feat: define Plan#useful_tasks_using

lib/roby/plan.rb

@@ -1317,8 +1317,28 @@ def remote_tasks
             end
         end
 
-        # Ensures that the given tasks will end up being processed without
-        # forcefully stopping anything
+        # Return all mission/permanent tasks that current depend on the given task
+        def useful_tasks_using(tasks)
+            all_tasks = compute_useful_tasks(
+                Array(tasks), graphs: default_useful_task_graphs.map(&:reverse)
+            ).to_set
+            all_tasks.compare_by_identity
+
+            result = []
+            @task_index.mission_tasks.dup.each do |t|
+                result << t if all_tasks.include?(t)
+            end
+            @task_index.permanent_tasks.dup.each do |t|
+                result << t if all_tasks.include?(t)
+            end
+            result
+        end
+
+        # Unmark mission/permanent tasks that depend on the tasks given as argument
+        #
+        # By doing so, it makes the tasks eligible for garbage collection. This
+        # is mostly used to shut down tasks from a specific task within their
+        # dependency graph.
         def make_useless(tasks)
             all_tasks = compute_useful_tasks(
                 Array(tasks), graphs: default_useful_task_graphs.map(&:reverse)

test/test_plan.rb

@@ -1169,6 +1169,49 @@ def action; end
             end
         end
 
+        describe "#useful_tasks_using" do
+            it "returns the given task if it is a mission" do
+                plan.add_mission_task(task = Tasks::Simple.new)
+                assert_equal Set[task], plan.useful_tasks_using(task)
+            end
+
+            it "returns the given task if it is permanent" do
+                plan.add_permanent_task(task = Tasks::Simple.new)
+                assert_equal Set[task], plan.useful_tasks_using(task)
+            end
+
+            it "returns parents of the given task that are missions" do
+                plan.add_mission_task(a = Tasks::Simple.new)
+                a.depends_on(b = Tasks::Simple.new)
+                plan.add_mission_task(c = Tasks::Simple.new)
+                b.depends_on(leaf = Tasks::Simple.new)
+                c.depends_on(leaf = Tasks::Simple.new)
+                assert_equal Set[b, c], plan.useful_tasks_using(leaf)
+            end
+
+            it "returns parents of the given task that are permanent" do
+                plan.add_permanent_task(a = Tasks::Simple.new)
+                a.depends_on(b = Tasks::Simple.new)
+                plan.add_permanent_task(c = Tasks::Simple.new)
+                b.depends_on(leaf = Tasks::Simple.new)
+                c.depends_on(leaf = Tasks::Simple.new)
+                assert_equal Set[b, c], plan.useful_tasks_using(leaf)
+                plan.add_permanent_task(a = Tasks::Simple.new)
+                a.depends_on(b = Tasks::Simple.new)
+                plan.add_permanent_task(c = Tasks::Simple.new)
+                b.depends_on(leaf = Tasks::Simple.new)
+                c.depends_on(leaf = Tasks::Simple.new)
+                assert_equal Set[b, c], plan.useful_tasks_using(leaf)
+            end
+
+            it "goes across useful graphs" do
+                plan.add_permanent_task(a = Tasks::Simple.new)
+                a.planned_by(b = Tasks::Simple.new)
+                b.depends_on(leaf = Tasks::Simple.new)
+                assert_equal Set[a], plan.useful_tasks_using(leaf)
+            end
+        end
+
         describe "#make_useless" do
             it "marks a mission task as non-mission" do
                 plan.add_mission_task(task = Roby::Task.new)