SCCNonlinearProblem has no field `u0` in SCCNonlinearSolve 1.7

[mx-p9a]

Describe the bug 🐞

When using Modelingtoolkit, I am running into this error for SCCNonlinearSolve@1.7 (not 1.6).
Note that for the MWE, I did not include the modelingtoolkit models and instead run SCCNonlinearSolve directly.

Expected behavior

Modelingtoolkit problem to just solve.

Minimal Reproducible Example 👇

# MWE: SCCNonlinearProblem missing `u0` field in SCCNonlinearSolve v1.7.0
# 
# ERROR: FieldError: type SCCNonlinearProblem has no field `u0`, 
#        available fields: `probs`, `explicitfuns!`, `f`, `p`, `parameters_alias`
#
# The bug is in SCCNonlinearSolve.jl line 39:
#   u0 = u0 !== nothing ? u0 : prob.u0
# But SCCNonlinearProblem does not have a `u0` field.
#

# --- Setup with BROKEN version ---
using Pkg
Pkg.activate(temp=true)
Pkg.add([
    PackageSpec(name="SciMLBase"),
    PackageSpec(name="SCCNonlinearSolve"),
    PackageSpec(name="NonlinearSolve"),
])


using SciMLBase
import SCCNonlinearSolve
import NonlinearSolve

println("SCCNonlinearSolve version: ", pkgversion(SCCNonlinearSolve))

# Create simple nonlinear subproblems
f1(u, p) = u[1]^2 - 2.0
f2(u, p) = u[1] - 1.0

prob1 = NonlinearProblem(f1, [1.0])
prob2 = NonlinearProblem(f2, [1.0])

# Create explicit functions (identity - just pass through)
explicitfun1!(p, sols) = nothing
explicitfun2!(p, sols) = nothing

# Create the SCC problem
scc_prob = SciMLBase.SCCNonlinearProblem(
    (prob1, prob2),
    (explicitfun1!, explicitfun2!),
    nothing,  # parameters
    false     # parameters_alias
)

println("Created SCCNonlinearProblem successfully")
println("Attempting to solve...")

# This triggers the bug - solve() is called without explicit u0,
# so it tries `prob.u0` but SCCNonlinearProblem has no `u0` field
sol = SciMLBase.solve(scc_prob)

println("Solution: ", sol.retcode)

