993 lines
36 KiB
Rust
993 lines
36 KiB
Rust
//! There are four type combiners: [Equate], [Sub], [Lub], and [Glb].
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//! Each implements the trait [TypeRelation] and contains methods for
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//! combining two instances of various things and yielding a new instance.
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//! These combiner methods always yield a `Result<T>`. To relate two
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//! types, you can use `infcx.at(cause, param_env)` which then allows
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//! you to use the relevant methods of [At](super::at::At).
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//!
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//! Combiners mostly do their specific behavior and then hand off the
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//! bulk of the work to [InferCtxt::super_combine_tys] and
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//! [InferCtxt::super_combine_consts].
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//!
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//! Combining two types may have side-effects on the inference contexts
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//! which can be undone by using snapshots. You probably want to use
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//! either [InferCtxt::commit_if_ok] or [InferCtxt::probe].
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//!
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//! On success, the LUB/GLB operations return the appropriate bound. The
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//! return value of `Equate` or `Sub` shouldn't really be used.
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//!
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//! ## Contravariance
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//!
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//! We explicitly track which argument is expected using
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//! [TypeRelation::a_is_expected], so when dealing with contravariance
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//! this should be correctly updated.
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use super::equate::Equate;
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use super::glb::Glb;
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use super::lub::Lub;
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use super::sub::Sub;
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use super::type_variable::TypeVariableValue;
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use super::{InferCtxt, MiscVariable, TypeTrace};
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use crate::traits::{Obligation, PredicateObligations};
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use rustc_data_structures::sso::SsoHashMap;
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use rustc_hir::def_id::DefId;
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use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
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use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
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use rustc_middle::traits::ObligationCause;
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use rustc_middle::ty::error::{ExpectedFound, TypeError};
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use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
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use rustc_middle::ty::subst::SubstsRef;
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use rustc_middle::ty::{self, InferConst, Ty, TyCtxt, TypeVisitable};
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use rustc_middle::ty::{IntType, UintType};
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use rustc_span::{Span, DUMMY_SP};
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#[derive(Clone)]
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pub struct CombineFields<'infcx, 'tcx> {
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pub infcx: &'infcx InferCtxt<'tcx>,
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pub trace: TypeTrace<'tcx>,
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pub cause: Option<ty::relate::Cause>,
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pub param_env: ty::ParamEnv<'tcx>,
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pub obligations: PredicateObligations<'tcx>,
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/// Whether we should define opaque types
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/// or just treat them opaquely.
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/// Currently only used to prevent predicate
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/// matching from matching anything against opaque
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/// types.
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pub define_opaque_types: bool,
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}
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#[derive(Copy, Clone, Debug)]
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pub enum RelationDir {
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SubtypeOf,
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SupertypeOf,
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EqTo,
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}
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impl<'tcx> InferCtxt<'tcx> {
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pub fn super_combine_tys<R>(
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&self,
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relation: &mut R,
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a: Ty<'tcx>,
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b: Ty<'tcx>,
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) -> RelateResult<'tcx, Ty<'tcx>>
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where
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R: TypeRelation<'tcx>,
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{
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let a_is_expected = relation.a_is_expected();
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match (a.kind(), b.kind()) {
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// Relate integral variables to other types
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(&ty::Infer(ty::IntVar(a_id)), &ty::Infer(ty::IntVar(b_id))) => {
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self.inner
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.borrow_mut()
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.int_unification_table()
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.unify_var_var(a_id, b_id)
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.map_err(|e| int_unification_error(a_is_expected, e))?;
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Ok(a)
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}
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(&ty::Infer(ty::IntVar(v_id)), &ty::Int(v)) => {
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self.unify_integral_variable(a_is_expected, v_id, IntType(v))
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}
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(&ty::Int(v), &ty::Infer(ty::IntVar(v_id))) => {
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self.unify_integral_variable(!a_is_expected, v_id, IntType(v))
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}
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(&ty::Infer(ty::IntVar(v_id)), &ty::Uint(v)) => {
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self.unify_integral_variable(a_is_expected, v_id, UintType(v))
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}
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(&ty::Uint(v), &ty::Infer(ty::IntVar(v_id))) => {
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self.unify_integral_variable(!a_is_expected, v_id, UintType(v))
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}
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// Relate floating-point variables to other types
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(&ty::Infer(ty::FloatVar(a_id)), &ty::Infer(ty::FloatVar(b_id))) => {
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self.inner
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.borrow_mut()
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.float_unification_table()
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.unify_var_var(a_id, b_id)
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.map_err(|e| float_unification_error(relation.a_is_expected(), e))?;
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Ok(a)
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}
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(&ty::Infer(ty::FloatVar(v_id)), &ty::Float(v)) => {
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self.unify_float_variable(a_is_expected, v_id, v)
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}
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(&ty::Float(v), &ty::Infer(ty::FloatVar(v_id))) => {
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self.unify_float_variable(!a_is_expected, v_id, v)
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}
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// All other cases of inference are errors
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(&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
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Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b)))
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}
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_ => ty::relate::super_relate_tys(relation, a, b),
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}
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}
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pub fn super_combine_consts<R>(
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&self,
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relation: &mut R,
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a: ty::Const<'tcx>,
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b: ty::Const<'tcx>,
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) -> RelateResult<'tcx, ty::Const<'tcx>>
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where
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R: ConstEquateRelation<'tcx>,
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{
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debug!("{}.consts({:?}, {:?})", relation.tag(), a, b);
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if a == b {
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return Ok(a);
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}
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let a = self.shallow_resolve(a);
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let b = self.shallow_resolve(b);
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let a_is_expected = relation.a_is_expected();
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match (a.kind(), b.kind()) {
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(
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ty::ConstKind::Infer(InferConst::Var(a_vid)),
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ty::ConstKind::Infer(InferConst::Var(b_vid)),
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) => {
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self.inner.borrow_mut().const_unification_table().union(a_vid, b_vid);
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return Ok(a);
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}
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// All other cases of inference with other variables are errors.
