Make boolean_indexing a separate flag from data_dependent_shapes

array_api_strict/_array_object.py

@@ -436,8 +436,8 @@ def _validate_index(self, key):
                             f"{len(key)=}, but masking is only specified in the "
                             "Array API when the array is the sole index."
                         )
-                    if not get_array_api_strict_flags()['data_dependent_shapes']:
-                        raise RuntimeError("Boolean array indexing (masking) requires data-dependent shapes, but the data_dependent_shapes flag has been disabled for array-api-strict")
+                    if not get_array_api_strict_flags()['boolean_indexing']:
+                        raise RuntimeError("Boolean array indexing (masking) requires data-dependent shapes, but the boolean_indexing flag has been disabled for array-api-strict")
 
                 elif i.dtype in _integer_dtypes and i.ndim != 0:
                     raise IndexError(

array_api_strict/_flags.py

@@ -25,6 +25,8 @@
 
 API_VERSION = default_version = "2022.12"
 
+BOOLEAN_INDEXING = True
+
 DATA_DEPENDENT_SHAPES = True
 
 all_extensions = (
@@ -46,6 +48,7 @@
 def set_array_api_strict_flags(
     *,
     api_version=None,
+    boolean_indexing=None,
     data_dependent_shapes=None,
     enabled_extensions=None,
 ):
@@ -67,6 +70,12 @@ def set_array_api_strict_flags(
       Note that 2021.12 is supported, but currently gives the same thing as
       2022.12 (except that the fft extension will be disabled).
 
+
+    - `boolean_indexing`: Whether indexing by a boolean array is supported.
+      Note that although boolean array indexing does result in data-dependent
+      shapes, this flag is independent of the `data_dependent_shapes` flag
+      (see below).
+
     - `data_dependent_shapes`: Whether data-dependent shapes are enabled in
       array-api-strict.
 
@@ -79,10 +88,12 @@ def set_array_api_strict_flags(
 
       - `unique_all`, `unique_counts`, `unique_inverse`, and `unique_values`.
       - `nonzero`
-      - Boolean array indexing
       - `repeat` when the `repeats` argument is an array (requires 2023.12
         version of the standard)
 
+      Note that while boolean indexing is also data-dependent, it is
+      controlled by a separate `boolean_indexing` flag (see above).
+
       See
       https://data-apis.org/array-api/latest/design_topics/data_dependent_output_shapes.html
       for more details.
@@ -102,8 +113,8 @@ def set_array_api_strict_flags(
     >>> # Set the standard version to 2021.12
     >>> set_array_api_strict_flags(api_version="2021.12")
 
-    >>> # Disable data-dependent shapes
-    >>> set_array_api_strict_flags(data_dependent_shapes=False)
+    >>> # Disable data-dependent shapes and boolean indexing
+    >>> set_array_api_strict_flags(data_dependent_shapes=False, boolean_indexing=False)
 
     >>> # Enable only the linalg extension (disable the fft extension)
     >>> set_array_api_strict_flags(enabled_extensions=["linalg"])
@@ -116,7 +127,7 @@ def set_array_api_strict_flags(
     ArrayAPIStrictFlags: A context manager to temporarily set the flags.
 
     """
-    global API_VERSION, DATA_DEPENDENT_SHAPES, ENABLED_EXTENSIONS
+    global API_VERSION, BOOLEAN_INDEXING, DATA_DEPENDENT_SHAPES, ENABLED_EXTENSIONS
 
     if api_version is not None:
         if api_version not in supported_versions:
@@ -126,6 +137,9 @@ def set_array_api_strict_flags(
         API_VERSION = api_version
         array_api_strict.__array_api_version__ = API_VERSION
 
+    if boolean_indexing is not None:
+        BOOLEAN_INDEXING = boolean_indexing
+
     if data_dependent_shapes is not None:
         DATA_DEPENDENT_SHAPES = data_dependent_shapes
 
@@ -169,7 +183,11 @@ def get_array_api_strict_flags():
     >>> from array_api_strict import get_array_api_strict_flags
     >>> flags = get_array_api_strict_flags()
     >>> flags
-    {'api_version': '2022.12', 'data_dependent_shapes': True, 'enabled_extensions': ('linalg', 'fft')}
+    {'api_version': '2022.12',
+     'boolean_indexing': True,
+     'data_dependent_shapes': True,
+     'enabled_extensions': ('linalg', 'fft')
+    }
 
     See Also
     --------
@@ -181,6 +199,7 @@ def get_array_api_strict_flags():
     """
     return {
         "api_version": API_VERSION,
+        "boolean_indexing": BOOLEAN_INDEXING,
         "data_dependent_shapes": DATA_DEPENDENT_SHAPES,
         "enabled_extensions": ENABLED_EXTENSIONS,
     }
@@ -215,9 +234,10 @@ def reset_array_api_strict_flags():
     ArrayAPIStrictFlags: A context manager to temporarily set the flags.
 
