2 files changed, 157 insertions, 0 deletions
diff --git a/third_party/python/attrs/attr/converters.py b/third_party/python/attrs/attr/converters.py
new file mode 100644
index 0000000000..4cada106b0
--- /dev/null
+++ b/third_party/python/attrs/attr/converters.py
@@ -0,0 +1,144 @@
+# SPDX-License-Identifier: MIT
+
+"""
+Commonly useful converters.
+"""
+
+
+import typing
+
+from ._compat import _AnnotationExtractor
+from ._make import NOTHING, Factory, pipe
+
+
+__all__ = [
+    "default_if_none",
+    "optional",
+    "pipe",
+    "to_bool",
+]
+
+
+def optional(converter):
+    """
+    A converter that allows an attribute to be optional. An optional attribute
+    is one which can be set to ``None``.
+
+    Type annotations will be inferred from the wrapped converter's, if it
+    has any.
+
+    :param callable converter: the converter that is used for non-``None``
+        values.
+
+    .. versionadded:: 17.1.0
+    """
+
+    def optional_converter(val):
+        if val is None:
+            return None
+        return converter(val)
+
+    xtr = _AnnotationExtractor(converter)
+
+    t = xtr.get_first_param_type()
+    if t:
+        optional_converter.__annotations__["val"] = typing.Optional[t]
+
+    rt = xtr.get_return_type()
+    if rt:
+        optional_converter.__annotations__["return"] = typing.Optional[rt]
+
+    return optional_converter
+
+
+def default_if_none(default=NOTHING, factory=None):
+    """
+    A converter that allows to replace ``None`` values by *default* or the
+    result of *factory*.
+
+    :param default: Value to be used if ``None`` is passed. Passing an instance
+       of `attrs.Factory` is supported, however the ``takes_self`` option
+       is *not*.
+    :param callable factory: A callable that takes no parameters whose result
+       is used if ``None`` is passed.
+
+    :raises TypeError: If **neither** *default* or *factory* is passed.
+    :raises TypeError: If **both** *default* and *factory* are passed.
+    :raises ValueError: If an instance of `attrs.Factory` is passed with
+       ``takes_self=True``.
+
+    .. versionadded:: 18.2.0
+    """
+    if default is NOTHING and factory is None:
+        raise TypeError("Must pass either `default` or `factory`.")
+
+    if default is not NOTHING and factory is not None:
+        raise TypeError(
+            "Must pass either `default` or `factory` but not both."
+        )
+
+    if factory is not None:
+        default = Factory(factory)
+
+    if isinstance(default, Factory):
+        if default.takes_self:
+            raise ValueError(
+                "`takes_self` is not supported by default_if_none."
+            )
+
+        def default_if_none_converter(val):
+            if val is not None:
+                return val
+
+            return default.factory()
+
+    else:
+
+        def default_if_none_converter(val):
+            if val is not None:
+                return val
+
+            return default
+
+    return default_if_none_converter
+
+
+def to_bool(val):
+    """
+    Convert "boolean" strings (e.g., from env. vars.) to real booleans.
+
+    Values mapping to :code:`True`:
+
+    - :code:`True`
+    - :code:`"true"` / :code:`"t"`
+    - :code:`"yes"` / :code:`"y"`
+    - :code:`"on"`
+    - :code:`"1"`
+    - :code:`1`
+
+    Values mapping to :code:`False`:
+
+    - :code:`False`
+    - :code:`"false"` / :code:`"f"`
+    - :code:`"no"` / :code:`"n"`
+    - :code:`"off"`
+    - :code:`"0"`
+    - :code:`0`
+
+    :raises ValueError: for any other value.
+
+    .. versionadded:: 21.3.0
+    """
+    if isinstance(val, str):
+        val = val.lower()
+    truthy = {True, "true", "t", "yes", "y", "on", "1", 1}
+    falsy = {False, "false", "f", "no", "n", "off", "0", 0}
+    try:
+        if val in truthy:
+            return True
+        if val in falsy:
+            return False
+    except TypeError:
+        # Raised when "val" is not hashable (e.g., lists)
+        pass
+    raise ValueError(f"Cannot convert value to bool: {val}")
diff --git a/third_party/python/attrs/attr/converters.pyi b/third_party/python/attrs/attr/converters.pyi
new file mode 100644
index 0000000000..5abb49f6d5
--- /dev/null
+++ b/third_party/python/attrs/attr/converters.pyi
@@ -0,0 +1,13 @@
+from typing import Callable, TypeVar, overload
+
+from . import _ConverterType
+
+_T = TypeVar("_T")
+
+def pipe(*validators: _ConverterType) -> _ConverterType: ...
+def optional(converter: _ConverterType) -> _ConverterType: ...
+@overload
+def default_if_none(default: _T) -> _ConverterType: ...
+@overload
+def default_if_none(*, factory: Callable[[], _T]) -> _ConverterType: ...
+def to_bool(val: str) -> bool: ...