BUG: merge_asof(tolerance=Timedelta) with ArrowDtype

doc/source/whatsnew/v2.2.0.rst

@@ -666,6 +666,7 @@ Reshaping
 - Bug in :func:`concat` renaming :class:`Series` when ``ignore_index=False`` (:issue:`15047`)
 - Bug in :func:`merge_asof` raising ``TypeError`` when ``by`` dtype is not ``object``, ``int64``, or ``uint64`` (:issue:`22794`)
 - Bug in :func:`merge_asof` raising incorrect error for string dtype (:issue:`56444`)
+- Bug in :func:`merge_asof` when using a :class:`Timedelta` tolerance on a :class:`ArrowDtype` column (:issue:`56486`)
 - Bug in :func:`merge` returning columns in incorrect order when left and/or right is empty (:issue:`51929`)
 - Bug in :meth:`DataFrame.melt` where an exception was raised if ``var_name`` was not a string (:issue:`55948`)
 - Bug in :meth:`DataFrame.melt` where it would not preserve the datetime (:issue:`55254`)

pandas/core/reshape/merge.py

@@ -2071,7 +2071,9 @@ def _validate_tolerance(self, left_join_keys: list[ArrayLike]) -> None:
                 f"with type {repr(lt.dtype)}"
             )
 
-            if needs_i8_conversion(lt.dtype):
+            if needs_i8_conversion(lt.dtype) or (
+                isinstance(lt, ArrowExtensionArray) and lt.dtype.kind in "mM"
+            ):
                 if not isinstance(self.tolerance, datetime.timedelta):
                     raise MergeError(msg)
                 if self.tolerance < Timedelta(0):
@@ -2137,15 +2139,21 @@ def _get_join_indexers(self) -> tuple[npt.NDArray[np.intp], npt.NDArray[np.intp]
         if tolerance is not None:
             # TODO: can we reuse a tolerance-conversion function from
             #  e.g. TimedeltaIndex?
-            if needs_i8_conversion(left_values.dtype):
+            if needs_i8_conversion(left_values.dtype) or (
+                isinstance(left_values, ArrowExtensionArray)
+                and left_values.dtype.kind in "mM"
+            ):
                 tolerance = Timedelta(tolerance)
                 # TODO: we have no test cases with PeriodDtype here; probably
                 #  need to adjust tolerance for that case.
                 if left_values.dtype.kind in "mM":
                     # Make sure the i8 representation for tolerance
                     #  matches that for left_values/right_values.
-                    lvs = ensure_wrapped_if_datetimelike(left_values)
-                    tolerance = tolerance.as_unit(lvs.unit)
+                    if isinstance(left_values, ArrowExtensionArray):
+                        unit = left_values.dtype.pyarrow_dtype.unit
+                    else:
+                        unit = ensure_wrapped_if_datetimelike(left_values).unit
+                    tolerance = tolerance.as_unit(unit)
 
                 tolerance = tolerance._value
 

pandas/tests/reshape/merge/test_merge_asof.py

@@ -3577,6 +3577,29 @@ def test_merge_asof_extension_dtype(dtype):
     tm.assert_frame_equal(result, expected)
 
 
+@td.skip_if_no("pyarrow")
+def test_merge_asof_pyarrow_td_tolerance():
+    # GH 56486
+    ser = pd.Series(
+        [datetime.datetime(2023, 1, 1)], dtype="timestamp[us, UTC][pyarrow]"
+    )
+    df = pd.DataFrame(
+        {
+            "timestamp": ser,
+            "value": [1],
+        }
+    )
+    result = merge_asof(df, df, on="timestamp", tolerance=Timedelta("1s"))
+    expected = pd.DataFrame(
+        {
+            "timestamp": ser,
+            "value_x": [1],
+            "value_y": [1],
+        }
+    )
+    tm.assert_frame_equal(result, expected)
+
+
 def test_merge_asof_read_only_ndarray():
     # GH 53513
     left = pd.Series([2], index=[2], name="left")