Module traits

Trait Resolution. See the rustc dev guide for more information on how this works.

Re-exports

pub use self::normalize::NormalizeExt;

pub use self::project::normalize_inherent_projection;

pub use self::project::normalize_projection_ty;

Modules

auto_trait

Support code for rustdoc and external tools. You really don’t want to be using this unless you need to.

coherence 🔒

See Rustc Dev Guide chapters on trait-resolution and trait-specialization for more info on how this works.

const_evaluatable

Checking that constant values used in types can be successfully evaluated.

dyn_compatibility 🔒

“Dyn-compatibility” refers to the ability for a trait to be converted to a trait object. In general, traits may only be converted to a trait object if certain criteria are met.

effects

engine 🔒

fulfill 🔒

misc

Miscellaneous type-system utilities that are too small to deserve their own modules.

normalize

Deeply normalize types using the old trait solver.

outlives_bounds

project

Code for projecting associated types out of trait references.

query

Experimental types for the trait query interface. The methods defined in this module are all based on canonicalization, which makes a canonical query by replacing unbound inference variables and regions, so that results can be reused more broadly. The providers for the queries defined here can be found in rustc_traits.

select 🔒

Candidate selection. See the rustc dev guide for more information on how this works.

solve

specialization_graph

specialize 🔒

Logic and data structures related to impl specialization, explained in greater detail below.

structural_normalize 🔒

util 🔒

vtable

wf

Structs

BoundVarReplacer

DerivedCause

DerivedHostCause

FulfillmentContext

The fulfillment context is used to drive trait resolution. It consists of a list of obligations that must be (eventually) satisfied. The job is to track which are satisfied, which yielded errors, and which are still pending. At any point, users can call select_where_possible, and the fulfillment context will try to do selection, retaining only those obligations that remain ambiguous. This may be helpful in pushing type inference along. Once all type inference constraints have been generated, the method select_all_or_error can be used to report any remaining ambiguous cases as errors.

FulfillmentError

FutureCompatOverlapError

IfExpressionCause

ImplDerivedCause

ImplDerivedHostCause

ImplSourceUserDefinedData

Identifies a particular impl in the source, along with a set of generic parameters from the impl’s type/lifetime parameters. The nested vector corresponds to the nested obligations attached to the impl’s type parameters.

InternedObligationCauseCode

MatchExpressionArmCause

MismatchedProjectionTypes

Normalized

Obligation

An Obligation represents some trait reference (e.g., i32: Eq) for which the “impl_source” must be found. The process of finding an “impl_source” is called “resolving” the Obligation. This process consists of either identifying an impl (e.g., impl Eq for i32) that satisfies the obligation, or else finding a bound that is in scope. The eventual result is usually a Selection (defined below).

ObligationCause

The reason why we incurred this obligation; used for error reporting.

ObligationCtxt

Used if you want to have pleasant experience when dealing with obligations outside of hir or mir typeck.

OldSolverError

OverlapError

Information pertinent to an overlapping impl error.

OverlapResult

PatternOriginExpr

Information about the origin expression of a pattern, relevant to diagnostics. Fields here refer to the scrutinee of a pattern. If the scrutinee isn’t given in the diagnostic, then this won’t exist.

PendingPredicateObligation

PlaceholderReplacer

The inverse of BoundVarReplacer: replaces placeholders with the bound vars from which they came.

ProjectionCache

The projection cache. Unlike the standard caches, this can include infcx-dependent type variables, therefore we have to roll the cache back each time we roll a snapshot back, to avoid assumptions on yet-unresolved inference variables. Types with placeholder regions also have to be removed when the respective snapshot ends.

ProjectionCacheKey

ProjectionCacheStorage

SelectionContext

SignatureMismatchData

UncoveredTyParams

UnifyReceiverContext

Enums

BuiltinImplSource

CodegenObligationError

These are the error cases for codegen_select_candidate.

DynCompatibilityViolation

DynCompatibilityViolationSolution

EvaluateConstErr

EvaluationResult

The result of trait evaluation. The order is important here as the evaluation of a list is the maximum of the evaluations.

FulfillmentErrorCode

FutureCompatOverlapErrorKind

ImplSource

Given the successful resolution of an obligation, the ImplSource indicates where the impl comes from.

InCrate

Whether we do the orphan check relative to this crate or to some remote crate.

IntercrateAmbiguityCause

IsConstable

Whether a value can be extracted into a const. Used for diagnostics around array repeat expressions.

IsFirstInputType

MethodViolationCode

Reasons a method might not be dyn-compatible.

ObligationCauseCode

OrphanCheckErr

OrphanCheckMode

OverflowError

Indicates that trait evaluation caused overflow and in which pass.

