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