diff -r 98fe7a10ace3 -r a4d7da18ac5c src/Pure/Thy/sessions.scala
--- a/src/Pure/Thy/sessions.scala	Thu Nov 26 20:49:40 2020 +0000
+++ b/src/Pure/Thy/sessions.scala	Thu Nov 26 23:23:19 2020 +0100
@@ -1465,6 +1465,9 @@
     def read_task_statistics(db: SQL.Database, name: String): List[Properties.T] =
       read_properties(db, name, Session_Info.task_statistics)
 
+    def read_theories(db: SQL.Database, name: String): List[String] =
+      read_theory_timings(db, name).flatMap(Markup.Name.unapply)
+
     def read_errors(db: SQL.Database, name: String): List[String] =
       Build_Log.uncompress_errors(read_bytes(db, name, Session_Info.errors), cache = xz_cache)