[ty] Preserve recursively-defined flag during normalization

[charliermarsh]

Summary

This PR allows the Unknown variant to retain a recursively-normalized flag so that it's not dropped during normalization.

Consider this motivating example:

class Count:
    def __init__(self):
        self.i = 0

class PositiveCount(Count):
    def increment(self):
        self.i = self.i + 1

    def decrement(self):
        if self.i != 0:
            self.i = self.i - 1

PositiveCount.i is initially inferred as Unknown in the subclass (the subclass doesn't see self.i = 0 upfront, because implicit_attribute_inner operates on a single class). Instead, it sees the self.i = self.i + 1 and self.i = self.i - 1 statements, which adds Divergent to the type. Recursive normalization drops the Divergent arms and marks the result recursive... but that flag doesn't have anywhere to go. Then, when evaluating self.i + 1, it walks the MRO and adds the Literal[0] from self.i = 0, so we have Unknown | Literal[0], but we've already "lost" the recursively-normalized flag.

I also considered #24272 which is more targeted, but this felt more structurally correct and less targeted.

Closes astral-sh/ty#3149.

[astral-sh-bot]

Typing conformance results

No changes detected ✅

Current numbers

The percentage of diagnostics emitted that were expected errors held steady at 86.60%. The percentage of expected errors that received a diagnostic held steady at 81.47%. The number of fully passing files held steady at 69/132.

[astral-sh-bot]

Memory usage report

Summary

Project	Old	New	Diff	Outcome
prefect	716.74MB	716.94MB	+0.03% (202.91kB)	⏫
sphinx	265.21MB	265.34MB	+0.05% (132.93kB)	⏫
trio	117.99MB	118.02MB	+0.03% (31.84kB)	⏫
flake8	48.07MB	48.08MB	+0.01% (4.21kB)	⏫

Significant changes

Click to expand detailed breakdown

prefect

Name	Old	New	Diff	Outcome
UnionType<'db>::from_two_elements_	5.24MB	5.37MB	+2.51% (134.76kB)	⏫
UnionType	3.52MB	3.53MB	+0.56% (20.09kB)	⏫
infer_definition_types	89.72MB	89.74MB	+0.02% (14.68kB)	⏫
infer_expression_types_impl	61.76MB	61.77MB	+0.01% (8.58kB)	⏫
Type<'db>::member_lookup_with_policy_	16.19MB	16.19MB	+0.03% (5.16kB)	⏫
Type<'db>::member_lookup_with_policy_::interned_arguments	5.76MB	5.77MB	+0.08% (4.67kB)	⏫
infer_deferred_types	14.72MB	14.73MB	+0.03% (3.84kB)	⏫
is_redundant_with_impl::interned_arguments	5.42MB	5.42MB	-0.07% (3.78kB)	⏫
infer_expression_type_impl	13.82MB	13.82MB	+0.02% (3.52kB)	⏫
loop_header_reachability	434.99kB	438.22kB	+0.74% (3.23kB)	⏫
StaticClassLiteral<'db>::try_mro_	5.86MB	5.87MB	+0.05% (2.83kB)	⏫
is_redundant_with_impl	5.51MB	5.51MB	-0.05% (2.71kB)	⏫
all_negative_narrowing_constraints_for_expression	2.62MB	2.62MB	-0.09% (2.45kB)	⏫
all_narrowing_constraints_for_expression	7.13MB	7.13MB	-0.03% (2.29kB)	⏫
StaticClassLiteral<'db>::implicit_attribute_inner_	9.93MB	9.94MB	+0.02% (1.73kB)	⏫
...			25 more

sphinx

Name	Old	New	Diff	Outcome
UnionType<'db>::from_two_elements_	1.38MB	1.41MB	+2.56% (36.09kB)	⏫
Type<'db>::member_lookup_with_policy_	6.51MB	6.53MB	+0.35% (23.17kB)	⏫
UnionType	1.24MB	1.26MB	+1.49% (18.97kB)	⏫
infer_expression_types_impl	21.48MB	21.49MB	+0.06% (13.66kB)	⏫
infer_definition_types	23.97MB	23.98MB	+0.05% (12.64kB)	⏫
infer_expression_type_impl	2.95MB	2.96MB	+0.20% (6.04kB)	⏫
is_redundant_with_impl::interned_arguments	2.02MB	2.02MB	+0.15% (3.01kB)	⏫
is_redundant_with_impl	1.78MB	1.78MB	+0.16% (2.95kB)	⏫
IntersectionType	880.59kB	883.23kB	+0.30% (2.65kB)	⏫
loop_header_reachability	378.58kB	381.22kB	+0.70% (2.64kB)	⏫
Type<'db>::member_lookup_with_policy_::interned_arguments	2.65MB	2.65MB	+0.09% (2.44kB)	⏫
TupleType<'db>::to_class_type_	161.37kB	163.07kB	+1.05% (1.70kB)	⏫
UnionType<'db>::from_two_elements_::interned_arguments	780.74kB	782.29kB	+0.20% (1.55kB)	⏫
infer_deferred_types	5.61MB	5.61MB	+0.02% (1.20kB)	⏫
infer_scope_types_impl	15.49MB	15.50MB	+0.01% (924.00B)	⏫
...			11 more

