Fix bug in circuit decompose (#8364)

* fix bug in circuit decompose

* add test

* Update test/python/circuit/test_circuit_operations.py

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/transpiler/passes/basis/decompose.py

@@ -128,9 +128,7 @@ class Decompose(TransformationPass):
             node.name in gates or any(fnmatch(node.name, p) for p in strings_list)
         ):
             return True
-        elif not has_label and (  # check if Gate type given
-            any(isinstance(node.op, op) for op in gate_type_list)
-        ):
+        elif any(isinstance(node.op, op) for op in gate_type_list):  # check if Gate type given
             return True
         else:
             return False

releasenotes/notes/decompose-fix-993f7242eaa69407.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - Fixed a bug in :meth:`.QuantumCircuit.decompose` that caused the
+    `gates_to_decompose` argument to be handled incorrectly.

test/python/circuit/test_circuit_operations.py

@@ -1265,3 +1265,10 @@ class TestCircuitPrivateOperations(QiskitTestCase):
         instruction = test._pop_previous_instruction_in_scope()
         self.assertEqual(list(last_instructions), [instruction])
         self.assertEqual({y}, set(test.parameters))
+
+    def test_decompose_gate_type(self):
+        """Test decompose specifying gate type."""
+        circuit = QuantumCircuit(1)
+        circuit.append(SGate(label="s_gate"), [0])
+        decomposed = circuit.decompose(gates_to_decompose=SGate)
+        self.assertNotIn("s", decomposed.count_ops())