DEPR: warn parameter in infer_freq (#45947)

* DEPR: warn parameter in infer_freq

* Add issue number

Author: mroeschke

doc/source/whatsnew/v1.5.0.rst

@@ -240,7 +240,7 @@ Other Deprecations
 - Deprecated :meth:`Series.is_monotonic` and :meth:`Index.is_monotonic` in favor of :meth:`Series.is_monotonic_increasing` and :meth:`Index.is_monotonic_increasing` (:issue:`45422`, :issue:`21335`)
 - Deprecated the ``__array_wrap__`` method of DataFrame and Series, rely on standard numpy ufuncs instead (:issue:`45451`)
 - Deprecated the behavior of :meth:`Series.fillna` and :meth:`DataFrame.fillna` with ``timedelta64[ns]`` dtype and incompatible fill value; in a future version this will cast to a common dtype (usually object) instead of raising, matching the behavior of other dtypes (:issue:`45746`)
--
+- Deprecated the ``warn`` parameter in :func:`infer_freq` (:issue:`45947`)
 
 
 .. ---------------------------------------------------------------------------

pandas/tests/tseries/frequencies/test_inference.py

@@ -502,3 +502,8 @@ def test_ms_vs_capital_ms():
 
     assert left == offsets.Milli()
     assert right == offsets.MonthBegin()
+
+
+def test_infer_freq_warn_deprecated():
+    with tm.assert_produces_warning(FutureWarning):
+        frequencies.infer_freq(date_range(2022, periods=3), warn=False)

pandas/tseries/frequencies.py

@@ -128,14 +128,14 @@ def get_offset(name: str) -> DateOffset:
 
 def infer_freq(index, warn: bool = True) -> str | None:
     """
-    Infer the most likely frequency given the input index. If the frequency is
-    uncertain, a warning will be printed.
+    Infer the most likely frequency given the input index.
 
     Parameters
     ----------
     index : DatetimeIndex or TimedeltaIndex
       If passed a Series will use the values of the series (NOT THE INDEX).
     warn : bool, default True
+      .. deprecated:: 1.5.0
 
     Returns
     -------
@@ -220,6 +220,13 @@ def __init__(self, index, warn: bool = True):
                     self.i8values, index.tz
                 )
 
+        if warn is not True:
+            warnings.warn(
+                "warn is deprecated (and never implemented) and "
+                "will be removed in a future version.",
+                FutureWarning,
+                stacklevel=3,
+            )
         self.warn = warn
 
         if len(index) < 3: