Normalize opaque types when converting ParamEnv to Reveal::All

Aaron1011 · Aaron1011 · commit ac9dfc3e7785 · 2020-07-22T00:57:43.000-04:00
Fixes #65918
diff --git a/src/librustc_middle/mir/interpret/queries.rs b/src/librustc_middle/mir/interpret/queries.rs
@@ -18,7 +18,7 @@ impl<'tcx> TyCtxt<'tcx> {
         let substs = InternalSubsts::identity_for_item(self, def_id);
         let instance = ty::Instance::new(def_id, substs);
         let cid = GlobalId { instance, promoted: None };
-        let param_env = self.param_env(def_id).with_reveal_all();
+        let param_env = self.param_env(def_id).with_reveal_all_normalized(self);
         self.const_eval_global_id(param_env, cid, None)
     }
 
diff --git a/src/librustc_middle/mir/interpret/value.rs b/src/librustc_middle/mir/interpret/value.rs
@@ -78,7 +78,7 @@ impl<'tcx> ConstValue<'tcx> {
         param_env: ParamEnv<'tcx>,
         ty: Ty<'tcx>,
     ) -> Option<u128> {
-        let size = tcx.layout_of(param_env.with_reveal_all().and(ty)).ok()?.size;
+        let size = tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(ty)).ok()?.size;
         self.try_to_bits(size)
     }
 
diff --git a/src/librustc_middle/query/mod.rs b/src/librustc_middle/query/mod.rs
@@ -864,11 +864,17 @@ rustc_queries! {
         /// type-checking etc, and it does not normalize specializable
         /// associated types. This is almost always what you want,
         /// unless you are doing MIR optimizations, in which case you
-        /// might want to use `reveal_all()` method to change modes.
         query param_env(def_id: DefId) -> ty::ParamEnv<'tcx> {
             desc { |tcx| "computing normalized predicates of `{}`", tcx.def_path_str(def_id) }
         }
 
+        /// Like `param_env`, but returns the `ParamEnv in `Reveal::All` mode.
+        /// Prefer this over `tcx.param_env(def_id).with_reveal_all_normalized(tcx)`,
+        /// as this method is more efficient.
+        query param_env_reveal_all_normalized(def_id: DefId) -> ty::ParamEnv<'tcx> {
+            desc { |tcx| "computing revealed normalized predicates of `{}`", tcx.def_path_str(def_id) }
+        }
+
         /// Trait selection queries. These are best used by invoking `ty.is_copy_modulo_regions()`,
         /// `ty.is_copy()`, etc, since that will prune the environment where possible.
         query is_copy_raw(env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
@@ -1527,5 +1533,9 @@ rustc_queries! {
                 ty::Instance::new(key.value.0.to_def_id(), key.value.2),