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(ty::ConstKind::Infer(InferConst::Var(_)), ty::ConstKind::Infer(_))
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| (ty::ConstKind::Infer(_), ty::ConstKind::Infer(InferConst::Var(_))) => {
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bug!("tried to combine ConstKind::Infer/ConstKind::Infer(InferConst::Var)")
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}
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(ty::ConstKind::Infer(InferConst::Var(vid)), _) => {
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return self.unify_const_variable(relation.param_env(), vid, b, a_is_expected);
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}
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(_, ty::ConstKind::Infer(InferConst::Var(vid))) => {
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return self.unify_const_variable(relation.param_env(), vid, a, !a_is_expected);
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}
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(ty::ConstKind::Unevaluated(..), _) if self.tcx.lazy_normalization() => {
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// FIXME(#59490): Need to remove the leak check to accommodate
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// escaping bound variables here.
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if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
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relation.const_equate_obligation(a, b);
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}
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return Ok(b);
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}
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(_, ty::ConstKind::Unevaluated(..)) if self.tcx.lazy_normalization() => {
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// FIXME(#59490): Need to remove the leak check to accommodate
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// escaping bound variables here.
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if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
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relation.const_equate_obligation(a, b);
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}
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return Ok(a);
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}
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_ => {}
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}
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ty::relate::super_relate_consts(relation, a, b)
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}
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/// Unifies the const variable `target_vid` with the given constant.
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///
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/// This also tests if the given const `ct` contains an inference variable which was previously
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/// unioned with `target_vid`. If this is the case, inferring `target_vid` to `ct`
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/// would result in an infinite type as we continuously replace an inference variable
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/// in `ct` with `ct` itself.
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///
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/// This is especially important as unevaluated consts use their parents generics.
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/// They therefore often contain unused substs, making these errors far more likely.
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///
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/// A good example of this is the following:
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///
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/// ```compile_fail,E0308
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/// #![feature(generic_const_exprs)]
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///
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/// fn bind<const N: usize>(value: [u8; N]) -> [u8; 3 + 4] {
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/// todo!()
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/// }
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///
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/// fn main() {
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/// let mut arr = Default::default();
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/// arr = bind(arr);
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/// }
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/// ```
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///
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/// Here `3 + 4` ends up as `ConstKind::Unevaluated` which uses the generics
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/// of `fn bind` (meaning that its substs contain `N`).
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///
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/// `bind(arr)` now infers that the type of `arr` must be `[u8; N]`.
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/// The assignment `arr = bind(arr)` now tries to equate `N` with `3 + 4`.
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///
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/// As `3 + 4` contains `N` in its substs, this must not succeed.
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///
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/// See `tests/ui/const-generics/occurs-check/` for more examples where this is relevant.
