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## Summary This allows us to handle self-referential bounds/constraints/defaults without panicking. Handles more cases from https://github.com/astral-sh/ty/issues/256 This also changes the way we infer the types of legacy TypeVars. Rather than understanding a constructor call to `typing[_extension].TypeVar` inside of any (arbitrarily nested) expression, and having to use a special `assigned_to` field of the semantic index to try to best-effort figure out what name the typevar was assigned to, we instead understand the creation of a legacy `TypeVar` only in the supported syntactic position (RHS of a simple un-annotated assignment with one target). In any other position, we just infer it as creating an opaque instance of `typing.TypeVar`. (This behavior matches all other type checkers.) So we now special-case TypeVar creation in `TypeInferenceBuilder`, as a special case of an assignment definition, rather than deeper inside call binding. This does mean we re-implement slightly more of argument-parsing, but in practice this is minimal and easy to handle correctly. This is easier to implement if we also make the RHS of a simple (no unpacking) one-target assignment statement no longer a standalone expression. Which is fine to do, because simple one-target assignments don't need to infer the RHS more than once. This is a bonus performance (0-3% across various projects) and significant memory-usage win, since most assignment statements are simple one-target assignment statements, meaning we now create many fewer standalone-expression salsa ingredients. This change does mean that inference of manually-constructed `TypeAliasType` instances can no longer find its Definition in `assigned_to`, which regresses go-to-definition for these aliases. In a future PR, `TypeAliasType` will receive the same treatment that `TypeVar` did in this PR (moving its special-case inference into `TypeInferenceBuilder` and supporting it only in the correct syntactic position, and lazily inferring its value type to support recursion), which will also fix the go-to-definition regression. (I decided a temporary edge-case regression is better in this case than doubling the size of this PR.) This PR also tightens up and fixes various aspects of the validation of `TypeVar` creation, as seen in the tests. We still (for now) treat all typevars as instances of `typing.TypeVar`, even if they were created using `typing_extensions.TypeVar`. This means we'll wrongly error on e.g. `T.__default__` on Python 3.11, even if `T` is a `typing_extensions.TypeVar` instance at runtime. We share this wrong behavior with both mypy and pyrefly. It will be easier to fix after we pull in https://github.com/python/typeshed/pull/14840. There are some issues that showed up here with typevar identity and `MarkTypeVarsInferable`; the fix here (using the new `original` field and `is_identical_to` methods on `BoundTypeVarInstance` and `TypeVarInstance`) is a bit kludgy, but it can go away when we eliminate `MarkTypeVarsInferable`. ## Test Plan Added and updated mdtests. ### Conformance suite impact The impact here is all positive: * We now correctly error on a legacy TypeVar with exactly one constraint type given. * We now correctly error on a legacy TypeVar with both an upper bound and constraints specified. ### Ecosystem impact Basically none; in the setuptools case we just issue slightly different errors on an invalid TypeVar definition, due to the modified validation code. --------- Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com> |
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| assignment | ||
| binary | ||
| boolean | ||
| boundness_declaredness | ||
| call | ||
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| comparison | ||
| comprehensions | ||
| conditional | ||
| dataclasses | ||
| declaration | ||
| diagnostics | ||
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| doc | ||
| exception | ||
| expression | ||
| function | ||
| generics | ||
| ide_support | ||
| import | ||
| literal | ||
| loops | ||
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| regression | ||
| scopes | ||
| shadowing | ||
| snapshots | ||
| stubs | ||
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| suppressions | ||
| type_compendium | ||
| type_of | ||
| type_properties | ||
| type_qualifiers | ||
| unary | ||
| with | ||
| .mdformat.toml | ||
| async.md | ||
| attributes.md | ||
| classes.md | ||
| cycle.md | ||
| decorators.md | ||
| del.md | ||
| deprecated.md | ||
| descriptor_protocol.md | ||
| enums.md | ||
| exhaustiveness_checking.md | ||
| final.md | ||
| implicit_type_aliases.md | ||
| instance_layout_conflict.md | ||
| intersection_types.md | ||
| invalid_syntax.md | ||
| known_constants.md | ||
| mdtest_config.md | ||
| mdtest_custom_typeshed.md | ||
| metaclass.md | ||
| mro.md | ||
| named_tuple.md | ||
| overloads.md | ||
| pep695_type_aliases.md | ||
| properties.md | ||
| protocols.md | ||
| public_types.md | ||
| statically_known_branches.md | ||
| sys_platform.md | ||
| sys_version_info.md | ||
| t_strings.md | ||
| terminal_statements.md | ||
| ty_extensions.md | ||
| typed_dict.md | ||
| union_types.md | ||
| unpacking.md | ||
| unreachable.md | ||