             }
         }
+
+        query normalize_opaque_types(key: &'tcx ty::List<ty::Predicate<'tcx>>) -> &'tcx ty::List<ty::Predicate<'tcx>> {
+            desc { "normalizing opaque types in {:?}", key }
+        }
     }
 }
diff --git a/src/librustc_middle/ty/layout.rs b/src/librustc_middle/ty/layout.rs
@@ -1921,7 +1921,7 @@ impl<'tcx> LayoutOf for LayoutCx<'tcx, TyCtxt<'tcx>> {
     /// Computes the layout of a type. Note that this implicitly
     /// executes in "reveal all" mode.
     fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyAndLayout {
-        let param_env = self.param_env.with_reveal_all();
+        let param_env = self.param_env.with_reveal_all_normalized(self.tcx);
         let ty = self.tcx.normalize_erasing_regions(param_env, ty);
         let layout = self.tcx.layout_raw(param_env.and(ty))?;
         let layout = TyAndLayout { ty, layout };
@@ -1945,7 +1945,7 @@ impl LayoutOf for LayoutCx<'tcx, ty::query::TyCtxtAt<'tcx>> {
     /// Computes the layout of a type. Note that this implicitly
     /// executes in "reveal all" mode.
     fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyAndLayout {
-        let param_env = self.param_env.with_reveal_all();
+        let param_env = self.param_env.with_reveal_all_normalized(*self.tcx);
         let ty = self.tcx.normalize_erasing_regions(param_env, ty);
         let layout = self.tcx.layout_raw(param_env.and(ty))?;
         let layout = TyAndLayout { ty, layout };
diff --git a/src/librustc_middle/ty/mod.rs b/src/librustc_middle/ty/mod.rs
@@ -1,5 +1,5 @@
 // ignore-tidy-filelength
-pub use self::fold::{TypeFoldable, TypeVisitor};
+pub use self::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 pub use self::AssocItemContainer::*;
 pub use self::BorrowKind::*;
 pub use self::IntVarValue::*;
@@ -1819,9 +1819,15 @@ impl<'tcx> ParamEnv<'tcx> {
     /// the desired behavior during codegen and certain other special
     /// contexts; normally though we want to use `Reveal::UserFacing`,
     /// which is the default.
-    pub fn with_reveal_all(mut self) -> Self {
-        self.packed_data |= 1;
-        self
+    /// All opaque types in the caller_bounds of the `ParamEnv`
+    /// will be normalized to their underlying types.
+    /// See PR #65989 and issue #65918 for more details
+    pub fn with_reveal_all_normalized(mut self) -> Self {
+        if self.packed_data & 1 == 1 {
+            return self;
+        }
+
+        ParamEnv::new(tcx.normalize_opaque_types(self.caller_bounds()), Reveal::All, self.def_id)
     }
 