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#[instrument(level = "debug", skip(self))]
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fn unify_const_variable(
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&self,
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param_env: ty::ParamEnv<'tcx>,
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target_vid: ty::ConstVid<'tcx>,
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ct: ty::Const<'tcx>,
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vid_is_expected: bool,
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) -> RelateResult<'tcx, ty::Const<'tcx>> {
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let (for_universe, span) = {
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let mut inner = self.inner.borrow_mut();
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let variable_table = &mut inner.const_unification_table();
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let var_value = variable_table.probe_value(target_vid);
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match var_value.val {
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ConstVariableValue::Known { value } => {
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bug!("instantiating {:?} which has a known value {:?}", target_vid, value)
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}
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ConstVariableValue::Unknown { universe } => (universe, var_value.origin.span),
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}
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};
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let value = ConstInferUnifier { infcx: self, span, param_env, for_universe, target_vid }
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.relate(ct, ct)?;
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self.inner.borrow_mut().const_unification_table().union_value(
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target_vid,
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ConstVarValue {
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origin: ConstVariableOrigin {
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kind: ConstVariableOriginKind::ConstInference,
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span: DUMMY_SP,
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},
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val: ConstVariableValue::Known { value },
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},
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);
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Ok(value)
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}
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fn unify_integral_variable(
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&self,
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vid_is_expected: bool,
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vid: ty::IntVid,
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val: ty::IntVarValue,
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) -> RelateResult<'tcx, Ty<'tcx>> {
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self.inner
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.borrow_mut()
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.int_unification_table()
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.unify_var_value(vid, Some(val))
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.map_err(|e| int_unification_error(vid_is_expected, e))?;
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match val {
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IntType(v) => Ok(self.tcx.mk_mach_int(v)),
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UintType(v) => Ok(self.tcx.mk_mach_uint(v)),
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}
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}
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fn unify_float_variable(
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&self,
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vid_is_expected: bool,
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vid: ty::FloatVid,
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val: ty::FloatTy,
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) -> RelateResult<'tcx, Ty<'tcx>> {
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self.inner
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.borrow_mut()
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.float_unification_table()
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.unify_var_value(vid, Some(ty::FloatVarValue(val)))
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.map_err(|e| float_unification_error(vid_is_expected, e))?;
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Ok(self.tcx.mk_mach_float(val))
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}
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}
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impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
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pub fn tcx(&self) -> TyCtxt<'tcx> {
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self.infcx.tcx
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}
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pub fn equate<'a>(&'a mut self, a_is_expected: bool) -> Equate<'a, 'infcx, 'tcx> {
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Equate::new(self, a_is_expected)
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}
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pub fn sub<'a>(&'a mut self, a_is_expected: bool) -> Sub<'a, 'infcx, 'tcx> {
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Sub::new(self, a_is_expected)
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}
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pub fn lub<'a>(&'a mut self, a_is_expected: bool) -> Lub<'a, 'infcx, 'tcx> {
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Lub::new(self, a_is_expected)
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}
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pub fn glb<'a>(&'a mut self, a_is_expected: bool) -> Glb<'a, 'infcx, 'tcx> {
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Glb::new(self, a_is_expected)
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}
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/// Here, `dir` is either `EqTo`, `SubtypeOf`, or `SupertypeOf`.
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/// The idea is that we should ensure that the type `a_ty` is equal
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/// to, a subtype of, or a supertype of (respectively) the type
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/// to which `b_vid` is bound.
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///
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/// Since `b_vid` has not yet been instantiated with a type, we
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/// will first instantiate `b_vid` with a *generalized* version
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/// of `a_ty`. Generalization introduces other inference
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/// variables wherever subtyping could occur.
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#[instrument(skip(self), level = "debug")]
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pub fn instantiate(
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&mut self,
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a_ty: Ty<'tcx>,
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dir: RelationDir,
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b_vid: ty::TyVid,
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a_is_expected: bool,
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) -> RelateResult<'tcx, ()> {
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use self::RelationDir::*;
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// Get the actual variable that b_vid has been inferred to
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debug_assert!(self.infcx.inner.borrow_mut().type_variables().probe(b_vid).is_unknown());
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// Generalize type of `a_ty` appropriately depending on the
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// direction. As an example, assume:
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//
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// - `a_ty == &'x ?1`, where `'x` is some free region and `?1` is an
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// inference variable,
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// - and `dir` == `SubtypeOf`.
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//
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// Then the generalized form `b_ty` would be `&'?2 ?3`, where
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// `'?2` and `?3` are fresh region/type inference
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// variables. (Down below, we will relate `a_ty <: b_ty`,
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// adding constraints like `'x: '?2` and `?1 <: ?3`.)
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let Generalization { ty: b_ty, needs_wf } = self.generalize(a_ty, b_vid, dir)?;
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debug!(?b_ty);
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self.infcx.inner.borrow_mut().type_variables().instantiate(b_vid, b_ty);
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if needs_wf {
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self.obligations.push(Obligation::new(
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self.tcx(),
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self.trace.cause.clone(),
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self.param_env,
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ty::Binder::dummy(ty::PredicateKind::WellFormed(b_ty.into())),
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));
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}
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// Finally, relate `b_ty` to `a_ty`, as described in previous comment.
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//
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// FIXME(#16847): This code is non-ideal because all these subtype
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// relations wind up attributed to the same spans. We need
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// to associate causes/spans with each of the relations in
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// the stack to get this right.
