BUG: Ensure boolean indexing of subclasses sets base correctly.

Corrects a mistake in gh-11246, where the base for this case was
set to the indexed subclass instance (like for a view). Since a
copy is made in this case, the base should be the new ndarray that
holds the indexed values.

Thanks to @yymao for noticing and reporting the bug in astropy.

2 files changed, 25 insertions, 7 deletions

diff --git a/numpy/core/src/multiarray/mapping.c b/numpy/core/src/multiarray/mapping.c
index 2fdb3ebf6..b50866b4d 100644
--- a/numpy/core/src/multiarray/mapping.c
+++ b/numpy/core/src/multiarray/mapping.c
@@ -1125,7 +1125,7 @@ array_boolean_subscript(PyArrayObject *self,
         ret = (PyArrayObject *)PyArray_NewFromDescrAndBase(
                 Py_TYPE(self), dtype,
                 1, &size, PyArray_STRIDES(ret), PyArray_BYTES(ret),
-                PyArray_FLAGS(self), (PyObject *)self, (PyObject *)self);
+                PyArray_FLAGS(self), (PyObject *)self, (PyObject *)tmp);
 
         if (ret == NULL) {
             Py_DECREF(tmp);
diff --git a/numpy/core/tests/test_indexing.py b/numpy/core/tests/test_indexing.py
index 1934d542a..99792cee7 100644
--- a/numpy/core/tests/test_indexing.py
+++ b/numpy/core/tests/test_indexing.py
@@ -580,15 +580,33 @@ class TestBroadcastedAssignments(object):
 
 class TestSubclasses(object):
     def test_basic(self):
+        # Test that indexing in various ways produces SubClass instances,
+        # and that the base is set up correctly: the original subclass
+        # instance for views, and a new ndarray for advanced/boolean indexing
+        # where a copy was made (latter a regression test for gh-11983).
         class SubClass(np.ndarray):
             pass
 
-        s = np.arange(5).view(SubClass)
-        assert_(isinstance(s[:3], SubClass))
-        assert_(s[:3].base is s)
-
-        assert_(isinstance(s[[0, 1, 2]], SubClass))
-        assert_(isinstance(s[s > 0], SubClass))
+        a = np.arange(5)
+        s = a.view(SubClass)
+        s_slice = s[:3]
+        assert_(type(s_slice) is SubClass)
+        assert_(s_slice.base is s)
+        assert_array_equal(s_slice, a[:3])
+
+        s_fancy = s[[0, 1, 2]]
+        assert_(type(s_fancy) is SubClass)
+        assert_(s_fancy.base is not s)
+        assert_(type(s_fancy.base) is np.ndarray)
+        assert_array_equal(s_fancy, a[[0, 1, 2]])
+        assert_array_equal(s_fancy.base, a[[0, 1, 2]])
+
+        s_bool = s[s > 0]
+        assert_(type(s_bool) is SubClass)
+        assert_(s_bool.base is not s)
+        assert_(type(s_bool.base) is np.ndarray)
+        assert_array_equal(s_bool, a[a > 0])
+        assert_array_equal(s_bool.base, a[a > 0])
 
     def test_finalize_gets_full_info(self):
         # Array finalize should be called on the filled array.