fix: open .. hinding .. should activate scoped attributes

src/Lean/Elab/Open.lean

@@ -76,6 +76,7 @@ def elabOpenDecl [MonadResolveName m] (stx : TSyntax ``Parser.Command.openDecl)
         addOpenDecl (OpenDecl.explicit idStx.getId declName)
     | `(Parser.Command.openDecl| $ns hiding $ids*) =>
       let ns ← resolveUniqueNamespace ns
+      activateScoped ns
       for id in ids do
         let _ ← resolveId ns id
       let ids := ids.map (·.getId) |>.toList

tests/lean/run/scopedHindingIssue.lean

@@ -0,0 +1,13 @@
+namespace Foo
+
+def x := 10
+
+scoped macro "~0~" : term => `(0)
+
+#check ~0~
+
+end Foo
+
+open Foo hiding x -- must open scoped notation and attributes too
+
+#check ~0~