[claude-tmgbedu]

Fixes task #3504.

Root cause

env() returns a dataclasses.Field with a default_factory; it only becomes a value when the class is processed by @dataclass. A Config subclass without @dataclass was never processed, so DatabaseConfig().default fell through to the class attribute — the raw Field.

Fix

_ConfigMeta.__call__ now lazily applies dataclass at first instantiation to every unprocessed Config class in the MRO (base first, so undecorated parents' fields are inherited). Decorated classes are untouched (eager __init_subclass__ processing was rejected: re-decoration turns every env() field into a required argument). Casting follows existing env() rules (int/bool by default type).

ADR 035 added and indexed.

Tests

• tests/support/test_config_without_dataclass.py: unset/set variable, int/bool casting, kwargs override, undecorated parent+child, decorated class not reprocessed (5/6 fail on main).
• Full suite (--ignore=tests/masoniteorm/postgres): 3294 passed, coverage 91.4%.

🤖 Generated with Claude Code

https://claude.ai/code/session_01SchgSwsSKsBpqmyLiFEuM1

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[claude-tmgbedu]

Verdict: REQUEST CHANGES. GitHub won't let me request changes on a PR from the same account, so this is posted as a comment.

Suite passes locally (3294 passed, Postgres ignored). The direct repro is fixed and the decorated-only path is unchanged. One inheritance case regresses, though.

1. support/config.py ensure_dataclass: a decorated child of an undecorated parent loses the parent's fields (regression).

   class P(Config):
       host: str = env("E_HOST", "localhost")
   @dataclass
   class C(P):
       port: int = env("E_PORT", 80)
   C().host   # AttributeError; fields(C) == ['port']

   @dataclass on C runs before P has been processed, so C never inherits host. On the first C() call, ensure_dataclass processes P, which deletes the Field class attribute. On main this returned the raw Field; now it raises AttributeError. The ADR's claim that undecorated parents are "processed first" only holds when every class in the chain is undecorated.
   Fix: process undecorated Config ancestors when a subclass is defined, for example in _ConfigMeta.__init__, or in Config.__init_subclass__, over cls.__mro__[1:]. The parent's body is complete by then and the child's decorator hasn't run yet. Only the leaf would stay lazy. Add a test for this case.

2. The Config base itself is mutated on first instantiation. reversed(cls.__mro__) includes Config, so the first X() turns Config into a dataclass (__eq__ is added and __hash__ becomes None). That is global, order-dependent state. Either skip Config (klass is not Config) or make Config an explicit @dataclass up front.

3. Thread safety (non-blocking, but say how it's handled). The check-then-decorate is not atomic. I couldn't trigger a race in 300 tries with 8 threads, but two threads constructing a never-instantiated class at the same moment would both run dataclass(klass). Either guard it with a threading.Lock (double-checked), or record in the ADR why concurrent double-processing is harmless. Also, dataclass(Q); dataclass(Q); Q() worked for me on CPython 3.15, which contradicts the reason the ADR gives for rejecting alternative 2. Please re-check that claim, or state which Python versions it applies to.

The ADR, its index entry and the no-comments convention all look fine otherwise.