From edffdfdf3bebc4d0162acc35912e2adca2eea083 Mon Sep 17 00:00:00 2001
From: Matthias Diener <mdiener@illinois.edu>
Date: Wed, 2 Oct 2024 16:34:29 -0500
Subject: [PATCH] add test, comment

---
 pyopencl/array.py  |  3 +++
 test/test_array.py | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/pyopencl/array.py b/pyopencl/array.py
index f3dd5e74..16e24945 100644
--- a/pyopencl/array.py
+++ b/pyopencl/array.py
@@ -75,6 +75,9 @@ def _get_common_dtype(obj1, obj2, queue):
         raise ValueError("PyOpenCL array has no queue; call .with_queue() to "
                 "add one in order to be able to perform operations")
 
+    # Note: We are calling np.result_type with pyopencl arrays here.
+    # Luckily, np.result_type only looks at the dtype of input arrays as of
+    # numpy v2.1.
     result = np.result_type(obj1, obj2)
 
     if not has_double_support(queue.device):
diff --git a/test/test_array.py b/test/test_array.py
index 4b648878..f9ec27a8 100644
--- a/test/test_array.py
+++ b/test/test_array.py
@@ -2393,6 +2393,24 @@ def test_xdg_cache_home(ctx_factory):
 # }}}
 
 
+def test_numpy_type_promotion_with_cl_arrays(ctx_factory):
+    ctx = ctx_factory()
+    queue = cl.CommandQueue(ctx)
+
+    class NotReallyAnArray:
+        @property
+        def dtype(self):
+            return np.dtype("float64")
+
+    # Make sure that np.result_type accesses only the dtype attribute of the
+    # class, not (e.g.) its data.
+    assert np.result_type(42, NotReallyAnArray()) == np.float64
+
+    from pyopencl.array import _get_common_dtype
+    assert _get_common_dtype(42, NotReallyAnArray(), queue) == np.float64
+    assert _get_common_dtype(42.0, NotReallyAnArray(), queue) == np.float64
+
+
 if __name__ == "__main__":
     if len(sys.argv) > 1:
         exec(sys.argv[1])
-- 
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