1 //! A nice interface for working with the infcx. The basic idea is to
2 //! do `infcx.at(cause, param_env)`, which sets the "cause" of the
3 //! operation as well as the surrounding parameter environment. Then
4 //! you can do something like `.sub(a, b)` or `.eq(a, b)` to create a
5 //! subtype or equality relationship respectively. The first argument
6 //! is always the "expected" output from the POV of diagnostics.
10 //! infcx.at(cause, param_env).sub(a, b)
11 //! // requires that `a <: b`, with `a` considered the "expected" type
13 //! infcx.at(cause, param_env).sup(a, b)
14 //! // requires that `b <: a`, with `a` considered the "expected" type
16 //! infcx.at(cause, param_env).eq(a, b)
17 //! // requires that `a == b`, with `a` considered the "expected" type
19 //! For finer-grained control, you can also do use `trace`:
21 //! infcx.at(...).trace(a, b).sub(&c, &d)
23 //! This will set `a` and `b` as the "root" values for
24 //! error-reporting, but actually operate on `c` and `d`. This is
25 //! sometimes useful when the types of `c` and `d` are not traceable
26 //! things. (That system should probably be refactored.)
30 use rustc_middle::ty::relate::{Relate, TypeRelation};
31 use rustc_middle::ty::Const;
33 pub struct At<'a, 'tcx> {
34 pub infcx: &'a InferCtxt<'a, 'tcx>,
35 pub cause: &'a ObligationCause<'tcx>,
36 pub param_env: ty::ParamEnv<'tcx>,
37 /// Whether we should define opaque types
38 /// or just treat them opaquely.
39 /// Currently only used to prevent predicate
40 /// matching from matching anything against opaque
42 pub define_opaque_types: bool,
45 pub struct Trace<'a, 'tcx> {
48 trace: TypeTrace<'tcx>,
51 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
55 cause: &'a ObligationCause<'tcx>,
56 param_env: ty::ParamEnv<'tcx>,
58 At { infcx: self, cause, param_env, define_opaque_types: true }
62 pub trait ToTrace<'tcx>: Relate<'tcx> + Copy {
65 cause: &ObligationCause<'tcx>,
72 impl<'a, 'tcx> At<'a, 'tcx> {
73 pub fn define_opaque_types(self, define_opaque_types: bool) -> Self {
74 Self { define_opaque_types, ..self }
77 /// Hacky routine for equating two impl headers in coherence.
78 pub fn eq_impl_headers(
80 expected: &ty::ImplHeader<'tcx>,
81 actual: &ty::ImplHeader<'tcx>,
82 ) -> InferResult<'tcx, ()> {
83 debug!("eq_impl_header({:?} = {:?})", expected, actual);
84 match (expected.trait_ref, actual.trait_ref) {
85 (Some(a_ref), Some(b_ref)) => self.eq(a_ref, b_ref),
86 (None, None) => self.eq(expected.self_ty, actual.self_ty),
87 _ => bug!("mk_eq_impl_headers given mismatched impl kinds"),
91 /// Makes `a <: b`, where `a` may or may not be expected.
92 pub fn sub_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()>
96 self.trace_exp(a_is_expected, a, b).sub(a, b)
99 /// Makes `actual <: expected`. For example, if type-checking a
100 /// call like `foo(x)`, where `foo: fn(i32)`, you might have
101 /// `sup(i32, x)`, since the "expected" type is the type that
102 /// appears in the signature.
103 pub fn sup<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
107 self.sub_exp(false, actual, expected)
110 /// Makes `expected <: actual`.
111 pub fn sub<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
115 self.sub_exp(true, expected, actual)
118 /// Makes `expected <: actual`.
119 pub fn eq_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()>
123 self.trace_exp(a_is_expected, a, b).eq(a, b)
126 /// Makes `expected <: actual`.
127 pub fn eq<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
131 self.trace(expected, actual).eq(expected, actual)
134 pub fn relate<T>(self, expected: T, variance: ty::Variance, actual: T) -> InferResult<'tcx, ()>
139 ty::Variance::Covariant => self.sub(expected, actual),
140 ty::Variance::Invariant => self.eq(expected, actual),
141 ty::Variance::Contravariant => self.sup(expected, actual),
143 // We could make this make sense but it's not readily
144 // exposed and I don't feel like dealing with it. Note
145 // that bivariance in general does a bit more than just
146 // *nothing*, it checks that the types are the same
147 // "modulo variance" basically.
