fix direct structural simplification for initialization systems

Author: ChrisRackauckas

src/systems/systemstructure.jl

@@ -636,7 +636,9 @@ function _structural_simplify!(state::TearingState, io; simplify = false,
     fullunknowns = [map(eq -> eq.lhs, observed(sys)); unknowns(sys)]
     @set! sys.observed = ModelingToolkit.topsort_equations(observed(sys), fullunknowns)
 
-    if sys isa ODESystem
+    ci = infer_clocks!(ClockInference(state))
+    # TODO: make it work with clocks
+    if sys isa ODESystem && all(isequal(Continuous()), ci.var_domain) && !all(all(x->!(typeof(x) <: Union{Sample,Hold,ShiftIndex}),io))
         isys = ModelingToolkit.generate_initializesystem(sys)
         !isempty(equations(isys)) &&
             (isys = structural_simplify(isys; fully_determined = false))

test/clock.jl

@@ -62,6 +62,7 @@ By inference:
 =>   Shift(x, 0, dt) := (Shift(x, -1, dt) + dt) / (1 - dt) # Discrete system
 =#
 
+
 ci, varmap = infer_clocks(sys)
 eqmap = ci.eq_domain
 tss, inputs = ModelingToolkit.split_system(deepcopy(ci))