Handle decorators in get_cost

Author: mateuszbaran

src/solvers/solver.jl

@@ -198,5 +198,11 @@ The method may be implemented by particular solvers if they store the cost at th
 iterate in the state, but by default it is obtained by calling `get_cost(p, get_iterate(s))`.
 """
 function get_cost(p::AbstractManoptProblem, s::AbstractManoptSolverState)
+    return _get_cost(p, s, dispatch_state_decorator(s))
+end
+function _get_cost(p::AbstractManoptProblem, s::AbstractManoptSolverState, ::Val{false})
     return get_cost(p, get_iterate(s))
 end
+function _get_cost(p::AbstractManoptProblem, s::AbstractManoptSolverState, ::Val{true})
+    return get_cost(p, s.state)
+end

test/solvers/test_quasi_Newton.jl

@@ -572,5 +572,9 @@ end
         solve!(mp, qns)
         @test get_cost(mp, qns) == f(M, get_iterate(qns))
 
+        @testset "get_cost with DebugSolverState" begin
+            dqns = DebugSolverState(qns, DebugMessages(:Info, :Always))
+            @test get_cost(mp, dqns) == f(M, get_iterate(dqns))
+        end
     end
 end