117 lines
3.9 KiB
Rust
117 lines
3.9 KiB
Rust
use crate::ty::{self, Ty, TyCtxt, InferConst};
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use crate::ty::error::{TypeError, ConstError};
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use crate::ty::relate::{self, Relate, TypeRelation, RelateResult};
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use crate::mir::interpret::ConstValue;
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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<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
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tcx: TyCtxt<'a, 'gcx, 'tcx>
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}
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impl<'a, 'gcx, 'tcx> Match<'a, 'gcx, 'tcx> {
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pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Match<'a, 'gcx, 'tcx> {
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Match { tcx }
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}
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}
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impl<'a, 'gcx, 'tcx> TypeRelation<'a, 'gcx, 'tcx> for Match<'a, 'gcx, 'tcx> {
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fn tag(&self) -> &'static str { "Match" }
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fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> { self.tcx }
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fn a_is_expected(&self) -> bool { true } // irrelevant
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fn relate_with_variance<T: Relate<'tcx>>(&mut self,
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_: ty::Variance,
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a: &T,
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b: &T)
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-> RelateResult<'tcx, T>
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{
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self.relate(a, b)
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}
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fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>)
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-> RelateResult<'tcx, ty::Region<'tcx>> {
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debug!("{}.regions({:?}, {:?})",
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self.tag(),
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a,
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b);
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Ok(a)
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}
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fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
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debug!("{}.tys({:?}, {:?})", self.tag(),
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a, b);
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if a == b { return Ok(a); }
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match (&a.sty, &b.sty) {
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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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}
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(&ty::Infer(_), _) |
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(_, &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) => {
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Ok(self.tcx().types.err)
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}
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_ => {
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relate::super_relate_tys(self, a, b)
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}
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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: &'tcx ty::LazyConst<'tcx>,
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b: &'tcx ty::LazyConst<'tcx>,
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) -> RelateResult<'tcx, &'tcx ty::LazyConst<'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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if let (&ty::LazyConst::Evaluated(a_eval), &ty::LazyConst::Evaluated(b_eval)) = (a, b) {
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match (a_eval.val, b_eval.val) {
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(_, ConstValue::Infer(InferConst::Fresh(_))) => {
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return Ok(a);
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}
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(ConstValue::Infer(_), _) | (_, ConstValue::Infer(_)) => {
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return Err(TypeError::ConstError(
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ConstError::Mismatch(relate::expected_found(self, &a, &b))
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));
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}
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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>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
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-> RelateResult<'tcx, ty::Binder<T>>
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where T: Relate<'tcx>
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{
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Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?))
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}
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}
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