fix: array parameters in nested @mtkmodel components

src/systems/abstractsystem.jl

@@ -1140,7 +1140,35 @@ namespace_parameters(sys::AbstractSystem) = parameters(sys, parameters(sys))
 
 function namespace_defaults(sys)
     defs = defaults(sys)
-    Dict((isparameter(k) ? parameters(sys, k) : unknowns(sys, k)) => namespace_expr(v, sys)
+    sys_params = Set(parameters(sys))
+    sys_unknowns = Set(unknowns(sys))
+
+    function should_namespace(val)
+        # If it's a parameter from parent scope, don't namespace it
+        if isparameter(val) && !(unwrap(val) in sys_params || unwrap(val) in sys_unknowns)
+            return false
+        end
+
+        # Check if the expression contains any parent scope parameters
+        # vars() collects all variables in an expression
+        try
+            expr_vars = vars(val; op = Nothing)
+            for var in expr_vars
+                var_unwrapped = unwrap(var)
+                # If any variable in the expression is from parent scope, don't namespace
+                if isparameter(var_unwrapped) && !(var_unwrapped in sys_params || var_unwrapped in sys_unknowns)
+                    return false
+                end
+            end
+        catch
+            # If vars() fails, fall back to default behavior
+        end
+
+        return true
+    end
+
+    Dict((isparameter(k) ? parameters(sys, k) : unknowns(sys, k)) =>
+         (should_namespace(v) ? namespace_expr(v, sys) : v)
     for (k, v) in pairs(defs))
 end
 

test/model_parsing.jl

@@ -935,6 +935,80 @@ end
     @test getdefault(main_sys.v1) == 13
 end
 
+@testset "Array parameters in nested @mtkmodel components" begin
+    # Test for issue where array parameters passed to nested models
+    # were not correctly resolved to their parent scope values
+    @mtkmodel InnerWithArrayParam begin
+        @parameters begin
+            a[1:2] = a
+        end
+        @variables begin
+            x(t)[1:2] = zeros(2)
+        end
+        @equations begin
+            D(x) ~ a
+        end
+    end
+
+    @mtkmodel OuterWithArrayParam begin
+        @parameters begin
+            a1 = 1
+            a2 = 2
+        end
+        @components begin
+            inner = InnerWithArrayParam(a = [a1+a2, a2])
+        end
+        @variables begin
+            y(t)[1:2] = zeros(2)
+        end
+        @equations begin
+            D(y) ~ [a1+a2, a2]
+        end
+    end
+
+    @named sys = OuterWithArrayParam()
+    sys = complete(sys)
+
+    # Check that the defaults are correctly mapped
+    defs = ModelingToolkit.defaults(sys)
+
+    # Find the keys for inner.a[1] and inner.a[2]
+    inner_a1_key = nothing
+    inner_a2_key = nothing
+    outer_a1_key = nothing
+    outer_a2_key = nothing
+
+    for (k, v) in defs
+        k_str = string(k)
+        if k_str == "inner₊a[1]"
+            inner_a1_key = k
+        elseif k_str == "inner₊a[2]"
+            inner_a2_key = k
+        elseif k_str == "a1"
+            outer_a1_key = k
+        elseif k_str == "a2"
+            outer_a2_key = k
+        end
+    end
+
+    @test inner_a1_key !== nothing
+    @test inner_a2_key !== nothing
+    @test outer_a1_key !== nothing
+    @test outer_a2_key !== nothing
+
+    # The inner array parameter elements should map to the outer parameters
+    @test isequal(defs[inner_a1_key], sys.a1 + sys.a2)
+    @test isequal(defs[inner_a2_key], sys.a2)
+    @test defs[outer_a1_key] == 1
+    @test defs[outer_a2_key] == 2
+
+    # Test that ODEProblem can be created successfully
+    prob = ODEProblem(mtkcompile(sys), [], (0.0, 1.0))
+    @test prob isa ODEProblem
+    # sol = solve(prob, Tsit5())
+    # @test sol[sys.y] ≈ sol[sys.inner.x]
+end
+
 @mtkmodel InnerModel begin
     @parameters begin
         p