     """
-    global API_VERSION, DATA_DEPENDENT_SHAPES, ENABLED_EXTENSIONS
+    global API_VERSION, BOOLEAN_INDEXING, DATA_DEPENDENT_SHAPES, ENABLED_EXTENSIONS
     API_VERSION = default_version
     array_api_strict.__array_api_version__ = API_VERSION
+    BOOLEAN_INDEXING = True
     DATA_DEPENDENT_SHAPES = True
     ENABLED_EXTENSIONS = default_extensions
 
@@ -242,10 +262,11 @@ class ArrayAPIStrictFlags:
     reset_array_api_strict_flags: Reset the flags to their default values.
 
     """
-    def __init__(self, *, api_version=None, data_dependent_shapes=None,
-                 enabled_extensions=None):
+    def __init__(self, *, api_version=None, boolean_indexing=None,
+                 data_dependent_shapes=None, enabled_extensions=None):
         self.kwargs = {
             "api_version": api_version,
+            "boolean_indexing": boolean_indexing,
             "data_dependent_shapes": data_dependent_shapes,
             "enabled_extensions": enabled_extensions,
         }
@@ -265,6 +286,11 @@ def set_flags_from_environment():
             api_version=os.environ["ARRAY_API_STRICT_API_VERSION"]
         )
 
+    if "ARRAY_API_STRICT_BOOLEAN_INDEXING" in os.environ:
+        set_array_api_strict_flags(
+            boolean_indexing=os.environ["ARRAY_API_STRICT_BOOLEAN_INDEXING"].lower() == "true"
+        )
+
     if "ARRAY_API_STRICT_DATA_DEPENDENT_SHAPES" in os.environ:
         set_array_api_strict_flags(
             data_dependent_shapes=os.environ["ARRAY_API_STRICT_DATA_DEPENDENT_SHAPES"].lower() == "true"

array_api_strict/tests/test_flags.py

@@ -13,6 +13,7 @@ def test_flags():
     flags = get_array_api_strict_flags()
     assert flags == {
         'api_version': '2022.12',
+        'boolean_indexing': True,
         'data_dependent_shapes': True,
         'enabled_extensions': ('linalg', 'fft'),
     }
@@ -22,13 +23,15 @@ def test_flags():
     flags = get_array_api_strict_flags()
     assert flags == {
         'api_version': '2022.12',
+        'boolean_indexing': True,
         'data_dependent_shapes': False,
         'enabled_extensions': ('linalg', 'fft'),
     }
     set_array_api_strict_flags(enabled_extensions=('fft',))
     flags = get_array_api_strict_flags()
     assert flags == {
         'api_version': '2022.12',
+        'boolean_indexing': True,
         'data_dependent_shapes': False,
         'enabled_extensions': ('fft',),
     }
@@ -41,6 +44,7 @@ def test_flags():
     flags = get_array_api_strict_flags()
     assert flags == {
         'api_version': '2021.12',
+        'boolean_indexing': True,
         'data_dependent_shapes': False,
         'enabled_extensions': ('linalg',),
     }
@@ -58,12 +62,14 @@ def test_flags():
     with pytest.warns(UserWarning):
         set_array_api_strict_flags(
             api_version='2021.12',
+            boolean_indexing=False,
             data_dependent_shapes=False,
             enabled_extensions=())
     reset_array_api_strict_flags()
     flags = get_array_api_strict_flags()
     assert flags == {
         'api_version': '2022.12',
+        'boolean_indexing': True,
         'data_dependent_shapes': True,
         'enabled_extensions': ('linalg', 'fft'),
     }
@@ -96,6 +102,17 @@ def test_data_dependent_shapes():
     pytest.raises(RuntimeError, lambda: unique_inverse(a))
     pytest.raises(RuntimeError, lambda: unique_values(a))
     pytest.raises(RuntimeError, lambda: nonzero(a))
+    a[mask] # No error (boolean indexing is a separate flag)
+
+def test_boolean_indexing():
+    a = asarray([0, 0, 1, 2, 2])
+    mask = asarray([True, False, True, False, True])
+
+    # Should not error
+    a[mask]
+
+    set_array_api_strict_flags(boolean_indexing=False)
+
     pytest.raises(RuntimeError, lambda: a[mask])
 
 linalg_examples = {

docs/api.rst

@@ -30,6 +30,10 @@ used by array-api-strict initially. They will not change the defaults used by
 
    A string representing the version number.
 
+.. envvar:: ARRAY_API_STRICT_BOOLEAN_INDEXING
+
+   "True" or "False" to enable or disable boolean indexing.
+
 .. envvar:: ARRAY_API_STRICT_DATA_DEPENDENT_SHAPES
 
    "True" or "False" to enable or disable data dependent shapes.