Error & Stacktrace ⚠️

ERROR: LoadError: FieldError: type SCCNonlinearProblem has no field `u0`, available fields: `probs`, `explicitfuns!`, `f`, `p`, `parameters_alias`
Stacktrace:
 [1] getproperty(prob::SCCNonlinearProblem{Vector{Float64}, false, Tuple{NonlinearProblem{Vector{Float64}, false, SciMLBase.NullParameters, NonlinearFunction{false, SciMLBase.FullSpecialize, typeof(f1), LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, @Kwargs{}, SciMLBase.StandardNonlinearProblem, Nothing, Nothing}, NonlinearProblem{Vector{Float64}, false, SciMLBase.NullParameters, NonlinearFunction{false, SciMLBase.FullSpecialize, typeof(f2), LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, @Kwargs{}, SciMLBase.StandardNonlinearProblem, Nothing, Nothing}}, Tuple{typeof(explicitfun1!), typeof(explicitfun2!)}, NonlinearFunction{false, SciMLBase.FullSpecialize, Returns{Nothing}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, Nothing, Val{false}}, name::Symbol)
   @ SciMLBase ~/.julia/packages/SciMLBase/hHrRi/src/problems/nonlinear_problems.jl:547
 [2] solve(prob::SCCNonlinearProblem{Vector{Float64}, false, Tuple{NonlinearProblem{Vector{Float64}, false, SciMLBase.NullParameters, NonlinearFunction{false, SciMLBase.FullSpecialize, typeof(f1), LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, @Kwargs{}, SciMLBase.StandardNonlinearProblem, Nothing, Nothing}, NonlinearProblem{Vector{Float64}, false, SciMLBase.NullParameters, NonlinearFunction{false, SciMLBase.FullSpecialize, typeof(f2), LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, @Kwargs{}, SciMLBase.StandardNonlinearProblem, Nothing, Nothing}}, Tuple{typeof(explicitfun1!), typeof(explicitfun2!)}, NonlinearFunction{false, SciMLBase.FullSpecialize, Returns{Nothing}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, Nothing, Val{false}}, alg::SCCNonlinearSolve.SCCAlg{Nothing, Nothing}; sensealg::Nothing, u0::Nothing, p::Nothing, kwargs::@Kwargs{})
   @ SCCNonlinearSolve ~/.julia/packages/SCCNonlinearSolve/6Z5wl/src/SCCNonlinearSolve.jl:39
 [3] solve(prob::SCCNonlinearProblem{Vector{Float64}, false, Tuple{NonlinearProblem{Vector{Float64}, false, SciMLBase.NullParameters, NonlinearFunction{false, SciMLBase.FullSpecialize, typeof(f1), LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, @Kwargs{}, SciMLBase.StandardNonlinearProblem, Nothing, Nothing}, NonlinearProblem{Vector{Float64}, false, SciMLBase.NullParameters, NonlinearFunction{false, SciMLBase.FullSpecialize, typeof(f2), LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, @Kwargs{}, SciMLBase.StandardNonlinearProblem, Nothing, Nothing}}, Tuple{typeof(explicitfun1!), typeof(explicitfun2!)}, NonlinearFunction{false, SciMLBase.FullSpecialize, Returns{Nothing}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, Nothing, Val{false}}; sensealg::Nothing, u0::Nothing, p::Nothing, kwargs::@Kwargs{})
   @ SCCNonlinearSolve ~/.julia/packages/SCCNonlinearSolve/6Z5wl/src/SCCNonlinearSolve.jl:28
 [4] solve(prob::SCCNonlinearProblem{Vector{Float64}, false, Tuple{NonlinearProblem{Vector{Float64}, false, SciMLBase.NullParameters, NonlinearFunction{false, SciMLBase.FullSpecialize, typeof(f1), LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, @Kwargs{}, SciMLBase.StandardNonlinearProblem, Nothing, Nothing}, NonlinearProblem{Vector{Float64}, false, SciMLBase.NullParameters, NonlinearFunction{false, SciMLBase.FullSpecialize, typeof(f2), LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, @Kwargs{}, SciMLBase.StandardNonlinearProblem, Nothing, Nothing}}, Tuple{typeof(explicitfun1!), typeof(explicitfun2!)}, NonlinearFunction{false, SciMLBase.FullSpecialize, Returns{Nothing}, LinearAlgebra.UniformScaling{Bool}, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, typeof(SciMLBase.DEFAULT_OBSERVED_NO_TIME), Nothing, Nothing, Nothing, Nothing}, Nothing, Val{false}})
   @ SCCNonlinearSolve ~/.julia/packages/SCCNonlinearSolve/6Z5wl/src/SCCNonlinearSolve.jl:26
 [5] top-level scope
   @ ~/code/scepter/ScepterMTK.jl/mwe_sccnonlinearsolve_bug.jl:61
 [6] include(mod::Module, _path::String)
   @ Base ./Base.jl:306
 [7] exec_options(opts::Base.JLOptions)
   @ Base ./client.jl:317
 [8] _start()
   @ Base ./client.jl:550
in expression starting at /Users/mx/code/scepter/ScepterMTK.jl/mwe_sccnonlinearsolve_bug.jl:61

Environment (please complete the following information):

