4 files changed, 29 insertions, 24 deletions
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 41a8bc10c8d..56c38baa2df 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -2221,7 +2221,7 @@ impl<'tcx> TyCtxt<'tcx> {
         let adt_def = self.adt_def(wrapper_def_id);
         let substs =
             InternalSubsts::for_item(self, wrapper_def_id, |param, substs| match param.kind {
-                GenericParamDefKind::Lifetime | GenericParamDefKind::Const => bug!(),
+                GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => bug!(),
                 GenericParamDefKind::Type { has_default, .. } => {
                     if param.index == 0 {
                         ty_param.into()
@@ -2416,7 +2416,7 @@ impl<'tcx> TyCtxt<'tcx> {
                 self.mk_region(ty::ReEarlyBound(param.to_early_bound_region_data())).into()
             }
             GenericParamDefKind::Type { .. } => self.mk_ty_param(param.index, param.name).into(),
-            GenericParamDefKind::Const => {
+            GenericParamDefKind::Const { .. } => {
                 self.mk_const_param(param.index, param.name, self.type_of(param.def_id)).into()
             }
         }
diff --git a/compiler/rustc_middle/src/ty/generics.rs b/compiler/rustc_middle/src/ty/generics.rs
index 79cd26f5668..ef46a419964 100644
--- a/compiler/rustc_middle/src/ty/generics.rs
+++ b/compiler/rustc_middle/src/ty/generics.rs
@@ -18,7 +18,9 @@ pub enum GenericParamDefKind {
         object_lifetime_default: ObjectLifetimeDefault,
         synthetic: Option<hir::SyntheticTyParamKind>,
     },
-    Const,
+    Const {
+        has_default: bool,
+    },
 }
 
 impl GenericParamDefKind {
@@ -26,14 +28,14 @@ impl GenericParamDefKind {
         match self {
             GenericParamDefKind::Lifetime => "lifetime",
             GenericParamDefKind::Type { .. } => "type",
-            GenericParamDefKind::Const => "constant",
+            GenericParamDefKind::Const { .. } => "constant",
         }
     }
     pub fn to_ord(&self, tcx: TyCtxt<'_>) -> ast::ParamKindOrd {
         match self {
             GenericParamDefKind::Lifetime => ast::ParamKindOrd::Lifetime,
             GenericParamDefKind::Type { .. } => ast::ParamKindOrd::Type,
-            GenericParamDefKind::Const => {
+            GenericParamDefKind::Const { .. } => {
                 ast::ParamKindOrd::Const { unordered: tcx.features().const_generics }
             }
         }
@@ -105,7 +107,7 @@ impl<'tcx> Generics {
             match param.kind {
                 GenericParamDefKind::Lifetime => own_counts.lifetimes += 1,
                 GenericParamDefKind::Type { .. } => own_counts.types += 1,
-                GenericParamDefKind::Const => own_counts.consts += 1,
+                GenericParamDefKind::Const { .. } => own_counts.consts += 1,
             }
         }
 
@@ -118,12 +120,10 @@ impl<'tcx> Generics {
         for param in &self.params {
             match param.kind {
                 GenericParamDefKind::Lifetime => (),
-                GenericParamDefKind::Type { has_default, .. } => {
+                GenericParamDefKind::Type { has_default, .. } |
+                GenericParamDefKind::Const { has_default } => {
                     own_defaults.types += has_default as usize;
                 }
-                GenericParamDefKind::Const => {
-                    // FIXME(const_generics:defaults)
-                }
             }
         }
 
@@ -146,7 +146,7 @@ impl<'tcx> Generics {
     pub fn own_requires_monomorphization(&self) -> bool {
         for param in &self.params {
             match param.kind {
-                GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => return true,
+                GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => return true,
                 GenericParamDefKind::Lifetime => {}
             }
         }
@@ -189,7 +189,7 @@ impl<'tcx> Generics {
     pub fn const_param(&'tcx self, param: &ParamConst, tcx: TyCtxt<'tcx>) -> &GenericParamDef {
         let param = self.param_at(param.index as usize, tcx);
         match param.kind {
-            GenericParamDefKind::Const => param,
+            GenericParamDefKind::Const { .. } => param,
             _ => bug!("expected const parameter, but found another generic parameter"),
         }
     }
diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs
index 23cedfd499e..f61b6946985 100644
--- a/compiler/rustc_middle/src/ty/instance.rs
+++ b/compiler/rustc_middle/src/ty/instance.rs
@@ -593,7 +593,7 @@ fn polymorphize<'tcx>(
                 },
 
             // Simple case: If parameter is a const or type parameter..
-            ty::GenericParamDefKind::Const | ty::GenericParamDefKind::Type { .. } if
+            ty::GenericParamDefKind::Const { .. } | ty::GenericParamDefKind::Type { .. } if
                 // ..and is within range and unused..
                 unused.contains(param.index).unwrap_or(false) =>
                     // ..then use the identity for this parameter.
diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
index 77f16688937..ad323df8a69 100644
--- a/compiler/rustc_middle/src/ty/print/mod.rs
+++ b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -193,17 +193,22 @@ pub trait Printer<'tcx>: Sized {
             .params
             .iter()
             .rev()
-            .take_while(|param| {
-                match param.kind {
-                    ty::GenericParamDefKind::Lifetime => false,
-                    ty::GenericParamDefKind::Type { has_default, .. } => {
-                        has_default
-                            && substs[param.index as usize]
-                                == GenericArg::from(
-                                    self.tcx().type_of(param.def_id).subst(self.tcx(), substs),
-                                )
-                    }
-                    ty::GenericParamDefKind::Const => false, // FIXME(const_generics_defaults)
+            .take_while(|param| match param.kind {
+                ty::GenericParamDefKind::Lifetime => false,
+                ty::GenericParamDefKind::Type { has_default, .. } => {
+                    has_default
+                        && substs[param.index as usize]
+                            == GenericArg::from(
+                                self.tcx().type_of(param.def_id).subst(self.tcx(), substs),
+                            )
+                }
+                ty::GenericParamDefKind::Const { has_default } => {
+                    has_default
+                        && substs[param.index as usize]
+                            == GenericArg::from(crate::ty::Const::from_anon_const(
+                                self.tcx(),
+                                param.def_id.expect_local(),
+                            ))
                 }
             })
             .count();