Skip to content
Branch: master
Find file Copy path
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
1231 lines (1075 sloc) 44 KB
//! Trait Resolution. See the [rustc guide] for more information on how this works.
//! [rustc guide]:
pub mod auto_trait;
mod chalk_fulfill;
mod coherence;
pub mod error_reporting;
mod engine;
mod fulfill;
mod project;
mod object_safety;
mod on_unimplemented;
mod select;
mod specialize;
mod structural_impls;
pub mod codegen;
mod util;
pub mod query;
use chalk_engine;
use crate::hir;
use crate::hir::def_id::DefId;
use crate::infer::{InferCtxt, SuppressRegionErrors};
use crate::infer::outlives::env::OutlivesEnvironment;
use crate::middle::region;
use crate::mir::interpret::ErrorHandled;
use rustc_macros::HashStable;
use syntax::ast;
use syntax_pos::{Span, DUMMY_SP};
use crate::ty::subst::{InternalSubsts, SubstsRef};
use crate::ty::{self, AdtKind, List, Ty, TyCtxt, GenericParamDefKind, ToPredicate};
use crate::ty::error::{ExpectedFound, TypeError};
use crate::ty::fold::{TypeFolder, TypeFoldable, TypeVisitor};
use crate::util::common::ErrorReported;
use std::fmt::Debug;
use std::rc::Rc;
pub use self::SelectionError::*;
pub use self::FulfillmentErrorCode::*;
pub use self::Vtable::*;
pub use self::ObligationCauseCode::*;
pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls};
pub use self::coherence::{OrphanCheckErr, OverlapResult};
pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
pub use self::project::MismatchedProjectionTypes;
pub use self::project::{normalize, normalize_projection_type, poly_project_and_unify_type};
pub use self::project::{ProjectionCache, ProjectionCacheSnapshot, Reveal, Normalized};
pub use self::object_safety::ObjectSafetyViolation;
pub use self::object_safety::MethodViolationCode;
pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
pub use self::specialize::{OverlapError, specialization_graph, translate_substs};
pub use self::specialize::find_associated_item;
pub use self::specialize::specialization_graph::FutureCompatOverlapError;
pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
pub use self::engine::{TraitEngine, TraitEngineExt};
pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs};
pub use self::util::{
supertraits, supertrait_def_ids, transitive_bounds, Supertraits, SupertraitDefIds,
pub use self::util::{expand_trait_aliases, TraitAliasExpander};
pub use self::chalk_fulfill::{
CanonicalGoal as ChalkCanonicalGoal,
FulfillmentContext as ChalkFulfillmentContext
pub use self::ObligationCauseCode::*;
pub use self::FulfillmentErrorCode::*;
pub use self::SelectionError::*;
pub use self::Vtable::*;
/// Whether to enable bug compatibility with issue #43355.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum IntercrateMode {
/// The mode that trait queries run in.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum TraitQueryMode {
// Standard/un-canonicalized queries get accurate
// spans etc. passed in and hence can do reasonable
// error reporting on their own.
// Canonicalized queries get dummy spans and hence
// must generally propagate errors to
// pre-canonicalization callsites.
/// An `Obligation` represents some trait reference (e.g., `int: Eq`) for
/// which the vtable must be found. The process of finding a vtable is
/// called "resolving" the `Obligation`. This process consists of
/// either identifying an `impl` (e.g., `impl Eq for int`) that
/// provides the required vtable, or else finding a bound that is in
/// scope. The eventual result is usually a `Selection` (defined below).
#[derive(Clone, PartialEq, Eq, Hash)]
pub struct Obligation<'tcx, T> {
/// The reason we have to prove this thing.
pub cause: ObligationCause<'tcx>,
/// The environment in which we should prove this thing.
pub param_env: ty::ParamEnv<'tcx>,
/// The thing we are trying to prove.
pub predicate: T,
/// If we started proving this as a result of trying to prove
/// something else, track the total depth to ensure termination.
/// If this goes over a certain threshold, we abort compilation --
/// in such cases, we can not say whether or not the predicate
/// holds for certain. Stupid halting problem; such a drag.
pub recursion_depth: usize,
pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
/// The reason why we incurred this obligation; used for error reporting.
