Merge #7080

7080: Implement ConstParams for HIR r=Veykril a=Veykril

r? @flodiebold 

Co-authored-by: Lukas Wirth <lukastw97@gmail.com>

crates/assists/src/ast_transform.rs

@@ -204,7 +204,8 @@ impl<'a> AstTransform<'a> for QualifyPaths<'a> {
             }
             PathResolution::Local(_)
             | PathResolution::TypeParam(_)
-            | PathResolution::SelfType(_) => None,
+            | PathResolution::SelfType(_)
+            | PathResolution::ConstParam(_) => None,
             PathResolution::Macro(_) => None,
             PathResolution::AssocItem(_) => None,
         }

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,
+    AdtId, AssocContainerId, AssocItemId, AssocItemLoc, AttrDefId, ConstId, ConstParamId,
-    FunctionId, GenericDefId, HasModule, ImplId, LifetimeParamId, LocalEnumVariantId, LocalFieldId,
+    DefWithBodyId, EnumId, FunctionId, GenericDefId, HasModule, ImplId, LifetimeParamId,
-    LocalModuleId, Lookup, ModuleId, StaticId, StructId, TraitId, TypeAliasId, TypeParamId,
+    LocalEnumVariantId, LocalFieldId, LocalModuleId, Lookup, ModuleId, StaticId, StructId, TraitId,
-    UnionId,
+    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,

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)
 ];
 

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,
+    db::HirDatabase, Const, ConstParam, Enum, Field, FieldSource, Function, Impl, LifetimeParam,
-    Module, Static, Struct, Trait, TypeAlias, TypeParam, Union, Variant,
+    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())
+    }
+}

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,
+        ConstParam, Crate, CrateDependency, DefWithBody, Enum, Field, FieldSource, Function,
-        HasVisibility, Impl, Label, LifetimeParam, Local, MacroDef, Module, ModuleDef, ScopeDef,
+        GenericDef, HasVisibility, Impl, Label, LifetimeParam, Local, MacroDef, Module, ModuleDef,
-        Static, Struct, Trait, Type, TypeAlias, TypeParam, Union, Variant, VariantDef,
+        ScopeDef, Static, Struct, Trait, Type, TypeAlias, TypeParam, Union, Variant, VariantDef,
     },
     has_source::HasSource,
     semantics::{PathResolution, Semantics, SemanticsScope},

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,
+    AssocItem, Callable, ConstParam, Crate, Field, Function, HirFileId, Impl, InFile, Label,
-    Local, MacroDef, Module, ModuleDef, Name, Path, ScopeDef, Trait, Type, TypeAlias, TypeParam,
+    LifetimeParam, Local, MacroDef, Module, ModuleDef, Name, Path, ScopeDef, Trait, Type,
-    VariantDef,
+    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),

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,
+    ConstId, ConstParamId, DefWithBodyId, EnumId, EnumVariantId, FieldId, FunctionId, GenericDefId,
-    LifetimeParamId, ModuleId, StaticId, StructId, TraitId, TypeAliasId, TypeParamId, UnionId,
+    ImplId, LifetimeParamId, ModuleId, StaticId, StructId, TraitId, TypeAliasId, TypeParamId,
-    VariantId,
+    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,

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)
         });

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,
+    AdtId, ConstParamId, GenericDefId, LifetimeParamId, LocalConstParamId, LocalLifetimeParamId,
-    TypeParamId,
+    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
     }
 }

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 =
+static EMPTY_GENERICS: GenericParams = GenericParams {
-    GenericParams { types: Arena::new(), lifetimes: Arena::new(), where_predicates: Vec::new() };
+    types: Arena::new(),
+    lifetimes: Arena::new(),
+    consts: Arena::new(),
+    where_predicates: Vec::new(),
+};
 