148 ty::Variance::Bivariant => panic!("Bivariant given to `relate()`"),
152 /// Computes the least-upper-bound, or mutual supertype, of two
153 /// values. The order of the arguments doesn't matter, but since
154 /// this can result in an error (e.g., if asked to compute LUB of
155 /// u32 and i32), it is meaningful to call one of them the
157 pub fn lub<T>(self, expected: T, actual: T) -> InferResult<'tcx, T>
161 self.trace(expected, actual).lub(expected, actual)
164 /// Computes the greatest-lower-bound, or mutual subtype, of two
165 /// values. As with `lub` order doesn't matter, except for error
167 pub fn glb<T>(self, expected: T, actual: T) -> InferResult<'tcx, T>
171 self.trace(expected, actual).glb(expected, actual)
174 /// Sets the "trace" values that will be used for
175 /// error-reporting, but doesn't actually perform any operation
176 /// yet (this is useful when you want to set the trace using
177 /// distinct values from those you wish to operate upon).
178 pub fn trace<T>(self, expected: T, actual: T) -> Trace<'a, 'tcx>
182 self.trace_exp(true, expected, actual)
185 /// Like `trace`, but the expected value is determined by the
186 /// boolean argument (if true, then the first argument `a` is the
187 /// "expected" value).
188 pub fn trace_exp<T>(self, a_is_expected: bool, a: T, b: T) -> Trace<'a, 'tcx>
192 let trace = ToTrace::to_trace(self.infcx.tcx, self.cause, a_is_expected, a, b);
193 Trace { at: self, trace, a_is_expected }
197 impl<'a, 'tcx> Trace<'a, 'tcx> {
198 /// Makes `a <: b` where `a` may or may not be expected (if
199 /// `a_is_expected` is true, then `a` is expected).
200 #[instrument(skip(self), level = "debug")]
201 pub fn sub<T>(self, a: T, b: T) -> InferResult<'tcx, ()>
205 let Trace { at, trace, a_is_expected } = self;
206 at.infcx.commit_if_ok(|_| {
207 let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
211 .map(move |_| InferOk { value: (), obligations: fields.obligations })
215 /// Makes `a == b`; the expectation is set by the call to
217 #[instrument(skip(self), level = "debug")]
218 pub fn eq<T>(self, a: T, b: T) -> InferResult<'tcx, ()>
222 let Trace { at, trace, a_is_expected } = self;
223 at.infcx.commit_if_ok(|_| {
224 let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
226 .equate(a_is_expected)
228 .map(move |_| InferOk { value: (), obligations: fields.obligations })
232 #[instrument(skip(self), level = "debug")]
233 pub fn lub<T>(self, a: T, b: T) -> InferResult<'tcx, T>
237 let Trace { at, trace, a_is_expected } = self;
238 at.infcx.commit_if_ok(|_| {
239 let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
243 .map(move |t| InferOk { value: t, obligations: fields.obligations })
247 #[instrument(skip(self), level = "debug")]
248 pub fn glb<T>(self, a: T, b: T) -> InferResult<'tcx, T>
252 let Trace { at, trace, a_is_expected } = self;
253 at.infcx.commit_if_ok(|_| {
254 let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
258 .map(move |t| InferOk { value: t, obligations: fields.obligations })
263 impl<'tcx> ToTrace<'tcx> for Ty<'tcx> {
266 cause: &ObligationCause<'tcx>,
270 ) -> TypeTrace<'tcx> {
272 cause: cause.clone(),
273 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
278 impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> {
281 cause: &ObligationCause<'tcx>,
285 ) -> TypeTrace<'tcx> {
286 TypeTrace { cause: cause.clone(), values: Regions(ExpectedFound::new(a_is_expected, a, b)) }
290 impl<'tcx> ToTrace<'tcx> for &'tcx Const<'tcx> {
293 cause: &ObligationCause<'tcx>,
297 ) -> TypeTrace<'tcx> {
299 cause: cause.clone(),
300 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
305 impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> {
308 cause: &ObligationCause<'tcx>,
312 ) -> TypeTrace<'tcx> {
313 TypeTrace { cause: cause.clone(), values: Terms(ExpectedFound::new(a_is_expected, a, b)) }
317 impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
320 cause: &ObligationCause<'tcx>,
324 ) -> TypeTrace<'tcx> {
326 cause: cause.clone(),
327 values: TraitRefs(ExpectedFound::new(a_is_expected, a, b)),
332 impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> {
335 cause: &ObligationCause<'tcx>,
339 ) -> TypeTrace<'tcx> {
341 cause: cause.clone(),
342 values: PolyTraitRefs(ExpectedFound::new(a_is_expected, a, b)),
347 impl<'tcx> ToTrace<'tcx> for ty::ProjectionTy<'tcx> {
350 cause: &ObligationCause<'tcx>,
354 ) -> TypeTrace<'tcx> {
355 let a_ty = tcx.mk_projection(a.item_def_id, a.substs);
356 let b_ty = tcx.mk_projection(b.item_def_id, b.substs);
358 cause: cause.clone(),
359 values: Terms(ExpectedFound::new(a_is_expected, a_ty.into(), b_ty.into())),