Remember to attach metadata back

Author: YingboMa

src/systems/abstractsystem.jl

@@ -501,9 +501,10 @@ function namespace_expr(O, sys, n = nameof(sys))
             map(a -> namespace_expr(a, sys, n)::Any, arguments(O))
         end
         if isvariable(O)
-            similarterm(O, renamespace(n, operation(O)), renamed)::T
+            similarterm(O, renamespace(n, operation(O)), renamed,
+                        metadata = metadata(O))::T
         else
-            similarterm(O, operation(O), renamed)::T
+            similarterm(O, operation(O), renamed, metadata = metadata(O))::T
         end
     elseif isvariable(O)
         renamespace(n, O)

test/dde.jl

@@ -82,3 +82,27 @@ sys = structural_simplify(sys)
 @test isequal(ModelingToolkit.get_noiseeqs(sys), [α * x(t) + γ;;])
 prob_mtk = SDDEProblem(sys, [x(t) => 1.0 + t], tspan; constant_lags = (τ,));
 @test_nowarn sol_mtk = solve(prob_mtk, RKMil())
+
+
+@variables t
+D = Differential(t)
+@parameters x(..) a
+
+function oscillator(;name, k=1.0, τ=0.01)
+    @parameters k=k τ=τ
+    @variables x(..)=0.1 y(t)=0.1 jcn(t)=0.0 delx(t)
+    eqs = [D(x(t)) ~ y,
+           D(y) ~ -k*x(t-τ)+jcn,
+           delx ~ x(t-τ)]
+    return System(eqs; name=name)
+end
+
+@named osc1 = oscillator(k=1.0, τ=0.01)
+@named osc2 = oscillator(k=2.0, τ=0.04)
+eqs = [osc1.jcn ~ osc2.delx,
+       osc2.jcn ~ osc1.delx]
+@named coupledOsc = System(eqs, t)
+@named coupledOsc = compose(coupledOsc, [osc1, osc2])
+sys = structural_simplify(coupledOsc)
+@test length(equations(sys)) == 4
+@test length(states(sys)) == 4