Merge pull request #1275 from SciML/myb/compose

Fix preference of defaults for composed models

Author: YingboMa

src/systems/abstractsystem.jl

@@ -420,7 +420,13 @@ Base.@deprecate default_p(x) defaults(x) false
 function defaults(sys::AbstractSystem)
     systems = get_systems(sys)
     defs = get_defaults(sys)
-    isempty(systems) ? defs : mapreduce(namespace_defaults, merge, systems; init=defs)
+    # `mapfoldr` is really important!!! We should prefer the base model for
+    # defaults, because people write:
+    #
+    # `compose(ODESystem(...; defaults=defs), ...)`
+    #
+    # Thus, right associativity is required and crucial for correctness.
+    isempty(systems) ? defs : mapfoldr(namespace_defaults, merge, systems; init=defs)
 end
 
 states(sys::AbstractSystem, v) = renamespace(sys, v)

test/components.jl

@@ -55,3 +55,26 @@ D = Differential(t)
 @named sys1 = extend(ODESystem([D(x3) ~ x3], t; name=:foo), sys1_partial)
 @named sys2 = compose(ODESystem([D(x4) ~ x4], t; name=:foo), sys1)
 @test_nowarn sys2.sys1.sys1_inner.x1 # test the correct nesting
+
+
+# compose tests
+@parameters t
+
+function record_fun(;name)
+    pars = @parameters a=10 b=100
+    ODESystem(Equation[], t, [], pars; name)
+end
+
+function first_model(;name)
+    @named foo=record_fun()
+
+    defs = Dict()
+    defs[foo.a] = 3
+    defs[foo.b] = 300
+    pars = @parameters x=2 y=20
+    compose(ODESystem(Equation[], t, [], pars; name, defaults=defs), foo)
+end
+@named goo = first_model()
+@unpack foo = goo
+@test ModelingToolkit.defaults(goo)[foo.a] == 3
+@test ModelingToolkit.defaults(goo)[foo.b] == 300