     /// Returns this same environment but with no caller bounds.
@@ -3067,6 +3073,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
     context::provide(providers);
     erase_regions::provide(providers);
     layout::provide(providers);
+    util::provide(providers);
     super::util::bug::provide(providers);
     *providers = ty::query::Providers {
         trait_impls_of: trait_def::trait_impls_of_provider,
diff --git a/src/librustc_middle/ty/query/keys.rs b/src/librustc_middle/ty/query/keys.rs
@@ -270,6 +270,17 @@ impl<'tcx> Key for Ty<'tcx> {
     }
 }
 
+impl<'tcx> Key for &'tcx ty::List<ty::Predicate<'tcx>> {
+    type CacheSelector = DefaultCacheSelector;
+
+    fn query_crate(&self) -> CrateNum {
+        LOCAL_CRATE
+    }
+    fn default_span(&self, _: TyCtxt<'_>) -> Span {
+        DUMMY_SP
+    }
+}
+
 impl<'tcx> Key for ty::ParamEnv<'tcx> {
     type CacheSelector = DefaultCacheSelector;
 
diff --git a/src/librustc_middle/ty/util.rs b/src/librustc_middle/ty/util.rs
@@ -3,11 +3,12 @@
 use crate::ich::NodeIdHashingMode;
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::mir::interpret::{sign_extend, truncate};
+use crate::ty::fold::TypeFolder;
 use crate::ty::layout::IntegerExt;
 use crate::ty::query::TyCtxtAt;
 use crate::ty::subst::{GenericArgKind, InternalSubsts, Subst, SubstsRef};
 use crate::ty::TyKind::*;
-use crate::ty::{self, DefIdTree, GenericParamDefKind, Ty, TyCtxt, TypeFoldable};
+use crate::ty::{self, DefIdTree, GenericParamDefKind, List, Ty, TyCtxt, TypeFoldable};
 use rustc_apfloat::Float as _;
 use rustc_ast::ast;
 use rustc_attr::{self as attr, SignedInt, UnsignedInt};
@@ -557,82 +558,84 @@ impl<'tcx> TyCtxt<'tcx> {
         def_id: DefId,
         substs: SubstsRef<'tcx>,
     ) -> Result<Ty<'tcx>, Ty<'tcx>> {
-        use crate::ty::fold::TypeFolder;
-
-        struct OpaqueTypeExpander<'tcx> {
-            // Contains the DefIds of the opaque types that are currently being
-            // expanded. When we expand an opaque type we insert the DefId of
-            // that type, and when we finish expanding that type we remove the
-            // its DefId.
-            seen_opaque_tys: FxHashSet<DefId>,
-            // Cache of all expansions we've seen so far. This is a critical
-            // optimization for some large types produced by async fn trees.
-            expanded_cache: FxHashMap<(DefId, SubstsRef<'tcx>), Ty<'tcx>>,
-            primary_def_id: DefId,
-            found_recursion: bool,
-            tcx: TyCtxt<'tcx>,
-        }
-
-        impl<'tcx> OpaqueTypeExpander<'tcx> {
-            fn expand_opaque_ty(
-                &mut self,
-                def_id: DefId,
-                substs: SubstsRef<'tcx>,
-            ) -> Option<Ty<'tcx>> {
-                if self.found_recursion {
-                    return None;
-                }
-                let substs = substs.fold_with(self);
-                if self.seen_opaque_tys.insert(def_id) {
-                    let expanded_ty = match self.expanded_cache.get(&(def_id, substs)) {
-                        Some(expanded_ty) => expanded_ty,
-                        None => {
-                            let generic_ty = self.tcx.type_of(def_id);
-                            let concrete_ty = generic_ty.subst(self.tcx, substs);
-                            let expanded_ty = self.fold_ty(concrete_ty);
-                            self.expanded_cache.insert((def_id, substs), expanded_ty);
-                            expanded_ty
-                        }
-                    };
-                    self.seen_opaque_tys.remove(&def_id);
-                    Some(expanded_ty)
-                } else {
-                    // If another opaque type that we contain is recursive, then it
-                    // will report the error, so we don't have to.
-                    self.found_recursion = def_id == self.primary_def_id;
-                    None
-                }
-            }
-        }
-
-        impl<'tcx> TypeFolder<'tcx> for OpaqueTypeExpander<'tcx> {
-            fn tcx(&self) -> TyCtxt<'tcx> {
-                self.tcx
-            }
-
-            fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-                if let ty::Opaque(def_id, substs) = t.kind {
-                    self.expand_opaque_ty(def_id, substs).unwrap_or(t)
-                } else if t.has_opaque_types() {
-                    t.super_fold_with(self)
-                } else {
-                    t
-                }
-            }
-        }
-
         let mut visitor = OpaqueTypeExpander {
             seen_opaque_tys: FxHashSet::default(),
             expanded_cache: FxHashMap::default(),
-            primary_def_id: def_id,
+            primary_def_id: Some(def_id),
             found_recursion: false,
+            check_recursion: true,
             tcx: self,
         };
+
         let expanded_type = visitor.expand_opaque_ty(def_id, substs).unwrap();
         if visitor.found_recursion { Err(expanded_type) } else { Ok(expanded_type) }
     }
 }
 
