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use crate::mir::Mutability;
use crate::ty::GenericArgKind;
use crate::ty::{self, GenericArgsRef, Ty, TyCtxt, TypeVisitableExt};
use rustc_hir::def_id::DefId;
use std::fmt::Debug;
use std::hash::Hash;
use std::iter;
/// See `simplify_type`.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable, HashStable)]
pub enum SimplifiedType {
Bool,
Char,
Int(ty::IntTy),
Uint(ty::UintTy),
Float(ty::FloatTy),
Adt(DefId),
Foreign(DefId),
Str,
Array,
Slice,
Ref(Mutability),
Ptr(Mutability),
Never,
Tuple(usize),
/// A trait object, all of whose components are markers
/// (e.g., `dyn Send + Sync`).
MarkerTraitObject,
Trait(DefId),
Closure(DefId),
Generator(DefId),
GeneratorWitness(DefId),
Function(usize),
Placeholder,
}
/// Generic parameters are pretty much just bound variables, e.g.
/// the type of `fn foo<'a, T>(x: &'a T) -> u32 { ... }` can be thought of as
/// `for<'a, T> fn(&'a T) -> u32`.
///
/// Typecheck of `foo` has to succeed for all possible generic arguments, so
/// during typeck, we have to treat its generic parameters as if they
/// were placeholders.
///
/// But when calling `foo` we only have to provide a specific generic argument.
/// In that case the generic parameters are instantiated with inference variables.
/// As we use `simplify_type` before that instantiation happens, we just treat
/// generic parameters as if they were inference variables in that case.
#[derive(PartialEq, Eq, Debug, Clone, Copy)]
pub enum TreatParams {
/// Treat parameters as infer vars. This is the correct mode for caching
/// an impl's type for lookup.
AsCandidateKey,
/// Treat parameters as placeholders in the given environment. This is the
/// correct mode for *lookup*, as during candidate selection.
///
/// This also treats projections with inference variables as infer vars
/// since they could be further normalized.
ForLookup,
/// Treat parameters as placeholders in the given environment. This is the
/// correct mode for *lookup*, as during candidate selection.
///
/// N.B. during deep rejection, this acts identically to `ForLookup`.
///
/// FIXME(-Ztrait-solver=next): Remove this variant and cleanup
/// the code.
NextSolverLookup,
}
/// During fast-rejection, we have the choice of treating projection types
/// as either simplifiable or not, depending on whether we expect the projection
/// to be normalized/rigid.
#[derive(PartialEq, Eq, Debug, Clone, Copy)]
pub enum TreatProjections {
/// In the old solver we don't try to normalize projections
/// when looking up impls and only access them by using the
/// current self type. This means that if the self type is
/// a projection which could later be normalized, we must not
/// treat it as rigid.
ForLookup,
/// We can treat projections in the self type as opaque as
/// we separately look up impls for the normalized self type.
NextSolverLookup,
}
/// Tries to simplify a type by only returning the outermost injective¹ layer, if one exists.
///
/// **This function should only be used if you need to store or retrieve the type from some
/// hashmap. If you want to quickly decide whether two types may unify, use the [DeepRejectCtxt]
/// instead.**
///
/// The idea is to get something simple that we can use to quickly decide if two types could unify,
/// for example during method lookup. If this function returns `Some(x)` it can only unify with
/// types for which this method returns either `Some(x)` as well or `None`.
///
/// A special case here are parameters and projections, which are only injective
/// if they are treated as placeholders.
///
/// For example when storing impls based on their simplified self type, we treat
/// generic parameters as if they were inference variables. We must not simplify them here,
/// as they can unify with any other type.
///
/// With projections we have to be even more careful, as treating them as placeholders
/// is only correct if they are fully normalized.
///
/// ¹ meaning that if the outermost layers are different, then the whole types are also different.
