Resolve error identifying vars in indexed SOS

pyomo/repn/plugins/nl_writer.py

@@ -684,7 +684,7 @@ def write(self, model):
         # variable order because the SOS constraint *could* reference a
         # variable not yet seen in the model.
         for block in component_map[SOSConstraint]:
-            for sos in block.component_objects(
+            for sos in block.component_data_objects(
                 SOSConstraint, active=True, descend_into=False, sort=sorter
             ):
                 for v in sos.variables:

pyomo/repn/tests/ampl/test_nlv2.py

@@ -35,6 +35,7 @@
     Constraint,
     Expression,
 )
+import pyomo.environ as pyo
 
 _invalid_1j = r'InvalidNumber\((\([-+0-9.e]+\+)?1j\)?\)'
 
@@ -955,6 +956,76 @@ def test_linear_constraint_npv_const(self):
 J0 2
 0 5
 1 10
+""",
+                OUT.getvalue(),
+            )
+        )
+
+    def test_indexed_sos_constraints(self):
+        # This tests the example from issue #2827
+        m = pyo.ConcreteModel()
+        m.A = pyo.Set(initialize=[1])
+        m.B = pyo.Set(initialize=[1, 2, 3])
+        m.C = pyo.Set(initialize=[1])
+
+        m.param_cx = pyo.Param(m.A, initialize={1: 1})
+        m.param_cy = pyo.Param(m.B, initialize={1: 2, 2: 3, 3: 1})
+
+        m.x = pyo.Var(m.A, domain=pyo.NonNegativeReals, bounds=(0, 40))
+        m.y = pyo.Var(m.B, domain=pyo.NonNegativeIntegers)
+
+        @m.Objective()
+        def OBJ(m):
+            return sum(m.param_cx[a] * m.x[a] for a in m.A) + sum(
+                m.param_cy[b] * m.y[b] for b in m.B
+            )
+
+        m.y[3].bounds = (2, 3)
+
+        m.mysos = pyo.SOSConstraint(
+            m.C, var=m.y, sos=1, index={1: [2, 3]}, weights={2: 25.0, 3: 18.0}
+        )
+
+        OUT = io.StringIO()
+        with LoggingIntercept() as LOG:
+            nl_writer.NLWriter().write(m, OUT, symbolic_solver_labels=True)
+        self.assertEqual(LOG.getvalue(), "")
+        self.assertEqual(
+            *nl_diff(
+                """g3 1 1 0        # problem unknown
+ 4 0 1 0 0      # vars, constraints, objectives, ranges, eqns
+ 0 0 0 0 0 0    # nonlinear constrs, objs; ccons: lin, nonlin, nd, nzlb
+ 0 0    # network constraints: nonlinear, linear
+ 0 0 0  # nonlinear vars in constraints, objectives, both
+ 0 0 0 1        # linear network variables; functions; arith, flags
+ 0 3 0 0 0      # discrete variables: binary, integer, nonlinear (b,c,o)
+ 0 4    # nonzeros in Jacobian, obj. gradient
+ 3 4    # max name lengths: constraints, variables
+ 0 0 0 0 0      # common exprs: b,c,o,c1,o1
+S0 2 sosno
+2 1
+3 1
+S0 2 ref
+2 25.0
+3 18.0
+O0 0    #OBJ
+n0
+x0      # initial guess
+r       #0 ranges (rhs's)
+b       #4 bounds (on variables)
+0 0 40  #x[1]
+2 0     #y[1]
+2 0     #y[2]
+0 2 3   #y[3]
+k3      #intermediate Jacobian column lengths
+0
+0
+0
+G0 4    #OBJ
+0 1
+1 2
+2 3
+3 1
 """,
                 OUT.getvalue(),
             )