+struct OpaqueTypeExpander<'tcx> {
+    // Contains the DefIds of the opaque types that are currently being
+    // expanded. When we expand an opaque type we insert the DefId of
+    // that type, and when we finish expanding that type we remove the
+    // its DefId.
+    seen_opaque_tys: FxHashSet<DefId>,
+    // Cache of all expansions we've seen so far. This is a critical
+    // optimization for some large types produced by async fn trees.
+    expanded_cache: FxHashMap<(DefId, SubstsRef<'tcx>), Ty<'tcx>>,
+    primary_def_id: Option<DefId>,
+    found_recursion: bool,
+    /// Whether or not to check for recursive opaque types.
+    /// This is `true` when we're explicitly checking for opaque type
+    /// recursion, and 'false' otherwise to avoid unecessary work.
+    check_recursion: bool,
+    tcx: TyCtxt<'tcx>,
+}
+
+impl<'tcx> OpaqueTypeExpander<'tcx> {
+    fn expand_opaque_ty(&mut self, def_id: DefId, substs: SubstsRef<'tcx>) -> Option<Ty<'tcx>> {
+        if self.found_recursion {
+            return None;
+        }
+        let substs = substs.fold_with(self);
+        if !self.check_recursion || self.seen_opaque_tys.insert(def_id) {
+            let expanded_ty = match self.expanded_cache.get(&(def_id, substs)) {
+                Some(expanded_ty) => expanded_ty,
+                None => {
+                    let generic_ty = self.tcx.type_of(def_id);
+                    let concrete_ty = generic_ty.subst(self.tcx, substs);
+                    let expanded_ty = self.fold_ty(concrete_ty);
+                    self.expanded_cache.insert((def_id, substs), expanded_ty);
+                    expanded_ty
+                }
+            };
+            if self.check_recursion {
+                self.seen_opaque_tys.remove(&def_id);
+            }
+            Some(expanded_ty)
+        } else {
+            // If another opaque type that we contain is recursive, then it
+            // will report the error, so we don't have to.
+            self.found_recursion = def_id == *self.primary_def_id.as_ref().unwrap();
+            None
+        }
+    }
+}
+
+impl<'tcx> TypeFolder<'tcx> for OpaqueTypeExpander<'tcx> {
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
+        if let ty::Opaque(def_id, substs) = t.kind {
+            self.expand_opaque_ty(def_id, substs).unwrap_or(t)
+        } else if t.has_opaque_types() {
+            t.super_fold_with(self)
+        } else {
+            t
+        }
+    }
+}
+
 impl<'tcx> ty::TyS<'tcx> {
     /// Returns the maximum value for the given numeric type (including `char`s)
     /// or returns `None` if the type is not numeric.
@@ -1142,3 +1145,24 @@ pub fn needs_drop_components(
 
 #[derive(Copy, Clone, Debug, HashStable, RustcEncodable, RustcDecodable)]
 pub struct AlwaysRequiresDrop;
+
+/// Normalizes all opaque types in the given value, replacing them
+/// with their underlying types.
+pub fn normalize_opaque_types(
+    tcx: TyCtxt<'tcx>,
+    val: &'tcx List<ty::Predicate<'tcx>>,
+) -> &'tcx List<ty::Predicate<'tcx>> {
+    let mut visitor = OpaqueTypeExpander {
+        seen_opaque_tys: FxHashSet::default(),
+        expanded_cache: FxHashMap::default(),
+        primary_def_id: None,
+        found_recursion: false,
+        check_recursion: false,
+        tcx,
+    };
+    val.fold_with(&mut visitor)
+}
+
+pub fn provide(providers: &mut ty::query::Providers<'_>) {
+    *providers = ty::query::Providers { normalize_opaque_types, ..*providers }
+}
diff --git a/src/librustc_mir/shim.rs b/src/librustc_mir/shim.rs
@@ -193,7 +193,7 @@ fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>)
             );
         }
         let patch = {
-            let param_env = tcx.param_env(def_id).with_reveal_all();
+            let param_env = tcx.param_env_reveal_all_normalized(def_id);
             let mut elaborator =
                 DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };
             let dropee = tcx.mk_place_deref(dropee_ptr);
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
@@ -328,7 +328,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
     ) -> ConstPropagator<'mir, 'tcx> {
         let def_id = source.def_id();
         let substs = &InternalSubsts::identity_for_item(tcx, def_id);
-        let param_env = tcx.param_env(def_id).with_reveal_all();
+        let param_env = tcx.param_env_reveal_all_normalized(def_id);
 
         let span = tcx.def_span(def_id);
         let can_const_prop = CanConstProp::check(body);
diff --git a/src/librustc_mir/transform/elaborate_drops.rs b/src/librustc_mir/transform/elaborate_drops.rs
@@ -25,7 +25,7 @@ impl<'tcx> MirPass<'tcx> for ElaborateDrops {
         debug!("elaborate_drops({:?} @ {:?})", src, body.span);
 
         let def_id = src.def_id();
-        let param_env = tcx.param_env(src.def_id()).with_reveal_all();
+        let param_env = tcx.param_env_reveal_all_normalized(src.def_id());
         let move_data = match MoveData::gather_moves(body, tcx, param_env) {
             Ok(move_data) => move_data,
             Err((move_data, _)) => {
diff --git a/src/librustc_mir/transform/inline.rs b/src/librustc_mir/transform/inline.rs
@@ -72,7 +72,7 @@ impl Inliner<'tcx> {
 
         let mut callsites = VecDeque::new();
 
