Add Chopper convenience method that just selects a set of names to create a single program (#897)

Author: marcoeilers

src/main/scala/viper/silver/ast/utility/chopper/Chopper.scala

@@ -75,6 +75,20 @@ trait ChopperLike { this: ViperGraphs with Cut =>
     chopWithMetrics(choppee)(selection, bound, penalty)._1
   }
 
+  /**
+    * chops `choppee` into a single Viper program containing only the selected members. See [[chop]] for more details.
+    *
+    * @param choppee   Targeted program.
+    * @param selection Specifies the names of all members that should be verified.
+    * @return Chopped program, if anything was selected.
+    */
+  def chop(
+            choppee: ast.Program,
+            selection: Set[String],
+          ): Option[ast.Program] = {
+    chopWithMetrics(choppee)(Some(m => selection.contains(m.name)))._1.headOption
+  }
+
   /**
     * chops `choppee` into multiple Viper programs and returns metrics. See [[chop]] for more details.
     *