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct ObligationCause<'tcx> {
pub span: Span,
/// The ID of the fn body that triggered this obligation. This is
/// used for region obligations to determine the precise
/// environment in which the region obligation should be evaluated
/// (in particular, closures can add new assumptions). See the
/// field `region_obligations` of the `FulfillmentContext` for more
/// information.
pub body_id: hir::HirId,
pub code: ObligationCauseCode<'tcx>
impl<'tcx> ObligationCause<'tcx> {
pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
match self.code {
ObligationCauseCode::CompareImplMethodObligation { .. } |
ObligationCauseCode::MainFunctionType |
ObligationCauseCode::StartFunctionType => {
ObligationCauseCode::MatchExpressionArm { arm_span, .. } => arm_span,
_ => self.span,
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub enum ObligationCauseCode<'tcx> {
/// Not well classified or should be obvious from the span.
/// A slice or array is WF only if `T: Sized`.
/// A tuple is WF only if its middle elements are `Sized`.
/// This is the trait reference from the given projection.
/// In an impl of trait `X` for type `Y`, type `Y` must
/// also implement all supertraits of `X`.
/// A type like `&'a T` is WF only if `T: 'a`.
/// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
/// Obligation incurred due to an object cast.
ObjectCastObligation(/* Object type */ Ty<'tcx>),
// Various cases where expressions must be sized/copy/etc:
/// L = X implies that L is Sized
/// (x1, .., xn) must be Sized
/// S { ... } must be Sized
/// Type of each variable must be Sized
/// Argument type must be Sized
/// Return type must be Sized
/// Yield type must be Sized
/// [T,..n] --> T must be Copy
/// Types of fields (other than the last, except for packed structs) in a struct must be sized.
FieldSized { adt_kind: AdtKind, last: bool },
/// Constant expressions must be sized.
/// static items must have `Sync` type
/// error derived when matching traits/impls; see ObligationCause for more details
CompareImplMethodObligation {
item_name: ast::Name,
impl_item_def_id: DefId,
trait_item_def_id: DefId,
/// Checking that this expression can be assigned where it needs to be
// FIXME(eddyb) #11161 is the original Expr required?
/// Computing common supertype in the arms of a match expression
MatchExpressionArm {
arm_span: Span,
source: hir::MatchSource,
prior_arms: Vec<Span>,
last_ty: Ty<'tcx>,
discrim_hir_id: hir::HirId,
/// Computing common supertype in the pattern guard for the arms of a match expression
MatchExpressionArmPattern { span: Span, ty: Ty<'tcx> },
/// Computing common supertype in an if expression
IfExpression {
then: Span,
outer: Option<Span>,
semicolon: Option<Span>,
/// Computing common supertype of an if expression with no else counter-part
/// `main` has wrong type
/// `start` has wrong type
/// intrinsic has wrong type
/// method receiver
/// `return` with no expression
/// `return` with an expression
/// Block implicit return
/// #[feature(trivial_bounds)] is not enabled
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct DerivedObligationCause<'tcx> {
/// The trait reference of the parent obligation that led to the
/// current obligation. Note that only trait obligations lead to
/// derived obligations, so we just store the trait reference here
/// directly.
parent_trait_ref: ty::PolyTraitRef<'tcx>,
/// The parent trait had this cause.
parent_code: Rc<ObligationCauseCode<'tcx>>
pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
/// The following types:
/// * `WhereClause`,
/// * `WellFormed`,
/// * `FromEnv`,
/// * `DomainGoal`,
/// * `Goal`,
/// * `Clause`,
/// * `Environment`,
/// * `InEnvironment`,
/// are used for representing the trait system in the form of
/// logic programming clauses. They are part of the interface
/// for the chalk SLG solver.
