src/Pure/consts.ML

 
 (* declarations *)
 
 fun declare authentic naming tags (c, declT) = map_consts (fn (decls, constraints, rev_abbrevs) =>
   let
-    val decl = {T = declT, typargs = typargs_of declT, tags = tags, authentic = authentic};
+    val tags' = tags |> Position.default_properties (Position.thread_data ());
+    val decl = {T = declT, typargs = typargs_of declT, tags = tags', authentic = authentic};
     val decls' = decls |> extend_decls naming (c, ((decl, NONE), serial ()));
   in (decls', constraints, rev_abbrevs) end);
 
 
 (* constraints *)

     val _ = Term.exists_subterm Term.is_Var rhs andalso err "Illegal schematic variables";
     val _ = null (Term.hidden_polymorphism rhs) orelse err "Extra type variables";
   in
     consts |> map_consts (fn (decls, constraints, rev_abbrevs) =>
       let
-        val decl = {T = T, typargs = typargs_of T, tags = tags, authentic = true};
+        val tags' = tags |> Position.default_properties (Position.thread_data ());
+        val decl = {T = T, typargs = typargs_of T, tags = tags', authentic = true};
         val abbr = {rhs = rhs, normal_rhs = normal_rhs, force_expand = force_expand};
         val decls' = decls
           |> extend_decls naming (c, ((decl, SOME abbr), serial ()));
         val rev_abbrevs' = rev_abbrevs
           |> fold (curry Symtab.cons_list mode) (rev_abbrev lhs rhs);