This doesn't matter
/// inside of the solver as we do not distinguish ambiguity from overflow. It does
/// however matter for diagnostics. If `T: Foo` resulted in overflow and `T: Bar`
/// in ambiguity without changing the inference state, we still want to tell the
/// user that `T: Baz` results in overflow.
pub fn unify_with(self, other: Certainty) -> Certainty {
match (self, other) {
(Certainty::Yes, Certainty::Yes) => Certainty::Yes,
(Certainty::Yes, Certainty::Maybe(_)) => other,
(Certainty::Maybe(_), Certainty::Yes) => self,
(Certainty::Maybe(a), Certainty::Maybe(b)) => Certainty::Maybe(a.unify_with(b)),
}
}
pub const fn overflow(suggest_increasing_limit: bool) -> Certainty {
Certainty::Maybe(MaybeCause::Overflow { suggest_increasing_limit })
}
}
/// Why we failed to evaluate a goal.
#[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
pub enum MaybeCause {
/// We failed due to ambiguity. This ambiguity can either
/// be a true ambiguity, i.e. there are multiple different answers,
/// or we hit a case where we just don't bother, e.g. `?x: Trait` goals.
Ambiguity,
/// We gave up due to an overflow, most often by hitting the recursion limit.
Overflow { suggest_increasing_limit: bool },
}
impl MaybeCause {
fn unify_with(self, other: MaybeCause) -> MaybeCause {
match (self, other) {
(MaybeCause::Ambiguity, MaybeCause::Ambiguity) => MaybeCause::Ambiguity,
(MaybeCause::Ambiguity, MaybeCause::Overflow { .. }) => other,
(MaybeCause::Overflow { .. }, MaybeCause::Ambiguity) => self,
(
MaybeCause::Overflow { suggest_increasing_limit: a },
MaybeCause::Overflow { suggest_increasing_limit: b },
) => MaybeCause::Overflow { suggest_increasing_limit: a || b },
}
}
}