Merge pull request #1149 from AayushSabharwal/as/null-sol-resid-prototype

feat: pass `resid_prototype` as `u` to null oop `NonlinearLeastSquaresProblem`

Author: ChrisRackauckas

src/solve.jl

@@ -776,7 +776,7 @@ function build_null_solution(
         resid = isnothing(prob.f.resid_prototype) ? Float64[] : copy(prob.f.resid_prototype)
         prob.f(resid, prob.u0, prob.p)
     else
-        resid = prob.f(prob.u0, prob.p)
+        resid = prob.f(prob.f.resid_prototype, prob.p)
     end
 
     if success

test/downstream/null_de.jl

@@ -1,4 +1,5 @@
 using ModelingToolkit, OrdinaryDiffEq, SteadyStateDiffEq, Test
+using StaticArrays
 using ModelingToolkit: t_nounits as t, D_nounits as D
 using ForwardDiff
 
@@ -77,3 +78,12 @@ sol = solve(unsatprob) # Success
     @test_nowarn ForwardDiff.derivative(x_at_1_num, 1.0)
     @test_nowarn ForwardDiff.derivative(x_at_1_anal, 1.0)
 end
+
+@testset "Null OOP NonlinearLeastSquaresProblem" begin
+    fn = NonlinearFunction{false}(; resid_prototype = SA[1.0]) do u, p
+        return zero(u)
+    end
+    prob = NonlinearLeastSquaresProblem(fn, nothing)
+    sol = solve(prob)
+    @test sol.resid isa SVector{1, Float64}
+end