5 files changed, 68 insertions, 14 deletions

diff --git a/crates/hir_def/src/generics.rs b/crates/hir_def/src/generics.rs
index bb8fca009..9b5b886c2 100644
--- a/crates/hir_def/src/generics.rs
+++ b/crates/hir_def/src/generics.rs
@@ -21,11 +21,11 @@ use crate::{
     keys,
     src::{HasChildSource, HasSource},
     type_ref::{LifetimeRef, TypeBound, TypeRef},
-    AdtId, GenericDefId, LifetimeParamId, LocalLifetimeParamId, LocalTypeParamId, Lookup,
-    TypeParamId,
+    AdtId, ConstParamId, GenericDefId, LifetimeParamId, LocalConstParamId, LocalLifetimeParamId,
+    LocalTypeParamId, Lookup, TypeParamId,
 };
 
-/// Data about a generic parameter (to a function, struct, impl, ...).
+/// Data about a generic type parameter (to a function, struct, impl, ...).
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct TypeParamData {
     pub name: Option<Name>,
@@ -33,12 +33,19 @@ pub struct TypeParamData {
     pub provenance: TypeParamProvenance,
 }
 
-/// Data about a generic parameter (to a function, struct, impl, ...).
+/// Data about a generic lifetime parameter (to a function, struct, impl, ...).
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct LifetimeParamData {
     pub name: Name,
 }
 
+/// Data about a generic const parameter (to a function, struct, impl, ...).
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct ConstParamData {
+    pub name: Name,
+    pub ty: TypeRef,
+}
+
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub enum TypeParamProvenance {
     TypeParamList,
@@ -51,6 +58,7 @@ pub enum TypeParamProvenance {
 pub struct GenericParams {
     pub types: Arena<TypeParamData>,
     pub lifetimes: Arena<LifetimeParamData>,
+    pub consts: Arena<ConstParamData>,
     pub where_predicates: Vec<WherePredicate>,
 }
 
@@ -76,6 +84,7 @@ pub enum WherePredicateTypeTarget {
 pub(crate) struct SourceMap {
     pub(crate) type_params: ArenaMap<LocalTypeParamId, Either<ast::Trait, ast::TypeParam>>,
     lifetime_params: ArenaMap<LocalLifetimeParamId, ast::LifetimeParam>,
+    const_params: ArenaMap<LocalConstParamId, ast::ConstParam>,
 }
 
 impl GenericParams {
@@ -268,6 +277,13 @@ impl GenericParams {
             let lifetime_ref = LifetimeRef::new_name(name);
             self.fill_bounds(&lower_ctx, &lifetime_param, Either::Right(lifetime_ref));
         }
+        for const_param in params.const_params() {
+            let name = const_param.name().map_or_else(Name::missing, |it| it.as_name());
+            let ty = const_param.ty().map_or(TypeRef::Error, |it| TypeRef::from_ast(lower_ctx, it));
+            let param = ConstParamData { name, ty };
+            let param_id = self.consts.alloc(param);
+            sm.const_params.insert(param_id, const_param.clone());
+        }
     }
 
     fn fill_where_predicates(&mut self, lower_ctx: &LowerCtx, where_clause: ast::WhereClause) {
@@ -353,12 +369,16 @@ impl GenericParams {
         });
     }
 
-    pub fn find_by_name(&self, name: &Name) -> Option<LocalTypeParamId> {
+    pub fn find_type_by_name(&self, name: &Name) -> Option<LocalTypeParamId> {
         self.types
             .iter()
             .find_map(|(id, p)| if p.name.as_ref() == Some(name) { Some(id) } else { None })
     }
 
+    pub fn find_const_by_name(&self, name: &Name) -> Option<LocalConstParamId> {
+        self.consts.iter().find_map(|(id, p)| if p.name == *name { Some(id) } else { None })
+    }
+
     pub fn find_trait_self_param(&self) -> Option<LocalTypeParamId> {
         self.types.iter().find_map(|(id, p)| {
             if p.provenance == TypeParamProvenance::TraitSelf {
@@ -390,6 +410,16 @@ impl HasChildSource<LocalLifetimeParamId> for GenericDefId {
     }
 }
 
+impl HasChildSource<LocalConstParamId> for GenericDefId {
+    type Value = ast::ConstParam;
+    fn child_source(
+        &self,
+        db: &dyn DefDatabase,
+    ) -> InFile<ArenaMap<LocalConstParamId, Self::Value>> {
+        GenericParams::new(db, *self).1.map(|source_maps| source_maps.const_params)
+    }
+}
+
 impl ChildBySource for GenericDefId {
     fn child_by_source(&self, db: &dyn DefDatabase) -> DynMap {
         let mut res = DynMap::default();
@@ -406,6 +436,10 @@ impl ChildBySource for GenericDefId {
             let id = LifetimeParamId { parent: *self, local_id };
             res[keys::LIFETIME_PARAM].insert(sm.with_value(src.clone()), id);
         }
+        for (local_id, src) in sm.value.const_params.iter() {
+            let id = ConstParamId { parent: *self, local_id };
+            res[keys::CONST_PARAM].insert(sm.with_value(src.clone()), id);
+        }
         res
     }
 }
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index 100dbf5d6..b6f510731 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -260,6 +260,7 @@ impl GenericParamsStorage {
     fn alloc(&mut self, params: GenericParams) -> GenericParamsId {
         if params.types.is_empty()
             && params.lifetimes.is_empty()
+            && params.consts.is_empty()
             && params.where_predicates.is_empty()
         {
             return GenericParamsId::EMPTY;
@@ -269,8 +270,12 @@ impl GenericParamsStorage {
     }
 }
 