• Temp project

  Activating new project at `/var/folders/7y/gscz13l92lg37k3dypjlfbdh0000gn/T/jl_lT7hud`
   Resolving package versions...
    Updating `/private/var/folders/7y/gscz13l92lg37k3dypjlfbdh0000gn/T/jl_lT7hud/Project.toml`
  [8913a72c] + NonlinearSolve v4.12.0
⌃ [9dfe8606] + SCCNonlinearSolve v1.6.0
  [0bca4576] + SciMLBase v2.128.0
    Updating `/private/var/folders/7y/gscz13l92lg37k3dypjlfbdh0000gn/T/jl_lT7hud/Manifest.toml`
  [47edcb42] + ADTypes v1.20.0
  [7d9f7c33] + Accessors v0.1.43
  [79e6a3ab] + Adapt v4.4.0
  [4fba245c] + ArrayInterface v7.22.0
  [4c555306] + ArrayLayouts v1.12.2
  [70df07ce] + BracketingNonlinearSolve v1.6.0
  [d360d2e6] + ChainRulesCore v1.26.0
  [38540f10] + CommonSolve v0.2.4
  [bbf7d656] + CommonSubexpressions v0.3.1
  [34da2185] + Compat v4.18.1
  [a33af91c] + CompositionsBase v0.1.2
  [2569d6c7] + ConcreteStructs v0.2.3
  [187b0558] + ConstructionBase v1.6.0
  [163ba53b] + DiffResults v1.1.0
  [b552c78f] + DiffRules v1.15.1
  [a0c0ee7d] + DifferentiationInterface v0.7.13
  [ffbed154] + DocStringExtensions v0.9.5
  [4e289a0a] + EnumX v1.0.5
  [f151be2c] + EnzymeCore v0.8.17
  [e2ba6199] + ExprTools v0.1.10
  [55351af7] + ExproniconLite v0.10.14
  [9aa1b823] + FastClosures v0.3.2
  [1a297f60] + FillArrays v1.15.0
  [6a86dc24] + FiniteDiff v2.29.0
  [f6369f11] + ForwardDiff v1.3.0
  [069b7b12] + FunctionWrappers v1.1.3
  [77dc65aa] + FunctionWrappersWrappers v0.1.3
  [46192b85] + GPUArraysCore v0.2.0
  [3587e190] + InverseFunctions v0.1.17
  [92d709cd] + IrrationalConstants v0.2.6
  [82899510] + IteratorInterfaceExtensions v1.0.0
  [692b3bcd] + JLLWrappers v1.7.1
  [ae98c720] + Jieko v0.2.1
  [ba0b0d4f] + Krylov v0.10.3
  [5078a376] + LazyArrays v2.9.4
  [87fe0de2] + LineSearch v0.1.4
  [7ed4a6bd] + LinearSolve v3.54.0
  [2ab3a3ac] + LogExpFunctions v0.3.29
  [e6f89c97] + LoggingExtras v1.2.0
  [1914dd2f] + MacroTools v0.5.16
  [bb5d69b7] + MaybeInplace v0.1.4
  [2e0e35c7] + Moshi v0.3.7
  [77ba4419] + NaNMath v1.1.3
  [8913a72c] + NonlinearSolve v4.12.0
  [be0214bd] + NonlinearSolveBase v2.9.0
  [5959db7a] + NonlinearSolveFirstOrder v1.10.0
  [9a2c21bd] + NonlinearSolveQuasiNewton v1.11.0
  [26075421] + NonlinearSolveSpectralMethods v1.6.0
  [d236fae5] + PreallocationTools v0.4.34
  [aea7be01] + PrecompileTools v1.3.3
  [21216c6a] + Preferences v1.5.1
  [3cdcf5f2] + RecipesBase v1.3.4
  [731186ca] + RecursiveArrayTools v3.42.0
  [189a3867] + Reexport v1.2.2
  [ae029012] + Requires v1.3.1
  [7e49a35a] + RuntimeGeneratedFunctions v0.5.16
⌃ [9dfe8606] + SCCNonlinearSolve v1.6.0
  [0bca4576] + SciMLBase v2.128.0
  [19f34311] + SciMLJacobianOperators v0.1.12
  [a6db7da4] + SciMLLogging v1.7.1
  [c0aeaf25] + SciMLOperators v1.14.1
  [431bcebd] + SciMLPublic v1.0.0
  [53ae85a6] + SciMLStructures v1.7.0
  [efcf1570] + Setfield v1.1.2
