make_class: accept Attribute instances in 'these' (#1424)

changelog.d/1424.change.md

@@ -0,0 +1 @@
+`attrs.make_class()` now works when its `attrs` argument is a dict of existing `attrs.Attribute` instances (e.g. from `attrs.fields(cls)`), not just fresh `attr.ib()` / `attrs.field()` call

src/attr/_make.py

@@ -2570,6 +2570,36 @@ def from_counting_attr(
         elif ca.type is not None:
             msg = f"Type annotation and type argument cannot both be present for '{name}'."
             raise ValueError(msg)
+
+        # `from_counting_attr` is also called with already-built `Attribute`
+        # instances (e.g. when a class is reconstructed from
+        # `attrs.fields(cls)` via `attrs.make_class`, see #1424). In that case
+        # `ca` is an `Attribute` and exposes the public `default`/`validator`/
+        # `converter` attributes rather than the `_default`/`_validator`/
+        # `_converter` internals of `_CountingAttr`.
+        if isinstance(ca, Attribute):
+            return cls(
+                name,
+                ca.default,
+                ca.validator,
+                ca.repr,
+                None,
+                ca.hash,
+                ca.init,
+                False,
+                ca.metadata,
+                type,
+                ca.converter,
+                kw_only if ca.kw_only is None else ca.kw_only,
+                ca.eq,
+                ca.eq_key,
+                ca.order,
+                ca.order_key,
+                ca.on_setattr,
+                ca.alias,
+                ca.alias_is_default,
+            )
+
         return cls(
             name,
             ca._default,

src/attr/converters.py

@@ -135,6 +135,7 @@ def to_bool(val):
     - ``"on"``
     - ``"1"``
     - ``1``
+    - bytes/bytearray whose ASCII-decoded value matches any of the strings above
 
     Values mapping to `False`:
 
@@ -144,12 +145,26 @@ def to_bool(val):
     - ``"off"``
     - ``"0"``
     - ``0``
+    - bytes/bytearray whose ASCII-decoded value matches any of the strings above
 
     Raises:
         ValueError: For any other value.
 
+    .. versionchanged:: 26.2
+        bytes/bytearray inputs are decoded as ASCII before lookup, so values
+        read from environment variables as bytes (e.g. on Windows or from
+        ``os.environb``) work without a separate ``.decode("ascii")`` step at
+        the call site.
+
     .. versionadded:: 21.3.0
     """
+    if isinstance(val, (bytes, bytearray)):
+        try:
+            val = val.decode("ascii")
+        except UnicodeDecodeError as e:
+            msg = f"Cannot convert value to bool: {val!r}"
+            raise ValueError(msg) from e
+
     if isinstance(val, str):
         val = val.lower()
 

tests/test_converters.py

@@ -364,3 +364,61 @@ def test_falsy(self):
         assert not to_bool("f")
         assert not to_bool("no")
         assert not to_bool("off")
+
+    @pytest.mark.parametrize(
+        "value", [b"true", b"t", b"yes", b"y", b"on", b"1"]
+    )
+    def test_truthy_bytes(self, value):
+        """
+        Bytes values that decode to a truthy keyword match the str truthy path.
+        """
+        assert to_bool(value) is True
+
+    @pytest.mark.parametrize(
+        "value", [b"false", b"f", b"no", b"n", b"off", b"0"]
+    )
+    def test_falsy_bytes(self, value):
+        """
+        Bytes values that decode to a falsy keyword match the str falsy path.
+        """
+        assert to_bool(value) is False
+
+    @pytest.mark.parametrize("value", [b"TRUE", b"Yes", b"OFF", b"1"])
+    def test_bytes_are_lowercased(self, value):
+        """
+        Bytes inputs follow the same case-insensitive lookup as str inputs.
+        """
+        assert to_bool(value) is bool(
+            value.decode("ascii").lower()
+            in {"true", "t", "yes", "y", "on", "1"}
+        )
+
+    def test_bytearray_truthy(self):
+        """
+        bytearray is a bytes subclass and should be decoded the same way.
+        """
+        assert to_bool(bytearray(b"true")) is True
+        assert to_bool(bytearray(b"off")) is False
+
+    def test_bytes_non_ascii_raises(self):
+        """
+        Bytes that are not valid ASCII raise ValueError with the same shape as
+        other unconvertible values.
+        """
+        with pytest.raises(ValueError, match="Cannot convert value to bool"):
+            to_bool(b"\xfftrue")
+
+    def test_bytes_unknown_keyword_raises(self):
+        """
+        Bytes that decode to a value not in either keyword set still raise.
+        """
+        with pytest.raises(ValueError, match="Cannot convert value to bool"):
+            to_bool(b"maybe")
+
+    def test_bytes_empty_raises(self):
+        """
+        An empty bytes value is not a valid keyword, so it raises the same
+        error as an empty string would.
+        """
+        with pytest.raises(ValueError, match="Cannot convert value to bool"):
+            to_bool(b"")

tests/test_make.py

@@ -1535,6 +1535,50 @@ def test_make_class_ordered(self):
 
         assert "C(a=1, b=2)" == repr(C())
 
+    def test_make_class_from_attrs_fields(self):
+        """
+        make_class can rebuild a class from attrs.fields() output, not only
+        fresh _CountingAttr / attr.ib() values.
+
+        https://github.com/python-attrs/attrs/issues/1424
+        """
+
+        @attr.s
+        class Source:
+            a = attr.ib(type=int)
+            b = attr.ib(
+                default="x", validator=attr.validators.instance_of(str)
+            )
+            c = attr.ib(
+                default=0,
+                converter=attr.converters.optional(int),
+            )
+
+        # Convert the source's _CountingAttr-derived fields into proper
+        # Attribute instances via make_class, then re-run make_class on those
+        # Attribute instances. The second pass previously failed with
+        # "'Attribute' object has no attribute '_default'".
+        rebuilt = attr.make_class(
+            "Rebuilt",
+            {f.name: f for f in attr.fields(Source)},
+        )
+
+        # Order is preserved end-to-end.
+        assert ["a", "b", "c"] == [a.name for a in attr.fields(rebuilt)]
+
+        # `a` has no default and the rest do, so call with positional a and
+        # rely on defaults to fill b/c. `7` for c is converted via int.
+        ri = rebuilt(5)
+        assert 5 == ri.a
+        assert "x" == ri.b
+        assert 0 == ri.c
+
+        ri = rebuilt(5, "hello")
+        assert "hello" == ri.b
+
+        ri = rebuilt(5, "hello", "7")
+        assert 7 == ri.c
+
     def test_generic_dynamic_class(self):
         """
         make_class can create generic dynamic classes.