Fix Ruby::UnannotatedEmptyCollection error

lib/lrama/counterexamples.rb

@@ -50,7 +50,7 @@ def setup_transitions
       @reverse_transitions = {}
 
       @states.states.each do |src_state|
-        trans = {}
+        trans = {} #: Hash[Grammar::Symbol, State]
 
         src_state.transitions.each do |shift, next_state|
           trans[shift.next_sym] = next_state
@@ -85,7 +85,7 @@ def setup_productions
 
       @states.states.each do |state|
         # LHS => Set(Item)
-        h = {}
+        h = {} #: Hash[Grammar::Symbol, Set[States::Item]]
 
         state.closure.each do |item|
           sym = item.lhs
@@ -165,7 +165,7 @@ def find_shift_conflict_shortest_state_items(reduce_path, conflict_state, confli
         end
 
         if target_state_item.item.beginning_of_rule?
-          queue = []
+          queue = [] #: Array[Array[StateItem]]
           queue << [target_state_item]
 
           # Find reverse production
@@ -234,8 +234,8 @@ def build_paths_from_state_items(state_items)
 
     def shortest_path(conflict_state, conflict_reduce_item, conflict_term)
       # queue: is an array of [Triple, [Path]]
-      queue = []
-      visited = {}
+      queue = [] #: Array[[Triple, Array[StartPath|TransitionPath|ProductionPath]]]
+      visited = {} #: Hash[Triple, true]
       start_state = @states.states.first #: Lrama::State
       raise "BUG: Start state should be just one kernel." if start_state.kernels.count != 1
 

lib/lrama/counterexamples/derivation.rb

@@ -18,7 +18,7 @@ def to_s
       alias :inspect :to_s
 
       def render_strings_for_report
-        result = []
+        result = [] #: Array[String]
         _render_for_report(self, 0, result, 0)
         result.map(&:rstrip)
       end

lib/lrama/counterexamples/example.rb

@@ -92,7 +92,7 @@ def _derivations(paths)
       end
 
       def find_derivation_for_symbol(state_item, sym)
-        queue = []
+        queue = [] #: Array[Array[StateItem]]
         queue << [state_item]
 
         while (sis = queue.shift)