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[red-knot] Statically known branches (#15019 )

## Summary

This changeset adds support for precise type-inference and
boundness-handling of definitions inside control-flow branches with
statically-known conditions, i.e. test-expressions whose truthiness we
can unambiguously infer as *always false* or *always true*.

This branch also includes:
- `sys.platform` support
- statically-known branches handling for Boolean expressions and while
  loops
- new `target-version` requirements in some Markdown tests which were
  now required due to the understanding of `sys.version_info` branches.

closes #12700 
closes #15034 

## Performance

### `tomllib`, -7%, needs to resolve one additional module (sys)

| Command | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `./red_knot_main --project /home/shark/tomllib` | 22.2 ± 1.3 | 19.1 |
25.6 | 1.00 |
| `./red_knot_feature --project /home/shark/tomllib` | 23.8 ± 1.6 | 20.8
| 28.6 | 1.07 ± 0.09 |

### `black`, -6%

| Command | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `./red_knot_main --project /home/shark/black` | 129.3 ± 5.1 | 119.0 |
137.8 | 1.00 |
| `./red_knot_feature --project /home/shark/black` | 136.5 ± 6.8 | 123.8
| 147.5 | 1.06 ± 0.07 |

## Test Plan

- New Markdown tests for the main feature in
  `statically-known-branches.md`
- New Markdown tests for `sys.platform`
- Adapted tests for `EllipsisType`, `Never`, etc

2024-12-21 11:33:10 +01:00

1.3 KiB

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NoReturn & Never

NoReturn is used to annotate the return type for functions that never return. Never is the bottom type, representing the empty set of Python objects. These two annotations can be used interchangeably.

Function Return Type Annotation

from typing import NoReturn

def stop() -> NoReturn:
    raise RuntimeError("no way")

# revealed: Never
reveal_type(stop())

Assignment

from typing_extensions import NoReturn, Never, Any

# error: [invalid-type-form] "Type `typing.Never` expected no type parameter"
x: Never[int]
a1: NoReturn
a2: Never
b1: Any
b2: int

def f():
    # revealed: Never
    reveal_type(a1)
    # revealed: Never
    reveal_type(a2)

    # Never is assignable to all types.
    v1: int = a1
    v2: str = a1
    # Other types are not assignable to Never except for Never (and Any).
    v3: Never = b1
    v4: Never = a2
    v5: Any = b2
    # error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to `Never`"
    v6: Never = 1

`typing.Never`

typing.Never is only available in Python 3.11 and later.

Python 3.11

[environment]
python-version = "3.11"

from typing import Never

reveal_type(Never)  # revealed: typing.Never

Python 3.10

[environment]
python-version = "3.10"

# error: [unresolved-import]
from typing import Never

1.3 KiB Raw Blame History