  [727e6d20] + SimpleNonlinearSolve v2.9.0
  [276daf66] + SpecialFunctions v2.6.1
  [90137ffa] + StaticArrays v1.9.15
  [1e83bf80] + StaticArraysCore v1.4.4
  [10745b16] + Statistics v1.11.1
  [2efcf032] + SymbolicIndexingInterface v0.3.46
  [a759f4b9] + TimerOutputs v0.5.29
  [1d5cc7b8] + IntelOpenMP_jll v2025.2.0+0
  [856f044c] + MKL_jll v2025.2.0+0
  [efe28fd5] + OpenSpecFun_jll v0.5.6+0
  [1317d2d5] + oneTBB_jll v2022.0.0+1
  [0dad84c5] + ArgTools v1.1.2
  [56f22d72] + Artifacts v1.11.0
  [2a0f44e3] + Base64 v1.11.0
  [ade2ca70] + Dates v1.11.0
  [8ba89e20] + Distributed v1.11.0
  [f43a241f] + Downloads v1.7.0
  [7b1f6079] + FileWatching v1.11.0
  [9fa8497b] + Future v1.11.0
  [b77e0a4c] + InteractiveUtils v1.11.0
  [ac6e5ff7] + JuliaSyntaxHighlighting v1.12.0
  [4af54fe1] + LazyArtifacts v1.11.0
  [b27032c2] + LibCURL v0.6.4
  [76f85450] + LibGit2 v1.11.0
  [8f399da3] + Libdl v1.11.0
  [37e2e46d] + LinearAlgebra v1.12.0
  [56ddb016] + Logging v1.11.0
  [d6f4376e] + Markdown v1.11.0
  [ca575930] + NetworkOptions v1.3.0
  [44cfe95a] + Pkg v1.12.1
  [de0858da] + Printf v1.11.0
  [9a3f8284] + Random v1.11.0
  [ea8e919c] + SHA v0.7.0
  [9e88b42a] + Serialization v1.11.0
  [6462fe0b] + Sockets v1.11.0
  [2f01184e] + SparseArrays v1.12.0
  [f489334b] + StyledStrings v1.11.0
  [fa267f1f] + TOML v1.0.3
  [a4e569a6] + Tar v1.10.0
  [cf7118a7] + UUIDs v1.11.0
  [4ec0a83e] + Unicode v1.11.0
  [e66e0078] + CompilerSupportLibraries_jll v1.3.0+1
  [deac9b47] + LibCURL_jll v8.15.0+0
  [e37daf67] + LibGit2_jll v1.9.0+0
  [29816b5a] + LibSSH2_jll v1.11.3+1
  [14a3606d] + MozillaCACerts_jll v2025.5.20
  [4536629a] + OpenBLAS_jll v0.3.29+0
  [05823500] + OpenLibm_jll v0.8.7+0
  [458c3c95] + OpenSSL_jll v3.5.4+0
  [bea87d4a] + SuiteSparse_jll v7.8.3+2
  [83775a58] + Zlib_jll v1.3.1+2
  [8e850b90] + libblastrampoline_jll v5.15.0+0
  [8e850ede] + nghttp2_jll v1.64.0+1
  [3f19e933] + p7zip_jll v17.7.0+0

• Output of versioninfo()

Julia Version 1.12.3
Commit 966d0af0fdf (2025-12-15 11:20 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: macOS (arm64-apple-darwin24.0.0)
  CPU: 12 × Apple M2 Max
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, apple-m2)
  GC: Built with stock GC
Threads: 1 default, 1 interactive, 1 GC (on 8 virtual cores)
Environment:
  JULIA_PKG_USE_CLI_GIT = true

Additional context

Add any other context about the problem here.

[ChrisRackauckas]

Ahh this was introduced with the new capturing logic. I'll get to it tomorrow, pulling back nonlinearsolvebase will stop it. Until then, there is a sick karaoke set to perform, but maybe the bots will get this right

[ChrisRackauckas]

Ahh this was introduced with the new capturing logic. I'll get to it tomorrow, pulling back nonlinearsolvebase will stop it. Until then, there is a sick karaoke set to perform, but maybe the bots will get this right