Add Const generic param to ty

Co-Authored-By: NGabriel Smith <yodaldevoid@users.noreply.github.com>

src/librustc/ty/mod.rs

@@ -837,7 +837,8 @@ pub enum GenericParamDefKind {
         has_default: bool,
         object_lifetime_default: ObjectLifetimeDefault,
         synthetic: Option<hir::SyntheticTyParamKind>,
-    }
+    },
+    Const,
 }
 
 #[derive(Clone, RustcEncodable, RustcDecodable)]
@@ -880,6 +881,7 @@ pub fn to_bound_region(&self) -> ty::BoundRegion {
 pub struct GenericParamCount {
     pub lifetimes: usize,
     pub types: usize,
+    pub consts: usize,
 }
 
 /// Information about the formal type/lifetime parameters associated
@@ -915,6 +917,7 @@ pub fn own_counts(&self) -> GenericParamCount {
             match param.kind {
                 GenericParamDefKind::Lifetime => own_counts.lifetimes += 1,
                 GenericParamDefKind::Type { .. } => own_counts.types += 1,
+                GenericParamDefKind::Const => own_counts.consts += 1,
             };
         }
 
@@ -924,7 +927,7 @@ pub fn own_counts(&self) -> GenericParamCount {
     pub fn requires_monomorphization(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> bool {
         for param in &self.params {
             match param.kind {
-                GenericParamDefKind::Type { .. } => return true,
+                GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => return true,
                 GenericParamDefKind::Lifetime => {}
             }
         }
@@ -944,7 +947,7 @@ pub fn region_param(&'tcx self,
         if let Some(index) = param.index.checked_sub(self.parent_count as u32) {
             let param = &self.params[index as usize];
             match param.kind {
-                ty::GenericParamDefKind::Lifetime => param,
+                GenericParamDefKind::Lifetime => param,
                 _ => bug!("expected lifetime parameter, but found another generic parameter")
             }
         } else {
@@ -961,7 +964,7 @@ pub fn type_param(&'tcx self,
         if let Some(index) = param.idx.checked_sub(self.parent_count as u32) {
             let param = &self.params[index as usize];
             match param.kind {
-                ty::GenericParamDefKind::Type {..} => param,
+                GenericParamDefKind::Type { .. } => param,
                 _ => bug!("expected type parameter, but found another generic parameter")
             }
         } else {
@@ -969,6 +972,23 @@ pub fn type_param(&'tcx self,
                .type_param(param, tcx)
         }
     }
+
+    /// Returns the `ConstParameterDef` associated with this `ParamConst`.
+    pub fn const_param(&'tcx self,
+                       param: &ParamConst,
+                       tcx: TyCtxt<'a, 'gcx, 'tcx>)
+                       -> &GenericParamDef {
+        if let Some(index) = param.index.checked_sub(self.parent_count as u32) {
+            let param = &self.params[index as usize];
+            match param.kind {
+                GenericParamDefKind::Const => param,
+                _ => bug!("expected const parameter, but found another generic parameter")
+            }
+        } else {
+            tcx.generics_of(self.parent.expect("parent_count>0 but no parent?"))
+                .const_param(param, tcx)
+        }
+    }
 }
 
 /// Bounds on generics.