forbid_extra_keys doesn't work with override(rename=...)

[anthrotype]

• cattrs version: 1.9.0
• Python version: 3.10.0
• Operating System: macOS 11.6 (x86_64)

Description

I would like to have cattrs strip the leading underscore in attribute names, both when unstructuring and when structuring.
I registered two hook factories that pass override(rename=a.name[1:] if a.name[0] == "_"). However when I also set forbid_extra_keys=True, I get an error saying "Extra fields in constructor for ...", for all the underscore-prefixed attributes.

Basically the forbid_extra_keys feature is ignoring the rename overrides, and the two features don't work together.

What I Did

from attr import define, has, fields
from cattr.gen import make_dict_unstructure_fn, make_dict_structure_fn, override
from cattr.converters import GenConverter


def strip_underscore_unstructure(cls):
    return make_dict_unstructure_fn(
        cls,
        converter,
        **{a.name: override(rename=a.name[1:]) for a in fields(cls) if a.name[0] == "_"}
    )


def strip_underscore_structure(cls):
    return make_dict_structure_fn(
        cls,
        converter,
        _cattrs_forbid_extra_keys=True,
        **{a.name: override(rename=a.name[1:]) for a in fields(cls) if a.name[0] == "_"}
    )


converter = GenConverter(forbid_extra_keys=True)
converter.register_structure_hook_factory(has, strip_underscore_structure)
converter.register_unstructure_hook_factory(has, strip_underscore_unstructure)


@define
class A:
    b: int
    _c: str

    @property
    def c(self):
        return self._c


a = A(1, "abc")


print(converter.unstructure(a))  # {'b': 1, 'c': 'abc'}


# Traceback (most recent call last):
#   File "/Users/clupo/Github/ufoLib2/test_cattrs.py", line 43, in <module>
#     converter.structure(converter.unstructure(a), A)
#   File "/Users/clupo/Github/cattrs/src/cattr/converters.py", line 300, in structure
#     return self._structure_func.dispatch(cl)(obj, cl)
#   File "<cattrs generated structure __main__.A>", line 8, in structure_A
# Exception: Extra fields in constructor for A: c
converter.structure(converter.unstructure(a), A)

[anthrotype]

If I change cattr/gen.py like this, it works. Feel free to use or adapt this patch below if you like (I don't have the time to make a PR right now). Thanks!

diff --git a/src/cattr/gen.py b/src/cattr/gen.py
index 5596d59..18dfd4b 100644
--- a/src/cattr/gen.py
+++ b/src/cattr/gen.py
@@ -245,6 +245,7 @@ def make_dict_structure_fn(
 
     lines.append(f"def {fn_name}(o, *_):")
     lines.append("  res = {")
+    allowed_fields = set()
     for a in attrs:
         an = a.name
         override = kwargs.pop(an, _neutral)
@@ -279,6 +280,7 @@ def make_dict_structure_fn(
 
         ian = an if (is_dc or an[0] != "_") else an[1:]
         kn = an if override.rename is None else override.rename
+        allowed_fields.add(kn)
         globs[f"type_{an}"] = t
         if a.default is NOTHING:
             if handler:
@@ -298,7 +300,6 @@ def make_dict_structure_fn(
 
     lines.append("    }")
     if _cattrs_forbid_extra_keys:
-        allowed_fields = {a.name for a in attrs}
         globs["__c_a"] = allowed_fields
         post_lines += [
             "  unknown_fields = set(o.keys()) - __c_a",

[Tinche]

Fixed on main, thanks!

[anthrotype]

Fixed on main

looking forward to v1.9.0 release ;)