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-rw-r--r-- | compiler/rustc_infer/src/infer/at.rs | 429 |
1 files changed, 429 insertions, 0 deletions
diff --git a/compiler/rustc_infer/src/infer/at.rs b/compiler/rustc_infer/src/infer/at.rs new file mode 100644 index 000000000..130214a65 --- /dev/null +++ b/compiler/rustc_infer/src/infer/at.rs @@ -0,0 +1,429 @@ +//! A nice interface for working with the infcx. The basic idea is to +//! do `infcx.at(cause, param_env)`, which sets the "cause" of the +//! operation as well as the surrounding parameter environment. Then +//! you can do something like `.sub(a, b)` or `.eq(a, b)` to create a +//! subtype or equality relationship respectively. The first argument +//! is always the "expected" output from the POV of diagnostics. +//! +//! Examples: +//! ```ignore (fragment) +//! infcx.at(cause, param_env).sub(a, b) +//! // requires that `a <: b`, with `a` considered the "expected" type +//! +//! infcx.at(cause, param_env).sup(a, b) +//! // requires that `b <: a`, with `a` considered the "expected" type +//! +//! infcx.at(cause, param_env).eq(a, b) +//! // requires that `a == b`, with `a` considered the "expected" type +//! ``` +//! For finer-grained control, you can also do use `trace`: +//! ```ignore (fragment) +//! infcx.at(...).trace(a, b).sub(&c, &d) +//! ``` +//! This will set `a` and `b` as the "root" values for +//! error-reporting, but actually operate on `c` and `d`. This is +//! sometimes useful when the types of `c` and `d` are not traceable +//! things. (That system should probably be refactored.) + +use super::*; + +use rustc_middle::ty::relate::{Relate, TypeRelation}; +use rustc_middle::ty::{Const, ImplSubject}; + +pub struct At<'a, 'tcx> { + pub infcx: &'a InferCtxt<'a, 'tcx>, + pub cause: &'a ObligationCause<'tcx>, + pub param_env: ty::ParamEnv<'tcx>, + /// Whether we should define opaque types + /// or just treat them opaquely. + /// Currently only used to prevent predicate + /// matching from matching anything against opaque + /// types. + pub define_opaque_types: bool, +} + +pub struct Trace<'a, 'tcx> { + at: At<'a, 'tcx>, + a_is_expected: bool, + trace: TypeTrace<'tcx>, +} + +impl<'a, 'tcx> InferCtxt<'a, 'tcx> { + #[inline] + pub fn at( + &'a self, + cause: &'a ObligationCause<'tcx>, + param_env: ty::ParamEnv<'tcx>, + ) -> At<'a, 'tcx> { + At { infcx: self, cause, param_env, define_opaque_types: true } + } + + /// Forks the inference context, creating a new inference context with the same inference + /// variables in the same state. This can be used to "branch off" many tests from the same + /// common state. Used in coherence. + pub fn fork(&self) -> Self { + Self { + tcx: self.tcx, + defining_use_anchor: self.defining_use_anchor, + considering_regions: self.considering_regions, + in_progress_typeck_results: self.in_progress_typeck_results, + inner: self.inner.clone(), + skip_leak_check: self.skip_leak_check.clone(), + lexical_region_resolutions: self.lexical_region_resolutions.clone(), + selection_cache: self.selection_cache.clone(), + evaluation_cache: self.evaluation_cache.clone(), + reported_trait_errors: self.reported_trait_errors.clone(), + reported_closure_mismatch: self.reported_closure_mismatch.clone(), + tainted_by_errors_flag: self.tainted_by_errors_flag.clone(), + err_count_on_creation: self.err_count_on_creation, + in_snapshot: self.in_snapshot.clone(), + universe: self.universe.clone(), + } + } +} + +pub trait ToTrace<'tcx>: Relate<'tcx> + Copy { + fn to_trace( + tcx: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx>; +} + +impl<'a, 'tcx> At<'a, 'tcx> { + pub fn define_opaque_types(self, define_opaque_types: bool) -> Self { + Self { define_opaque_types, ..self } + } + + /// Hacky routine for equating two impl headers in coherence. + pub fn eq_impl_headers( + self, + expected: &ty::ImplHeader<'tcx>, + actual: &ty::ImplHeader<'tcx>, + ) -> InferResult<'tcx, ()> { + debug!("eq_impl_header({:?} = {:?})", expected, actual); + match (expected.trait_ref, actual.trait_ref) { + (Some(a_ref), Some(b_ref)) => self.eq(a_ref, b_ref), + (None, None) => self.eq(expected.self_ty, actual.self_ty), + _ => bug!