Module rustc_trait_selection::traits

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

Re-exports

• pub use self::project::NormalizeExt;
• pub use self::project::normalize_inherent_projection;
• pub use self::project::normalize_projection_type;
• pub use self::FulfillmentErrorCode::*;
• pub use self::ImplSource::*;
• pub use self::ObligationCauseCode::*;
• pub use self::SelectionError::*;

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.
• engine 🔒
• error_reporting
• fulfill 🔒
• misc
  Miscellaneous type-system utilities that are too small to deserve their own modules.
• object_safety 🔒
  “Object safety” refers to the ability for a trait to be converted to an object. In general, traits may only be converted to an object if all of their methods meet certain criteria. In particular, they must:
• 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_match 🔒
• structural_normalize 🔒
• util 🔒
• vtable
• wf

Structs

• DerivedObligationCause
• 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
• ImplDerivedObligationCause
• ImplSourceUserDefinedData
  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.
• 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.
• OverlapError
  Information pertinent to an overlapping impl error.
• OverlapResult
• PendingPredicateObligation
• 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
• SelectionOutputTypeParameterMismatch
• SupertraitDefIds
• TraitAliasExpander
  “Trait alias expansion” is the process of expanding a sequence of trait references into another sequence by transitively following all trait aliases. e.g. If you have bounds like Foo + Send, a trait alias trait Foo = Bar + Sync;, and another trait alias trait Bar = Read + Write, then the bounds would expand to Read + Write + Sync + Send. Expansion is done via a DFS (depth-first search), and the visited field is used to avoid cycles.
• UnifyReceiverContext

Enums

• BuiltinImplSource
• CodegenObligationError
  These are the error cases for codegen_select_candidate.
• DefiningAnchor
• 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.
• IntercrateAmbiguityCause
• MethodViolationCode
  Reasons a method might not be object-safe.
• ObjectSafetyViolation
• ObligationCauseCode
• OrphanCheckErr
• OverflowError
  Indicates that trait evaluation caused overflow and in which pass.
• ProjectionCacheEntry
• Reveal
  Depending on the stage of compilation, we want projection to be more or less conservative.
• 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

• StructurallyNormalizeExt
• TraitEngine
• TraitEngineExt

Functions

• add_placeholder_note
• astconv_object_safety_violations
  Returns the object safety violations that affect astconv – currently, Self in supertraits. This is needed because object_safety_violations can’t be used during type collection.
• check_args_compatible
• do_normalize_predicates 🔒
• elaborate
• expand_trait_aliases
• fully_normalize
  Normalize a type and process all resulting obligations, returning any errors.
• get_vtable_index_of_object_method
  Given an upcast trait object described by object, returns the index of the method method_def_id (which should be part of object.upcast_trait_ref) within the vtable for object.
• 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.
• 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 object-safe 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
  Checks the coherence orphan rules. impl_def_id should be the DefId of a trait impl. To pass, either the trait must be local, or else two conditions must be satisfied:
• overlapping_impls
  If there are types that satisfy both impls, returns Some with a suitably-freshened ImplHeader with those types substituted. 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
• search_for_structural_match_violation
  This method traverses the structure of ty, trying to find an instance of an ADT (i.e. struct or enum) that doesn’t implement the structural-match traits, or a generic type parameter (which cannot be determined to be structural-match).
• subst_and_check_impossible_predicates 🔒
• supertrait_def_ids
• supertraits
• transitive_bounds
• 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 super_predicates_that_define_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 a subst for the requested impl, translate it to a subst 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.
• 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.

Type Aliases

• EvaluationCache
• NormalizedTy
• PolyTraitObligation
• PredicateObligation
• PredicateObligations
• Selection
• SelectionCache
• SelectionResult
  When performing resolution, it is typically the case that there can be one of three outcomes:
• TraitObligation