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.
9 //! ```ignore (fragment)
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`:
20 //! ```ignore (fragment)
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, ImplSubject};
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 }
61 /// Forks the inference context, creating a new inference context with the same inference
62 /// variables in the same state. This can be used to "branch off" many tests from the same
63 /// common state. Used in coherence.
64 pub fn fork(&self) -> Self {
67 defining_use_anchor: self.defining_use_anchor,
68 in_progress_typeck_results: self.in_progress_typeck_results,
69 inner: self.inner.clone(),
70 skip_leak_check: self.skip_leak_check.clone(),
71 lexical_region_resolutions: self.lexical_region_resolutions.clone(),
72 selection_cache: self.selection_cache.clone(),
73 evaluation_cache: self.evaluation_cache.clone(),
74 reported_trait_errors: self.reported_trait_errors.clone(),
75 reported_closure_mismatch: self.reported_closure_mismatch.clone(),
76 tainted_by_errors_flag: self.tainted_by_errors_flag.clone(),
77 err_count_on_creation: self.err_count_on_creation,
78 in_snapshot: self.in_snapshot.clone(),
79 universe: self.universe.clone(),
84 pub trait ToTrace<'tcx>: Relate<'tcx> + Copy {
87 cause: &ObligationCause<'tcx>,
94 impl<'a, 'tcx> At<'a, 'tcx> {
95 pub fn define_opaque_types(self, define_opaque_types: bool) -> Self {
96 Self { define_opaque_types, ..self }
99 /// Hacky routine for equating two impl headers in coherence.
100 pub fn eq_impl_headers(
102 expected: &ty::ImplHeader<'tcx>,
103 actual: &ty::ImplHeader<'tcx>,
104 ) -> InferResult<'tcx, ()> {
105 debug!("eq_impl_header({:?} = {:?})", expected, actual);
106 match (expected.trait_ref, actual.trait_ref) {
107 (Some(a_ref), Some(b_ref)) => self.eq(a_ref, b_ref),
108 (None, None) => self.eq(expected.self_ty, actual.self_ty),
109 _ => bug!("mk_eq_impl_headers given mismatched impl kinds"),
113 /// Makes `a <: b`, where `a` may or may not be expected.
114 pub fn sub_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()>
118 self.trace_exp(a_is_expected, a, b).sub(a, b)
121 /// Makes `actual <: expected`. For example, if type-checking a
122 /// call like `foo(x)`, where `foo: fn(i32)`, you might have
123 /// `sup(i32, x)`, since the "expected" type is the type that
124 /// appears in the signature.
125 pub fn sup<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
129 self.sub_exp(false, actual, expected)
132 /// Makes `expected <: actual`.
133 pub fn sub<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
137 self.sub_exp(true, expected, actual)
140 /// Makes `expected <: actual`.
141 pub fn eq_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()>
145 self.trace_exp(a_is_expected, a, b).eq(a, b)
148 /// Makes `expected <: actual`.
149 pub fn eq<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
153 self.trace(expected, actual).eq(expected, actual)
156 pub fn relate<T>(self, expected: T, variance: ty::Variance, actual: T) -> InferResult<'tcx, ()>
161 ty::Variance::Covariant => self.sub(expected, actual),
162 ty::Variance::Invariant => self.eq(expected, actual),
163 ty::Variance::Contravariant => self.sup(expected, actual),
165 // We could make this make sense but it's not readily
166 // exposed and I don't feel like dealing with it. Note
167 // that bivariance in general does a bit more than just
168 // *nothing*, it checks that the types are the same
169 // "modulo variance" basically.
170 ty::Variance::Bivariant => panic!("Bivariant given to `relate()`"),
174 /// Computes the least-upper-bound, or mutual supertype, of two
175 /// values. The order of the arguments doesn't matter, but since
176 /// this can result in an error (e.g., if asked to compute LUB of
177 /// u32 and i32), it is meaningful to call one of them the
179 pub fn lub<T>(self, expected: T, actual: T) -> InferResult<'tcx, T>
183 self.trace(expected, actual).lub(expected, actual)
186 /// Computes the greatest-lower-bound, or mutual subtype, of two
187 /// values. As with `lub` order doesn't matter, except for error
189 pub fn glb<T>(self, expected: T, actual: T) -> InferResult<'tcx, T>
193 self.trace(expected, actual).glb(expected, actual)
196 /// Sets the "trace" values that will be used for
197 /// error-reporting, but doesn't actually perform any operation
198 /// yet (this is useful when you want to set the trace using
199 /// distinct values from those you wish to operate upon).
200 pub fn trace<T>(self, expected: T, actual: T) -> Trace<'a, 'tcx>
204 self.trace_exp(true, expected, actual)
207 /// Like `trace`, but the expected value is determined by the
208 /// boolean argument (if true, then the first argument `a` is the
209 /// "expected" value).