pub fn simplify_type<'tcx>(
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,
treat_params: TreatParams,
) -> Option<SimplifiedType> {
match *ty.kind() {
ty::Bool => Some(SimplifiedType::Bool),
ty::Char => Some(SimplifiedType::Char),
ty::Int(int_type) => Some(SimplifiedType::Int(int_type)),
ty::Uint(uint_type) => Some(SimplifiedType::Uint(uint_type)),
ty::Float(float_type) => Some(SimplifiedType::Float(float_type)),
ty::Adt(def, _) => Some(SimplifiedType::Adt(def.did())),
ty::Str => Some(SimplifiedType::Str),
ty::Array(..) => Some(SimplifiedType::Array),
ty::Slice(..) => Some(SimplifiedType::Slice),
ty::RawPtr(ptr) => Some(SimplifiedType::Ptr(ptr.mutbl)),
ty::Dynamic(trait_info, ..) => match trait_info.principal_def_id() {
Some(principal_def_id) if !tcx.trait_is_auto(principal_def_id) => {
Some(SimplifiedType::Trait(principal_def_id))
}
_ => Some(SimplifiedType::MarkerTraitObject),
},
ty::Ref(_, _, mutbl) => Some(SimplifiedType::Ref(mutbl)),
ty::FnDef(def_id, _) | ty::Closure(def_id, _) => Some(SimplifiedType::Closure(def_id)),
ty::Generator(def_id, _, _) => Some(SimplifiedType::Generator(def_id)),
ty::GeneratorWitness(def_id, _) => Some(SimplifiedType::GeneratorWitness(def_id)),
ty::Never => Some(SimplifiedType::Never),
ty::Tuple(tys) => Some(SimplifiedType::Tuple(tys.len())),
ty::FnPtr(f) => Some(SimplifiedType::Function(f.skip_binder().inputs().len())),
ty::Placeholder(..) => Some(SimplifiedType::Placeholder),
ty::Param(_) => match treat_params {
TreatParams::ForLookup | TreatParams::NextSolverLookup => {
Some(SimplifiedType::Placeholder)
}
TreatParams::AsCandidateKey => None,
},
ty::Alias(..) => match treat_params {
// When treating `ty::Param` as a placeholder, projections also
// don't unify with anything else as long as they are fully normalized.
//
// We will have to be careful with lazy normalization here.
// FIXME(lazy_normalization): This is probably not right...
TreatParams::ForLookup if !ty.has_non_region_infer() => {
Some(SimplifiedType::Placeholder)
}
TreatParams::NextSolverLookup => Some(SimplifiedType::Placeholder),
TreatParams::ForLookup | TreatParams::AsCandidateKey => None,
},
ty::Foreign(def_id) => Some(SimplifiedType::Foreign(def_id)),
ty::Bound(..) | ty::Infer(_) | ty::Error(_) => None,
}
}
impl SimplifiedType {
pub fn def(self) -> Option<DefId> {
match self {
SimplifiedType::Adt(d)
| SimplifiedType::Foreign(d)
| SimplifiedType::Trait(d)
| SimplifiedType::Closure(d)
| SimplifiedType::Generator(d)
| SimplifiedType::GeneratorWitness(d) => Some(d),
_ => None,
}
}
}
/// Given generic arguments from an obligation and an impl,
/// could these two be unified after replacing parameters in the
/// the impl with inference variables.
///
/// For obligations, parameters won't be replaced by inference
/// variables and only unify with themselves. We treat them
/// the same way we treat placeholders.
///
/// We also use this function during coherence. For coherence the
/// impls only have to overlap for some value, so we treat parameters
/// on both sides like inference variables. This behavior is toggled
/// using the `treat_obligation_params` field.
#[derive(Debug, Clone, Copy)]
pub struct DeepRejectCtxt {
pub treat_obligation_params: TreatParams,
}
impl DeepRejectCtxt {
pub fn args_refs_may_unify<'tcx>(
self,
obligation_args: GenericArgsRef<'tcx>,
impl_args: GenericArgsRef<'tcx>,
) -> bool {
iter::zip(obligation_args, impl_args).all(|(obl, imp)| {
match (obl.unpack(), imp.unpack()) {
// We don't fast reject based on regions for now.
(GenericArgKind::Lifetime(_), GenericArgKind::Lifetime(_)) => true,
(GenericArgKind::Type(obl), GenericArgKind::Type(imp)) => {
self.types_may_unify(obl, imp)
}
(GenericArgKind::Const(obl), GenericArgKind::Const(imp)) => {
self.consts_may_unify(obl, imp)
}
_ => bug!("kind mismatch: {obl} {imp}"),
}
})
}
pub fn types_may_unify<'tcx>(self, obligation_ty: Ty<'tcx>, impl_ty: Ty<'tcx>) -> bool {
match impl_ty.kind() {
// Start by checking whether the type in the impl may unify with
// pretty much everything. Just return `true` in that case.
ty::Param(_) | ty::Error(_) | ty::Alias(..) => return true,
// These types only unify with inference variables or their own
// variant.
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Adt(..)
| ty::Str
| ty::Array(..)
| ty::Slice(..)
| ty::RawPtr(..)
| ty::Dynamic(..)
| ty::Ref(..)
| ty::Never
| ty::Tuple(..)
| ty::FnPtr(..)
| ty::Foreign(..) => {}
ty::FnDef(..)
| ty::Closure(..)
| ty::Generator(..)
| ty::GeneratorWitness(..)
| ty::Placeholder(..)
| ty::Bound(..)
| ty::Infer(_) => bug!("unexpected impl_ty: {impl_ty}"),
}
let k = impl_ty.kind();
match *obligation_ty.kind() {
// Purely rigid types, use structural equivalence.