 #[derive(Default, Debug, Eq, PartialEq)]
 struct ItemTreeData {

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,
+    ConstId, ConstParamId, EnumId, EnumVariantId, FieldId, FunctionId, ImplId, LifetimeParamId,
-    StructId, TraitId, TypeAliasId, TypeParamId, UnionId,
+    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();
 

crates/hir_def/src/lib.rs

@@ -231,6 +231,13 @@ 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),

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,
+    AdtId, AssocContainerId, ConstId, ConstParamId, ContainerId, DefWithBodyId, EnumId,
-    FunctionId, GenericDefId, HasModule, ImplId, LocalModuleId, Lookup, ModuleDefId, ModuleId,
+    EnumVariantId, FunctionId, GenericDefId, HasModule, ImplId, LocalModuleId, Lookup, ModuleDefId,
-    StaticId, StructId, TraitId, TypeAliasId, TypeParamId, VariantId,
+    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_) => {

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,
+    db::DefDatabase, expr::ExprId, ConstParamId, DefWithBodyId, FunctionId, GenericDefId, ImplId,
-    TypeParamId, VariantId,
+    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>>;
 

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);

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,
+    AdtId, AssocContainerId, AssocItemId, ConstId, ConstParamId, EnumId, EnumVariantId, FunctionId,
-    HasModule, ImplId, LocalFieldId, Lookup, StaticId, StructId, TraitId, TypeAliasId, TypeParamId,
+    GenericDefId, HasModule, ImplId, LocalFieldId, Lookup, StaticId, StructId, TraitId,
-    UnionId, VariantId,
+    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],

crates/hir_ty/src/tests/simple.rs

@@ -2375,3 +2375,19 @@ 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
+        "#]],
+    );
+}

crates/ide/src/display/navigation_target.rs

@@ -24,6 +24,7 @@ pub enum SymbolKind {
     Impl,
     Field,
     TypeParam,
+    ConstParam,
     LifetimeParam,
     ValueParam,
     SelfParam,
@@ -225,6 +226,7 @@ impl TryToNav for Definition {
             Definition::TypeParam(it) => Some(it.to_nav(db)),
             Definition::LifetimeParam(it) => Some(it.to_nav(db)),
             Definition::Label(it) => Some(it.to_nav(db)),
+            Definition::ConstParam(it) => Some(it.to_nav(db)),
         }
     }
 }
@@ -485,6 +487,23 @@ impl ToNav for hir::LifetimeParam {
     }
 }
 
+impl ToNav for hir::ConstParam {
+    fn to_nav(&self, db: &RootDatabase) -> NavigationTarget {
+        let src = self.source(db);
+        let full_range = src.value.syntax().text_range();
+        NavigationTarget {
+            file_id: src.file_id.original_file(db),
+            name: self.name(db).to_string().into(),
+            kind: Some(SymbolKind::ConstParam),
+            full_range,
+            focus_range: src.value.name().map(|n| n.syntax().text_range()),
+            container_name: None,
+            description: None,
+            docs: None,
+        }
+    }
+}
+
 /// Get a description of a symbol.
 ///
 /// e.g. `struct Name`, `enum Name`, `fn Name`

crates/ide/src/doc_links.rs

@@ -193,6 +193,7 @@ fn rewrite_intra_doc_link(
         Definition::SelfType(_)
         | Definition::Local(_)
         | Definition::TypeParam(_)
+        | Definition::ConstParam(_)
         | Definition::LifetimeParam(_)
         | Definition::Label(_) => return None,
     }?;

crates/ide/src/hover.rs

@@ -370,7 +370,10 @@ fn hover_for_definition(db: &RootDatabase, def: Definition) -> Option<Markup> {
                 Adt::Enum(it) => from_def_source(db, it, mod_path),
             })
         }
-        Definition::TypeParam(_) | Definition::LifetimeParam(_) | Definition::Label(_) => {
+        Definition::TypeParam(_)
+        | Definition::LifetimeParam(_)
+        | Definition::ConstParam(_)
+        | Definition::Label(_) => {
             // FIXME: Hover for generic param
             None
         }

crates/ide/src/references.rs

@@ -1144,4 +1144,20 @@ fn foo<'a>() -> &'a () {
             "#]],
         );
     }
+
+    #[test]
+    fn test_find_const_param() {
+        check(
+            r#"
+fn foo<const FOO<|>: usize>() -> usize {
+    FOO
+}
+"#,
+            expect![[r#"
+                FOO ConstParam FileId(0) 7..23 13..16 Other
+
+                FileId(0) 42..45 Other
+            "#]],
+        );
+    }
 }

crates/ide/src/syntax_highlighting.rs

@@ -819,6 +819,7 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
         },
         Definition::SelfType(_) => HighlightTag::Symbol(SymbolKind::Impl),
         Definition::TypeParam(_) => HighlightTag::Symbol(SymbolKind::TypeParam),
+        Definition::ConstParam(_) => HighlightTag::Symbol(SymbolKind::ConstParam),
         Definition::Local(local) => {
             let tag = if local.is_param(db) {
                 HighlightTag::Symbol(SymbolKind::ValueParam)

crates/ide/src/syntax_highlighting/tags.rs

@@ -77,6 +77,7 @@ impl HighlightTag {
                 SymbolKind::Function => "function",
                 SymbolKind::TypeAlias => "type_alias",
                 SymbolKind::TypeParam => "type_param",
+                SymbolKind::ConstParam => "const_param",
                 SymbolKind::LifetimeParam => "lifetime",
                 SymbolKind::Macro => "macro",
                 SymbolKind::Local => "variable",

crates/ide/src/syntax_highlighting/test_data/highlighting.html

@@ -118,6 +118,10 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="keyword control">loop</span> <span class="punctuation">{</span><span class="punctuation">}</span>
 <span class="punctuation">}</span>
 
+<span class="keyword">fn</span> <span class="function declaration">const_param</span><span class="punctuation">&lt;</span><span class="keyword">const</span> <span class="const_param declaration">FOO</span><span class="punctuation">:</span> <span class="builtin_type">usize</span><span class="punctuation">&gt;</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="builtin_type">usize</span> <span class="punctuation">{</span>
+    <span class="const_param">FOO</span>
+<span class="punctuation">}</span>
+
 <span class="keyword">use</span> <span class="module">ops</span><span class="operator">::</span><span class="trait">Fn</span><span class="punctuation">;</span>
 <span class="keyword">fn</span> <span class="function declaration">baz</span><span class="punctuation">&lt;</span><span class="type_param declaration">F</span><span class="punctuation">:</span> <span class="trait">Fn</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">&gt;</span><span class="punctuation">(</span><span class="value_param declaration callable">f</span><span class="punctuation">:</span> <span class="type_param">F</span><span class="punctuation">)</span> <span class="punctuation">{</span>
     <span class="value_param callable">f</span><span class="punctuation">(</span><span class="punctuation">)</span>

crates/ide/src/syntax_highlighting/tests.rs

@@ -91,6 +91,10 @@ fn never() -> ! {
     loop {}
 }
 
+fn const_param<const FOO: usize>() -> usize {
+    FOO
+}
+
 use ops::Fn;
 fn baz<F: Fn() -> ()>(f: F) {
     f()

crates/ide_db/src/defs.rs

@@ -6,8 +6,8 @@
 // FIXME: this badly needs rename/rewrite (matklad, 2020-02-06).
 
 use hir::{
-    db::HirDatabase, Crate, Field, HasVisibility, Impl, Label, LifetimeParam, Local, MacroDef,
+    db::HirDatabase, ConstParam, Crate, Field, HasVisibility, Impl, Label, LifetimeParam, Local,
-    Module, ModuleDef, Name, PathResolution, Semantics, TypeParam, Visibility,
+    MacroDef, Module, ModuleDef, Name, PathResolution, Semantics, TypeParam, Visibility,
 };
 use syntax::{
     ast::{self, AstNode},
@@ -26,6 +26,7 @@ pub enum Definition {
     Local(Local),
     TypeParam(TypeParam),
     LifetimeParam(LifetimeParam),
+    ConstParam(ConstParam),
     Label(Label),
 }
 