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match dir {
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EqTo => self.equate(a_is_expected).relate(a_ty, b_ty),
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SubtypeOf => self.sub(a_is_expected).relate(a_ty, b_ty),
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SupertypeOf => self.sub(a_is_expected).relate_with_variance(
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ty::Contravariant,
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ty::VarianceDiagInfo::default(),
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a_ty,
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b_ty,
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),
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}?;
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Ok(())
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}
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/// Attempts to generalize `ty` for the type variable `for_vid`.
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/// This checks for cycle -- that is, whether the type `ty`
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/// references `for_vid`. The `dir` is the "direction" for which we
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/// a performing the generalization (i.e., are we producing a type
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/// that can be used as a supertype etc).
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///
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/// Preconditions:
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///
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/// - `for_vid` is a "root vid"
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#[instrument(skip(self), level = "trace", ret)]
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fn generalize(
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&self,
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ty: Ty<'tcx>,
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for_vid: ty::TyVid,
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dir: RelationDir,
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) -> RelateResult<'tcx, Generalization<'tcx>> {
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// Determine the ambient variance within which `ty` appears.
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// The surrounding equation is:
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//
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// ty [op] ty2
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//
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// where `op` is either `==`, `<:`, or `:>`. This maps quite
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// naturally.
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let ambient_variance = match dir {
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RelationDir::EqTo => ty::Invariant,
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RelationDir::SubtypeOf => ty::Covariant,
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RelationDir::SupertypeOf => ty::Contravariant,
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};
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trace!(?ambient_variance);
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let for_universe = match self.infcx.inner.borrow_mut().type_variables().probe(for_vid) {
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v @ TypeVariableValue::Known { .. } => {
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bug!("instantiating {:?} which has a known value {:?}", for_vid, v,)
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}
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TypeVariableValue::Unknown { universe } => universe,
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};
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trace!(?for_universe);
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trace!(?self.trace);
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let mut generalize = Generalizer {
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infcx: self.infcx,
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cause: &self.trace.cause,
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for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables().sub_root_var(for_vid),
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for_universe,
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ambient_variance,
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needs_wf: false,
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root_ty: ty,
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param_env: self.param_env,
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cache: SsoHashMap::new(),
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};
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let ty = generalize.relate(ty, ty)?;
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let needs_wf = generalize.needs_wf;
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Ok(Generalization { ty, needs_wf })
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}
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pub fn add_const_equate_obligation(
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&mut self,
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a_is_expected: bool,
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a: ty::Const<'tcx>,
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b: ty::Const<'tcx>,
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) {
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let predicate = if a_is_expected {
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ty::PredicateKind::ConstEquate(a, b)
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} else {
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ty::PredicateKind::ConstEquate(b, a)
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};
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self.obligations.push(Obligation::new(
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self.tcx(),
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self.trace.cause.clone(),
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self.param_env,
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ty::Binder::dummy(predicate),
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));
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}
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pub fn mark_ambiguous(&mut self) {
|
|
self.obligations.push(Obligation::new(
|
|
self.tcx(),
|
|
self.trace.cause.clone(),
|
|
self.param_env,
|
|
ty::Binder::dummy(ty::PredicateKind::Ambiguous),
|
|
));
|
|
}
|
|
}
|
|
|
|
struct Generalizer<'cx, 'tcx> {
|
|
infcx: &'cx InferCtxt<'tcx>,
|
|
|
|
/// The span, used when creating new type variables and things.
|
|
cause: &'cx ObligationCause<'tcx>,
|
|
|
|
/// The vid of the type variable that is in the process of being
|
|
/// instantiated; if we find this within the type we are folding,
|
|
/// that means we would have created a cyclic type.
|
|
for_vid_sub_root: ty::TyVid,
|
|
|
|
/// The universe of the type variable that is in the process of
|
|
/// being instantiated. Any fresh variables that we create in this
|
|
/// process should be in that same universe.
|
|
for_universe: ty::UniverseIndex,
|
|
|
|
/// Track the variance as we descend into the type.
|
|
ambient_variance: ty::Variance,
|
|
|
|
/// See the field `needs_wf` in `Generalization`.
|
|
needs_wf: bool,
|
|
|
|
/// The root type that we are generalizing. Used when reporting cycles.
|
|
root_ty: Ty<'tcx>,
|
|
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
|
|
cache: SsoHashMap<Ty<'tcx>, Ty<'tcx>>,
|
|
}
|
|
|
|
/// Result from a generalization operation. This includes
|
|
/// not only the generalized type, but also a bool flag
|
|
/// indicating whether further WF checks are needed.
