16 files changed, 173 insertions, 37 deletions

diff --git a/crates/hir/src/code_model.rs b/crates/hir/src/code_model.rs
index b7ded3478..97b7a8b5f 100644
--- a/crates/hir/src/code_model.rs
+++ b/crates/hir/src/code_model.rs
@@ -18,10 +18,10 @@ use hir_def::{
     resolver::{HasResolver, Resolver},
     src::HasSource as _,
     type_ref::{Mutability, TypeRef},
-    AdtId, AssocContainerId, AssocItemId, AssocItemLoc, AttrDefId, ConstId, DefWithBodyId, EnumId,
-    FunctionId, GenericDefId, HasModule, ImplId, LifetimeParamId, LocalEnumVariantId, LocalFieldId,
-    LocalModuleId, Lookup, ModuleId, StaticId, StructId, TraitId, TypeAliasId, TypeParamId,
-    UnionId,
+    AdtId, AssocContainerId, AssocItemId, AssocItemLoc, AttrDefId, ConstId, ConstParamId,
+    DefWithBodyId, EnumId, FunctionId, GenericDefId, HasModule, ImplId, LifetimeParamId,
+    LocalEnumVariantId, LocalFieldId, LocalModuleId, Lookup, ModuleId, StaticId, StructId, TraitId,
+    TypeAliasId, TypeParamId, UnionId,
 };
 use hir_def::{find_path::PrefixKind, item_scope::ItemInNs, visibility::Visibility};
 use hir_expand::{
@@ -1125,7 +1125,12 @@ impl GenericDef {
                 id: LifetimeParamId { parent: self.into(), local_id },
             })
             .map(GenericParam::LifetimeParam);
-        ty_params.chain(lt_params).collect()
+        let const_params = generics
+            .consts
+            .iter()
+            .map(|(local_id, _)| ConstParam { id: ConstParamId { parent: self.into(), local_id } })
+            .map(GenericParam::ConstParam);
+        ty_params.chain(lt_params).chain(const_params).collect()
     }
 
     pub fn type_params(self, db: &dyn HirDatabase) -> Vec<TypeParam> {
@@ -1237,8 +1242,9 @@ impl Label {
 pub enum GenericParam {
     TypeParam(TypeParam),
     LifetimeParam(LifetimeParam),
+    ConstParam(ConstParam),
 }
-impl_from!(TypeParam, LifetimeParam for GenericParam);
+impl_from!(TypeParam, LifetimeParam, ConstParam for GenericParam);
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct TypeParam {
@@ -1300,6 +1306,26 @@ impl LifetimeParam {
     }
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub struct ConstParam {
+    pub(crate) id: ConstParamId,
+}
+
+impl ConstParam {
+    pub fn name(self, db: &dyn HirDatabase) -> Name {
+        let params = db.generic_params(self.id.parent);
+        params.consts[self.id.local_id].name.clone()
+    }
+
+    pub fn module(self, db: &dyn HirDatabase) -> Module {
+        self.id.parent.module(db.upcast()).into()
+    }
+
+    pub fn parent(self, _db: &dyn HirDatabase) -> GenericDef {
+        self.id.parent.into()
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct Impl {
     pub(crate) id: ImplId,
diff --git a/crates/hir/src/from_id.rs b/crates/hir/src/from_id.rs
index a0792b9a6..2422887e3 100644
--- a/crates/hir/src/from_id.rs
+++ b/crates/hir/src/from_id.rs
@@ -44,6 +44,7 @@ from_id![
     (hir_def::ImplId, crate::Impl),
     (hir_def::TypeParamId, crate::TypeParam),
     (hir_def::LifetimeParamId, crate::LifetimeParam),
+    (hir_def::ConstParamId, crate::ConstParam),
     (hir_expand::MacroDefId, crate::MacroDef)
 ];
 
diff --git a/crates/hir/src/has_source.rs b/crates/hir/src/has_source.rs
index 0dc07c33e..dd7c0c570 100644
--- a/crates/hir/src/has_source.rs
+++ b/crates/hir/src/has_source.rs
@@ -10,8 +10,8 @@ use hir_expand::InFile;
 use syntax::ast;
 
 use crate::{
-    db::HirDatabase, Const, Enum, Field, FieldSource, Function, Impl, LifetimeParam, MacroDef,
-    Module, Static, Struct, Trait, TypeAlias, TypeParam, Union, Variant,
+    db::HirDatabase, Const, ConstParam, Enum, Field, FieldSource, Function, Impl, LifetimeParam,
+    MacroDef, Module, Static, Struct, Trait, TypeAlias, TypeParam, Union, Variant,
 };
 
 pub trait HasSource {
@@ -140,3 +140,11 @@ impl HasSource for LifetimeParam {
         child_source.map(|it| it[self.id.local_id].clone())
     }
 }
+
+impl HasSource for ConstParam {
+    type Ast = ast::ConstParam;
+    fn source(self, db: &dyn HirDatabase) -> InFile<Self::Ast> {
+        let child_source = self.id.parent.child_source(db.upcast());
+        child_source.map(|it| it[self.id.local_id].clone())
+    }
+}
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 7ac9fd507..8ac27e2dd 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -34,9 +34,9 @@ pub use crate::{
     attrs::{HasAttrs, Namespace},
     code_model::{
         Access, Adt, AsAssocItem, AssocItem, AssocItemContainer, Callable, CallableKind, Const,
-        Crate, CrateDependency, DefWithBody, Enum, Field, FieldSource, Function, GenericDef,
-        HasVisibility, Impl, Label, LifetimeParam, Local, MacroDef, Module, ModuleDef, ScopeDef,
-        Static, Struct, Trait, Type, TypeAlias, TypeParam, Union, Variant, VariantDef,
+        ConstParam, Crate, CrateDependency, DefWithBody, Enum, Field, FieldSource, Function,
+        GenericDef, HasVisibility, Impl, Label, LifetimeParam, Local, MacroDef, Module, ModuleDef,
+        ScopeDef, Static, Struct, Trait, Type, TypeAlias, TypeParam, Union, Variant, VariantDef,
     },
     has_source::HasSource,
     semantics::{PathResolution, Semantics, SemanticsScope},
diff --git a/crates/hir/src/semantics.rs b/crates/hir/src/semantics.rs
index 67cd16e31..cd689c869 100644
--- a/crates/hir/src/semantics.rs
+++ b/crates/hir/src/semantics.rs
@@ -25,9 +25,9 @@ use crate::{
     diagnostics::Diagnostic,
     semantics::source_to_def::{ChildContainer, SourceToDefCache, SourceToDefCtx},
     source_analyzer::{resolve_hir_path, SourceAnalyzer},
-    AssocItem, Callable, Crate, Field, Function, HirFileId, Impl, InFile, Label, LifetimeParam,
-    Local, MacroDef, Module, ModuleDef, Name, Path, ScopeDef, Trait, Type, TypeAlias, TypeParam,
-    VariantDef,
+    AssocItem, Callable, ConstParam, Crate, Field, Function, HirFileId, Impl, InFile, Label,
+    LifetimeParam, Local, MacroDef, Module, ModuleDef, Name, Path, ScopeDef, Trait, Type,
+    TypeAlias, TypeParam, VariantDef,
 };
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -38,6 +38,7 @@ pub enum PathResolution {
     Local(Local),
     /// A generic parameter
     TypeParam(TypeParam),
+    ConstParam(ConstParam),
     SelfType(Impl),
     Macro(MacroDef),
     AssocItem(AssocItem),
@@ -59,7 +60,9 @@ impl PathResolution {
             PathResolution::Def(ModuleDef::TypeAlias(alias)) => {
                 Some(TypeNs::TypeAliasId((*alias).into()))
             }
-            PathResolution::Local(_) | PathResolution::Macro(_) => None,
+            PathResolution::Local(_) | PathResolution::Macro(_) | PathResolution::ConstParam(_) => {
+                None
+            }
             PathResolution::TypeParam(param) => Some(TypeNs::GenericParam((*param).into())),
             PathResolution::SelfType(impl_def) => Some(TypeNs::SelfType((*impl_def).into())),
             PathResolution::AssocItem(AssocItem::Const(_))
@@ -744,6 +747,7 @@ to_def_impls![
     (crate::Variant, ast::Variant, enum_variant_to_def),
     (crate::TypeParam, ast::TypeParam, type_param_to_def),
     (crate::LifetimeParam, ast::LifetimeParam, lifetime_param_to_def),
+    (crate::ConstParam, ast::ConstParam, const_param_to_def),
     (crate::MacroDef, ast::MacroRules, macro_rules_to_def),
     (crate::Local, ast::IdentPat, bind_pat_to_def),
     (crate::Label, ast::Label, label_to_def),
diff --git a/crates/hir/src/semantics/source_to_def.rs b/crates/hir/src/semantics/source_to_def.rs
index 424e6e8a9..4b9ebff72 100644
--- a/crates/hir/src/semantics/source_to_def.rs
+++ b/crates/hir/src/semantics/source_to_def.rs
@@ -6,9 +6,9 @@ use hir_def::{
     dyn_map::DynMap,
     expr::{LabelId, PatId},
     keys::{self, Key},
-    ConstId, DefWithBodyId, EnumId, EnumVariantId, FieldId, FunctionId, GenericDefId, ImplId,
-    LifetimeParamId, ModuleId, StaticId, StructId, TraitId, TypeAliasId, TypeParamId, UnionId,
-    VariantId,
+    ConstId, ConstParamId, DefWithBodyId, EnumId, EnumVariantId, FieldId, FunctionId, GenericDefId,
+    ImplId, LifetimeParamId, ModuleId, StaticId, StructId, TraitId, TypeAliasId, TypeParamId,
+    UnionId, VariantId,
 };
 use hir_expand::{name::AsName, AstId, MacroDefKind};
 use rustc_hash::FxHashMap;
@@ -157,6 +157,18 @@ impl SourceToDefCtx<'_, '_> {
         dyn_map[keys::LIFETIME_PARAM].get(&src).copied()
     }
 
