DOC: add note on copy keyword to the 2.0 migration guide

Author: rgommers

doc/source/numpy_2_0_migration_guide.rst

@@ -383,3 +383,23 @@ Note about pickled files
 NumPy 2.0 is designed to load pickle files created with NumPy 1.26,
 and vice versa. For versions 1.25 and earlier loading NumPy 2.0
 pickle file will throw an exception.
+
+
+Adapting to changes in the ``copy`` keyword
+-------------------------------------------
+
+The :ref:`copy keyword behavior changes <copy-keyword-changes-2.0>` in
+`~numpy.asarray`, `~numpy.array` and `ndarray.__array__
+<numpy.ndarray.__array__>` may require these changes:
+
+1. Code using ``np.array(..., copy=False)`` can in most cases be changed to
+   ``np.asarray(...)``. Older code tended to use ``np.array`` like this because
+   it had less overhead than the default ``np.asarray`` copy-if-needed
+   behavior. This is no longer true, and ``np.asarray`` is the preferred function.
+2. For code that explicitly needs to pass ``None/False`` meaning "copy if
+   needed" in a way that's compatible with NumPy 1.x and 2.x, see
+   `scipy#20172 <https://github.com/scipy/scipy/pull/20172>`__ for an example
+   of how to do so.
+3. For any ``__array__`` method on a non-NumPy array-like object, a
+   ``copy=None`` keyword can be added to the signature - this will work with
+   older NumPy versions as well.

doc/source/release/2.0.0-notes.rst

@@ -1253,6 +1253,8 @@ Any out of bound axis value will now error, make sure to use
 
 (`gh-25149 <https://github.com/numpy/numpy/pull/25149>`__)
 
+.. _copy-keyword-changes-2.0:
+
 New ``copy`` keyword meaning for ``array`` and ``asarray`` constructors
 -----------------------------------------------------------------------