|
|
#[derive(Debug)]
|
|
struct Generalization<'tcx> {
|
|
ty: Ty<'tcx>,
|
|
|
|
/// If true, then the generalized type may not be well-formed,
|
|
/// even if the source type is well-formed, so we should add an
|
|
/// additional check to enforce that it is. This arises in
|
|
/// particular around 'bivariant' type parameters that are only
|
|
/// constrained by a where-clause. As an example, imagine a type:
|
|
///
|
|
/// struct Foo<A, B> where A: Iterator<Item = B> {
|
|
/// data: A
|
|
/// }
|
|
///
|
|
/// here, `A` will be covariant, but `B` is
|
|
/// unconstrained. However, whatever it is, for `Foo` to be WF, it
|
|
/// must be equal to `A::Item`. If we have an input `Foo<?A, ?B>`,
|
|
/// then after generalization we will wind up with a type like
|
|
/// `Foo<?C, ?D>`. When we enforce that `Foo<?A, ?B> <: Foo<?C,
|
|
/// ?D>` (or `>:`), we will wind up with the requirement that `?A
|
|
/// <: ?C`, but no particular relationship between `?B` and `?D`
|
|
/// (after all, we do not know the variance of the normalized form
|
|
/// of `A::Item` with respect to `A`). If we do nothing else, this
|
|
/// may mean that `?D` goes unconstrained (as in #41677). So, in
|
|
/// this scenario where we create a new type variable in a
|
|
/// bivariant context, we set the `needs_wf` flag to true. This
|
|
/// will force the calling code to check that `WF(Foo<?C, ?D>)`
|
|
/// holds, which in turn implies that `?C::Item == ?D`. So once
|
|
/// `?C` is constrained, that should suffice to restrict `?D`.
|
|
needs_wf: bool,
|
|
}
|
|
|
|
impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
|
|
fn tcx(&self) -> TyCtxt<'tcx> {
|
|
self.infcx.tcx
|
|
}
|
|
|
|
fn intercrate(&self) -> bool {
|
|
self.infcx.intercrate
|
|
}
|
|
|
|
fn param_env(&self) -> ty::ParamEnv<'tcx> {
|
|
self.param_env
|
|
}
|
|
|
|
fn tag(&self) -> &'static str {
|
|
"Generalizer"
|
|
}
|
|
|
|
fn a_is_expected(&self) -> bool {
|
|
true
|
|
}
|
|
|
|
fn mark_ambiguous(&mut self) {
|
|
span_bug!(self.cause.span, "opaque types are handled in `tys`");
|
|
}
|
|
|
|
fn binders<T>(
|
|
&mut self,
|
|
a: ty::Binder<'tcx, T>,
|
|
b: ty::Binder<'tcx, T>,
|
|
) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
|
|
where
|
|
T: Relate<'tcx>,
|
|
{
|
|
Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
|
|
}
|
|
|
|
fn relate_item_substs(
|
|
&mut self,
|
|
item_def_id: DefId,
|
|
a_subst: SubstsRef<'tcx>,
|
|
b_subst: SubstsRef<'tcx>,
|
|
) -> RelateResult<'tcx, SubstsRef<'tcx>> {
|
|
if self.ambient_variance == ty::Variance::Invariant {
|
|
// Avoid fetching the variance if we are in an invariant
|
|
// context; no need, and it can induce dependency cycles
|
|
// (e.g., #41849).
|
|
relate::relate_substs(self, a_subst, b_subst)
|
|
} else {
|
|
let tcx = self.tcx();
|
|
let opt_variances = tcx.variances_of(item_def_id);
|
|
relate::relate_substs_with_variances(
|
|
self,
|
|
item_def_id,
|
|
&opt_variances,
|
|
a_subst,
|
|
b_subst,
|
|
true,
|
|
)
|
|
}
|
|
}
|
|
|
|
fn relate_with_variance<T: Relate<'tcx>>(
|
|
&mut self,
|
|
variance: ty::Variance,
|
|
_info: ty::VarianceDiagInfo<'tcx>,
|
|
a: T,
|
|
b: T,
|
|
) -> RelateResult<'tcx, T> {
|
|
let old_ambient_variance = self.ambient_variance;
|
|
self.ambient_variance = self.ambient_variance.xform(variance);
|
|
|
|
let result = self.relate(a, b);
|
|
self.ambient_variance = old_ambient_variance;
|
|
result
|
|
}
|
|
|
|
fn tys(&mut self, t: Ty<'tcx>, t2: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
|
|
assert_eq!(t, t2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
|
|
|
|
if let Some(&result) = self.cache.get(&t) {
|
|
return Ok(result);
|
|
}
|
|
debug!("generalize: t={:?}", t);
|
|
|
|
// Check to see whether the type we are generalizing references
|
|
// any other type variable related to `vid` via
|
|
// subtyping. This is basically our "occurs check", preventing
|
|
// us from creating infinitely sized types.
