src/Pure/Tools/build.scala

     extends PartialFunction[String, Session_Info]
   {
     def apply(name: String): Session_Info = graph.get_node(name)
     def isDefinedAt(name: String): Boolean = graph.defined(name)
 
-    def selection(requirements: Boolean, all_sessions: Boolean,
-      session_groups: List[String], sessions: List[String]): (List[String], Session_Tree) =
-    {
-      val bad_sessions = sessions.filterNot(isDefinedAt(_))
+    def selection(
+      requirements: Boolean = false,
+      all_sessions: Boolean = false,
+      session_groups: List[String] = Nil,
+      exclude_sessions: List[String] = Nil,
+      sessions: List[String] = Nil): (List[String], Session_Tree) =
+    {
+      val bad_sessions =
+        SortedSet((exclude_sessions ::: sessions).filterNot(isDefinedAt(_)): _*).toList
       if (bad_sessions.nonEmpty) error("Undefined session(s): " + commas_quote(bad_sessions))
 
+      val excluded = graph.all_succs(exclude_sessions).toSet
       val pre_selected =
       {
         if (all_sessions) graph.keys
         else {
           val select_group = session_groups.toSet

           (for {
             (name, (info, _)) <- graph.iterator
             if info.select || select(name) || apply(name).groups.exists(select_group)
           } yield name).toList
         }
-      }
+      }.filterNot(excluded)
+
       val selected =
         if (requirements) (graph.all_preds(pre_selected).toSet -- pre_selected).toList
         else pre_selected
 
       val graph1 = graph.restrict(graph.all_preds(selected).toSet)

     options: Options,
     inlined_files: Boolean,
     dirs: List[Path],
     sessions: List[String]): Deps =
   {
-    val (_, tree) = find_sessions(options, dirs = dirs).selection(false, false, Nil, sessions)
+    val (_, tree) = find_sessions(options, dirs = dirs).selection(sessions = sessions)
     dependencies(inlined_files = inlined_files, tree = tree)
   }
 
   def session_content(
     options: Options,

     list_files: Boolean = false,
     check_keywords: Set[String] = Set.empty,
     no_build: Boolean = false,
     system_mode: Boolean = false,
     verbose: Boolean = false,
+    exclude_sessions: List[String] = Nil,
     sessions: List[String] = Nil): Map[String, Int] =
   {
     /* session tree and dependencies */
 
     val full_tree = find_sessions(options.int("completion_limit") = 0, dirs, select_dirs)
     val (selected, selected_tree) =
-      full_tree.selection(requirements, all_sessions, session_groups, sessions)
+      full_tree.selection(requirements, all_sessions, session_groups, exclude_sessions, sessions)
 
     val deps = dependencies(progress, true, verbose, list_files, check_keywords, selected_tree)
 
     def make_stamp(name: String): String =
       sources_stamp(selected_tree(name).entry_digest :: deps.sources(name))

     list_files: Boolean = false,
     check_keywords: Set[String] = Set.empty,
     no_build: Boolean = false,
     system_mode: Boolean = false,
     verbose: Boolean = false,
+    exclude_sessions: List[String] = Nil,
     sessions: List[String] = Nil): Int =
   {
     val results =
-      build_results(options, progress, requirements, all_sessions,
-        build_heap, clean_build, dirs, select_dirs, session_groups, max_jobs,
-        list_files, check_keywords, no_build, system_mode, verbose, sessions)
+      build_results(options, progress, requirements, all_sessions, build_heap, clean_build,
+        dirs, select_dirs, session_groups, max_jobs, list_files, check_keywords,
+        no_build, system_mode, verbose, exclude_sessions, sessions)
 
     val rc = (0 /: results)({ case (rc1, (_, rc2)) => rc1 max rc2 })
     if (rc != 0 && (verbose || !no_build)) {
       val unfinished =
         (for ((name, r) <- results.iterator if r != 0) yield name).toList.sorted

           Properties.Value.Int(max_jobs) ::
           Properties.Value.Boolean(list_files) ::
           Properties.Value.Boolean(no_build) ::
           Properties.Value.Boolean(system_mode) ::
           Properties.Value.Boolean(verbose) ::
-          Command_Line.Chunks(
-              dirs, select_dirs, session_groups, check_keywords, build_options, sessions) =>
+          Command_Line.Chunks(dirs, select_dirs, session_groups, check_keywords,
+              build_options, exclude_sessions, sessions) =>
             val options = (Options.init() /: build_options)(_ + _)
             val progress = new Console_Progress(verbose)
             progress.interrupt_handler {
               build(options, progress, requirements, all_sessions, build_heap, clean_build,
                 dirs.map(Path.explode(_)), select_dirs.map(Path.explode(_)), session_groups,
                 max_jobs, list_files, check_keywords.toSet, no_build, system_mode,
-                verbose, sessions)
+                verbose, exclude_sessions, sessions)
             }
         case _ => error("Bad arguments:\n" + cat_lines(args))
       }
     }
   }