the environment round here is awfully empty

capitalism

2 files changed, 15 insertions, 23 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
index b1ac02d9fed..8a1be7ea172 100644
--- a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
+++ b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
@@ -72,17 +72,16 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
                 // We were unable to unify the abstract constant with
                 // a constant found in the caller bounds, there are
                 // now three possible cases here.
-                //
-                // - The substs are concrete enough that we can simply
-                //   try and evaluate the given constant.
-                // - The abstract const still references an inference
-                //   variable, in this case we return `TooGeneric`.
-                // - The abstract const references a generic parameter,
-                //   this means that we emit an error here.
                 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
                 enum FailureKind {
+                    /// The abstract const still references an inference
+                    /// variable, in this case we return `TooGeneric`.
                     MentionsInfer,
+                    /// The abstract const references a generic parameter,
+                    /// this means that we emit an error here.
                     MentionsParam,
+                    /// The substs are concrete enough that we can simply
+                    /// try and evaluate the given constant.
                     Concrete,
                 }
                 let mut failure_kind = FailureKind::Concrete;
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index 69f66f6e6b1..e6a1cf58fe3 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -200,22 +200,15 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             if let Some(def) = aty.ty_adt_def() {
                 // We also want to be able to select the array's type's original
                 // signature with no type arguments resolved
-                flags.push((
-                    sym::_Self,
-                    Some(format!("[{}]", self.tcx.type_of(def.did).to_string())),
-                ));
-                let tcx = self.tcx;
-                if let Some(len) = len.try_eval_usize(tcx, ty::ParamEnv::empty()) {
-                    flags.push((
-                        sym::_Self,
-                        Some(format!("[{}; {}]", self.tcx.type_of(def.did).to_string(), len)),
-                    ));
-                } else {
-                    flags.push((
-                        sym::_Self,
-                        Some(format!("[{}; _]", self.tcx.type_of(def.did).to_string())),
-                    ));
-                }
+                let type_string = self.tcx.type_of(def.did).to_string();
+                flags.push((sym::_Self, Some(format!("[{}]", type_string))));
+
+                let len = len.val.try_to_value().and_then(|v| v.try_to_machine_usize(self.tcx));
+                let string = match len {
+                    Some(n) => format!("[{}; {}]", type_string, n),
+                    None => format!("[{}; _]", type_string),
+                };
+                flags.push((sym::_Self, Some(string)));
             }
         }
         if let ty::Dynamic(traits, _) = self_ty.kind() {