|
|
let result = match *t.kind() {
|
|
ty::Infer(ty::TyVar(vid)) => {
|
|
let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
|
|
let sub_vid = self.infcx.inner.borrow_mut().type_variables().sub_root_var(vid);
|
|
if sub_vid == self.for_vid_sub_root {
|
|
// If sub-roots are equal, then `for_vid` and
|
|
// `vid` are related via subtyping.
|
|
Err(TypeError::CyclicTy(self.root_ty))
|
|
} else {
|
|
let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
|
|
match probe {
|
|
TypeVariableValue::Known { value: u } => {
|
|
debug!("generalize: known value {:?}", u);
|
|
self.relate(u, u)
|
|
}
|
|
TypeVariableValue::Unknown { universe } => {
|
|
match self.ambient_variance {
|
|
// Invariant: no need to make a fresh type variable.
|
|
ty::Invariant => {
|
|
if self.for_universe.can_name(universe) {
|
|
return Ok(t);
|
|
}
|
|
}
|
|
|
|
// Bivariant: make a fresh var, but we
|
|
// may need a WF predicate. See
|
|
// comment on `needs_wf` field for
|
|
// more info.
|
|
ty::Bivariant => self.needs_wf = true,
|
|
|
|
// Co/contravariant: this will be
|
|
// sufficiently constrained later on.
|
|
ty::Covariant | ty::Contravariant => (),
|
|
}
|
|
|
|
let origin =
|
|
*self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
|
|
let new_var_id = self
|
|
.infcx
|
|
.inner
|
|
.borrow_mut()
|
|
.type_variables()
|
|
.new_var(self.for_universe, origin);
|
|
let u = self.tcx().mk_ty_var(new_var_id);
|
|
|
|
// Record that we replaced `vid` with `new_var_id` as part of a generalization
|
|
// operation. This is needed to detect cyclic types. To see why, see the
|
|
// docs in the `type_variables` module.
|
|
self.infcx.inner.borrow_mut().type_variables().sub(vid, new_var_id);
|
|
debug!("generalize: replacing original vid={:?} with new={:?}", vid, u);
|
|
Ok(u)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => {
|
|
// No matter what mode we are in,
|
|
// integer/floating-point types must be equal to be
|
|
// relatable.
|
|
Ok(t)
|
|
}
|
|
ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
|
|
let s = self.relate(substs, substs)?;
|
|
Ok(if s == substs { t } else { self.infcx.tcx.mk_opaque(def_id, s) })
|
|
}
|
|
_ => relate::super_relate_tys(self, t, t),
|
|
}?;
|
|
|
|
self.cache.insert(t, result);
|
|
Ok(result)
|
|
}
|
|
|
|
fn regions(
|
|
&mut self,
|
|
r: ty::Region<'tcx>,
|
|
r2: ty::Region<'tcx>,
|
|
) -> RelateResult<'tcx, ty::Region<'tcx>> {
|
|
assert_eq!(r, r2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
|
|
|
|
debug!("generalize: regions r={:?}", r);
|
|
|
|
match *r {
|
|
// Never make variables for regions bound within the type itself,
|
|
// nor for erased regions.
|
|
ty::ReLateBound(..) | ty::ReErased => {
|
|
return Ok(r);
|
|
}
|
|
|
|
ty::RePlaceholder(..)
|
|
| ty::ReVar(..)
|
|
| ty::ReStatic
|
|
| ty::ReEarlyBound(..)
|
|
| ty::ReFree(..) => {
|
|
// see common code below
|
|
}
|
|
}
|
|
|
|
// If we are in an invariant context, we can re-use the region
|
|
// as is, unless it happens to be in some universe that we
|
|
// can't name. (In the case of a region *variable*, we could
|
|
// use it if we promoted it into our universe, but we don't
|
|
// bother.)
|
|
if let ty::Invariant = self.ambient_variance {
|
|
let r_universe = self.infcx.universe_of_region(r);
|
|
if self.for_universe.can_name(r_universe) {
|
|
return Ok(r);
|
|
}
|
|
}
|
|
|
|
// FIXME: This is non-ideal because we don't give a
|
|
// very descriptive origin for this region variable.
