From 8cbf93f516febf42bf147c0694fb817dcc86cd3a Mon Sep 17 00:00:00 2001
From: lillian542 <Lillian.frederiksen@xanadu.ai>
Date: Tue, 7 May 2024 14:21:25 -0400
Subject: [PATCH] update transforms and gradients using decompose

---
 pennylane/gradients/finite_difference.py             | 1 +
 pennylane/gradients/parameter_shift.py               | 1 +
 pennylane/transforms/compile.py                      | 6 +++++-
 pennylane/transforms/optimization/merge_rotations.py | 5 ++++-
 pennylane/transforms/transpile.py                    | 5 ++++-
 5 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/pennylane/gradients/finite_difference.py b/pennylane/gradients/finite_difference.py
index e478bc65383..05a353b44cd 100644
--- a/pennylane/gradients/finite_difference.py
+++ b/pennylane/gradients/finite_difference.py
@@ -203,6 +203,7 @@ def _expand_transform_finite_diff(
         stopping_condition=_finite_diff_stopping_condition,
         skip_initial_state_prep=False,
         name="finite_diff",
+        error=qml.operation.DecompositionUndefinedError,
     )
     if new_tape is tape:
         return [tape], postprocessing
diff --git a/pennylane/gradients/parameter_shift.py b/pennylane/gradients/parameter_shift.py
index ef2709e7af5..9036378f712 100644
--- a/pennylane/gradients/parameter_shift.py
+++ b/pennylane/gradients/parameter_shift.py
@@ -780,6 +780,7 @@ def _expand_transform_param_shift(
         stopping_condition=_param_shift_stopping_condition,
         skip_initial_state_prep=False,
         name="param_shift",
+        error=qml.operation.DecompositionUndefinedError,
     )
     if new_tape is tape:
         return [tape], postprocessing
diff --git a/pennylane/transforms/compile.py b/pennylane/transforms/compile.py
index a2421a9845a..50bb7104989 100644
--- a/pennylane/transforms/compile.py
+++ b/pennylane/transforms/compile.py
@@ -190,7 +190,11 @@ def stop_at(obj):
             return obj.name in basis_set and (not getattr(obj, "only_visual", False))
 
         [expanded_tape], _ = qml.devices.preprocess.decompose(
-            tape, stopping_condition=stop_at, max_expansion=expand_depth, name="compile"
+            tape,
+            stopping_condition=stop_at,
+            max_expansion=expand_depth,
+            name="compile",
+            error=qml.operation.DecompositionUndefinedError,
         )
 
         # Apply the full set of compilation transforms num_passes times
diff --git a/pennylane/transforms/optimization/merge_rotations.py b/pennylane/transforms/optimization/merge_rotations.py
index e3a7362ae0d..2c8178c1997 100644
--- a/pennylane/transforms/optimization/merge_rotations.py
+++ b/pennylane/transforms/optimization/merge_rotations.py
@@ -123,7 +123,10 @@ def stop_at(obj):
         return not isinstance(obj, Adjoint)
 
     [expanded_tape], _ = qml.devices.preprocess.decompose(
-        tape, stopping_condition=stop_at, name="merge_rotations"
+        tape,
+        stopping_condition=stop_at,
+        name="merge_rotations",
+        error=qml.operation.DecompositionUndefinedError,
     )
     list_copy = expanded_tape.operations
     new_operations = []
diff --git a/pennylane/transforms/transpile.py b/pennylane/transforms/transpile.py
index f2f6e4e0870..8e9fa68e666 100644
--- a/pennylane/transforms/transpile.py
+++ b/pennylane/transforms/transpile.py
@@ -168,7 +168,10 @@ def stop_at(obj):
             return (obj.name in all_ops) and (not getattr(obj, "only_visual", False))
 
         [expanded_tape], _ = qml.devices.preprocess.decompose(
-            tape, stopping_condition=stop_at, name="transpile"
+            tape,
+            stopping_condition=stop_at,
+            name="transpile",
+            error=qml.operation.DecompositionUndefinedError,
         )
         # make copy of ops
         list_op_copy = expanded_tape.operations.copy()