From c5da5ea15a17a2c0e95495619555b77488e2811b Mon Sep 17 00:00:00 2001
From: "Lumberbot (aka Jack)"
 <39504233+meeseeksmachine@users.noreply.github.com>
Date: Fri, 27 Oct 2023 18:43:34 +0200
Subject: [PATCH] Backport PR #55707 on branch 2.1.x (REF: Avoid np.can_cast
 for scalar inference for NEP 50) (#55716)

Backport PR #55707: REF: Avoid np.can_cast for scalar inference for NEP 50

Co-authored-by: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>
---
 ci/run_tests.sh            |  3 ++-
 pandas/core/dtypes/cast.py | 25 +++++++++++++++++++++++--
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/ci/run_tests.sh b/ci/run_tests.sh
index 48ef21686a26f..6a70ea1df3e71 100755
--- a/ci/run_tests.sh
+++ b/ci/run_tests.sh
@@ -10,7 +10,8 @@ echo PYTHONHASHSEED=$PYTHONHASHSEED
 
 COVERAGE="-s --cov=pandas --cov-report=xml --cov-append --cov-config=pyproject.toml"
 
-PYTEST_CMD="MESONPY_EDITABLE_VERBOSE=1 PYTHONDEVMODE=1 PYTHONWARNDEFAULTENCODING=1 pytest -r fEs -n $PYTEST_WORKERS --dist=loadfile $TEST_ARGS $COVERAGE $PYTEST_TARGET"
+# TODO: Support NEP 50 and remove NPY_PROMOTION_STATE
+PYTEST_CMD="NPY_PROMOTION_STATE=legacy MESONPY_EDITABLE_VERBOSE=1 PYTHONDEVMODE=1 PYTHONWARNDEFAULTENCODING=1 pytest -r fEs -n $PYTEST_WORKERS --dist=loadfile $TEST_ARGS $COVERAGE $PYTEST_TARGET"
 
 if [[ "$PATTERN" ]]; then
   PYTEST_CMD="$PYTEST_CMD -m \"$PATTERN\""
diff --git a/pandas/core/dtypes/cast.py b/pandas/core/dtypes/cast.py
index 8ed57e9bf5532..9a9a8ed22f282 100644
--- a/pandas/core/dtypes/cast.py
+++ b/pandas/core/dtypes/cast.py
@@ -700,7 +700,7 @@ def _maybe_promote(dtype: np.dtype, fill_value=np.nan):
             dtype = np.dtype(np.object_)
 
         elif issubclass(dtype.type, np.integer):
-            if not np.can_cast(fill_value, dtype):
+            if not np_can_cast_scalar(fill_value, dtype):  # type: ignore[arg-type]
                 # upcast to prevent overflow
                 mst = np.min_scalar_type(fill_value)
                 dtype = np.promote_types(dtype, mst)
@@ -1892,4 +1892,25 @@ def _dtype_can_hold_range(rng: range, dtype: np.dtype) -> bool:
     """
     if not len(rng):
         return True
-    return np.can_cast(rng[0], dtype) and np.can_cast(rng[-1], dtype)
+    return np_can_cast_scalar(rng.start, dtype) and np_can_cast_scalar(rng.stop, dtype)
+
+
+def np_can_cast_scalar(element: Scalar, dtype: np.dtype) -> bool:
+    """
+    np.can_cast pandas-equivalent for pre 2-0 behavior that allowed scalar
+    inference
+
+    Parameters
+    ----------
+    element : Scalar
+    dtype : np.dtype
+
+    Returns
+    -------
+    bool
+    """
+    try:
+        np_can_hold_element(dtype, element)
+        return True
+    except (LossySetitemError, NotImplementedError):
+        return False