|
|
Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.cause.span), self.for_universe))
|
|
}
|
|
|
|
fn consts(
|
|
&mut self,
|
|
c: ty::Const<'tcx>,
|
|
c2: ty::Const<'tcx>,
|
|
) -> RelateResult<'tcx, ty::Const<'tcx>> {
|
|
assert_eq!(c, c2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
|
|
|
|
match c.kind() {
|
|
ty::ConstKind::Infer(InferConst::Var(vid)) => {
|
|
let mut inner = self.infcx.inner.borrow_mut();
|
|
let variable_table = &mut inner.const_unification_table();
|
|
let var_value = variable_table.probe_value(vid);
|
|
match var_value.val {
|
|
ConstVariableValue::Known { value: u } => {
|
|
drop(inner);
|
|
self.relate(u, u)
|
|
}
|
|
ConstVariableValue::Unknown { universe } => {
|
|
if self.for_universe.can_name(universe) {
|
|
Ok(c)
|
|
} else {
|
|
let new_var_id = variable_table.new_key(ConstVarValue {
|
|
origin: var_value.origin,
|
|
val: ConstVariableValue::Unknown { universe: self.for_universe },
|
|
});
|
|
Ok(self.tcx().mk_const(new_var_id, c.ty()))
|
|
}
|
|
}
|
|
}
|
|
}
|
|
ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }) => {
|
|
let substs = self.relate_with_variance(
|
|
ty::Variance::Invariant,
|
|
ty::VarianceDiagInfo::default(),
|
|
substs,
|
|
substs,
|
|
)?;
|
|
Ok(self.tcx().mk_const(ty::UnevaluatedConst { def, substs }, c.ty()))
|
|
}
|
|
_ => relate::super_relate_consts(self, c, c),
|
|
}
|
|
}
|
|
}
|
|
|
|
pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
|
|
/// Register an obligation that both constants must be equal to each other.
|
|
///
|
|
/// If they aren't equal then the relation doesn't hold.
|
|
fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>);
|
|
}
|
|
|
|
fn int_unification_error<'tcx>(
|
|
a_is_expected: bool,
|
|
v: (ty::IntVarValue, ty::IntVarValue),
|
|
) -> TypeError<'tcx> {
|
|
let (a, b) = v;
|
|
TypeError::IntMismatch(ExpectedFound::new(a_is_expected, a, b))
|
|
}
|
|
|
|
fn float_unification_error<'tcx>(
|
|
a_is_expected: bool,
|
|
v: (ty::FloatVarValue, ty::FloatVarValue),
|
|
) -> TypeError<'tcx> {
|
|
let (ty::FloatVarValue(a), ty::FloatVarValue(b)) = v;
|
|
TypeError::FloatMismatch(ExpectedFound::new(a_is_expected, a, b))
|
|
}
|
|
|
|
struct ConstInferUnifier<'cx, 'tcx> {
|
|
infcx: &'cx InferCtxt<'tcx>,
|
|
|
|
span: Span,
|
|
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
|
|
for_universe: ty::UniverseIndex,
|
|
|
|
/// The vid of the const variable that is in the process of being
|
|
/// instantiated; if we find this within the const we are folding,
|
|
/// that means we would have created a cyclic const.
|
|
target_vid: ty::ConstVid<'tcx>,
|
|
}
|
|
|
|
// We use `TypeRelation` here to propagate `RelateResult` upwards.
|
|
//
|
|
// Both inputs are expected to be the same.
|
|
impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
|
|
fn tcx(&self) -> TyCtxt<'tcx> {
|
|
self.infcx.tcx
|
|
}
|
|
|
|
fn intercrate(&self) -> bool {
|
|
assert!(!self.infcx.intercrate);
|
|
false
|
|
}
|
|
|
|
fn param_env(&self) -> ty::ParamEnv<'tcx> {
|
|
self.param_env
|
|
}
|
|
|
|
fn tag(&self) -> &'static str {
|
|
"ConstInferUnifier"
|
|
}
|
|
|
|
fn a_is_expected(&self) -> bool {
|
|
true
|
|
}
|
|
|
|
fn mark_ambiguous(&mut self) {
|
|
bug!()
|
|
}
|
|
|
|
fn relate_with_variance<T: Relate<'tcx>>(
|
|
&mut self,
|
|
_variance: ty::Variance,
|
|
_info: ty::VarianceDiagInfo<'tcx>,
|
|
a: T,
|
|
b: T,
|
|
) -> RelateResult<'tcx, T> {
|
|
// We don't care about variance here.