+    pub(super) fn const_param_to_def(
+        &mut self,
+        src: InFile<ast::ConstParam>,
+    ) -> Option<ConstParamId> {
+        let container: ChildContainer =
+            self.find_generic_param_container(src.as_ref().map(|it| it.syntax()))?.into();
+        let db = self.db;
+        let dyn_map =
+            &*self.cache.entry(container).or_insert_with(|| container.child_by_source(db));
+        dyn_map[keys::CONST_PARAM].get(&src).copied()
+    }
+
     // FIXME: use DynMap as well?
     pub(super) fn macro_rules_to_def(
         &mut self,
diff --git a/crates/hir/src/source_analyzer.rs b/crates/hir/src/source_analyzer.rs
index bddc49c05..30a8e513d 100644
--- a/crates/hir/src/source_analyzer.rs
+++ b/crates/hir/src/source_analyzer.rs
@@ -479,6 +479,7 @@ pub(crate) fn resolve_hir_path(
                 ValueNs::StructId(it) => PathResolution::Def(Struct::from(it).into()),
                 ValueNs::EnumVariantId(it) => PathResolution::Def(Variant::from(it).into()),
                 ValueNs::ImplSelf(impl_id) => PathResolution::SelfType(impl_id.into()),
+                ValueNs::GenericParam(it) => PathResolution::ConstParam(it.into()),
             };
             Some(res)
         });
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_) => {
diff --git a/crates/hir_ty/src/db.rs b/crates/hir_ty/src/db.rs
index 66bdb8e88..f3567c49e 100644
--- a/crates/hir_ty/src/db.rs
+++ b/crates/hir_ty/src/db.rs
@@ -5,8 +5,8 @@ use std::sync::Arc;
 use arena::map::ArenaMap;
 use base_db::{impl_intern_key, salsa, CrateId, Upcast};
 use hir_def::{
-    db::DefDatabase, expr::ExprId, DefWithBodyId, FunctionId, GenericDefId, ImplId, LocalFieldId,
-    TypeParamId, VariantId,
+    db::DefDatabase, expr::ExprId, ConstParamId, DefWithBodyId, FunctionId, GenericDefId, ImplId,
+    LocalFieldId, TypeParamId, VariantId,
 };
 
