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>,
39 pub struct Trace<'a, 'tcx> {
42 trace: TypeTrace<'tcx>,
45 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
49 cause: &'a ObligationCause<'tcx>,
50 param_env: ty::ParamEnv<'tcx>,
52 At { infcx: self, cause, param_env }
55 /// Forks the inference context, creating a new inference context with the same inference
56 /// variables in the same state. This can be used to "branch off" many tests from the same
57 /// common state. Used in coherence.
58 pub fn fork(&self) -> Self {
60 tcx: self.tcx.clone(),
61 defining_use_anchor: self.defining_use_anchor.clone(),
62 in_progress_typeck_results: self.in_progress_typeck_results.clone(),
63 inner: self.inner.clone(),
64 skip_leak_check: self.skip_leak_check.clone(),
65 lexical_region_resolutions: self.lexical_region_resolutions.clone(),
66 selection_cache: self.selection_cache.clone(),
67 evaluation_cache: self.evaluation_cache.clone(),
68 reported_trait_errors: self.reported_trait_errors.clone(),
69 reported_closure_mismatch: self.reported_closure_mismatch.clone(),
70 tainted_by_errors_flag: self.tainted_by_errors_flag.clone(),
71 err_count_on_creation: self.err_count_on_creation,
72 in_snapshot: self.in_snapshot.clone(),
73 universe: self.universe.clone(),
78 pub trait ToTrace<'tcx>: Relate<'tcx> + Copy {
81 cause: &ObligationCause<'tcx>,
88 impl<'a, 'tcx> At<'a, 'tcx> {
89 /// Hacky routine for equating two impl headers in coherence.
90 pub fn eq_impl_headers(
92 expected: &ty::ImplHeader<'tcx>,
93 actual: &ty::ImplHeader<'tcx>,
94 ) -> InferResult<'tcx, ()> {
95 debug!("eq_impl_header({:?} = {:?})", expected, actual);
96 match (expected.trait_ref, actual.trait_ref) {
97 (Some(a_ref), Some(b_ref)) => self.eq(a_ref, b_ref),
98 (None, None) => self.eq(expected.self_ty, actual.self_ty),
99 _ => bug!("mk_eq_impl_headers given mismatched impl kinds"),
103 /// Makes `a <: b`, where `a` may or may not be expected.
104 pub fn sub_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()>
108 self.trace_exp(a_is_expected, a, b).sub(a, b)
111 /// Makes `actual <: expected`. For example, if type-checking a
112 /// call like `foo(x)`, where `foo: fn(i32)`, you might have
113 /// `sup(i32, x)`, since the "expected" type is the type that
114 /// appears in the signature.
115 pub fn sup<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
119 self.sub_exp(false, actual, expected)
122 /// Makes `expected <: actual`.
123 pub fn sub<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
127 self.sub_exp(true, expected, actual)
130 /// Makes `expected <: actual`.
131 pub fn eq_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()>
135 self.trace_exp(a_is_expected, a, b).eq(a, b)
138 /// Makes `expected <: actual`.
139 pub fn eq<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
143 self.trace(expected, actual).eq(expected, actual)
146 pub fn relate<T>(self, expected: T, variance: ty::Variance, actual: T) -> InferResult<'tcx, ()>
151 ty::Variance::Covariant => self.sub(expected, actual),
152 ty::Variance::Invariant => self.eq(expected, actual),
153 ty::Variance::Contravariant => self.sup(expected, actual),
155 // We could make this make sense but it's not readily
156 // exposed and I don't feel like dealing with it. Note
157 // that bivariance in general does a bit more than just
158 // *nothing*, it checks that the types are the same
159 // "modulo variance" basically.
160 ty::Variance::Bivariant => panic!("Bivariant given to `relate()`"),
164 /// Computes the least-upper-bound, or mutual supertype, of two
165 /// values. The order of the arguments doesn't matter, but since
166 /// this can result in an error (e.g., if asked to compute LUB of
167 /// u32 and i32), it is meaningful to call one of them the
169 pub fn lub<T>(self, expected: T, actual: T) -> InferResult<'tcx, T>
173 self.trace(expected, actual).lub(expected, actual)
176 /// Computes the greatest-lower-bound, or mutual subtype, of two
177 /// values. As with `lub` order doesn't matter, except for error
179 pub fn glb<T>(self, expected: T, actual: T) -> InferResult<'tcx, T>
183 self.trace(expected, actual).glb(expected, actual)
186 /// Sets the "trace" values that will be used for
187 /// error-reporting, but doesn't actually perform any operation
188 /// yet (this is useful when you want to set the trace using
189 /// distinct values from those you wish to operate upon).
