API: Forbid Q<->m safe casting

That is, uint64 <-> timedelta64.

Allowing this casting was weird, because Q<->q is forbidden, yet q and m are both int64.

This fixes gh-12927

3 files changed, 25 insertions, 3 deletions

diff --git a/numpy/core/src/multiarray/scalartypes.c.src b/numpy/core/src/multiarray/scalartypes.c.src
index 9adca6773..6f652f59e 100644
--- a/numpy/core/src/multiarray/scalartypes.c.src
+++ b/numpy/core/src/multiarray/scalartypes.c.src
@@ -4060,8 +4060,11 @@ initialize_casting_tables(void)
     _npy_can_cast_safely_table[_FROM_NUM][NPY_STRING] = 1;
     _npy_can_cast_safely_table[_FROM_NUM][NPY_UNICODE] = 1;
 
-    /* Allow casts from any integer to the TIMEDELTA type */
-#if @from_isint@ || @from_isuint@
+#if @from_isint@ && NPY_SIZEOF_TIMEDELTA >= _FROM_BSIZE
+    /* Allow casts from smaller or equal signed integers to the TIMEDELTA type */
+    _npy_can_cast_safely_table[_FROM_NUM][NPY_TIMEDELTA] = 1;
+#elif @from_isuint@ && NPY_SIZEOF_TIMEDELTA > _FROM_BSIZE
+    /* Allow casts from smaller unsigned integers to the TIMEDELTA type */
     _npy_can_cast_safely_table[_FROM_NUM][NPY_TIMEDELTA] = 1;
 #endif
 
diff --git a/numpy/core/tests/test_datetime.py b/numpy/core/tests/test_datetime.py
index a10e6dbe0..71f579525 100644
--- a/numpy/core/tests/test_datetime.py
+++ b/numpy/core/tests/test_datetime.py
@@ -75,6 +75,15 @@ class TestDateTime(object):
         # Can cast safely/same_kind from integer to timedelta
         assert_(np.can_cast('i8', 'm8', casting='same_kind'))
         assert_(np.can_cast('i8', 'm8', casting='safe'))
+        assert_(np.can_cast('i4', 'm8', casting='same_kind'))
+        assert_(np.can_cast('i4', 'm8', casting='safe'))
+        assert_(np.can_cast('u4', 'm8', casting='same_kind'))
+        assert_(np.can_cast('u4', 'm8', casting='safe'))
+
+        # Cannot cast safely from unsigned integer of the same size, which
+        # could overflow
+        assert_(not np.can_cast('u8', 'm8', casting='same_kind'))
+        assert_(not np.can_cast('u8', 'm8', casting='safe'))
 
         # Cannot cast safely/same_kind from float to timedelta
         assert_(not np.can_cast('f4', 'm8', casting='same_kind'))
diff --git a/numpy/core/tests/test_scalarmath.py b/numpy/core/tests/test_scalarmath.py
index 854df5590..c84380cd9 100644
--- a/numpy/core/tests/test_scalarmath.py
+++ b/numpy/core/tests/test_scalarmath.py
@@ -11,7 +11,7 @@ import numpy as np
 from numpy.testing import (
     assert_, assert_equal, assert_raises, assert_almost_equal,
     assert_array_equal, IS_PYPY, suppress_warnings, _gen_alignment_data,
-    assert_warns
+    assert_warns, assert_raises_regex,
     )
 
 types = [np.bool_, np.byte, np.ubyte, np.short, np.ushort, np.intc, np.uintc,
@@ -293,6 +293,16 @@ class TestModulus(object):
                 rem = operator.mod(finf, fone)
                 assert_(np.isnan(rem), 'dt: %s' % dt)
 
+    def test_inplace_floordiv_handling(self):
+        # issue gh-12927
+        # this only applies to in-place floordiv //=, because the output type
+        # promotes to float which does not fit
+        a = np.array([1, 2], np.int64)
+        b = np.array([1, 2], np.uint64)
+        pattern = 'could not be coerced to provided output parameter'
+        with assert_raises_regex(TypeError, pattern):
+            a //= b
+
 
 class TestComplexDivision(object):
     def test_zero_division(self):