Remove shrink_to_tcx_lifetime

There's no longer two distinct gcx and tcx lifetimes which made this
necessary (or, at least, the code compiles -- it's possible we got
better at normalizing, but that seems unlikely).

Author: Mark-Simulacrum

src/librustc/traits/query/type_op/ascribe_user_type.rs

@@ -1,4 +1,4 @@
-use crate::infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
+use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
 use crate::traits::query::Fallible;
 use crate::hir::def_id::DefId;
 use crate::ty::{ParamEnvAnd, Ty, TyCtxt};
@@ -37,12 +37,6 @@ impl<'tcx> super::QueryTypeOp<'tcx> for AscribeUserType<'tcx> {
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, ()>> {
         tcx.type_op_ascribe_user_type(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, ()>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, ()>> {
-        v
-    }
 }
 
 BraceStructTypeFoldableImpl! {

src/librustc/traits/query/type_op/eq.rs

@@ -1,4 +1,4 @@
-use crate::infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
+use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
 use crate::traits::query::Fallible;
 use crate::ty::{ParamEnvAnd, Ty, TyCtxt};
 
@@ -34,12 +34,6 @@ impl<'tcx> super::QueryTypeOp<'tcx> for Eq<'tcx> {
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, ()>> {
         tcx.type_op_eq(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, ()>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, ()>> {
-        v
-    }
 }
 
 BraceStructTypeFoldableImpl! {

src/librustc/traits/query/type_op/implied_outlives_bounds.rs

@@ -1,4 +1,4 @@
-use crate::infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
+use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
 use crate::traits::query::outlives_bounds::OutlivesBound;
 use crate::traits::query::Fallible;
 use crate::ty::{ParamEnvAnd, Ty, TyCtxt};
@@ -38,12 +38,6 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ImpliedOutlivesBounds<'tcx> {
 
         tcx.implied_outlives_bounds(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, Self::QueryResponse>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, Self::QueryResponse>> {
-        v
-    }
 }
 
 BraceStructTypeFoldableImpl! {

src/librustc/traits/query/type_op/mod.rs

@@ -1,6 +1,6 @@
 use crate::infer::canonical::{
-    Canonical, Canonicalized, CanonicalizedQueryResponse, OriginalQueryValues,
-    QueryRegionConstraints, QueryResponse,
+    Canonicalized, CanonicalizedQueryResponse, OriginalQueryValues,
+    QueryRegionConstraints,
 };
 use crate::infer::{InferCtxt, InferOk};
 use std::fmt;
@@ -66,22 +66,6 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Sized + TypeFoldable<'tcx> + 'tcx {
         canonicalized: Canonicalized<'tcx, ParamEnvAnd<'tcx, Self>>,
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, Self::QueryResponse>>;
 
-    /// Casts a lifted query result (which is in the tcx lifetime)
-    /// into the tcx lifetime. This is always just an identity cast,
-    /// but the generic code doesn't realize it -- put another way, in
-    /// the generic code, we have a `Lifted<'tcx, Self::QueryResponse>`
-    /// and we want to convert that to a `Self::QueryResponse`. This is
-    /// not a priori valid, so we can't do it -- but in practice, it
-    /// is always a no-op (e.g., the lifted form of a type,
-    /// `Ty<'tcx>`, is a subtype of `Ty<'tcx>`). So we have to push
-    /// the operation into the impls that know more specifically what
-    /// `QueryResponse` is. This operation would (maybe) be nicer with
-    /// something like HKTs or GATs, since then we could make
-    /// `QueryResponse` parametric and `'tcx` and `'tcx` etc.
-    fn shrink_to_tcx_lifetime(
-        lifted_query_result: &'a CanonicalizedQueryResponse<'tcx, Self::QueryResponse>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, Self::QueryResponse>>;
-
     fn fully_perform_into(
         query_key: ParamEnvAnd<'tcx, Self>,
         infcx: &InferCtxt<'_, 'tcx>,
@@ -99,7 +83,6 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Sized + TypeFoldable<'tcx> + 'tcx {
         let canonical_self =
             infcx.canonicalize_hr_query_hack(&query_key, &mut canonical_var_values);
         let canonical_result = Self::perform_query(infcx.tcx, canonical_self)?;
-        let canonical_result = Self::shrink_to_tcx_lifetime(&canonical_result);
 
