BUG: Added test and release note and removed line shifts pandas-dev#46071

Author: KingOfTheShow69

doc/source/whatsnew/v1.5.0.rst

@@ -827,7 +827,7 @@ Datetimelike
 - Bug in :meth:`DatetimeIndex.resolution` incorrectly returning "day" instead of "nanosecond" for nanosecond-resolution indexes (:issue:`46903`)
 - Bug in :class:`Timestamp` with an integer or float value and ``unit="Y"`` or ``unit="M"`` giving slightly-wrong results (:issue:`47266`)
 - Bug in :class:`.DatetimeArray` construction when passed another :class:`.DatetimeArray` and ``freq=None`` incorrectly inferring the freq from the given array (:issue:`47296`)
--
+- Bug in :func:`to_datetime` where ``infer_datetime_format`` fallback would not run if ``errors=coerce`` (:issue:`46071`)
 
 Timedelta
 ^^^^^^^^^

pandas/core/tools/datetimes.py

@@ -215,7 +215,6 @@ def _maybe_cache(
     cache_array : Series
         Cache of converted, unique dates. Can be empty
     """
-
     from pandas import Series
 
     cache_array = Series(dtype=object)
@@ -392,6 +391,7 @@ def _convert_listlike_datetimes(
         raise TypeError(
             "arg must be a string, datetime, list, tuple, 1-d array, or Series"
         )
+
     # warn if passing timedelta64, raise for PeriodDtype
     # NB: this must come after unit transformation
     orig_arg = arg
@@ -411,6 +411,7 @@ def _convert_listlike_datetimes(
 
     if infer_datetime_format and format is None:
         format = _guess_datetime_format_for_array(arg, dayfirst=dayfirst)
+
     if format is not None:
         # There is a special fast-path for iso8601 formatted
         # datetime strings, so in those cases don't use the inferred
@@ -427,6 +428,7 @@ def _convert_listlike_datetimes(
         )
         if res is not None:
             return res
+
     assert format is None or infer_datetime_format
     utc = tz == "utc"
     result, tz_parsed = objects_to_datetime64ns(
@@ -438,6 +440,7 @@ def _convert_listlike_datetimes(
         require_iso8601=require_iso8601,
         allow_object=True,
     )
+
     if tz_parsed is not None:
         # We can take a shortcut since the datetime64 numpy array
         # is in UTC
@@ -492,7 +495,7 @@ def _array_strptime_with_fallback(
     else:
         if "%Z" in fmt or "%z" in fmt:
             return _return_parsed_timezone_results(result, timezones, tz, name)
-        # GH#46071
+
         if infer_datetime_format and np.isnan(result).any():
             return None
 
@@ -513,6 +516,7 @@ def _to_datetime_with_format(
     Try parsing with the given format, returning None on failure.
     """
     result = None
+
     # shortcut formatting here
     if fmt == "%Y%m%d":
         # pass orig_arg as float-dtype may have been converted to
@@ -1028,7 +1032,6 @@ def to_datetime(
                    '2020-01-01 18:00:00+00:00', '2020-01-01 19:00:00+00:00'],
                   dtype='datetime64[ns, UTC]', freq=None)
     """
-
     if arg is None:
         return None
 

pandas/tests/arrays/test_datetimes.py

@@ -639,3 +639,21 @@ def test_tz_localize_t2d(self):
 
         roundtrip = expected.tz_localize("US/Pacific")
         tm.assert_datetime_array_equal(roundtrip, dta)
+
+    @pytest.mark.parametrize(
+        "error",
+        ["coerce", "raise"],
+    )
+    def test_coerce_fallback(self, error):
+        # GH#46071
+        s = pd.Series(["6/30/2025", "1 27 2024"])
+        expected = pd.Series(
+            [pd.Timestamp("2025-06-30 00:00:00"), pd.Timestamp("2024-01-27 00:00:00")]
+        )
+
+        result = pd.to_datetime(s, errors=error, infer_datetime_format=True)
+
+        if error == "coerce":
+            assert result[1] is not pd.NaT
+
+        tm.assert_series_equal(expected, result)