Test parameters + defaults in initialization propagation

Fixes #2774

Author: ChrisRackauckas

src/systems/diffeqs/abstractodesystem.jl

@@ -823,7 +823,9 @@ function get_u0(
     if parammap !== nothing
         defs = mergedefaults(defs, parammap, ps)
     end
-    obs = filter!(x -> !(x[1] isa Number), map(x -> x.rhs => x.lhs, observed(sys)))
+
+    obs = filter!(x -> !(x[1] isa Number),
+        map(x -> isparameter(x.rhs) ? x.lhs => x.rhs : x.rhs => x.lhs, observed(sys)))
     observedmap = isempty(obs) ? Dict() : todict(obs)
     defs = mergedefaults(defs, observedmap, u0map, dvs)
     if symbolic_u0

test/guess_propagation.jl

@@ -73,3 +73,38 @@ prob = ODEProblem(sys, [], tspan, [])
 
 @test prob.f.initializeprob[x] == -1.0
 sol = solve(prob.f.initializeprob; show_trace = Val(true))
+
+# Test parameters + defaults
+# https://github.com/SciML/ModelingToolkit.jl/issues/2774
+
+@parameters x0
+@variables x(t)
+@variables y(t) = x
+@mtkbuild sys = ODESystem([x ~ x0, D(y) ~ x], t)
+prob = ODEProblem(sys, [], (0.0, 1.0), [x0 => 1.0])
+@test prob[x] == 1.0
+@test prob[y] == 1.0
+
+@parameters x0
+@variables x(t)
+@variables y(t) = x0
+@mtkbuild sys = ODESystem([x ~ x0, D(y) ~ x], t)
+prob = ODEProblem(sys, [], (0.0, 1.0), [x0 => 1.0])
+prob[x] == 1.0
+prob[y] == 1.0
+
+@parameters x0
+@variables x(t)
+@variables y(t) = x0
+@mtkbuild sys = ODESystem([x ~ y, D(y) ~ x], t)
+prob = ODEProblem(sys, [], (0.0, 1.0), [x0 => 1.0])
+prob[x] == 1.0
+prob[y] == 1.0
+
+@parameters x0
+@variables x(t) = x0
+@variables y(t) = x
+@mtkbuild sys = ODESystem([x ~ y, D(y) ~ x], t)
+prob = ODEProblem(sys, [], (0.0, 1.0), [x0 => 1.0])
+prob[x] == 1.0
+prob[y] == 1.0