Struct rustc_middle::ty::ParamEnv

pub struct ParamEnv<'tcx> {
    packed: CopyTaggedPtr<&'tcx List<Predicate<'tcx>>, Reveal, true>,
}

When type checking, we use the ParamEnv to track details about the set of where-clauses that are in scope at this particular point.

Fields

packed: CopyTaggedPtr<&'tcx List<Predicate<'tcx>>, Reveal, true>

This packs both caller bounds and the reveal enum into one pointer.

Caller bounds are Obligations that the caller must satisfy. This is basically the set of bounds on the in-scope type parameters, translated into Obligations, and elaborated and normalized.

Use the caller_bounds() method to access.

Typically, this is Reveal::UserFacing, but during codegen we want Reveal::All.

Note: This is packed, use the reveal() method to access it.

Implementations

impl<'tcx> ParamEnv<'tcx>

pub fn empty() -> Self

Construct a trait environment suitable for contexts where there are no where-clauses in scope. Hidden types (like impl Trait) are left hidden, so this is suitable for ordinary type-checking.

pub fn caller_bounds(self) -> &'tcx List<Predicate<'tcx>>

pub fn reveal(self) -> Reveal

pub fn reveal_all() -> Self

Construct a trait environment with no where-clauses in scope where the values of all impl Trait and other hidden types are revealed. This is suitable for monomorphized, post-typeck environments like codegen or doing optimizations.

N.B., if you want to have predicates in scope, use ParamEnv::new, or invoke param_env.with_reveal_all().

pub fn new(caller_bounds: &'tcx List<Predicate<'tcx>>, reveal: Reveal) -> Self

Construct a trait environment with the given set of predicates.

pub fn with_user_facing(self) -> Self

pub fn with_reveal_all_normalized(self, tcx: TyCtxt<'tcx>) -> Self

Returns a new parameter environment with the same clauses, but which "reveals" the true results of projections in all cases (even for associated types that are specializable). This is the desired behavior during codegen and certain other special contexts; normally though we want to use Reveal::UserFacing, which is the default. All opaque types in the caller_bounds of the ParamEnv will be normalized to their underlying types. See PR #65989 and issue #65918 for more details

pub fn without_caller_bounds(self) -> Self

Returns this same environment but with no caller bounds.

pub fn and<T: TypeFoldable<'tcx>>(self, value: T) -> ParamEnvAnd<'tcx, T>

Creates a suitable environment in which to perform trait queries on the given value. When type-checking, this is simply the pair of the environment plus value. But when reveal is set to All, then if value does not reference any type parameters, we will pair it with the empty environment. This improves caching and is generally invisible.

N.B., we preserve the environment when type-checking because it is possible for the user to have wacky where-clauses like where Box<u32>: Copy, which are clearly never satisfiable. We generally want to behave as if they were true, although the surrounding function is never reachable.

Trait Implementations

impl<'tcx> Clone for ParamEnv<'tcx>

fn clone(&self) -> ParamEnv<'tcx>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'tcx> Copy for ParamEnv<'tcx>

impl<'tcx> Debug for ParamEnv<'tcx>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'tcx> Eq for ParamEnv<'tcx>

impl<'tcx> Hash for ParamEnv<'tcx>

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for ParamEnv<'tcx>

fn hash_stable(
    &self,
    hcx: &mut StableHashingContext<'a>,
    hasher: &mut StableHasher
)

impl<'tcx> Key for ParamEnv<'tcx>

type CacheSelector = DefaultCacheSelector

fn query_crate(&self) -> CrateNum

Given an instance of this key, what crate is it referring to? This is used to find the provider.

fn default_span(&self, _: TyCtxt<'_>) -> Span

In the event that a cycle occurs, if no explicit span has been given for a query with key self, what span should we use?

impl<'a, 'tcx> Lift<'tcx> for ParamEnv<'a>

type Lifted = ParamEnv<'tcx>

fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted>

impl<'tcx> PartialEq<ParamEnv<'tcx>> for ParamEnv<'tcx>

fn eq(&self, other: &ParamEnv<'tcx>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &ParamEnv<'tcx>) -> bool

This method tests for !=.

impl<'tcx> StructuralEq for ParamEnv<'tcx>

impl<'tcx> StructuralPartialEq for ParamEnv<'tcx>

impl<'tcx> TypeFoldable<'tcx> for ParamEnv<'tcx>

fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self

fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool

fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self

fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool

fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool

Returns true if self has any late-bound regions that are either bound by binder or bound by some binder outside of binder. If binder is ty::INNERMOST, this indicates whether there are any late-bound regions that appear free.

fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool

Returns true if this self has any regions that escape binder (and hence are not bound by it).

fn has_escaping_bound_vars(&self) -> bool

fn has_type_flags(&self, flags: TypeFlags) -> bool

fn has_projections(&self) -> bool

fn has_opaque_types(&self) -> bool

fn references_error(&self) -> bool

fn has_param_types_or_consts(&self) -> bool

fn has_infer_regions(&self) -> bool

fn has_infer_types(&self) -> bool

fn has_infer_types_or_consts(&self) -> bool

fn needs_infer(&self) -> bool

fn has_placeholders(&self) -> bool

fn needs_subst(&self) -> bool

fn has_free_regions(&self) -> bool

"Free" regions in this context means that it has any region that is not (a) erased or (b) late-bound.

fn has_erased_regions(&self) -> bool

fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.

fn is_global(&self) -> bool

Indicates whether this value references only 'global' generic parameters that are the same regardless of what fn we are in. This is used for caching.

fn has_late_bound_regions(&self) -> bool

True if there are any late-bound regions

fn still_further_specializable(&self) -> bool

Indicates whether this value still has parameters/placeholders/inference variables which could be replaced later, in a way that would change the results of impl specialization.

fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool

A visitor that does not recurse into types, works like fn walk_shallow in Ty.