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum WhereClause<'tcx> {
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum WellFormed<'tcx> {
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum FromEnv<'tcx> {
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum DomainGoal<'tcx> {
pub type PolyDomainGoal<'tcx> = ty::Binder<DomainGoal<'tcx>>;
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum QuantifierKind {
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum GoalKind<'tcx> {
Implies(Clauses<'tcx>, Goal<'tcx>),
And(Goal<'tcx>, Goal<'tcx>),
Quantified(QuantifierKind, ty::Binder<Goal<'tcx>>),
Subtype(Ty<'tcx>, Ty<'tcx>),
pub type Goal<'tcx> = &'tcx GoalKind<'tcx>;
pub type Goals<'tcx> = &'tcx List<Goal<'tcx>>;
impl<'tcx> DomainGoal<'tcx> {
pub fn into_goal(self) -> GoalKind<'tcx> {
pub fn into_program_clause(self) -> ProgramClause<'tcx> {
ProgramClause {
goal: self,
hypotheses: ty::List::empty(),
category: ProgramClauseCategory::Other,
impl<'tcx> GoalKind<'tcx> {
pub fn from_poly_domain_goal(
domain_goal: PolyDomainGoal<'tcx>,
tcx: TyCtxt<'tcx>,
) -> GoalKind<'tcx> {
match domain_goal.no_bound_vars() {
Some(p) => p.into_goal(),
None => GoalKind::Quantified(
domain_goal.map_bound(|p| tcx.mk_goal(p.into_goal()))
/// This matches the definition from Page 7 of "A Proof Procedure for the Logic of Hereditary
/// Harrop Formulas".
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum Clause<'tcx> {
impl Clause<'tcx> {
pub fn category(self) -> ProgramClauseCategory {
match self {
Clause::Implies(clause) => clause.category,
Clause::ForAll(clause) => clause.skip_binder().category,
/// Multiple clauses.
pub type Clauses<'tcx> = &'tcx List<Clause<'tcx>>;
/// A "program clause" has the form `D :- G1, ..., Gn`. It is saying
/// that the domain goal `D` is true if `G1...Gn` are provable. This
/// is equivalent to the implication `G1..Gn => D`; we usually write
/// it with the reverse implication operator `:-` to emphasize the way
/// that programs are actually solved (via backchaining, which starts
/// with the goal to solve and proceeds from there).
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub struct ProgramClause<'tcx> {
/// This goal will be considered true ...
pub goal: DomainGoal<'tcx>,
/// ... if we can prove these hypotheses (there may be no hypotheses at all):
pub hypotheses: Goals<'tcx>,
/// Useful for filtering clauses.
pub category: ProgramClauseCategory,
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub enum ProgramClauseCategory {
/// A set of clauses that we assume to be true.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub struct Environment<'tcx> {
pub clauses: Clauses<'tcx>,
impl Environment<'tcx> {
pub fn with<G>(self, goal: G) -> InEnvironment<'tcx, G> {
InEnvironment {
environment: self,
/// Something (usually a goal), along with an environment.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
pub struct InEnvironment<'tcx, G> {
pub environment: Environment<'tcx>,
pub goal: G,
pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
pub enum SelectionError<'tcx> {
EnumTypeFoldableImpl! {
impl<'tcx> TypeFoldable<'tcx> for SelectionError<'tcx> {
(SelectionError::OutputTypeParameterMismatch)(a, b, c),
pub struct FulfillmentError<'tcx> {
pub obligation: PredicateObligation<'tcx>,
pub code: FulfillmentErrorCode<'tcx>
pub enum FulfillmentErrorCode<'tcx> {
TypeError<'tcx>), // always comes from a SubtypePredicate
/// When performing resolution, it is typically the case that there
/// can be one of three outcomes:
/// - `Ok(Some(r))`: success occurred with result `r`
/// - `Ok(None)`: could not definitely determine anything, usually due
/// to inconclusive type inference.
/// - `Err(e)`: error `e` occurred
pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
/// Given the successful resolution of an obligation, the `Vtable`
/// indicates where the vtable comes from. Note that while we call this
/// a "vtable", it does not necessarily indicate dynamic dispatch at
/// runtime. `Vtable` instances just tell the compiler where to find
/// methods, but in generic code those methods are typically statically
/// dispatched -- only when an object is constructed is a `Vtable`
/// instance reified into an actual vtable.
/// For example, the vtable may be tied to a specific impl (case A),
/// or it may be relative to some bound that is in scope (case B).