-        let param_env = self.tcx.param_env(self.source.def_id()).with_reveal_all();
+        let param_env = self.tcx.param_env_reveal_all_normalized(self.source.def_id());
 
         // Only do inlining into fn bodies.
         let id = self.tcx.hir().as_local_hir_id(self.source.def_id().expect_local());
diff --git a/src/librustc_mir_build/hair/pattern/mod.rs b/src/librustc_mir_build/hair/pattern/mod.rs
@@ -781,7 +781,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         // Use `Reveal::All` here because patterns are always monomorphic even if their function
         // isn't.
-        let param_env_reveal_all = self.param_env.with_reveal_all();
+        let param_env_reveal_all = self.param_env.with_reveal_all_normalized(self.tcx);
         let substs = self.typeck_results.node_substs(id);
         let instance = match ty::Instance::resolve(self.tcx, param_env_reveal_all, def_id, substs) {
             Ok(Some(i)) => i,
diff --git a/src/librustc_symbol_mangling/v0.rs b/src/librustc_symbol_mangling/v0.rs
@@ -271,7 +271,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
         let key = self.tcx.def_key(impl_def_id);
         let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };
 
-        let mut param_env = self.tcx.param_env(impl_def_id).with_reveal_all();
+        let mut param_env = self.tcx.param_env_reveal_all_normalized(impl_def_id);
         if !substs.is_empty() {
             param_env = param_env.subst(self.tcx, substs);
         }
diff --git a/src/librustc_ty/instance.rs b/src/librustc_ty/instance.rs
@@ -137,7 +137,7 @@ fn resolve_associated_item<'tcx>(
                 });
 
             let substs = tcx.infer_ctxt().enter(|infcx| {
-                let param_env = param_env.with_reveal_all();
+                let param_env = param_env.with_reveal_all_normalized(tcx);
                 let substs = rcvr_substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
                 let substs = translate_substs(
                     &infcx,
diff --git a/src/librustc_ty/ty.rs b/src/librustc_ty/ty.rs
@@ -276,6 +276,10 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
     traits::normalize_param_env_or_error(tcx, def_id, unnormalized_env, cause)
 }
 
+fn param_env_reveal_all_normalized(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
+    tcx.param_env(def_id).with_reveal_all_normalized(tcx)
+}
+
 fn crate_disambiguator(tcx: TyCtxt<'_>, crate_num: CrateNum) -> CrateDisambiguator {
     assert_eq!(crate_num, LOCAL_CRATE);
     tcx.sess.local_crate_disambiguator()
@@ -503,6 +507,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
         adt_sized_constraint,
         def_span,
         param_env,
+        param_env_reveal_all_normalized,
         trait_of_item,
         crate_disambiguator,
         original_crate_name,

