fix: fix substitute not propagating to pdeps, defs, guesses and subsystems

Author: AayushSabharwal

src/systems/abstractsystem.jl

@@ -2940,7 +2940,14 @@ function Symbolics.substitute(sys::AbstractSystem, rules::Union{Vector{<:Pair},
         rules = todict(map(r -> Symbolics.unwrap(r[1]) => Symbolics.unwrap(r[2]),
             collect(rules)))
         eqs = fast_substitute(equations(sys), rules)
-        ODESystem(eqs, get_iv(sys); name = nameof(sys))
+        pdeps = fast_substitute(parameter_dependencies(sys), rules)
+        defs = Dict(fast_substitute(k, rules) => fast_substitute(v, rules)
+        for (k, v) in defaults(sys))
+        guess = Dict(fast_substitute(k, rules) => fast_substitute(v, rules)
+        for (k, v) in guesses(sys))
+        subsys = map(s -> substitute(s, rules), get_systems(sys))
+        ODESystem(eqs, get_iv(sys); name = nameof(sys), defaults = defs,
+            guesses = guess, parameter_dependencies = pdeps, systems = subsys)
     else
         error("substituting symbols is not supported for $(typeof(sys))")
     end

test/odesystem.jl

@@ -1315,3 +1315,19 @@ end
     @named sys = compose(sys, sys) # nest into a hierarchical system
     @test t === sys.t === sys.sys.t
 end
+
+@testset "Substituting preserves parameter dependencies, defaults, guesses" begin
+    @parameters p1 p2
+    @variables x(t) y(t)
+    @named sys = ODESystem([D(x) ~ y + p2], t; parameter_dependencies = [p2 ~ 2p1],
+        defaults = [p1 => 1.0, p2 => 2.0], guesses = [p1 => 2.0, p2 => 3.0])
+    @parameters p3
+    sys2 = substitute(sys, [p1 => p3])
+    @test length(parameters(sys2)) == 1
+    @test is_parameter(sys2, p3)
+    @test !is_parameter(sys2, p1)
+    @test length(ModelingToolkit.defaults(sys2)) == 2
+    @test ModelingToolkit.defaults(sys2)[p3] == 1.0
+    @test length(ModelingToolkit.guesses(sys2)) == 2
+    @test ModelingToolkit.guesses(sys2)[p3] == 2.0
+end