("mk_eq_impl_headers given mismatched impl kinds"), + } + } + + /// Makes `a <: b`, where `a` may or may not be expected. + /// + /// See [`At::trace_exp`] and [`Trace::sub`] for a version of + /// this method that only requires `T: Relate<'tcx>` + pub fn sub_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()> + where + T: ToTrace<'tcx>, + { + self.trace_exp(a_is_expected, a, b).sub(a, b) + } + + /// Makes `actual <: expected`. For example, if type-checking a + /// call like `foo(x)`, where `foo: fn(i32)`, you might have + /// `sup(i32, x)`, since the "expected" type is the type that + /// appears in the signature. + /// + /// See [`At::trace`] and [`Trace::sub`] for a version of + /// this method that only requires `T: Relate<'tcx>` + pub fn sup<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()> + where + T: ToTrace<'tcx>, + { + self.sub_exp(false, actual, expected) + } + + /// Makes `expected <: actual`. + /// + /// See [`At::trace`] and [`Trace::sub`] for a version of + /// this method that only requires `T: Relate<'tcx>` + pub fn sub<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()> + where + T: ToTrace<'tcx>, + { + self.sub_exp(true, expected, actual) + } + + /// Makes `expected <: actual`. + /// + /// See [`At::trace_exp`] and [`Trace::eq`] for a version of + /// this method that only requires `T: Relate<'tcx>` + pub fn eq_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()> + where + T: ToTrace<'tcx>, + { + self.trace_exp(a_is_expected, a, b).eq(a, b) + } + + /// Makes `expected <: actual`. + /// + /// See [`At::trace`] and [`Trace::eq`] for a version of + /// this method that only requires `T: Relate<'tcx>` + pub fn eq<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()> + where + T: ToTrace<'tcx>, + { + self.trace(expected, actual).eq(expected, actual) + } + + pub fn relate<T>(self, expected: T, variance: ty::Variance, actual: T) -> InferResult<'tcx, ()> + where + T: ToTrace<'tcx>, + { + match variance { + ty::Variance::Covariant => self.sub(expected, actual), + ty::Variance::Invariant => self.eq(expected, actual), + ty::Variance::Contravariant => self.sup(expected, actual), + + // We could make this make sense but it's not readily + // exposed and I don't feel like dealing with it. Note + // that bivariance in general does a bit more than just + // *nothing*, it checks that the types are the same + // "modulo variance" basically. + ty::Variance::Bivariant => panic!("Bivariant given to `relate()`"), + } + } + + /// Computes the least-upper-bound, or mutual supertype, of two + /// values. The order of the arguments doesn't matter, but since + /// this can result in an error (e.g., if asked to compute LUB of + /// u32 and i32), it is meaningful to call one of them the + /// "expected type". + /// + /// See [`At::trace`] and [`Trace::lub`] for a version of + /// this method that only requires `T: Relate<'tcx>` + pub fn lub<T>(self, expected: T, actual: T) -> InferResult<'tcx, T> + where + T: ToTrace<'tcx>, + { + self.trace(expected, actual).lub(expected, actual) + } + + /// Computes the greatest-lower-bound, or mutual subtype, of two + /// values. As with `lub` order doesn't matter, except for error + /// cases. + /// + /// See [`At::trace`] and [`Trace::glb`] for a version of + /// this method that only requires `T: Relate<'tcx>` + pub fn glb<T>(self, expected: T, actual: T) -> InferResult<'tcx, T> + where + T: ToTrace<'tcx>, + { + self.trace(expected, actual).glb(expected, actual) + } + + /// Sets the "trace" values that will be used for + /// error-reporting, but doesn't actually perform any operation + /// yet (this is useful when you want to set the trace using + /// distinct values from those you wish to operate upon). + pub fn trace<T>(self, expected: T, actual: T) -> Trace<'a, 'tcx> + where + T: ToTrace<'tcx>, + { + self.trace_exp(true, expected, actual) + } + + /// Like `trace`, but the expected value is determined by the + /// boolean argument (if true, then the first argument `a` is the + /// "expected" value). + pub fn trace_exp<T>(self, a_is_expected: bool, a: T, b: T) -> Trace<'a, 'tcx> + where + T: ToTrace<'tcx>, + { + let trace = ToTrace::to_trace(self.infcx.tcx, self.cause, a_is_expected, a, b); + Trace { at: self, trace, a_is_expected } + } +} + +impl<'a, 'tcx> Trace<'a, 'tcx> { + /// Makes `a <: b` where `a` may or may not be expected (if + /// `a_is_expected` is true, then `a` is expected). + #[instrument(skip(self), level = "debug")] + pub fn sub<T>(self, a: T, b: T) -> InferResult<'tcx, ()> + where + T: Relate<'tcx>, + { + let Trace { at, trace, a_is_expected } = self; + at.infcx.commit_if_ok(|_| { + let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types); + fields + .sub(a_is_expected) + .relate(a, b) + .map(move |_| InferOk { value: (), obligations: fields.obligations }) + }) + } + + /// Makes `a == b`; the expectation is set by the call to + /// `trace()`. + #[instrument(skip(self), level = "debug")] + pub fn eq<T>(self, a: T, b: T) -> InferResult<'tcx, ()> + where + T: Relate<'tcx>, + { + let Trace { at, trace, a_is_expected } = self; + at.infcx.commit_if_ok(|_| { + let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types); + fields + .equate(a_is_expected) + .relate(a, b) + .map(move |_| InferOk { value: (), obligations: fields.obligations }) + }) + } + + #[instrument(skip(self), level = "debug")] + pub fn lub<T>(self, a: T, b: T) -> InferResult<'tcx, T> + where + T: Relate<'tcx>, + { + let Trace { at, trace, a_is_expected } = self; + at.infcx.commit_if_ok(|_| { + let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types); + fields + .lub(a_is_expected) + .relate(a, b) + .map(move |t| InferOk { value: t, obligations: fields.obligations }) + }) + } + + #[instrument(skip(self), level = "debug")] + pub fn glb<T>(self, a: T, b: T) -> InferResult<'tcx, T> + where + T: Relate<'tcx>, + { + let Trace { at, trace, a_is_expected } = self; + at.infcx.commit_if_ok(|_| { + let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types); + fields + .glb(a_is_expected) + .relate(a, b) + .map(move |t| InferOk { value: t, obligations: fields.obligations }) + }) + } +} + +impl<'tcx> ToTrace<'tcx> for ImplSubject<'tcx> { + fn to_trace( + tcx: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx> { + match (a, b) { + (ImplSubject::Trait(trait_ref_a), ImplSubject::Trait(trait_ref_b)) => { + ToTrace::to_trace(tcx, cause, a_is_expected, trait_ref_a, trait_ref_b) + } + (ImplSubject::Inherent(ty_a), ImplSubject::Inherent(ty_b)) => { + ToTrace::to_trace(tcx, cause, a_is_expected, ty_a, ty_b) + } + (ImplSubject::Trait(_), ImplSubject::Inherent(_)) + | (ImplSubject::Inherent(_), ImplSubject::Trait(_)) => { + bug!("can not trace TraitRef and Ty"); + } + } + } +} + +impl<'tcx> ToTrace<'tcx> for Ty<'tcx> { + fn to_trace( + _: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx> { + TypeTrace { + cause: cause.clone(), + values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())), + } + } +} + +impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> { + fn to_trace( + _: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx> { + TypeTrace { cause: cause.clone(), values: Regions(ExpectedFound::new(a_is_expected, a, b)) } + } +} + +impl<'tcx> ToTrace<'tcx> for Const<'tcx> { + fn to_trace( + _: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx> { + TypeTrace { + cause: cause.clone(), + values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())), + } + } +} + +impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> { + fn to_trace( + _: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx> { + TypeTrace { cause: cause.clone(), values: Terms(ExpectedFound::new(a_is_expected, a, b)) } + } +} + +impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> { + fn to_trace( + _: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx> { + TypeTrace { + cause: cause.clone(), + values: TraitRefs(ExpectedFound::new(a_is_expected, a, b)), + } + } +} + +impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> { + fn to_trace( + _: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx> { + TypeTrace { + cause: cause.clone(), + values: PolyTraitRefs(ExpectedFound::new(a_is_expected, a, b)), + } + } +} + +impl<'tcx> ToTrace<'tcx> for ty::ProjectionTy<'tcx> { + fn to_trace( + tcx: TyCtxt<'tcx>, + cause: &ObligationCause<'tcx>, + a_is_expected: bool, + a: Self, + b: Self, + ) -> TypeTrace<'tcx> { + let a_ty = tcx.mk_projection(a.item_def_id, a.substs); + let b_ty = tcx.mk_projection(b.item_def_id, b.substs); + TypeTrace { + cause: cause.clone(), + values: Terms(ExpectedFound::new(a_is_expected, a_ty.into(), b_ty.into())), + } + } +} |