Allow looping with all actions

spec/fsm_spec.lua

@@ -276,6 +276,85 @@ describe("fsm", function ()
         assert.is_same({"warn", "panic"}, m.transitions())
       end)
     end)
+
+    describe("with looping", function ()
+      local done_before_loop = false
+      local done_leave_green = false
+      local done_enter_green = false
+      local done_after_loop = false
+
+      function reset_flags()
+        done_before_loop = false
+        done_leave_green = false
+        done_enter_green = false
+        done_after_loop = false
+      end
+
+      before_each(function ()
+        reset_flags()
+
+        m = fsm.create({
+          initial = "green",
+          events = {
+            {name = "warn",  from = "green",  to = "yellow"},
+            {name = "loop",  from = "green",  to = "green"},
+            {name = "panic", from = "yellow", to = "red"   },
+            {name = "calm",  from = "red",    to = "yellow"},
+            {name = "clear", from = "yellow", to = "green" }
+          },
+          callbacks = {
+            on_before_loop = function () done_before_loop = true end,
+            on_leave_green = function () done_leave_green = true end,
+            on_enter_green = function () done_enter_green = true end,
+            on_after_loop = function () done_after_loop = true end,
+          }
+        })
+      end)
+
+      it("starts with green", function ()
+        assert.are_equal("green", m.current)
+        assert.is_not_true(done_before_loop)
+        assert.is_not_true(done_leave_green)
+        assert.is_true(done_enter_green)
+        assert.is_not_true(done_after_loop)
+      end)
+
+      it("reports current transitions to be warn and loop", function ()
+        assert.is_same({"warn", "loop"}, m.transitions())
+      end)
+
+      it("warn leads to yellow and correct actions", function ()
+        reset_flags()
+        m.warn()
+        assert.are_equal("yellow", m.current)
+        assert.is_not_true(done_before_loop)
+        assert.is_true(done_leave_green)
+        assert.is_not_true(done_enter_green)
+        assert.is_not_true(done_after_loop)
+      end)
+
+      it("clear leads to green and correct actions", function ()
+        m.warn()
+        reset_flags()
+        m.clear()
+        assert.are_equal("green", m.current)
+        assert.is_not_true(done_before_loop)
+        assert.is_not_true(done_leave_green)
+        assert.is_true(done_enter_green)
+        assert.is_not_true(done_after_loop)
+      end)
+
+      it("loop leads to green and correct actions", function ()
+        reset_flags()
+        m.loop()
+        assert.are_equal("green", m.current)
+        assert.is_true(done_before_loop)
+        assert.is_true(done_leave_green)
+        assert.is_true(done_enter_green)
+        assert.is_true(done_after_loop)
+      end)
+
+    end)
   end)
 
   describe("#is_pending", function ()

src/fsm.lua

@@ -9,6 +9,7 @@ M.SUCCEEDED     = 1
 M.NO_TRANSITION = 2
 M.PENDING       = 3
 M.CANCELLED     = 4
+M.NO_OP         = 5
 
 local function do_callback(handler, args)
   if handler then
@@ -64,7 +65,7 @@ local function build_transition(self, event, states)
       return M.CANCELLED
     end
 
-    if from == to then
+    if to == M.NO_OP then
       after_event(self, event, from, to, args)
       return M.NO_TRANSITION
     end
@@ -142,7 +143,7 @@ function M.create(cfg, target)
       table.insert(events_for_state[fr], event)
 
       -- Allow no-op transition if `to` is not specified.
-      states_for_event[event][fr] = to or fr
+      states_for_event[event][fr] = to or M.NO_OP
     end
   end