fix: use metadata from variable in equation for clock inference

lib/ModelingToolkitTearing/src/clock_inference/clock_inference.jl

@@ -86,7 +86,7 @@ function (iec::InferEquationClosure)(ieq::Int, eq::Equation, is_initialization_e
     empty!(varsbuf)
     empty!(hyperedge)
     # get variables in equation
-    SU.search_variables!(varsbuf, eq; is_atomic = MTKBase.OperatorIsAtomic{SU.Operator}())
+    SU.search_variables!(varsbuf, eq)
     # add the equation to the hyperedge
     eq_node = if is_initialization_equation
         ClockVertex.InitEquation(ieq)
@@ -99,6 +99,11 @@ function (iec::InferEquationClosure)(ieq::Int, eq::Equation, is_initialization_e
         # if this is just a single variable, add it to the hyperedge
         if idx isa Int
             push!(hyperedge, ClockVertex.Variable(idx))
+            d = get_time_domain(var)
+            if is_concrete_time_domain(d)
+                push!(hyperedge, ClockVertex.Clock(d))
+            end
+
             # we don't immediately `continue` here because this variable might be a
             # `Sample` or similar and we want the clock information from it if it is.
         end

lib/ModelingToolkitTearing/test/runtests.jl

@@ -42,3 +42,17 @@ end
     @test !Graphs.has_edge(ts.structure.graph, BipartiteEdge(2, x_idx))
     @test !SU.query(isequal(x), equations(ts)[2].rhs)
 end
+
+@testset "Clock inference doesn't only rely on `fullvars` for metadata clock information" begin
+    @variables y(t) l(t)
+    k = ShiftIndex(Clock(0.1))
+    eqs = [
+        y(k) ~ -Sample()(l),
+        D(l) ~ 20*(Hold()(y) - l)
+    ]
+
+    @named cl = System(eqs, t)
+    # It should throw this error, not one saying it can't find a clock for an
+    # inferreddiscrete partition
+    @test_throws ModelingToolkit.HybridSystemNotSupportedException mtkcompile(cl)
+end