-static EMPTY_GENERICS: GenericParams =
-    GenericParams { types: Arena::new(), lifetimes: Arena::new(), where_predicates: Vec::new() };
+static EMPTY_GENERICS: GenericParams = GenericParams {
+    types: Arena::new(),
+    lifetimes: Arena::new(),
+    consts: Arena::new(),
+    where_predicates: Vec::new(),
+};
 
 #[derive(Default, Debug, Eq, PartialEq)]
 struct ItemTreeData {
diff --git a/crates/hir_def/src/keys.rs b/crates/hir_def/src/keys.rs
index 9c585de2c..89b3ed868 100644
--- a/crates/hir_def/src/keys.rs
+++ b/crates/hir_def/src/keys.rs
@@ -8,8 +8,8 @@ use syntax::{ast, AstNode, AstPtr};
 
 use crate::{
     dyn_map::{DynMap, Policy},
-    ConstId, EnumId, EnumVariantId, FieldId, FunctionId, ImplId, LifetimeParamId, StaticId,
-    StructId, TraitId, TypeAliasId, TypeParamId, UnionId,
+    ConstId, ConstParamId, EnumId, EnumVariantId, FieldId, FunctionId, ImplId, LifetimeParamId,
+    StaticId, StructId, TraitId, TypeAliasId, TypeParamId, UnionId,
 };
 
 pub type Key<K, V> = crate::dyn_map::Key<InFile<K>, V, AstPtrPolicy<K, V>>;
@@ -29,6 +29,7 @@ pub const TUPLE_FIELD: Key<ast::TupleField, FieldId> = Key::new();
 pub const RECORD_FIELD: Key<ast::RecordField, FieldId> = Key::new();
 pub const TYPE_PARAM: Key<ast::TypeParam, TypeParamId> = Key::new();
 pub const LIFETIME_PARAM: Key<ast::LifetimeParam, LifetimeParamId> = Key::new();
+pub const CONST_PARAM: Key<ast::ConstParam, ConstParamId> = Key::new();
 
 pub const MACRO: Key<ast::MacroCall, MacroDefId> = Key::new();
 
diff --git a/crates/hir_def/src/lib.rs b/crates/hir_def/src/lib.rs
index ba09a9126..25f460504 100644
--- a/crates/hir_def/src/lib.rs
+++ b/crates/hir_def/src/lib.rs
@@ -232,6 +232,13 @@ pub struct LifetimeParamId {
 pub type LocalLifetimeParamId = Idx<generics::LifetimeParamData>;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct ConstParamId {
+    pub parent: GenericDefId,
+    pub local_id: LocalConstParamId,
+}
+pub type LocalConstParamId = Idx<generics::ConstParamData>;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum ContainerId {
     ModuleId(ModuleId),
     DefWithBodyId(DefWithBodyId),
diff --git a/crates/hir_def/src/resolver.rs b/crates/hir_def/src/resolver.rs
index f8cc5e075..129f1dbac 100644
--- a/crates/hir_def/src/resolver.rs
+++ b/crates/hir_def/src/resolver.rs
@@ -20,9 +20,9 @@ use crate::{
     path::{ModPath, PathKind},
     per_ns::PerNs,
     visibility::{RawVisibility, Visibility},
-    AdtId, AssocContainerId, ConstId, ContainerId, DefWithBodyId, EnumId, EnumVariantId,
-    FunctionId, GenericDefId, HasModule, ImplId, LocalModuleId, Lookup, ModuleDefId, ModuleId,
-    StaticId, StructId, TraitId, TypeAliasId, TypeParamId, VariantId,
+    AdtId, AssocContainerId, ConstId, ConstParamId, ContainerId, DefWithBodyId, EnumId,
+    EnumVariantId, FunctionId, GenericDefId, HasModule, ImplId, LocalModuleId, Lookup, ModuleDefId,
+    ModuleId, StaticId, StructId, TraitId, TypeAliasId, TypeParamId, VariantId,
 };
 
 #[derive(Debug, Clone, Default)]
@@ -93,6 +93,7 @@ pub enum ValueNs {
     StaticId(StaticId),
     StructId(StructId),
     EnumVariantId(EnumVariantId),
+    GenericParam(ConstParamId),
 }
 
 impl Resolver {
@@ -163,7 +164,7 @@ impl Resolver {
                 }
 
                 Scope::GenericParams { params, def } => {
-                    if let Some(local_id) = params.find_by_name(first_name) {
+                    if let Some(local_id) = params.find_type_by_name(first_name) {
                         let idx = if path.segments.len() == 1 { None } else { Some(1) };
                         return Some((
                             TypeNs::GenericParam(TypeParamId { local_id, parent: *def }),
@@ -285,11 +286,17 @@ impl Resolver {
                 Scope::ExprScope(_) => continue,
 
                 Scope::GenericParams { params, def } if n_segments > 1 => {
-                    if let Some(local_id) = params.find_by_name(first_name) {
+                    if let Some(local_id) = params.find_type_by_name(first_name) {
                         let ty = TypeNs::GenericParam(TypeParamId { local_id, parent: *def });
                         return Some(ResolveValueResult::Partial(ty, 1));
                     }
                 }
+                Scope::GenericParams { params, def } if n_segments == 1 => {
+                    if let Some(local_id) = params.find_const_by_name(first_name) {
+                        let val = ValueNs::GenericParam(ConstParamId { local_id, parent: *def });
+                        return Some(ResolveValueResult::ValueNs(val));
+                    }
+                }
                 Scope::GenericParams { .. } => continue,
 
                 Scope::ImplDefScope(impl_) => {