/// ```
/// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
/// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
/// impl Clone for int { ... } // Impl_3
/// fn foo<T:Clone>(concrete: Option<Box<int>>,
/// param: T,
/// mixed: Option<T>) {
/// // Case A: Vtable points at a specific impl. Only possible when
/// // type is concretely known. If the impl itself has bounded
/// // type parameters, Vtable will carry resolutions for those as well:
/// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
/// // Case B: Vtable must be provided by caller. This applies when
/// // type is a type parameter.
/// param.clone(); // VtableParam
/// // Case C: A mix of cases A and B.
/// mixed.clone(); // Vtable(Impl_1, [VtableParam])
/// }
/// ```
/// ### The type parameter `N`
/// See explanation on `VtableImplData`.
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
pub enum Vtable<'tcx, N> {
/// Vtable identifying a particular impl.
VtableImpl(VtableImplData<'tcx, N>),
/// Vtable for auto trait implementations.
/// This carries the information and nested obligations with regards
/// to an auto implementation for a trait `Trait`. The nested obligations
/// ensure the trait implementation holds for all the constituent types.
/// Successful resolution to an obligation provided by the caller
/// for some type parameter. The `Vec<N>` represents the
/// obligations incurred from normalizing the where-clause (if
/// any).
/// Virtual calls through an object.
VtableObject(VtableObjectData<'tcx, N>),
/// Successful resolution for a builtin trait.
/// Vtable automatically generated for a closure. The `DefId` is the ID
/// of the closure expression. This is a `VtableImpl` in spirit, but the
/// impl is generated by the compiler and does not appear in the source.
VtableClosure(VtableClosureData<'tcx, N>),
/// Same as above, but for a function pointer type with the given signature.
VtableFnPointer(VtableFnPointerData<'tcx, N>),
/// Vtable automatically generated for a generator.
VtableGenerator(VtableGeneratorData<'tcx, N>),
/// Vtable for a trait alias.
VtableTraitAlias(VtableTraitAliasData<'tcx, N>),
/// Identifies a particular impl in the source, along with a set of
/// substitutions from the impl's type/lifetime parameters. The
/// `nested` vector corresponds to the nested obligations attached to
/// the impl's type parameters.
/// The type parameter `N` indicates the type used for "nested
/// obligations" that are required by the impl. During type check, this
/// is `Obligation`, as one might expect. During codegen, however, this
/// is `()`, because codegen only requires a shallow resolution of an
/// impl, and nested obligations are satisfied later.
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
pub struct VtableImplData<'tcx, N> {
pub impl_def_id: DefId,
pub substs: SubstsRef<'tcx>,
pub nested: Vec<N>
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
pub struct VtableGeneratorData<'tcx, N> {
pub generator_def_id: DefId,
pub substs: ty::GeneratorSubsts<'tcx>,
/// Nested obligations. This can be non-empty if the generator
/// signature contains associated types.
pub nested: Vec<N>
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
pub struct VtableClosureData<'tcx, N> {
pub closure_def_id: DefId,
pub substs: ty::ClosureSubsts<'tcx>,
/// Nested obligations. This can be non-empty if the closure
/// signature contains associated types.
pub nested: Vec<N>
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
pub struct VtableAutoImplData<N> {
pub trait_def_id: DefId,
pub nested: Vec<N>
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
pub struct VtableBuiltinData<N> {
pub nested: Vec<N>
/// A vtable for some object-safe trait `Foo` automatically derived
/// for the object type `Foo`.
#[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable, HashStable)]
pub struct VtableObjectData<'tcx, N> {
/// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
/// The vtable is formed by concatenating together the method lists of
/// the base object trait and all supertraits; this is the start of
/// `upcast_trait_ref`'s methods in that vtable.
pub vtable_base: usize,
pub nested: Vec<N>,
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
pub struct VtableFnPointerData<'tcx, N> {
pub fn_ty: Ty<'tcx>,
pub nested: Vec<N>
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
pub struct VtableTraitAliasData<'tcx, N> {
pub alias_def_id: DefId,
pub substs: SubstsRef<'tcx>,
pub nested: Vec<N>,
/// Creates predicate obligations from the generic bounds.
pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
param_env: ty::ParamEnv<'tcx>,
generic_bounds: &ty::InstantiatedPredicates<'tcx>)
-> PredicateObligations<'tcx>
util::predicates_for_generics(cause, 0, param_env, generic_bounds)
/// Determines whether the type `ty` is known to meet `bound` and
/// returns true if so. Returns false if `ty` either does not meet
/// `bound` or is not known to meet bound (note that this is
/// conservative towards *no impl*, which is the opposite of the
/// `evaluate` methods).
pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
infcx: &InferCtxt<'a, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
ty: Ty<'tcx>,
def_id: DefId,
span: Span,
) -> bool {
debug!("type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
let trait_ref = ty::TraitRef {
substs: infcx.tcx.mk_substs_trait(ty, &[]),
let obligation = Obligation {
cause: ObligationCause::misc(span, hir::DUMMY_HIR_ID),
recursion_depth: 0,
predicate: trait_ref.to_predicate(),
let result = infcx.predicate_must_hold_modulo_regions(&obligation);
debug!("type_known_to_meet_ty={:?} bound={} => {:?}",
ty, infcx.tcx.def_path_str(def_id), result);
if result && (ty.has_infer_types() || ty.has_closure_types()) {
// Because of inference "guessing", selection can sometimes claim
// to succeed while the success requires a guess. To ensure
// this function's result remains infallible, we must confirm
// that guess. While imperfect, I believe this is sound.
// The handling of regions in this area of the code is terrible,
// see issue #29149. We should be able to improve on this with
// NLL.
let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
// We can use a dummy node-id here because we won't pay any mind
// to region obligations that arise (there shouldn't really be any
// anyhow).
let cause = ObligationCause::misc(span, hir::DUMMY_HIR_ID);
fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
// Note: we only assume something is `Copy` if we can
// *definitively* show that it implements `Copy`. Otherwise,
// assume it is move; linear is always ok.
match fulfill_cx.select_all_or_error(infcx) {
Ok(()) => {
debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
Err(e) => {
debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} errors={:?}",
} else {
fn do_normalize_predicates<'tcx>(
tcx: TyCtxt<'tcx>,
region_context: DefId,
cause: ObligationCause<'tcx>,
elaborated_env: ty::ParamEnv<'tcx>,
predicates: Vec<ty::Predicate<'tcx>>,
) -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported> {
"do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
let span = cause.span;
tcx.infer_ctxt().enter(|infcx| {
// FIXME. We should really... do something with these region
// obligations. But this call just continues the older
// behavior (i.e., doesn't cause any new bugs), and it would
// take some further refactoring to actually solve them. In
// particular, we would have to handle implied bounds
// properly, and that code is currently largely confined to
// regionck (though I made some efforts to extract it
// out). -nmatsakis
// @arielby: In any case, these obligations are checked
// by wfcheck anyway, so I'm not sure we have to check
// them here too, and we will remove this function when
// we move over to lazy normalization *anyway*.
let fulfill_cx = FulfillmentContext::new_ignoring_regions();
let predicates = match fully_normalize(
) {
Ok(predicates) => predicates,
Err(errors) => {
infcx.report_fulfillment_errors(&errors, None, false);
return Err(ErrorReported)
debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
let region_scope_tree = region::ScopeTree::default();
// We can use the `elaborated_env` here; the region code only
// cares about declarations like `'a: 'b`.
let outlives_env = OutlivesEnvironment::new(elaborated_env);
let predicates = match infcx.fully_resolve(&predicates) {
Ok(predicates) => predicates,
Err(fixup_err) => {
// If we encounter a fixup error, it means that some type
// variable wound up unconstrained. I actually don't know
// if this can happen, and I certainly don't expect it to
// happen often, but if it did happen it probably
// represents a legitimate failure due to some kind of
// unconstrained variable, and it seems better not to ICE,
// all things considered.
tcx.sess.span_err(span, &fixup_err.to_string());
return Err(ErrorReported)
if predicates.has_local_value() {
// FIXME: shouldn't we, you know, actually report an error here? or an ICE?
