Incorrect marking of Expected expression when unpacking tuple and using type annotations

[alvesvaren]

Environment data

• Language Server version: v2020.12.0
• OS and version: Arch Linux 5.9.12-arch1-1
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.9.0

Expected behaviour

data: Tuple[List[str], ...] = *map(example),

works fine without any problems with Pylance (because this works in python)

Actual behaviour

data: Tuple[List[str], ...] = *map(example),

Pylance displays an error: Expected expression and selects the *-sign before the map statement

Logs

Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: setFileOpened
Background analysis message: markFilesDirty
[FG] parsing: /home/alve/dev/AoC-2020/8.py (1ms)
[FG] binding: /home/alve/dev/AoC-2020/8.py (0ms)
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: analyze
[BG(1)] analyzing: /home/alve/dev/AoC-2020/8.py ...
[BG(1)]   parsing: /home/alve/dev/AoC-2020/8.py (4ms)
[BG(1)]   binding: /home/alve/dev/AoC-2020/8.py (0ms)
[BG(1)]   checking: /home/alve/dev/AoC-2020/8.py (9ms)
[BG(1)] analyzing: /home/alve/dev/AoC-2020/8.py (13ms)
Background analysis message: resumeAnalysis
Background analysis message: setFileOpened
Background analysis message: markFilesDirty
[FG] parsing: /home/alve/dev/AoC-2020/8.py (6ms)
[FG] binding: /home/alve/dev/AoC-2020/8.py (1ms)
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: analyze
[BG(1)] analyzing: /home/alve/dev/AoC-2020/8.py ...
[BG(1)]   parsing: /home/alve/dev/AoC-2020/8.py (5ms)
[BG(1)]   binding: /home/alve/dev/AoC-2020/8.py (1ms)
[BG(1)]   checking: /home/alve/dev/AoC-2020/8.py (39ms)
[BG(1)] analyzing: /home/alve/dev/AoC-2020/8.py (46ms)
Background analysis message: resumeAnalysis
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: markFilesDirty
Background analysis message: analyze
Background analysis message: setFileOpened
Background analysis message: markFilesDirty
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
[FG] parsing: /home/alve/dev/AoC-2020/8.py (3ms)
[FG] binding: /home/alve/dev/AoC-2020/8.py (0ms)
Background analysis message: analyze
[BG(1)] analyzing: /home/alve/dev/AoC-2020/8.py ...
[BG(1)]   parsing: /home/alve/dev/AoC-2020/8.py (2ms)
[BG(1)]   binding: /home/alve/dev/AoC-2020/8.py (0ms)
[BG(1)]   checking: /home/alve/dev/AoC-2020/8.py (4ms)
[BG(1)] analyzing: /home/alve/dev/AoC-2020/8.py (6ms)
Background analysis message: resumeAnalysis
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: markFilesDirty
Background analysis message: analyze
[FG] parsing: /home/alve/.vscode/extensions/ms-python.vscode-pylance-2020.12.0/dist/typeshed-fallback/stdlib/2and3/_typeshed/__init__.pyi [fs read 0ms] (20ms)
[FG] binding: /home/alve/.vscode/extensions/ms-python.vscode-pylance-2020.12.0/dist/typeshed-fallback/stdlib/2and3/_typeshed/__init__.pyi (1ms)
[FG] parsing: /home/alve/.vscode/extensions/ms-python.vscode-pylance-2020.12.0/dist/typeshed-fallback/third_party/2and3/typing_extensions.pyi [fs read 0ms] (8ms)
[FG] binding: /home/alve/.vscode/extensions/ms-python.vscode-pylance-2020.12.0/dist/typeshed-fallback/third_party/2and3/typing_extensions.pyi (1ms)
[FG] parsing: /tmp/pyright-4278-BZYzwhKCkMnJ/builtins-4278-1Yvrj78E1t3t-.py [fs read 1ms] (126ms)
[FG] binding: /tmp/pyright-4278-BZYzwhKCkMnJ/builtins-4278-1Yvrj78E1t3t-.py (21ms)
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange

Code Snippet / Additional information

from typing import List, Tuple, Any

example: Any = (["example code", "example code"])

data: Tuple[List[str], ...] = *map(str.split, example),

[erictraut]

The code snippet that you've provided contains a syntax error because of a comma at the end. The Python interpreter reports an error ("SyntaxError: unexpected EOF while parsing").

If I delete the final comma, the Python interpreter reports "SyntaxError: can't use starred expression here". So I think Pylance is reporting the correct error here.

[alvesvaren]

oh, I had the wrong snippet. I edited the issue, still the same problem, and no syntax error in python

[erictraut]

Thanks for the bug report. I've confirmed that this is a bug in the parser. It's specific to the case where the LHS of an assignment is a variable with a type annotation and the RHS is a non-parenthesized tuple that starts with an unpack operator.

This will be fixed in the next release. I've added your sample as a unit test.

While you're waiting for the next release, you can work around the issue by enclosing the RHS (right hand side) of the assignment in parentheses.

[jakebailey]

This issue has been fixed in version 2020.12.1, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/master/CHANGELOG.md#2020121-9-december-2020