Module rustc_trait_selection::traits
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Trait Resolution. See the rustc dev guide for more information on how this works.
Re-exports
pub use self::FulfillmentErrorCode::*;pub use self::ImplSource::*;pub use self::ObligationCauseCode::*;pub use self::SelectionError::*;Modules
Support code for rustdoc and external tools.
You really don’t want to be using this unless you need to.
Defines a Chalk-based
TraitEngineSee Rustc Dev Guide chapters on trait-resolution and trait-specialization for more info on
how this works.
Checking that constant values used in types can be successfully evaluated.
engine 🔒
fulfill 🔒
Miscellaneous type-system utilities that are too small to deserve their own modules.
“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:
project 🔒
Code for projecting associated types out of trait references.
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.
Logic and data structures related to impl specialization, explained in
greater detail below.
util 🔒
Structs
A chalk environment and goal.
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.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.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).The reason why we incurred this obligation; used for error reporting.
Used if you want to have pleasant experience when dealing
with obligations outside of hir or mir typeck.
Information pertinent to an overlapping impl error.
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.
“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.Enums
These are the error cases for
codegen_select_candidate.The result of trait evaluation. The order is important
here as the evaluation of a list is the maximum of the
evaluations.
Given the successful resolution of an obligation, the
ImplSource
indicates where the impl comes from.Reasons a method might not be object-safe.
Indicates that trait evaluation caused overflow and in which pass.
Depending on the stage of compilation, we want projection to be
more or less conservative.
Whether to skip the leak check, as part of a future compatibility warning step.
The mode that trait queries run in.
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
Functions
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.Normalize a type and process all resulting obligations, returning any errors
Process a bound (and any nested obligations that come from it) to completion.
This is a convenience function for traits that have no generic arguments, such
as auto traits, and builtin traits like Copy or Sized.
Process an obligation (and any nested obligations that come from it) to
completion, returning any errors
Process a set of obligations (and any nested obligations that come from them)
to completion
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.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.
Checks whether a trait’s method is impossible to call on a given impl.
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.Normalizes any associated type projections in
value, replacing
them with a fully resolved type where possible. The return value
combines the normalized result and any additional obligations that
were incurred as result.Normalizes the parameter environment, reporting errors if they occur.
The guts of
normalize: normalize a specific projection like <T as Trait>::Item. The result is always a type (and possibly
additional obligations). If ambiguity arises, which implies that
there are unresolved type variables in the projection, we will
substitute a fresh type variable $X and generate a new
obligation <T as Trait>::Item == $X for later.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:If there are types that satisfy both impls, invokes
on_overlap
with a suitably-freshened ImplHeader with those types
substituted. Otherwise, invokes no_overlap.Creates predicate obligations from the generic bounds.
Prepare the segments for a vtable
This method traverses the structure of
ty, trying to find any
types that are not allowed to be used in a const generic.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).A specialized variant of
elaborate_trait_refs that only elaborates trait references that may
define the given associated type assoc_name. It uses the
super_predicates_that_define_assoc_type 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).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).
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).Casts a trait reference into a reference to one of its super
traits; returns
None if target_trait_def_id is not a
supertrait.Given a trait
trait_ref, iterates the vtable entries
that come from trait_ref, including its supertraits.Find slot base for trait methods within vtable entries of another trait
Find slot offset for trait vptr within vtable entries of another trait
Type Definitions
When performing resolution, it is typically the case that there
can be one of three outcomes: