maybe this is better??

crates/hir/src/display.rs

@@ -401,8 +401,7 @@ fn write_where_clause(def: GenericDefId, f: &mut HirFormatter) -> Result<(), Hir
 
 impl HirDisplay for Const {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
-        let module_id = self.module(f.db).id;
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
-        write_visibility(module_id, self.visibility(f.db), f)?;
         let data = f.db.const_data(self.id);
         write!(f, "const ")?;
         match &data.name {
@@ -410,15 +409,6 @@ impl HirDisplay for Const {
             None => write!(f, "_: ")?,
         }
         data.type_ref.hir_fmt(f)?;
-        let ast_id_map = f.db.ast_id_map(data.file_id);
-        let ast_node = ast_id_map.get(data.ast_id);
-        if let Some(syntax_node) = f.db.parse_or_expand(data.file_id) {
-            let ast_node = ast_node.to_node(&syntax_node);
-            if let Some(body) = ast_node.body() {
-                write!(f, " = {}", body)?;
-            }
-        }
-
         Ok(())
     }
 }

crates/hir/src/lib.rs

@@ -1457,6 +1457,17 @@ impl Const {
         db.const_data(self.id).name.clone()
     }
 
+    pub fn value(self, db: &dyn HirDatabase) -> Option<ast::Expr> {
+        let loc = self.id.lookup(db.upcast());
+        let item_tree = loc.id.item_tree(db.upcast());
+        let ast_id = item_tree[loc.id.value].ast_id;
+        let ast_id_map = db.ast_id_map(loc.id.file_id());
+        let ast_ptr = ast_id_map.get(ast_id);
+        let syntax_node = db.parse_or_expand(loc.id.file_id())?;
+        let ast_node = ast_ptr.to_node(&syntax_node);
+        ast_node.body()
+    }
+
     pub fn ty(self, db: &dyn HirDatabase) -> Type {
         let data = db.const_data(self.id);
         let resolver = self.id.resolver(db.upcast());

crates/hir_def/src/data.rs

@@ -2,7 +2,7 @@
 
 use std::sync::Arc;
 
-use hir_expand::{ast_id_map::FileAstId, name::Name, HirFileId, InFile};
+use hir_expand::{name::Name, InFile};
 use syntax::ast;
 
 use crate::{
@@ -255,8 +255,6 @@ pub struct ConstData {
     pub name: Option<Name>,
     pub type_ref: Interned<TypeRef>,
     pub visibility: RawVisibility,
-    pub ast_id: FileAstId<ast::Const>,
-    pub file_id: HirFileId,
 }
 
 impl ConstData {
@@ -269,8 +267,6 @@ impl ConstData {
             name: konst.name.clone(),
             type_ref: konst.type_ref.clone(),
             visibility: item_tree[konst.visibility].clone(),
-            ast_id: konst.ast_id.clone(),
-            file_id: loc.id.file_id(),
         })
     }
 }

crates/ide/src/hover/render.rs

@@ -1,6 +1,6 @@
 //! Logic for rendering the different hover messages
 use either::Either;
-use hir::{AsAssocItem, HasAttrs, HasSource, HirDisplay, Semantics, TypeInfo};
+use hir::{AsAssocItem, Const, HasAttrs, HasSource, HirDisplay, Semantics, TypeInfo};
 use ide_db::{
     base_db::SourceDatabase,
     defs::Definition,
@@ -352,7 +352,7 @@ pub(super) fn definition(
         Definition::Function(it) => label_and_docs(db, it),
         Definition::Adt(it) => label_and_docs(db, it),
         Definition::Variant(it) => label_and_docs(db, it),
-        Definition::Const(it) => label_and_docs(db, it),
+        Definition::Const(it) => const_label_value_and_docs(db, it),
         Definition::Static(it) => label_and_docs(db, it),
         Definition::Trait(it) => label_and_docs(db, it),
         Definition::TypeAlias(it) => label_and_docs(db, it),
@@ -381,6 +381,21 @@ where
     (label, docs)
 }
 
+fn const_label_value_and_docs(
+    db: &RootDatabase,
+    konst: Const,
+) -> (String, Option<hir::Documentation>) {
+    let label = if let Some(expr) = konst.value(db) {
+        format!("{} = {}", konst.display(db), expr)
+    } else {
+        konst.display(db).to_string()
+    };
+
+    let docs = konst.attrs(db).docs();
+
+    (label, docs)
+}
+
 fn definition_mod_path(db: &RootDatabase, def: &Definition) -> Option<String> {
     if let Definition::GenericParam(_) = def {
         return None;