2 files changed, 92 insertions, 0 deletions
diff --git a/third_party/python/attrs/attr/setters.py b/third_party/python/attrs/attr/setters.py
new file mode 100644
index 0000000000..12ed6750df
--- /dev/null
+++ b/third_party/python/attrs/attr/setters.py
@@ -0,0 +1,73 @@
+# SPDX-License-Identifier: MIT
+
+"""
+Commonly used hooks for on_setattr.
+"""
+
+
+from . import _config
+from .exceptions import FrozenAttributeError
+
+
+def pipe(*setters):
+    """
+    Run all *setters* and return the return value of the last one.
+
+    .. versionadded:: 20.1.0
+    """
+
+    def wrapped_pipe(instance, attrib, new_value):
+        rv = new_value
+
+        for setter in setters:
+            rv = setter(instance, attrib, rv)
+
+        return rv
+
+    return wrapped_pipe
+
+
+def frozen(_, __, ___):
+    """
+    Prevent an attribute to be modified.
+
+    .. versionadded:: 20.1.0
+    """
+    raise FrozenAttributeError()
+
+
+def validate(instance, attrib, new_value):
+    """
+    Run *attrib*'s validator on *new_value* if it has one.
+
+    .. versionadded:: 20.1.0
+    """
+    if _config._run_validators is False:
+        return new_value
+
+    v = attrib.validator
+    if not v:
+        return new_value
+
+    v(instance, attrib, new_value)
+
+    return new_value
+
+
+def convert(instance, attrib, new_value):
+    """
+    Run *attrib*'s converter -- if it has one --  on *new_value* and return the
+    result.
+
+    .. versionadded:: 20.1.0
+    """
+    c = attrib.converter
+    if c:
+        return c(new_value)
+
+    return new_value
+
+
+# Sentinel for disabling class-wide *on_setattr* hooks for certain attributes.
+# autodata stopped working, so the docstring is inlined in the API docs.
+NO_OP = object()
diff --git a/third_party/python/attrs/attr/setters.pyi b/third_party/python/attrs/attr/setters.pyi
new file mode 100644
index 0000000000..72f7ce4761
--- /dev/null
+++ b/third_party/python/attrs/attr/setters.pyi
@@ -0,0 +1,19 @@
+from typing import Any, NewType, NoReturn, TypeVar
+
+from . import Attribute, _OnSetAttrType
+
+_T = TypeVar("_T")
+
+def frozen(
+    instance: Any, attribute: Attribute[Any], new_value: Any
+) -> NoReturn: ...
+def pipe(*setters: _OnSetAttrType) -> _OnSetAttrType: ...
+def validate(instance: Any, attribute: Attribute[_T], new_value: _T) -> _T: ...
+
+# convert is allowed to return Any, because they can be chained using pipe.
+def convert(
+    instance: Any, attribute: Attribute[Any], new_value: Any
+) -> Any: ...
+
+_NoOpType = NewType("_NoOpType", object)
+NO_OP: _NoOpType