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Str
| ty::Never
| ty::Foreign(_) => obligation_ty == impl_ty,
ty::Ref(_, obl_ty, obl_mutbl) => match k {
&ty::Ref(_, impl_ty, impl_mutbl) => {
obl_mutbl == impl_mutbl && self.types_may_unify(obl_ty, impl_ty)
}
_ => false,
},
ty::Adt(obl_def, obl_args) => match k {
&ty::Adt(impl_def, impl_args) => {
obl_def == impl_def && self.args_refs_may_unify(obl_args, impl_args)
}
_ => false,
},
ty::Slice(obl_ty) => {
matches!(k, &ty::Slice(impl_ty) if self.types_may_unify(obl_ty, impl_ty))
}
ty::Array(obl_ty, obl_len) => match k {
&ty::Array(impl_ty, impl_len) => {
self.types_may_unify(obl_ty, impl_ty)
&& self.consts_may_unify(obl_len, impl_len)
}
_ => false,
},
ty::Tuple(obl) => match k {
&ty::Tuple(imp) => {
obl.len() == imp.len()
&& iter::zip(obl, imp).all(|(obl, imp)| self.types_may_unify(obl, imp))
}
_ => false,
},
ty::RawPtr(obl) => match k {
ty::RawPtr(imp) => obl.mutbl == imp.mutbl && self.types_may_unify(obl.ty, imp.ty),
_ => false,
},
ty::Dynamic(obl_preds, ..) => {
// Ideally we would walk the existential predicates here or at least
// compare their length. But considering that the relevant `Relate` impl
// actually sorts and deduplicates these, that doesn't work.
matches!(k, ty::Dynamic(impl_preds, ..) if
obl_preds.principal_def_id() == impl_preds.principal_def_id()
)
}
ty::FnPtr(obl_sig) => match k {
ty::FnPtr(impl_sig) => {
let ty::FnSig { inputs_and_output, c_variadic, unsafety, abi } =
obl_sig.skip_binder();
let impl_sig = impl_sig.skip_binder();
abi == impl_sig.abi
&& c_variadic == impl_sig.c_variadic
&& unsafety == impl_sig.unsafety
&& inputs_and_output.len() == impl_sig.inputs_and_output.len()
&& iter::zip(inputs_and_output, impl_sig.inputs_and_output)
.all(|(obl, imp)| self.types_may_unify(obl, imp))
}
_ => false,
},
// Impls cannot contain these types as these cannot be named directly.
ty::FnDef(..) | ty::Closure(..) | ty::Generator(..) => false,
// Placeholder types don't unify with anything on their own
ty::Placeholder(..) | ty::Bound(..) => false,
// Depending on the value of `treat_obligation_params`, we either
// treat generic parameters like placeholders or like inference variables.
ty::Param(_) => match self.treat_obligation_params {
TreatParams::ForLookup | TreatParams::NextSolverLookup => false,
TreatParams::AsCandidateKey => true,
},
ty::Infer(ty::IntVar(_)) => impl_ty.is_integral(),
ty::Infer(ty::FloatVar(_)) => impl_ty.is_floating_point(),
ty::Infer(_) => true,
// As we're walking the whole type, it may encounter projections
// inside of binders and what not, so we're just going to assume that
// projections can unify with other stuff.
//
// Looking forward to lazy normalization this is the safer strategy anyways.
ty::Alias(..) => true,
ty::Error(_) => true,
ty::GeneratorWitness(..) => {
bug!("unexpected obligation type: {:?}", obligation_ty)
}
}
}
pub fn consts_may_unify(self, obligation_ct: ty::Const<'_>, impl_ct: ty::Const<'_>) -> bool {
match impl_ct.kind() {
ty::ConstKind::Expr(_)
| ty::ConstKind::Param(_)
| ty::ConstKind::Unevaluated(_)
| ty::ConstKind::Error(_) => {
return true;
}
ty::ConstKind::Value(_) => {}
ty::ConstKind::Infer(_) | ty::ConstKind::Bound(..) | ty::ConstKind::Placeholder(_) => {
bug!("unexpected impl arg: {:?}", impl_ct)
}
}
let k = impl_ct.kind();
match obligation_ct.kind() {
ty::ConstKind::Param(_) => match self.treat_obligation_params {
TreatParams::ForLookup | TreatParams::NextSolverLookup => false,
TreatParams::AsCandidateKey => true,
},
// Placeholder consts don't unify with anything on their own
ty::ConstKind::Placeholder(_) => false,
// As we don't necessarily eagerly evaluate constants,
// they might unify with any value.
ty::ConstKind::Expr(_) | ty::ConstKind::Unevaluated(_) | ty::ConstKind::Error(_) => {
true
}
ty::ConstKind::Value(obl) => match k {
ty::ConstKind::Value(imp) => obl == imp,
_ => true,
},
ty::ConstKind::Infer(_) => true,
ty::ConstKind::Bound(..) => {
bug!("unexpected obl const: {:?}", obligation_ct)
}
}
}
}