trio

Name	Old	New	Diff	Outcome
infer_definition_types	7.73MB	7.73MB	+0.08% (6.33kB)	⏫
UnionType<'db>::from_two_elements_	281.39kB	287.30kB	+2.10% (5.90kB)	⏫
UnionType	304.84kB	308.94kB	+1.34% (4.09kB)	⏫
infer_expression_types_impl	7.08MB	7.08MB	+0.04% (3.00kB)	⏫
infer_expression_type_impl	1.32MB	1.32MB	+0.18% (2.37kB)	⏫
Type<'db>::member_lookup_with_policy_	1.81MB	1.81MB	+0.12% (2.29kB)	⏫
StaticClassLiteral<'db>::try_mro_	822.56kB	823.75kB	+0.14% (1.19kB)	⏫
Type<'db>::member_lookup_with_policy_::interned_arguments	909.39kB	910.30kB	+0.10% (936.00B)	⏫
loop_header_reachability	133.23kB	134.12kB	+0.67% (912.00B)	⏫
Type<'db>::class_member_with_policy_	2.00MB	2.00MB	+0.04% (776.00B)	⏫
all_narrowing_constraints_for_expression	589.21kB	589.80kB	+0.10% (600.00B)	⏫
infer_deferred_types	2.38MB	2.38MB	+0.02% (588.00B)	⏫
Specialization	462.36kB	462.86kB	+0.11% (512.00B)	⏫
Type<'db>::try_call_dunder_get_	1.37MB	1.37MB	+0.04% (508.00B)	⏫
TupleType<'db>::to_class_type_	51.62kB	52.04kB	+0.82% (432.00B)	⏫
...			14 more

flake8

Name	Old	New	Diff	Outcome
UnionType<'db>::from_two_elements_	83.43kB	85.64kB	+2.65% (2.21kB)	⏫
UnionType	101.28kB	101.94kB	+0.65% (672.00B)	⏫
infer_definition_types	1.87MB	1.87MB	+0.02% (312.00B)	⏫
Type<'db>::class_member_with_policy_	568.68kB	568.97kB	+0.05% (292.00B)	⏫
infer_expression_types_impl	1.07MB	1.07MB	+0.02% (216.00B)	⏫
StaticClassLiteral<'db>::implicit_attribute_inner_	313.34kB	313.51kB	+0.06% (180.00B)	⏫
is_redundant_with_impl::interned_arguments	139.56kB	139.39kB	-0.12% (176.00B)	⏫
IntersectionType	68.56kB	68.40kB	-0.24% (168.00B)	⏫
Type<'db>::member_lookup_with_policy_	487.16kB	487.31kB	+0.03% (160.00B)	⏫
infer_expression_type_impl	141.97kB	142.12kB	+0.11% (156.00B)	⏫
TupleType<'db>::to_class_type_	15.58kB	15.73kB	+0.98% (156.00B)	⏫
Type<'db>::member_lookup_with_policy_::interned_arguments	228.11kB	228.21kB	+0.04% (104.00B)	⏫
Type<'db>::class_member_with_policy_::interned_arguments	306.41kB	306.52kB	+0.03% (104.00B)	⏫
is_redundant_with_impl	136.72kB	136.63kB	-0.07% (96.00B)	⏫
infer_deferred_types	692.50kB	692.54kB	+0.01% (36.00B)	⏫
...			5 more

[astral-sh-bot]

ecosystem-analyzer results

No diagnostic changes detected ✅

Full report with detailed diff (timing results)

[AlexWaygood]

Can we add a regression test for this?

[charliermarsh]

Added, sorry. (This was present in https://github.com/astral-sh/ruff/pull/24272/changes#diff-19ac4a4d9337821d0bbfb544ab4e3fda87df59c6ea06065b77d3fcf5cf682ec2R2809 but forgot to carry it over.)