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Reject stale GenericAlias parameters on Python 3.15 #9069

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Merged
youknowone merged 6 commits into from
Oct 12, 2026
Merged

Reject stale GenericAlias parameters on Python 3.15 #9069

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9c3351f
Reject GenericAlias parameters added after caching
youknowdot Oct 11, 2026
e92e032
Compute GenericAlias parameters lazily for Python 3.15
youknowdot Oct 11, 2026
c643a85
Check GenericAlias recursion at lazy parameter materialization
youknowdot Oct 11, 2026
0dd2d8b
Keep finite GenericAlias stack stress native-specific
youknowdot Oct 11, 2026
5ceff65
Materialize union parameters lazily like GenericAlias
youknowdot Oct 11, 2026
4809c5b
Consolidate union regressions in the typing snippet
youknowdot Oct 12, 2026
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Reject GenericAlias parameters added after caching 
Validate stale cached parameters and retain the Python regression without obsolete reference prerequisites.

Assisted-by: OpenAI Codex:model identifier unavailable
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@youknowdot
youknowdot committed Oct 11, 2026
commit 9c3351f155a31d8f99c96f118b808cf77ac5422c
5 changes: 4 additions & 1 deletion crates/vm/src/builtins/genericalias.rs
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Expand Up @@ -558,7 +558,10 @@ pub(crate) fn subs_parameters(
if let Some(iparam) = tuple_index(parameters.as_slice(), arg) {
subst.call((arg_items[iparam].clone(),), vm)?
} else {
subs_tvars(arg.clone(), parameters, &arg_items, vm)?
return Err(vm.new_type_error(format!(

@chatgpt-codex-connector chatgpt-codex-connector Bot Oct 11, 2026

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P2 Badge Defer stale checks until the parameter cache is materialized

When __typing_subst__ is added before an alias's first parameter lookup, this return treats the parameter as stale even though Python 3.15 has not cached __parameters__ yet. For example, let late.__parameters__ == (T,), create GenericAlias(list, late), set late.__typing_subst__ = lambda x: x, and evaluate alias[int]; Python returns list[int], but PyGenericAlias::new eagerly saved (T,), so late misses tuple_index and this branch raises. Lazily materialize or track the parameter cache so the guard applies only after it was actually cached.

AGENTS.md reference: AGENTS.md:L7-L7

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"argument {} with __typing_subst__ was not found in __parameters__",
arg.repr(vm)?
)));
}
} else {
subs_tvars(arg.clone(), parameters, &arg_items, vm)?
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22 changes: 22 additions & 0 deletions extra_tests/snippets/stdlib_typing.py
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Expand Up @@ -89,3 +89,25 @@ def __module__(self):
)
assert alias_namespace["alias"].__module__ is None
assert alias_module_lookups == []


# GenericAlias rejects parameters added after its parameter tuple was cached.
from types import GenericAlias


class LateParameter:
def __repr__(self):
return "late_parameter"


first = LateParameter()
first.__typing_subst__ = lambda value: value
late = LateParameter()
alias = GenericAlias(dict, (first, late))
assert alias.__parameters__ == (first,)
late.__typing_subst__ = lambda value: value
with assert_raises(TypeError) as caught:
alias[0]
assert str(caught.exception) == (
"argument late_parameter with __typing_subst__ was not found in __parameters__"
Comment on lines +109 to +112

@chatgpt-codex-connector chatgpt-codex-connector Bot Oct 10, 2026

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P1 Badge Remove the newly added test logic

This new assertion block adds test logic to extra_tests/snippets/stdlib_typing.py, while the repository's critical test-code policy permits test-file changes only for adding or removing expected-failure decorators and explicitly forbids modifying assertions, logic, or data. Remove this addition from the test file or change the repository policy first; it cannot land in its current form.

AGENTS.md reference: AGENTS.md:L273-L280

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)