ProjectionCacheEntry

ScrubbedTraitError

A trait error with most of its information removed. This is the error returned by an ObligationCtxt by default, and suitable if you just want to see if a predicate holds, and don’t particularly care about the error itself (except for if it’s an ambiguity or true error).

SelectionError

SkipLeakCheck

Whether to skip the leak check, as part of a future compatibility warning step.

StatementAsExpression

TraitQueryMode

The mode that trait queries run in.

WellFormedLoc

The ‘location’ at which we try to perform HIR-based wf checking. This information is used to obtain an hir::Ty, which we can walk in order to obtain precise spans for any ‘nested’ types (e.g. Foo in Option<Foo>).

Traits

FromSolverError

StructurallyNormalizeExt

TraitEngine

TraitEngineExt

Functions

add_placeholder_note

do_normalize_predicates 🔒

dyn_compatibility_violations_for_assoc_item

Returns Some(_) if this item makes the containing trait dyn-incompatible.

elaborate

evaluate_const

Evaluates a type system constant returning a ConstKind::Error in cases where CTFE failed and returning the passed in constant if it was not fully concrete (i.e. depended on generic parameters or inference variables)

expand_trait_aliases

Return the trait and projection predicates that come from eagerly expanding the trait aliases in the list of clauses. For each trait predicate, record a stack of spans that trace from the user-written trait alias bound. For projection predicates, just record the span of the projection itself.

hir_ty_lowering_dyn_compatibility_violations

Returns the dyn-compatibility violations that affect HIR ty lowering.

impl_item_is_final

impossible_predicates

Normalizes the predicates and checks whether they hold in an empty environment. If this returns true, then either normalize encountered an error or one of the predicates did not hold. Used when creating vtables to check for unsatisfiable methods. This should not be used during analysis.

instantiate_and_check_impossible_predicates 🔒

is_impossible_associated_item 🔒

Checks whether a trait’s associated item is impossible to reference on a given impl.

is_vtable_safe_method

We say a method is vtable safe if it can be invoked on a trait object. Note that dyn-compatible traits can have some non-vtable-safe methods, so long as they require Self: Sized or otherwise ensure that they cannot be used when Self = Trait.

normalize_param_env_or_error

Normalizes the parameter environment, reporting errors if they occur.

orphan_check_trait_ref

Checks whether a trait-ref is potentially implementable by a crate.

overlapping_impls

If there are types that satisfy both impls, returns Some with a suitably-freshened ImplHeader with those types instantiated. Otherwise, returns None.

pred_known_to_hold_modulo_regions 🔒

FIXME(@lcnr): this function doesn’t seem right and shouldn’t exist?

predicates_for_generics

Creates predicate obligations from the generic bounds.

provide

replace_param_and_infer_args_with_placeholder 🔒

Replaces args that reference param or infer variables with suitable placeholders. This function is meant to remove these param and infer args when they’re not actually needed to evaluate a constant.

supertrait_def_ids

Computes the def-ids of the transitive supertraits of trait_def_id. This (intentionally) does not compute the full elaborated super-predicates but just the set of def-ids. It is used to identify which traits may define a given associated type to help avoid cycle errors, and to make size estimates for vtable layout computation.

supertraits

transitive_bounds_that_define_assoc_item

A specialized variant of elaborate that only elaborates trait references that may define the given associated item with the name assoc_name. It uses the explicit_supertraits_containing_assoc_item query to avoid enumerating super-predicates that aren’t related to assoc_item. This is used when resolving types like Self::Item or T::Item and helps to avoid cycle errors (see e.g. #35237).

translate_args

Given the generic parameters for the requested impl, translate it to the generic parameters appropriate for the actual item definition (whether it be in that impl, a parent impl, or the trait).

translate_args_with_cause

Like translate_args, but obligations from the parent implementation are registered with the provided ObligationCause.

try_evaluate_const

Evaluates a type system constant making sure to not allow constants that depend on generic parameters or inference variables to succeed in evaluating.

type_known_to_meet_bound_modulo_regions

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).

upcast_choices

Casts a trait reference into a reference to one of its super traits; returns None if target_trait_def_id is not a supertrait.

with_replaced_escaping_bound_vars

Executes f on value after replacing all escaping bound variables with placeholders and then replaces these placeholders with the original bound variables in the result.

Type Aliases

EvaluationCache

NormalizedTerm

ObligationInspector

A callback that can be provided to inspect_typeck. Invoked on evaluation of root obligations.

PolyTraitObligation

PredicateObligation

PredicateObligations

Selection

SelectionCache

SelectionResult

When performing resolution, it is typically the case that there can be one of three outcomes:

TraitObligation