REF: share Index.join (pandas-dev#42238)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -3870,6 +3870,7 @@ def _reindex_non_unique(
     # --------------------------------------------------------------------
     # Join Methods
 
+    @final
     @_maybe_return_indexers
     def join(
         self,
@@ -3901,6 +3902,19 @@ def join(
         self_is_mi = isinstance(self, ABCMultiIndex)
         other_is_mi = isinstance(other, ABCMultiIndex)
 
+        if isinstance(self, ABCDatetimeIndex) and isinstance(other, ABCDatetimeIndex):
+            if (self.tz is None) ^ (other.tz is None):
+                # Raise instead of casting to object below.
+                raise TypeError("Cannot join tz-naive with tz-aware DatetimeIndex")
+
+        if not self._is_multi and not other._is_multi:
+            # We have specific handling for MultiIndex below
+            pself, pother = self._maybe_promote(other)
+            if pself is not self or pother is not other:
+                return pself.join(
+                    pother, how=how, level=level, return_indexers=True, sort=sort
+                )
+
         lindexer: np.ndarray | None
         rindexer: np.ndarray | None
 

pandas/core/indexes/datetimelike.py

@@ -506,6 +506,8 @@ class DatetimeTimedeltaMixin(DatetimeIndexOpsMixin):
     _is_monotonic_decreasing = Index.is_monotonic_decreasing
     _is_unique = Index.is_unique
 
+    _join_precedence = 10
+
     def _with_freq(self, freq):
         arr = self._data._with_freq(freq)
         return type(self)._simple_new(arr, name=self._name)
@@ -679,38 +681,3 @@ def _union(self, other, sort):
             return result
         else:
             return super()._union(other, sort=sort)._with_freq("infer")
-
-    # --------------------------------------------------------------------
-    # Join Methods
-    _join_precedence = 10
-
-    def join(
-        self,
-        other,
-        how: str = "left",
-        level=None,
-        return_indexers: bool = False,
-        sort: bool = False,
-    ):
-        """
-        See Index.join
-        """
-        pself, pother = self._maybe_promote(other)
-        if pself is not self or pother is not other:
-            return pself.join(
-                pother, how=how, level=level, return_indexers=return_indexers, sort=sort
-            )
-
-        self._maybe_utc_convert(other)  # raises if we dont have tzawareness compat
-        return Index.join(
-            self,
-            other,
-            how=how,
-            level=level,
-            return_indexers=return_indexers,
-            sort=sort,
-        )
-
-    def _maybe_utc_convert(self: _T, other: Index) -> tuple[_T, Index]:
-        # Overridden by DatetimeIndex
-        return self, other