BUG: CategoricalIndex.reindex fails when Index passed with labels all in category (pandas-dev#38492)

Author: GYHHAHA

doc/source/whatsnew/v1.3.0.rst

@@ -170,7 +170,7 @@ Bug fixes
 Categorical
 ^^^^^^^^^^^
 
--
+- Bug in ``CategoricalIndex.reindex`` failed when ``Index`` passed with elements all in category (:issue:`28690`)
 -
 
 Datetimelike

pandas/core/indexes/category.py

@@ -428,7 +428,7 @@ def reindex(self, target, method=None, level=None, limit=None, tolerance=None):
         if len(missing):
             cats = self.categories.get_indexer(target)
 
-            if (cats == -1).any():
+            if not isinstance(cats, CategoricalIndex) or (cats == -1).any():
                 # coerce to a regular index here!
                 result = Index(np.array(self), name=self.name)
                 new_target, indexer, _ = result._reindex_non_unique(np.array(target))

pandas/tests/indexes/categorical/test_reindex.py

@@ -1,7 +1,7 @@
 import numpy as np
 import pytest
 
-from pandas import Categorical, CategoricalIndex, Index, Series
+from pandas import Categorical, CategoricalIndex, DataFrame, Index, Series
 import pandas._testing as tm
 
 
@@ -59,3 +59,35 @@ def test_reindex_missing_category(self):
         msg = "'fill_value=-1' is not present in this Categorical's categories"
         with pytest.raises(TypeError, match=msg):
             ser.reindex([1, 2, 3, 4, 5], fill_value=-1)
+
+    @pytest.mark.parametrize(
+        "index_df,index_res,index_exp",
+        [
+            (
+                CategoricalIndex([], categories=["A"]),
+                Index(["A"]),
+                Index(["A"]),
+            ),
+            (
+                CategoricalIndex([], categories=["A"]),
+                Index(["B"]),
+                Index(["B"]),
+            ),
+            (
+                CategoricalIndex([], categories=["A"]),
+                CategoricalIndex(["A"]),
+                CategoricalIndex(["A"]),
+            ),
+            (
+                CategoricalIndex([], categories=["A"]),
+                CategoricalIndex(["B"]),
+                CategoricalIndex(["B"]),
+            ),
+        ],
+    )
+    def test_reindex_not_category(self, index_df, index_res, index_exp):
+        # GH: 28690
+        df = DataFrame(index=index_df)
+        result = df.reindex(index=index_res)
+        expected = DataFrame(index=index_exp)
+        tm.assert_frame_equal(result, expected)