Pattern matching list literals yields incorrect type check errors

[MC-DeltaT]

If a list literal is used directly as the argument to a match statement, then Pylance seems to want a wildcard case, or else it thinks the match will fall through, even if the other cases cover all possible types.
If the list is bound to a variable instead, then no type check error occurs, as expected.

Environment data

• Language Server version: 2022.3.1
• OS and version: Windows 10 build 19044.1586
• Python version: 3.10.2

Expected behaviour

The code passes the type check with no errors regardless of whether the list is a variable or literal.

Actual behaviour

Pylance reports an error:

Function with declared type of "int" must return value
  Type "None" cannot be assigned to type "int"

Logs

[Info  - 12:30:04 pm] (10944) Pylance language server 2022.3.1 (pyright bd47ac0b) starting
[Info  - 12:30:04 pm] (10944) Server root directory: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist
[Info  - 12:30:04 pm] (10944) No pyproject.toml file found.
[Info  - 12:30:04 pm] (10944) Setting pythonPath for service "<default>": "C:\Users\Reece Jones\AppData\Local\Programs\Python\Python310\python.exe"
[Warn  - 12:30:04 pm] (10944) stubPath typings is not a valid directory.
[Info  - 12:30:04 pm] (10944) Assuming Python platform Windows
[Info  - 12:30:04 pm] (10944) Search paths for <default>
[Info  - 12:30:04 pm] (10944)   c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib
[Info  - 12:30:04 pm] (10944)   typings
[Info  - 12:30:04 pm] (10944)   c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stubs\...
[Info  - 12:30:04 pm] (10944)   c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\bundled\stubs
[Info  - 12:30:04 pm] (10944) Searching for source files
[Info  - 12:30:04 pm] (10944) No source files found.
(10944) [IDX(FG)] index libraries  (index) ...
(10944) [IDX(FG)]   read stdlib indices (38ms)
(10944) [IDX(FG)] index libraries  (index) [succeed] (38ms)
(10944) [FG] parsing: c:\Users\Reece Jones\Desktop\test.py (12ms)
(10944) [FG] parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\builtins.pyi [fs read 3ms] (104ms)
(10944) [FG] binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\builtins.pyi (33ms)
(10944) [FG] binding: c:\Users\Reece Jones\Desktop\test.py (0ms)
[Info  - 12:30:05 pm] (10944) Background analysis(1) root directory: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist
[Info  - 12:30:05 pm] (10944) Background analysis(1) started
(10944) Background analysis message: setConfigOptions
(10944) Background analysis message: setImportResolver
(10944) Background analysis message: ensurePartialStubPackages
(10944) Background analysis message: setTrackedFiles
(10944) Background analysis message: markAllFilesDirty
(10944) Background analysis message: setFileOpened
(10944) Background analysis message: getDiagnosticsForRange
(10944) Background analysis message: getSemanticTokens full
(10944) [BG(1)] getSemanticTokens full at c:\Users\Reece Jones\Desktop\test.py ...
(10944) [BG(1)]   parsing: c:\Users\Reece Jones\Desktop\test.py (11ms)
(10944) [BG(1)]   parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\builtins.pyi [fs read 2ms] (99ms)
(10944) [BG(1)]   binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\builtins.pyi (36ms)
(10944) [BG(1)]   binding: c:\Users\Reece Jones\Desktop\test.py (1ms)
(10944) [BG(1)]   parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\typing_extensions.pyi [fs read 2ms] (7ms)
(10944) [BG(1)]   binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\typing_extensions.pyi (1ms)
(10944) [BG(1)]   parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\typing.pyi [fs read 0ms] (35ms)
(10944) [BG(1)]   binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\typing.pyi (11ms)
(10944) [BG(1)]   parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\_typeshed\__init__.pyi [fs read 0ms] (7ms)
(10944) [BG(1)]   binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\_typeshed\__init__.pyi (1ms)
(10944) [BG(1)]   parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\types.pyi [fs read 1ms] (24ms)
(10944) [BG(1)]   binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\types.pyi (6ms)
(10944) [BG(1)]   parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\abc.pyi [fs read 0ms] (2ms)
(10944) [BG(1)]   binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\abc.pyi (0ms)
(10944) [BG(1)] getSemanticTokens full at c:\Users\Reece Jones\Desktop\test.py (263ms)
(10944) Background analysis message: analyze
(10944) [BG(1)] analyzing: c:\Users\Reece Jones\Desktop\test.py ...
(10944) [BG(1)]   checking: c:\Users\Reece Jones\Desktop\test.py ...
(10944) [BG(1)]     parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\collections\abc.pyi [fs read 1ms] (1ms)
(10944) [BG(1)]     binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\collections\abc.pyi ...
(10944) [BG(1)]       parsing: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\_collections_abc.pyi [fs read 1ms] (2ms)
(10944) [BG(1)]       binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\_collections_abc.pyi (1ms)
(10944) [BG(1)]     binding: c:\Users\Reece Jones\.vscode\extensions\ms-python.vscode-pylance-2022.3.1\dist\typeshed-fallback\stdlib\collections\abc.pyi (4ms)
(10944) [BG(1)]   checking: c:\Users\Reece Jones\Desktop\test.py (25ms)
(10944) [BG(1)] analyzing: c:\Users\Reece Jones\Desktop\test.py (25ms)
(10944) Background analysis message: getDiagnosticsForRange
(10944) Background analysis message: getSemanticTokens range
(10944) [BG(1)] getSemanticTokens range 0:0 - 6:0 at c:\Users\Reece Jones\Desktop\test.py (0ms)
(10944) Background analysis message: resumeAnalysis

Code Snippet / Additional information

Causes error:

def test() -> int:
    match [10]:
        case [value]:
            return value
        case [*values]:
            return values[0]

Doesn't cause error:

def test() -> int:
    l = [10]
    match l:
        case [value]:
            return value
        case [*values]:
            return values[0]

[erictraut]

Thanks for the bug report. This will be fixed in the next release.

[bschnurr]

This issue has been fixed in version 2022.3.2, which we've just released. You can find the changelog here: CHANGELOG.md