         let param_env = query_key.param_env;
 

src/librustc/traits/query/type_op/normalize.rs

@@ -1,4 +1,4 @@
-use crate::infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
+use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
 use std::fmt;
 use crate::traits::query::Fallible;
 use crate::ty::fold::TypeFoldable;
@@ -38,25 +38,13 @@ where
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, Self::QueryResponse>> {
         T::type_op_method(tcx, canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, T>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, T>> {
-        T::shrink_to_tcx_lifetime(v)
-    }
 }
 
 pub trait Normalizable<'tcx>: fmt::Debug + TypeFoldable<'tcx> + Lift<'tcx> + Copy {
     fn type_op_method(
         tcx: TyCtxt<'tcx>,
         canonicalized: Canonicalized<'tcx, ParamEnvAnd<'tcx, Normalize<Self>>>,
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, Self>>;
-
-    /// Converts from the `'tcx` (lifted) form of `Self` into the `tcx`
-    /// form of `Self`.
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, Self>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, Self>>;
 }
 
 impl Normalizable<'tcx> for Ty<'tcx> {
@@ -66,12 +54,6 @@ impl Normalizable<'tcx> for Ty<'tcx> {
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, Self>> {
         tcx.type_op_normalize_ty(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, Self>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, Self>> {
-        v
-    }
 }
 
 impl Normalizable<'tcx> for ty::Predicate<'tcx> {
@@ -81,12 +63,6 @@ impl Normalizable<'tcx> for ty::Predicate<'tcx> {
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, Self>> {
         tcx.type_op_normalize_predicate(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, Self>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, Self>> {
-        v
-    }
 }
 
 impl Normalizable<'tcx> for ty::PolyFnSig<'tcx> {
@@ -96,12 +72,6 @@ impl Normalizable<'tcx> for ty::PolyFnSig<'tcx> {
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, Self>> {
         tcx.type_op_normalize_poly_fn_sig(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, Self>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, Self>> {
-        v
-    }
 }
 
 impl Normalizable<'tcx> for ty::FnSig<'tcx> {
@@ -111,12 +81,6 @@ impl Normalizable<'tcx> for ty::FnSig<'tcx> {
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, Self>> {
         tcx.type_op_normalize_fn_sig(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, Self>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, Self>> {
-        v
-    }
 }
 
 BraceStructTypeFoldableImpl! {

src/librustc/traits/query/type_op/outlives.rs

@@ -1,4 +1,4 @@
-use crate::infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
+use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
 use crate::traits::query::dropck_outlives::trivial_dropck_outlives;
 use crate::traits::query::dropck_outlives::DropckOutlivesResult;
 use crate::traits::query::Fallible;
@@ -53,12 +53,6 @@ impl super::QueryTypeOp<'tcx> for DropckOutlives<'tcx> {
 
         tcx.dropck_outlives(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        lifted_query_result: &'a CanonicalizedQueryResponse<'tcx, Self::QueryResponse>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, Self::QueryResponse>> {
-        lifted_query_result
-    }
 }
 
 BraceStructTypeFoldableImpl! {

src/librustc/traits/query/type_op/prove_predicate.rs

@@ -1,4 +1,4 @@
-use crate::infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
+use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
 use crate::traits::query::Fallible;
 use crate::ty::{ParamEnvAnd, Predicate, TyCtxt};
 
@@ -43,12 +43,6 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, ()>> {
         tcx.type_op_prove_predicate(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, ()>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, ()>> {
-        v
-    }
 }
 
 BraceStructTypeFoldableImpl! {

src/librustc/traits/query/type_op/subtype.rs

@@ -1,4 +1,4 @@
-use crate::infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
+use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
 use crate::traits::query::Fallible;
 use crate::ty::{ParamEnvAnd, Ty, TyCtxt};
 
@@ -34,12 +34,6 @@ impl<'tcx> super::QueryTypeOp<'tcx> for Subtype<'tcx> {
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, ()>> {
         tcx.type_op_subtype(canonicalized)
     }
-
-    fn shrink_to_tcx_lifetime(
-        v: &'a CanonicalizedQueryResponse<'tcx, ()>,
-    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, ()>> {
-        v
-    }
 }
 
 BraceStructTypeFoldableImpl! {