Original file line number	Diff line number	Diff line change
`@@ -18,7 +18,7 @@ impl<'tcx> TyCtxt<'tcx> {`
`18`	`18`	`let substs = InternalSubsts::identity_for_item(self, def_id);`
`19`	`19`	`let instance = ty::Instance::new(def_id, substs);`
`20`	`20`	`let cid = GlobalId { instance, promoted: None };`
`21`		`- let param_env = self.param_env(def_id).with_reveal_all();`
	`21`	`+ let param_env = self.param_env(def_id).with_reveal_all_normalized(self);`
`22`	`22`	`self.const_eval_global_id(param_env, cid, None)`
`23`	`23`	`}`
`24`	`24`
Original file line number	Diff line number	Diff line change
`@@ -78,7 +78,7 @@ impl<'tcx> ConstValue<'tcx> {`
`78`	`78`	`param_env: ParamEnv<'tcx>,`
`79`	`79`	`ty: Ty<'tcx>,`
`80`	`80`	`) -> Option<u128> {`
`81`		`- let size = tcx.layout_of(param_env.with_reveal_all().and(ty)).ok()?.size;`
	`81`	`+ let size = tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(ty)).ok()?.size;`
`82`	`82`	`self.try_to_bits(size)`
`83`	`83`	`}`
`84`	`84`
Original file line number	Diff line number	Diff line change
`@@ -864,11 +864,17 @@ rustc_queries! {`
`864`	`864`	`/// type-checking etc, and it does not normalize specializable`
`865`	`865`	`/// associated types. This is almost always what you want,`
`866`	`866`	`/// unless you are doing MIR optimizations, in which case you`
`867`		- /// might want to use `reveal_all()` method to change modes.
`868`	`867`	`query param_env(def_id: DefId) -> ty::ParamEnv<'tcx> {`
`869`	`868`	desc { \|tcx\| "computing normalized predicates of `{}`", tcx.def_path_str(def_id) }
`870`	`869`	`}`
`871`	`870`
	`871`	+ /// Like `param_env`, but returns the `ParamEnv in `Reveal::All` mode.
	`872`	+ /// Prefer this over `tcx.param_env(def_id).with_reveal_all_normalized(tcx)`,
	`873`	`+ /// as this method is more efficient.`
	`874`	`+ query param_env_reveal_all_normalized(def_id: DefId) -> ty::ParamEnv<'tcx> {`
	`875`	+ desc { \|tcx\| "computing revealed normalized predicates of `{}`", tcx.def_path_str(def_id) }
	`876`	`+ }`
	`877`	`+`
`872`	`878`	/// Trait selection queries. These are best used by invoking `ty.is_copy_modulo_regions()`,
`873`	`879`	/// `ty.is_copy()`, etc, since that will prune the environment where possible.
`874`	`880`	`query is_copy_raw(env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {`
`@@ -1527,5 +1533,9 @@ rustc_queries! {`
`1527`	`1533`	`ty::Instance::new(key.value.0.to_def_id(), key.value.2),`
`1528`	`1534`	`}`
`1529`	`1535`	`}`
	`1536`	`+`
	`1537`	`+ query normalize_opaque_types(key: &'tcx ty::List<ty::Predicate<'tcx>>) -> &'tcx ty::List<ty::Predicate<'tcx>> {`
	`1538`	`+ desc { "normalizing opaque types in {:?}", key }`
	`1539`	`+ }`
`1530`	`1540`	`}`
`1531`	`1541`	`}`
Original file line number	Diff line number	Diff line change
`@@ -193,7 +193,7 @@ fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>)`
`193`	`193`	`);`
`194`	`194`	`}`
`195`	`195`	`let patch = {`
`196`		`- let param_env = tcx.param_env(def_id).with_reveal_all();`
	`196`	`+ let param_env = tcx.param_env_reveal_all_normalized(def_id);`
`197`	`197`	`let mut elaborator =`
`198`	`198`	`DropShimElaborator { body: &body, patch: MirPatch::new(&body), tcx, param_env };`
`199`	`199`	`let dropee = tcx.mk_place_deref(dropee_ptr);`
Original file line number	Diff line number	Diff line change
`@@ -271,7 +271,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {`
`271`	`271`	`let key = self.tcx.def_key(impl_def_id);`
`272`	`272`	`let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };`
`273`	`273`
`274`		`- let mut param_env = self.tcx.param_env(impl_def_id).with_reveal_all();`
	`274`	`+ let mut param_env = self.tcx.param_env_reveal_all_normalized(impl_def_id);`
`275`	`275`	`if !substs.is_empty() {`
`276`	`276`	`param_env = param_env.subst(self.tcx, substs);`
`277`	`277`	`}`