|
|
self.relate(a, b)
|
|
}
|
|
|
|
fn binders<T>(
|
|
&mut self,
|
|
a: ty::Binder<'tcx, T>,
|
|
b: ty::Binder<'tcx, T>,
|
|
) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
|
|
where
|
|
T: Relate<'tcx>,
|
|
{
|
|
Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
|
|
}
|
|
|
|
#[instrument(level = "debug", skip(self), ret)]
|
|
fn tys(&mut self, t: Ty<'tcx>, _t: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
|
|
debug_assert_eq!(t, _t);
|
|
|
|
match t.kind() {
|
|
&ty::Infer(ty::TyVar(vid)) => {
|
|
let vid = self.infcx.inner.borrow_mut().type_variables().root_var(vid);
|
|
let probe = self.infcx.inner.borrow_mut().type_variables().probe(vid);
|
|
match probe {
|
|
TypeVariableValue::Known { value: u } => {
|
|
debug!("ConstOccursChecker: known value {:?}", u);
|
|
self.tys(u, u)
|
|
}
|
|
TypeVariableValue::Unknown { universe } => {
|
|
if self.for_universe.can_name(universe) {
|
|
return Ok(t);
|
|
}
|
|
|
|
let origin =
|
|
*self.infcx.inner.borrow_mut().type_variables().var_origin(vid);
|
|
let new_var_id = self
|
|
.infcx
|
|
.inner
|
|
.borrow_mut()
|
|
.type_variables()
|
|
.new_var(self.for_universe, origin);
|
|
Ok(self.tcx().mk_ty_var(new_var_id))
|
|
}
|
|
}
|
|
}
|
|
ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => Ok(t),
|
|
_ => relate::super_relate_tys(self, t, t),
|
|
}
|
|
}
|
|
|
|
fn regions(
|
|
&mut self,
|
|
r: ty::Region<'tcx>,
|
|
_r: ty::Region<'tcx>,
|
|
) -> RelateResult<'tcx, ty::Region<'tcx>> {
|
|
debug_assert_eq!(r, _r);
|
|
debug!("ConstInferUnifier: r={:?}", r);
|
|
|
|
match *r {
|
|
// Never make variables for regions bound within the type itself,
|
|
// nor for erased regions.
|
|
ty::ReLateBound(..) | ty::ReErased => {
|
|
return Ok(r);
|
|
}
|
|
|
|
ty::RePlaceholder(..)
|
|
| ty::ReVar(..)
|
|
| ty::ReStatic
|
|
| ty::ReEarlyBound(..)
|
|
| ty::ReFree(..) => {
|
|
// see common code below
|
|
}
|
|
}
|
|
|
|
let r_universe = self.infcx.universe_of_region(r);
|
|
if self.for_universe.can_name(r_universe) {
|
|
return Ok(r);
|
|
} else {
|
|
// FIXME: This is non-ideal because we don't give a
|
|
// very descriptive origin for this region variable.
|
|
Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.span), self.for_universe))
|
|
}
|
|
}
|
|
|
|
#[instrument(level = "debug", skip(self))]
|
|
fn consts(
|
|
&mut self,
|
|
c: ty::Const<'tcx>,
|
|
_c: ty::Const<'tcx>,
|
|
) -> RelateResult<'tcx, ty::Const<'tcx>> {
|
|
debug_assert_eq!(c, _c);
|
|
|
|
match c.kind() {
|
|
ty::ConstKind::Infer(InferConst::Var(vid)) => {
|
|
// Check if the current unification would end up
|
|
// unifying `target_vid` with a const which contains
|
|
// an inference variable which is unioned with `target_vid`.
|
|
//
|
|
// Not doing so can easily result in stack overflows.
|
|
if self
|
|
.infcx
|
|
.inner
|
|
.borrow_mut()
|
|
.const_unification_table()
|
|
.unioned(self.target_vid, vid)
|
|
{
|
|
return Err(TypeError::CyclicConst(c));
|
|
}
|
|
|
|
let var_value =
|
|
self.infcx.inner.borrow_mut().const_unification_table().probe_value(vid);
|
|
match var_value.val {
|
|
ConstVariableValue::Known { value: u } => self.consts(u, u),
|
|
ConstVariableValue::Unknown { universe } => {
|
|
if self.for_universe.can_name(universe) {
|
|
Ok(c)
|
|
} else {
|
|
let new_var_id =
|
|
self.infcx.inner.borrow_mut().const_unification_table().new_key(
|
|
ConstVarValue {
|
|
origin: var_value.origin,
|
|
val: ConstVariableValue::Unknown {
|
|
universe: self.for_universe,
|
|
},
|
|
},
|
|
);
|
|
Ok(self.tcx().mk_const(new_var_id, c.ty()))
|
|
}
|
|
}
|
|
}
|
|
}
|
|
ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs }) => {
|
|
let substs = self.relate_with_variance(
|
|
ty::Variance::Invariant,
|
|
ty::VarianceDiagInfo::default(),
|
|
substs,
|
|
substs,
|
|
)?;
|
|
|
|
Ok(self.tcx().mk_const(ty::UnevaluatedConst { def, substs }, c.ty()))
|
|
}
|
|
_ => relate::super_relate_consts(self, c, c),
|
|
}
|
|
}
|
|
}
|