210 pub fn trace_exp<T>(self, a_is_expected: bool, a: T, b: T) -> Trace<'a, 'tcx>
214 let trace = ToTrace::to_trace(self.infcx.tcx, self.cause, a_is_expected, a, b);
215 Trace { at: self, trace, a_is_expected }
219 impl<'a, 'tcx> Trace<'a, 'tcx> {
220 /// Makes `a <: b` where `a` may or may not be expected (if
221 /// `a_is_expected` is true, then `a` is expected).
222 #[instrument(skip(self), level = "debug")]
223 pub fn sub<T>(self, a: T, b: T) -> InferResult<'tcx, ()>
227 let Trace { at, trace, a_is_expected } = self;
228 at.infcx.commit_if_ok(|_| {
229 let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
233 .map(move |_| InferOk { value: (), obligations: fields.obligations })
237 /// Makes `a == b`; the expectation is set by the call to
239 #[instrument(skip(self), level = "debug")]
240 pub fn eq<T>(self, a: T, b: T) -> InferResult<'tcx, ()>
244 let Trace { at, trace, a_is_expected } = self;
245 at.infcx.commit_if_ok(|_| {
246 let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
248 .equate(a_is_expected)
250 .map(move |_| InferOk { value: (), obligations: fields.obligations })
254 #[instrument(skip(self), level = "debug")]
255 pub fn lub<T>(self, a: T, b: T) -> InferResult<'tcx, T>
259 let Trace { at, trace, a_is_expected } = self;
260 at.infcx.commit_if_ok(|_| {
261 let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
265 .map(move |t| InferOk { value: t, obligations: fields.obligations })
269 #[instrument(skip(self), level = "debug")]
270 pub fn glb<T>(self, a: T, b: T) -> InferResult<'tcx, T>
274 let Trace { at, trace, a_is_expected } = self;
275 at.infcx.commit_if_ok(|_| {
276 let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
280 .map(move |t| InferOk { value: t, obligations: fields.obligations })
285 impl<'tcx> ToTrace<'tcx> for ImplSubject<'tcx> {
288 cause: &ObligationCause<'tcx>,
292 ) -> TypeTrace<'tcx> {
294 (ImplSubject::Trait(trait_ref_a), ImplSubject::Trait(trait_ref_b)) => {
295 ToTrace::to_trace(tcx, cause, a_is_expected, trait_ref_a, trait_ref_b)
297 (ImplSubject::Inherent(ty_a), ImplSubject::Inherent(ty_b)) => {
298 ToTrace::to_trace(tcx, cause, a_is_expected, ty_a, ty_b)
300 (ImplSubject::Trait(_), ImplSubject::Inherent(_))
301 | (ImplSubject::Inherent(_), ImplSubject::Trait(_)) => {
302 bug!("can not trace TraitRef and Ty");
308 impl<'tcx> ToTrace<'tcx> for Ty<'tcx> {
311 cause: &ObligationCause<'tcx>,
315 ) -> TypeTrace<'tcx> {
317 cause: cause.clone(),
318 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
323 impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> {
326 cause: &ObligationCause<'tcx>,
330 ) -> TypeTrace<'tcx> {
331 TypeTrace { cause: cause.clone(), values: Regions(ExpectedFound::new(a_is_expected, a, b)) }
335 impl<'tcx> ToTrace<'tcx> for Const<'tcx> {
338 cause: &ObligationCause<'tcx>,
342 ) -> TypeTrace<'tcx> {
344 cause: cause.clone(),
345 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
350 impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> {
353 cause: &ObligationCause<'tcx>,
357 ) -> TypeTrace<'tcx> {
358 TypeTrace { cause: cause.clone(), values: Terms(ExpectedFound::new(a_is_expected, a, b)) }
362 impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
365 cause: &ObligationCause<'tcx>,
369 ) -> TypeTrace<'tcx> {
371 cause: cause.clone(),
372 values: TraitRefs(ExpectedFound::new(a_is_expected, a, b)),
377 impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> {
380 cause: &ObligationCause<'tcx>,
384 ) -> TypeTrace<'tcx> {
386 cause: cause.clone(),
387 values: PolyTraitRefs(ExpectedFound::new(a_is_expected, a, b)),
392 impl<'tcx> ToTrace<'tcx> for ty::ProjectionTy<'tcx> {
395 cause: &ObligationCause<'tcx>,
399 ) -> TypeTrace<'tcx> {
400 let a_ty = tcx.mk_projection(a.item_def_id, a.substs);
401 let b_ty = tcx.mk_projection(b.item_def_id, b.substs);
403 cause: cause.clone(),
404 values: Terms(ExpectedFound::new(a_is_expected, a_ty.into(), b_ty.into())),