feat: InitialFailure if initialization fails

Author: vyudu

lib/ImplicitDiscreteSolve/src/solve.jl

@@ -56,6 +56,10 @@ function _initialize_dae!(integrator, prob::ImplicitDiscreteProblem,
             NonlinearProblem{isinplace(f)}(_f, u, initstate)
         end
         sol = solve(prob, SimpleNewtonRaphson())
-        integrator.u = sol
+        if sol.retcode == ReturnCode.Success
+            integrator.u = sol
+        else
+            integrator.sol = SciMLBase.solution_new_retcode(integrator.sol, ReturnCode.InitialFailure)
+        end
     end
 end

lib/ImplicitDiscreteSolve/test/runtests.jl

@@ -3,6 +3,7 @@ using Test
 using ImplicitDiscreteSolve
 using OrdinaryDiffEqCore
 using OrdinaryDiffEqSDIRK
+using SciMLBase
 
 # Test implicit Euler using ImplicitDiscreteProblem
 @testset "Implicit Euler" begin
@@ -105,3 +106,16 @@ end
     integ = init(idprob, IDSolve())
     @test integ.cache.prob isa NonlinearProblem
 end
+
+@testset "InitialFailure thrown" begin
+    function bad(u_next, u, p, t) 
+        [u_next[1] - u_next[2], u_next[1] - 3, u_next[2] - 4]
+    end
+
+    u0 = [3., 4.]
+    idprob = ImplicitDiscreteProblem(bad, u0, (0, 0), [])
+    integ = init(idprob, IDSolve())
+    @test check_error(integ) == ReturnCode.InitialFailure
+    sol = solve(idprob, IDSolve())
+    @test length(sol.u) == 1
+end