conformance: fix generics_defaults — flag ParamSpec-after-TypeVarTuple when TVT has no default#2310
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ashishpatel26 wants to merge 2 commits into
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…le without TVT default
The conformance test for `class Foo6(Generic[*Ts, P])` was missing an
`# E` marker. The spec only permits a defaulted `ParamSpec` to follow a
`TypeVarTuple` when the `TypeVarTuple` **also has a default**; in the
test `Ts` had no default, so the class is ambiguous (exactly like the
`TypeVar`-after-`TypeVarTuple` rule) and raises `TypeError` at runtime.
Changes:
- Add `TsD = TypeVarTuple("TsD", default=Unpack[tuple[int, str]])` for
the valid case.
- Mark `class Foo6(Generic[*Ts, P])` as `# E` (Ts has no default).
- Add `class Foo6b(Generic[*TsD, P])` as the spec-valid case (both
`TsD` and `P` have defaults) with corresponding assertions.
- Clarify the spec prose to state the "TypeVarTuple **with a default**"
condition explicitly and show a counter-example.
- Update all six checker result TOMLs.
Fixes: python#2211
srittau
added
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topic: conformance tests
Collaborator
|
This is probably something where the spec was just not worded well enough. There is kind of an implicit default for type var tuples in this case, which is the empty tuple. I don't think the changing the conformance tests makes sense here. |
Member
|
the consensus in the issue seemed to be that it's a bug in CPython that we should fix there |
pyrefly, pyright, and zuban were missing `conformant = "Partial"` after conformance_automated changed from Pass to Fail. The validate_results script requires conformant to be explicitly set when automated is Fail.
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Summary
Fixes #2211.
The spec states that a
ParamSpecwith a default may follow aTypeVarTupleonly when theTypeVarTuplealso has a default (to avoid ambiguity). The existing conformance testclass Foo6(Generic[*Ts, P])hadTswithout a default but was missing an# Emarker, effectively telling type checkers to accept code that raisesTypeErrorat runtime.Changes:
conformance/tests/generics_defaults.pyTsD = TypeVarTuple("TsD", default=Unpack[tuple[int, str]])for the valid case.class Foo6(Generic[*Ts, P])as# E—Tshas no default, so this is ambiguous.class Foo6b(Generic[*TsD, P])(no error) — bothTsDandPcarry defaults.test_foo6(which exercised the now-invalid class) withtest_foo6b.docs/spec/generics.rstclass Bar[*Ts, **P = [float, bool]]: ... # Type checker error.conformance/results/*/generics_defaults.toml— updated for all six checkers.Test plan
conformance/tests/generics_defaults.pychanges reviewed for correctness./)