1 use crate::ty::error::TypeError;
2 use crate::ty::relate::{self, Relate, RelateResult, TypeRelation};
3 use crate::ty::{self, InferConst, Ty, TyCtxt};
5 /// A type "A" *matches* "B" if the fresh types in B could be
6 /// substituted with values so as to make it equal to A. Matching is
7 /// intended to be used only on freshened types, and it basically
8 /// indicates if the non-freshened versions of A and B could have been
11 /// It is only an approximation. If it yields false, unification would
12 /// definitely fail, but a true result doesn't mean unification would
13 /// succeed. This is because we don't track the "side-constraints" on
14 /// type variables, nor do we track if the same freshened type appears
15 /// more than once. To some extent these approximations could be
16 /// fixed, given effort.
18 /// Like subtyping, matching is really a binary relation, so the only
19 /// important thing about the result is Ok/Err. Also, matching never
20 /// affects any type variables or unification state.
21 pub struct Match<'tcx> {
23 param_env: ty::ParamEnv<'tcx>,
26 impl<'tcx> Match<'tcx> {
27 pub fn new(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Match<'tcx> {
28 Match { tcx, param_env }
32 impl<'tcx> TypeRelation<'tcx> for Match<'tcx> {
33 fn tag(&self) -> &'static str {
36 fn tcx(&self) -> TyCtxt<'tcx> {
40 fn intercrate(&self) -> bool {
44 fn param_env(&self) -> ty::ParamEnv<'tcx> {
47 fn a_is_expected(&self) -> bool {
51 fn mark_ambiguous(&mut self) {
55 fn relate_with_variance<T: Relate<'tcx>>(
58 _: ty::VarianceDiagInfo<'tcx>,
61 ) -> RelateResult<'tcx, T> {
65 #[instrument(skip(self), level = "debug")]
70 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
74 #[instrument(skip(self), level = "debug")]
75 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
80 match (a.kind(), b.kind()) {
83 &ty::Infer(ty::FreshTy(_))
84 | &ty::Infer(ty::FreshIntTy(_))
85 | &ty::Infer(ty::FreshFloatTy(_)),
88 (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
89 Err(TypeError::Sorts(relate::expected_found(self, a, b)))
92 (&ty::Error(_), _) | (_, &ty::Error(_)) => Ok(self.tcx().ty_error()),
94 _ => relate::super_relate_tys(self, a, b),
102 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
103 debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
108 match (a.kind(), b.kind()) {
109 (_, ty::ConstKind::Infer(InferConst::Fresh(_))) => {
113 (ty::ConstKind::Infer(_), _) | (_, ty::ConstKind::Infer(_)) => {
114 return Err(TypeError::ConstMismatch(relate::expected_found(self, a, b)));
120 relate::super_relate_consts(self, a, b)
125 a: ty::Binder<'tcx, T>,
126 b: ty::Binder<'tcx, T>,
127 ) -> RelateResult<'tcx, ty::Binder<'tcx, T>>
131 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))