} else {
// FIXME: this is gonna need to be removed ...
/// Normalizes the parameter environment, reporting errors if they occur.
pub fn normalize_param_env_or_error<'tcx>(
tcx: TyCtxt<'tcx>,
region_context: DefId,
unnormalized_env: ty::ParamEnv<'tcx>,
cause: ObligationCause<'tcx>,
) -> ty::ParamEnv<'tcx> {
// I'm not wild about reporting errors here; I'd prefer to
// have the errors get reported at a defined place (e.g.,
// during typeck). Instead I have all parameter
// environments, in effect, going through this function
// and hence potentially reporting errors. This ensures of
// course that we never forget to normalize (the
// alternative seemed like it would involve a lot of
// manual invocations of this fn -- and then we'd have to
// deal with the errors at each of those sites).
// In any case, in practice, typeck constructs all the
// parameter environments once for every fn as it goes,
// and errors will get reported then; so after typeck we
// can be sure that no errors should occur.
debug!("normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
region_context, unnormalized_env, cause);
let mut predicates: Vec<_> =
util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
let elaborated_env = ty::ParamEnv::new(
// HACK: we are trying to normalize the param-env inside *itself*. The problem is that
// normalization expects its param-env to be already normalized, which means we have
// a circularity.
// The way we handle this is by normalizing the param-env inside an unnormalized version
// of the param-env, which means that if the param-env contains unnormalized projections,
// we'll have some normalization failures. This is unfortunate.
// Lazy normalization would basically handle this by treating just the
// normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
// Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
// types, so to make the situation less bad, we normalize all the predicates *but*
// the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
// then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
// This works fairly well because trait matching does not actually care about param-env
// TypeOutlives predicates - these are normally used by regionck.
let outlives_predicates: Vec<_> = predicates.drain_filter(|predicate| {
match predicate {
ty::Predicate::TypeOutlives(..) => true,
_ => false
debug!("normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
predicates, outlives_predicates);
let non_outlives_predicates =
match do_normalize_predicates(tcx, region_context, cause.clone(),
elaborated_env, predicates) {
Ok(predicates) => predicates,
// An unnormalized env is better than nothing.
Err(ErrorReported) => {
debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
return elaborated_env
debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
// Not sure whether it is better to include the unnormalized TypeOutlives predicates
// here. I believe they should not matter, because we are ignoring TypeOutlives param-env
// predicates here anyway. Keeping them here anyway because it seems safer.
let outlives_env: Vec<_> =
let outlives_env = ty::ParamEnv::new(
let outlives_predicates =
match do_normalize_predicates(tcx, region_context, cause,
outlives_env, outlives_predicates) {
Ok(predicates) => predicates,
// An unnormalized env is better than nothing.
Err(ErrorReported) => {
debug!("normalize_param_env_or_error: errored resolving outlives predicates");
return elaborated_env
debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
let mut predicates = non_outlives_predicates;
debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
pub fn fully_normalize<'a, 'tcx, T>(
infcx: &InferCtxt<'a, 'tcx>,
mut fulfill_cx: FulfillmentContext<'tcx>,
cause: ObligationCause<'tcx>,
param_env: ty::ParamEnv<'tcx>,
value: &T,
) -> Result<T, Vec<FulfillmentError<'tcx>>>
T: TypeFoldable<'tcx>,
debug!("fully_normalize_with_fulfillcx(value={:?})", value);
let selcx = &mut SelectionContext::new(infcx);
let Normalized { value: normalized_value, obligations } =
project::normalize(selcx, param_env, cause, value);
debug!("fully_normalize: normalized_value={:?} obligations={:?}",
for obligation in obligations {
fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
debug!("fully_normalize: select_all_or_error start");
debug!("fully_normalize: select_all_or_error complete");
let resolved_value = infcx.resolve_vars_if_possible(&normalized_value);
debug!("fully_normalize: resolved_value={:?}", resolved_value);
/// Normalizes the predicates and checks whether they hold in an empty
/// environment. If this returns false, then either normalize
/// encountered an error or one of the predicates did not hold. Used
/// when creating vtables to check for unsatisfiable methods.