 use crate::{
@@ -37,6 +37,9 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[salsa::cycle(crate::lower::impl_self_ty_recover)]
     fn impl_self_ty(&self, def: ImplId) -> Binders<Ty>;
 
+    #[salsa::invoke(crate::lower::const_param_ty_query)]
+    fn const_param_ty(&self, def: ConstParamId) -> Ty;
+
     #[salsa::invoke(crate::lower::impl_trait_query)]
     fn impl_trait(&self, def: ImplId) -> Option<Binders<TraitRef>>;
 
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index 80d7ed10e..5d541104e 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -89,6 +89,7 @@ impl<'a> InferenceContext<'a> {
                     return None;
                 }
             }
+            ValueNs::GenericParam(it) => return Some(self.db.const_param_ty(it)),
         };
 
         let ty = self.db.value_ty(typable);
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index 8da56cd11..222f61a11 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -16,9 +16,9 @@ use hir_def::{
     path::{GenericArg, Path, PathSegment, PathSegments},
     resolver::{HasResolver, Resolver, TypeNs},
     type_ref::{TypeBound, TypeRef},
-    AdtId, AssocContainerId, AssocItemId, ConstId, EnumId, EnumVariantId, FunctionId, GenericDefId,
-    HasModule, ImplId, LocalFieldId, Lookup, StaticId, StructId, TraitId, TypeAliasId, TypeParamId,
-    UnionId, VariantId,
+    AdtId, AssocContainerId, AssocItemId, ConstId, ConstParamId, EnumId, EnumVariantId, FunctionId,
+    GenericDefId, HasModule, ImplId, LocalFieldId, Lookup, StaticId, StructId, TraitId,
+    TypeAliasId, TypeParamId, UnionId, VariantId,
 };
 use hir_expand::name::Name;
 use smallvec::SmallVec;
@@ -1221,6 +1221,15 @@ pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binde
     Binders::new(generics.len(), Ty::from_hir(&ctx, &impl_data.target_type))
 }
 
+pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
+    let parent_data = db.generic_params(def.parent);
+    let data = &parent_data.consts[def.local_id];
+    let resolver = def.parent.resolver(db.upcast());
+    let ctx = TyLoweringContext::new(db, &resolver);
+
+    Ty::from_hir(&ctx, &data.ty)
+}
+
 pub(crate) fn impl_self_ty_recover(
     db: &dyn HirDatabase,
     _cycle: &[String],
diff --git a/crates/hir_ty/src/tests/simple.rs b/crates/hir_ty/src/tests/simple.rs
index a61282d5a..bd6beea99 100644
--- a/crates/hir_ty/src/tests/simple.rs
+++ b/crates/hir_ty/src/tests/simple.rs
@@ -2375,3 +2375,20 @@ fn infer_operator_overload() {
         "#]],
     );
 }
+
+
+#[test]
+fn infer_const_params() {
+    check_infer(
+        r#"
+        fn foo<const FOO: usize>() {
+            let bar = FOO;
+        }
+        "#,
+        expect![[r#"
+            27..49 '{     ...FOO; }': ()
+            37..40 'bar': usize
+            43..46 'FOO': usize
+        "#]],
+    );
+}