handle advance error further up.

lib/trailblazer/workflow/advance.rb

@@ -10,9 +10,12 @@ class Advance <  Trailblazer::Activity::Railway
       terminus :invalid_event
 
       step task: :compute_catch_event_tuple, Output(:failure) => Track(:invalid_event)
-      step task: :find_position_options
+      step task: :find_position_options, Output(:failure) => Track(:invalid_event)
       step task: :advance
 
+      # DISCUSS: what we actually want here is a "catch_event tuple", the event we want to trigger.
+      #          currently, we receive an {event_label}, find that in the iteration_set and thus
+      #          get the catch event.
       def compute_catch_event_tuple((ctx, flow_options), **)
         iteration_set, event_label = flow_options[:iteration_set], flow_options[:event_label]
 
@@ -46,9 +49,11 @@ def position_options_from_iteration(iteration)
       def find_position_options((ctx, flow_options), **)
         state_resolver = flow_options[:state_guards]
 
-        _, state_options = state_resolver.(*flow_options[:catch_event_tuple], [ctx], **ctx.to_hash)
-
-        # raise unless state_options # FIXME.
+        (_, state_options), possible_states = state_resolver.(*flow_options[:catch_event_tuple], [ctx], **ctx.to_hash)
+        unless state_options
+          flow_options[:errors] = "No state configuration found for #{possible_states.inspect}"
+          return Activity::Left, [ctx, flow_options]  # FIXME: make this nicer.
+        end
 
         lanes_cfg = flow_options[:lanes]
         fixme_tuples = state_options[:suspend_tuples].collect { |tuple| {"tuple" => tuple} }

lib/trailblazer/workflow/collaboration/state.rb

@@ -15,13 +15,10 @@ def call(lane_label, catch_id, args, **kws)
           # First, find all state guards that "point to" this catch event.
           possible_states = @table.find_all { |state_name, cfg| cfg[:catch_tuples].include?([lane_label, catch_id]) }
 
-
           # Execute those, the first returning true indicates the configuration.
           target_state = possible_states.find { |state_name, cfg| @guards.(state_name, args, **kws) }
 
-          raise "No state configuration found for #{possible_states.inspect}" if target_state.nil?
-
-          target_state
+          return target_state, possible_states
         end
       end
     end

test/advance_test.rb

@@ -26,12 +26,22 @@ class AdvanceTest < Minitest::Spec
     assert_equal signal.inspect, %(#<Trailblazer::Activity::End semantic=:success>)
 
 
-    #@ unknown event label
+  #@ unknown event label
     flow_options = flow_options.merge!(event_label: "XXX unknown ~~~")
 
     signal, (ctx, flow_options) = Trailblazer::Workflow::Advance.([ctx_for_advance, flow_options])
 
     assert_equal signal.inspect, %(#<Trailblazer::Activity::End semantic=:invalid_event>)
+
+  #@ no state guard matches
+  # DISCUSS: should we stop on a different terminus here to indicate that we found matching guards, but they were all unmet?
+    flow_options = flow_options.merge!(event_label: "☝ ⏵︎Update")
+    ctx_for_advance = {model: Posting.new(state: "~~~undefined~~~")}
+
+    signal, (ctx, flow_options) = Trailblazer::Workflow::Advance.([ctx_for_advance, flow_options])
+
+    assert_equal signal.inspect, %(#<Trailblazer::Activity::End semantic=:invalid_event>)
+    assert_equal flow_options[:errors], %(No state configuration found for [[\"⏸︎ Update [00u]\", {:suspend_tuples=>[[\"lifecycle\", \"suspend-Gateway_0fnbg3r\"], [\"UI\", \"suspend-Gateway_0nxerxv\"], [\"approver\", \"~suspend~\"]], :catch_tuples=>[[\"UI\", \"catch-before-Activity_0j78uzd\"]]}]])
   end
 end