fn normalize_and_test_predicates<'tcx>(
tcx: TyCtxt<'tcx>,
predicates: Vec<ty::Predicate<'tcx>>,
) -> bool {
let result = tcx.infer_ctxt().enter(|infcx| {
let param_env = ty::ParamEnv::reveal_all();
let mut selcx = SelectionContext::new(&infcx);
let mut fulfill_cx = FulfillmentContext::new();
let cause = ObligationCause::dummy();
let Normalized { value: predicates, obligations } =
normalize(&mut selcx, param_env, cause.clone(), &predicates);
for obligation in obligations {
fulfill_cx.register_predicate_obligation(&infcx, obligation);
for predicate in predicates {
let obligation = Obligation::new(cause.clone(), param_env, predicate);
fulfill_cx.register_predicate_obligation(&infcx, obligation);
debug!("normalize_and_test_predicates(predicates={:?}) = {:?}",
predicates, result);
fn substitute_normalize_and_test_predicates<'tcx>(
tcx: TyCtxt<'tcx>,
key: (DefId, SubstsRef<'tcx>),
) -> bool {
let predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
let result = normalize_and_test_predicates(tcx, predicates);
debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}",
key, result);
/// Given a trait `trait_ref`, iterates the vtable entries
/// that come from `trait_ref`, including its supertraits.
#[inline] // FIXME(#35870): avoid closures being unexported due to `impl Trait`.
fn vtable_methods<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::PolyTraitRef<'tcx>,
) -> &'tcx [Option<(DefId, SubstsRef<'tcx>)>] {
debug!("vtable_methods({:?})", trait_ref);
supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
let trait_methods = tcx.associated_items(trait_ref.def_id())
.filter(|item| item.kind == ty::AssocKind::Method);
// Now list each method's DefId and InternalSubsts (for within its trait).
// If the method can never be called from this object, produce None. |trait_method| {
debug!("vtable_methods: trait_method={:?}", trait_method);
let def_id = trait_method.def_id;
// Some methods cannot be called on an object; skip those.
if !tcx.is_vtable_safe_method(trait_ref.def_id(), &trait_method) {
debug!("vtable_methods: not vtable safe");
return None;
// the method may have some early-bound lifetimes, add
// regions for those
let substs = trait_ref.map_bound(|trait_ref|
InternalSubsts::for_item(tcx, def_id, |param, _|
match param.kind {
GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
GenericParamDefKind::Type { .. } |
GenericParamDefKind::Const => {
trait_ref.substs[param.index as usize]
// the trait type may have higher-ranked lifetimes in it;
// so erase them if they appear, so that we get the type
// at some particular call site
let substs = tcx.normalize_erasing_late_bound_regions(
// It's possible that the method relies on where clauses that
// do not hold for this particular set of type parameters.
// Note that this method could then never be called, so we
// do not want to try and codegen it, in that case (see #23435).
let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
if !normalize_and_test_predicates(tcx, predicates.predicates) {
debug!("vtable_methods: predicates do not hold");
return None;
Some((def_id, substs))
impl<'tcx, O> Obligation<'tcx, O> {
pub fn new(cause: ObligationCause<'tcx>,
param_env: ty::ParamEnv<'tcx>,
predicate: O)
-> Obligation<'tcx, O>
Obligation { cause, param_env, recursion_depth: 0, predicate }
fn with_depth(cause: ObligationCause<'tcx>,
recursion_depth: usize,
param_env: ty::ParamEnv<'tcx>,
predicate: O)
-> Obligation<'tcx, O>
Obligation { cause, param_env, recursion_depth, predicate }
pub fn misc(span: Span,
body_id: hir::HirId,
param_env: ty::ParamEnv<'tcx>,
trait_ref: O)
-> Obligation<'tcx, O> {
Obligation::new(ObligationCause::misc(span, body_id), param_env, trait_ref)
pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
Obligation { cause: self.cause.clone(),
param_env: self.param_env,
recursion_depth: self.recursion_depth,
predicate: value }
impl<'tcx> ObligationCause<'tcx> {
pub fn new(span: Span,
body_id: hir::HirId,
code: ObligationCauseCode<'tcx>)
-> ObligationCause<'tcx> {
ObligationCause { span, body_id, code }
pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
ObligationCause { span, body_id, code: MiscObligation }
pub fn dummy() -> ObligationCause<'tcx> {
ObligationCause { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation }
impl<'tcx, N> Vtable<'tcx, N> {
pub fn nested_obligations(self) -> Vec<N> {
match self {
VtableImpl(i) => i.nested,
VtableParam(n) => n,
VtableBuiltin(i) => i.nested,
VtableAutoImpl(d) => d.nested,
VtableClosure(c) => c.nested,
VtableGenerator(c) => c.nested,
VtableObject(d) => d.nested,
VtableFnPointer(d) => d.nested,
VtableTraitAlias(d) => d.nested,
pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
match self {
VtableImpl(i) => VtableImpl(VtableImplData {
impl_def_id: i.impl_def_id,
substs: i.substs,
nested: i.nested.into_iter().map(f).collect(),
VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
nested: i.nested.into_iter().map(f).collect(),
VtableObject(o) => VtableObject(VtableObjectData {
upcast_trait_ref: o.upcast_trait_ref,
vtable_base: o.vtable_base,
nested: o.nested.into_iter().map(f).collect(),
VtableAutoImpl(d) => VtableAutoImpl(VtableAutoImplData {
trait_def_id: d.trait_def_id,
nested: d.nested.into_iter().map(f).collect(),
VtableClosure(c) => VtableClosure(VtableClosureData {
closure_def_id: c.closure_def_id,
substs: c.substs,
nested: c.nested.into_iter().map(f).collect(),
VtableGenerator(c) => VtableGenerator(VtableGeneratorData {
generator_def_id: c.generator_def_id,
substs: c.substs,
nested: c.nested.into_iter().map(f).collect(),
VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
fn_ty: p.fn_ty,
nested: p.nested.into_iter().map(f).collect(),
VtableTraitAlias(d) => VtableTraitAlias(VtableTraitAliasData {
alias_def_id: d.alias_def_id,
substs: d.substs,
nested: d.nested.into_iter().map(f).collect(),
impl<'tcx> FulfillmentError<'tcx> {
fn new(obligation: PredicateObligation<'tcx>,
code: FulfillmentErrorCode<'tcx>)
-> FulfillmentError<'tcx>
FulfillmentError { obligation: obligation, code: code }
impl<'tcx> TraitObligation<'tcx> {
fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
self.predicate.map_bound(|p| p.self_ty())
pub fn provide(providers: &mut ty::query::Providers<'_>) {
*providers = ty::query::Providers {
is_object_safe: object_safety::is_object_safe_provider,
specialization_graph_of: specialize::specialization_graph_provider,
specializes: specialize::specializes,
codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
pub trait ExClauseFold<'tcx>
Self: chalk_engine::context::Context + Clone,
fn fold_ex_clause_with<F: TypeFolder<'tcx>>(
ex_clause: &chalk_engine::ExClause<Self>,
folder: &mut F,
) -> chalk_engine::ExClause<Self>;
fn visit_ex_clause_with<V: TypeVisitor<'tcx>>(
ex_clause: &chalk_engine::ExClause<Self>,
visitor: &mut V,
) -> bool;
pub trait ChalkContextLift<'tcx>
Self: chalk_engine::context::Context + Clone,
type LiftedExClause: Debug + 'tcx;
type LiftedDelayedLiteral: Debug + 'tcx;
type LiftedLiteral: Debug + 'tcx;
fn lift_ex_clause_to_tcx(
ex_clause: &chalk_engine::ExClause<Self>,
tcx: TyCtxt<'tcx>,
) -> Option<Self::LiftedExClause>;
fn lift_delayed_literal_to_tcx(
ex_clause: &chalk_engine::DelayedLiteral<Self>,
tcx: TyCtxt<'tcx>,
) -> Option<Self::LiftedDelayedLiteral>;
fn lift_literal_to_tcx(
ex_clause: &chalk_engine::Literal<Self>,
tcx: TyCtxt<'tcx>,
) -> Option<Self::LiftedLiteral>;
You can’t perform that action at this time.