| use crate::ty::error::TypeError; |
| use crate::ty::relate::{self, Relate, RelateResult, TypeRelation}; |
| use crate::ty::{self, InferConst, Ty, TyCtxt}; |
| |
| /// A type "A" *matches* "B" if the fresh types in B could be |
| /// substituted with values so as to make it equal to A. Matching is |
| /// intended to be used only on freshened types, and it basically |
| /// indicates if the non-freshened versions of A and B could have been |
| /// unified. |
| /// |
| /// It is only an approximation. If it yields false, unification would |
| /// definitely fail, but a true result doesn't mean unification would |
| /// succeed. This is because we don't track the "side-constraints" on |
| /// type variables, nor do we track if the same freshened type appears |
| /// more than once. To some extent these approximations could be |
| /// fixed, given effort. |
| /// |
| /// Like subtyping, matching is really a binary relation, so the only |
| /// important thing about the result is Ok/Err. Also, matching never |
| /// affects any type variables or unification state. |
| pub struct Match<'tcx> { |
| tcx: TyCtxt<'tcx>, |
| param_env: ty::ParamEnv<'tcx>, |
| } |
| |
| impl Match<'tcx> { |
| pub fn new(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Match<'tcx> { |
| Match { tcx, param_env } |
| } |
| } |
| |
| impl TypeRelation<'tcx> for Match<'tcx> { |
| fn tag(&self) -> &'static str { |
| "Match" |
| } |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.tcx |
| } |
| fn param_env(&self) -> ty::ParamEnv<'tcx> { |
| self.param_env |
| } |
| fn a_is_expected(&self) -> bool { |
| true |
| } // irrelevant |
| |
| fn relate_with_variance<T: Relate<'tcx>>( |
| &mut self, |
| _: ty::Variance, |
| a: &T, |
| b: &T, |
| ) -> RelateResult<'tcx, T> { |
| self.relate(a, b) |
| } |
| |
| fn regions( |
| &mut self, |
| a: ty::Region<'tcx>, |
| b: ty::Region<'tcx>, |
| ) -> RelateResult<'tcx, ty::Region<'tcx>> { |
| debug!("{}.regions({:?}, {:?})", self.tag(), a, b); |
| Ok(a) |
| } |
| |
| fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { |
| debug!("{}.tys({:?}, {:?})", self.tag(), a, b); |
| if a == b { |
| return Ok(a); |
| } |
| |
| match (&a.kind, &b.kind) { |
| (_, &ty::Infer(ty::FreshTy(_))) |
| | (_, &ty::Infer(ty::FreshIntTy(_))) |
| | (_, &ty::Infer(ty::FreshFloatTy(_))) => Ok(a), |
| |
| (&ty::Infer(_), _) | (_, &ty::Infer(_)) => { |
| Err(TypeError::Sorts(relate::expected_found(self, &a, &b))) |
| } |
| |
| (&ty::Error, _) | (_, &ty::Error) => Ok(self.tcx().types.err), |
| |
| _ => relate::super_relate_tys(self, a, b), |
| } |
| } |
| |
| fn consts( |
| &mut self, |
| a: &'tcx ty::Const<'tcx>, |
| b: &'tcx ty::Const<'tcx>, |
| ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> { |
| debug!("{}.consts({:?}, {:?})", self.tag(), a, b); |
| if a == b { |
| return Ok(a); |
| } |
| |
| match (a.val, b.val) { |
| (_, ty::ConstKind::Infer(InferConst::Fresh(_))) => { |
| return Ok(a); |
| } |
| |
| (ty::ConstKind::Infer(_), _) | (_, ty::ConstKind::Infer(_)) => { |
| return Err(TypeError::ConstMismatch(relate::expected_found(self, &a, &b))); |
| } |
| |
| _ => {} |
| } |
| |
| relate::super_relate_consts(self, a, b) |
| } |
| |
| fn binders<T>( |
| &mut self, |
| a: &ty::Binder<T>, |
| b: &ty::Binder<T>, |
| ) -> RelateResult<'tcx, ty::Binder<T>> |
| where |
| T: Relate<'tcx>, |
| { |
| Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?)) |
| } |
| } |