@@ -39,6 +40,7 @@ impl Definition {
             Definition::Local(it) => Some(it.module(db)),
             Definition::TypeParam(it) => Some(it.module(db)),
             Definition::LifetimeParam(it) => Some(it.module(db)),
+            Definition::ConstParam(it) => Some(it.module(db)),
             Definition::Label(it) => Some(it.module(db)),
         }
     }
@@ -52,6 +54,7 @@ impl Definition {
             Definition::Local(_) => None,
             Definition::TypeParam(_) => None,
             Definition::LifetimeParam(_) => None,
+            Definition::ConstParam(_) => None,
             Definition::Label(_) => None,
         }
     }
@@ -79,6 +82,7 @@ impl Definition {
             Definition::Local(it) => it.name(db)?,
             Definition::TypeParam(it) => it.name(db),
             Definition::LifetimeParam(it) => it.name(db),
+            Definition::ConstParam(it) => it.name(db),
             Definition::Label(it) => it.name(db),
         };
         Some(name)
@@ -233,6 +237,10 @@ impl NameClass {
                     let def = sema.to_def(&it)?;
                     Some(NameClass::Definition(Definition::TypeParam(def)))
                 },
+                ast::ConstParam(it) => {
+                    let def = sema.to_def(&it)?;
+                    Some(NameClass::Definition(Definition::ConstParam(def)))
+                },
                 _ => None,
             }
         }
@@ -417,6 +425,7 @@ impl From<PathResolution> for Definition {
             PathResolution::TypeParam(par) => Definition::TypeParam(par),
             PathResolution::Macro(def) => Definition::Macro(def),
             PathResolution::SelfType(impl_def) => Definition::SelfType(impl_def),
+            PathResolution::ConstParam(par) => Definition::ConstParam(par),
         }
     }
 }

crates/rust-analyzer/src/semantic_tokens.rs

@@ -44,6 +44,7 @@ define_semantic_token_types![
     (ESCAPE_SEQUENCE, "escapeSequence"),
     (FORMAT_SPECIFIER, "formatSpecifier"),
     (GENERIC, "generic"),
+    (CONST_PARAMETER, "constParameter"),
     (LIFETIME, "lifetime"),
     (LABEL, "label"),
     (PUNCTUATION, "punctuation"),

crates/rust-analyzer/src/to_proto.rs

@@ -42,6 +42,7 @@ pub(crate) fn symbol_kind(symbol_kind: SymbolKind) -> lsp_types::SymbolKind {
         SymbolKind::Field => lsp_types::SymbolKind::Field,
         SymbolKind::Static => lsp_types::SymbolKind::Constant,
         SymbolKind::Const => lsp_types::SymbolKind::Constant,
+        SymbolKind::ConstParam => lsp_types::SymbolKind::Constant,
         SymbolKind::Impl => lsp_types::SymbolKind::Object,
         SymbolKind::Local
         | SymbolKind::SelfParam
@@ -378,6 +379,7 @@ fn semantic_token_type_and_modifiers(
             SymbolKind::Impl => lsp_types::SemanticTokenType::TYPE,
             SymbolKind::Field => lsp_types::SemanticTokenType::PROPERTY,
             SymbolKind::TypeParam => lsp_types::SemanticTokenType::TYPE_PARAMETER,
+            SymbolKind::ConstParam => semantic_tokens::CONST_PARAMETER,
             SymbolKind::LifetimeParam => semantic_tokens::LIFETIME,
             SymbolKind::Label => semantic_tokens::LABEL,
             SymbolKind::ValueParam => lsp_types::SemanticTokenType::PARAMETER,