190 pub fn trace<T>(self, expected: T, actual: T) -> Trace<'a, 'tcx>
194 self.trace_exp(true, expected, actual)
197 /// Like `trace`, but the expected value is determined by the
198 /// boolean argument (if true, then the first argument `a` is the
199 /// "expected" value).
200 pub fn trace_exp<T>(self, a_is_expected: bool, a: T, b: T) -> Trace<'a, 'tcx>
204 let trace = ToTrace::to_trace(self.infcx.tcx, self.cause, a_is_expected, a, b);
205 Trace { at: self, trace, a_is_expected }
209 impl<'a, 'tcx> Trace<'a, 'tcx> {
210 /// Makes `a <: b` where `a` may or may not be expected (if
211 /// `a_is_expected` is true, then `a` is expected).
212 #[instrument(skip(self), level = "debug")]
213 pub fn sub<T>(self, a: T, b: T) -> InferResult<'tcx, ()>
217 let Trace { at, trace, a_is_expected } = self;
218 at.infcx.commit_if_ok(|_| {
219 let mut fields = at.infcx.combine_fields(trace, at.param_env);
223 .map(move |_| InferOk { value: (), obligations: fields.obligations })
227 /// Makes `a == b`; the expectation is set by the call to
229 #[instrument(skip(self), level = "debug")]
230 pub fn eq<T>(self, a: T, b: T) -> InferResult<'tcx, ()>
234 let Trace { at, trace, a_is_expected } = self;
235 at.infcx.commit_if_ok(|_| {
236 let mut fields = at.infcx.combine_fields(trace, at.param_env);
238 .equate(a_is_expected)
240 .map(move |_| InferOk { value: (), obligations: fields.obligations })
244 #[instrument(skip(self), level = "debug")]
245 pub fn lub<T>(self, a: T, b: T) -> InferResult<'tcx, T>
249 let Trace { at, trace, a_is_expected } = self;
250 at.infcx.commit_if_ok(|_| {
251 let mut fields = at.infcx.combine_fields(trace, at.param_env);
255 .map(move |t| InferOk { value: t, obligations: fields.obligations })
259 #[instrument(skip(self), level = "debug")]
260 pub fn glb<T>(self, a: T, b: T) -> InferResult<'tcx, T>
264 let Trace { at, trace, a_is_expected } = self;
265 at.infcx.commit_if_ok(|_| {
266 let mut fields = at.infcx.combine_fields(trace, at.param_env);
270 .map(move |t| InferOk { value: t, obligations: fields.obligations })
275 impl<'tcx> ToTrace<'tcx> for Ty<'tcx> {
278 cause: &ObligationCause<'tcx>,
282 ) -> TypeTrace<'tcx> {
284 cause: cause.clone(),
285 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
290 impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> {
293 cause: &ObligationCause<'tcx>,
297 ) -> TypeTrace<'tcx> {
298 TypeTrace { cause: cause.clone(), values: Regions(ExpectedFound::new(a_is_expected, a, b)) }
302 impl<'tcx> ToTrace<'tcx> for Const<'tcx> {
305 cause: &ObligationCause<'tcx>,
309 ) -> TypeTrace<'tcx> {
311 cause: cause.clone(),
312 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
317 impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> {
320 cause: &ObligationCause<'tcx>,
324 ) -> TypeTrace<'tcx> {
325 TypeTrace { cause: cause.clone(), values: Terms(ExpectedFound::new(a_is_expected, a, b)) }
329 impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
332 cause: &ObligationCause<'tcx>,
336 ) -> TypeTrace<'tcx> {
338 cause: cause.clone(),
339 values: TraitRefs(ExpectedFound::new(a_is_expected, a, b)),
344 impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> {
347 cause: &ObligationCause<'tcx>,
351 ) -> TypeTrace<'tcx> {
353 cause: cause.clone(),
354 values: PolyTraitRefs(ExpectedFound::new(a_is_expected, a, b)),
359 impl<'tcx> ToTrace<'tcx> for ty::ProjectionTy<'tcx> {
362 cause: &ObligationCause<'tcx>,
366 ) -> TypeTrace<'tcx> {
367 let a_ty = tcx.mk_projection(a.item_def_id, a.substs);
368 let b_ty = tcx.mk_projection(b.item_def_id, b.substs);
370 cause: cause.clone(),
371 values: Terms(ExpectedFound::new(a_is_expected, a_ty.into(), b_ty.into())),