Default values in functions are always Unknown

[thesadru]

Environment data

• Language Server version: 2021.11.0
• OS and version: Windows 10
• Python version: 3.9.6

Expected behavior

Default values should be properly detected

Actual behavior

If a default value in a function contains a call statement then the callable will always be Unknown.

Static type-checking however still works.

Logs

Background analysis message: getDiagnosticsForRange
Background analysis message: resumeAnalysis
Background analysis message: getDiagnosticsForRange
Background analysis message: markFilesDirty
Background analysis message: analyze
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
Background analysis message: markFilesDirty
Background analysis message: analyze
Background analysis message: invalidateAndForceReanalysis
Background analysis message: invalidateAndForceReanalysis
Background analysis message: markFilesDirty
[Info  - 19:21:51] Searching for source files
[Info  - 19:21:51] Found 1 source file
Background analysis message: setTrackedFiles
Background analysis message: markAllFilesDirty
Background analysis message: analyze
[BG(1)] analyzing: c:\Users\D\code\random\test.py ...
[BG(1)]   parsing: c:\Users\D\code\random\test.py (75ms)
[BG(1)]   parsing: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\builtins.pyi [fs read 0ms] (38ms)
[BG(1)]   binding: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\builtins.pyi (28ms)
[BG(1)]   binding: c:\Users\D\code\random\test.py (1ms)
[BG(1)]   checking: c:\Users\D\code\random\test.py ...
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\__init__.py [fs read 1ms] (4ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\__init__.py (0ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\applications.py [fs read 1ms] (49ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\applications.py (3ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\applications.py [fs read 1ms] (8ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\applications.py (1ms)
[BG(1)]     parsing: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\typing_extensions.pyi [fs read 1ms] (3ms)
[BG(1)]     binding: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\typing_extensions.pyi (2ms)
[BG(1)]     parsing: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\typing.pyi [fs read 1ms] (9ms)
[BG(1)]     binding: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\typing.pyi (5ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\routing.py [fs read 1ms] (28ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\routing.py (5ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\params.py [fs read 1ms] (7ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\params.py (2ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\responses.py [fs read 1ms] (17ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\responses.py (7ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\datastructures.py [fs read 1ms] (3ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\datastructures.py (1ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\middleware\__init__.py [fs read 0ms] (4ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\middleware\__init__.py (0ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\requests.py [fs read 3ms] (12ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\starlette\requests.py (3ms)
[BG(1)]     parsing: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\collections\abc.pyi [fs read 1ms] (2ms)
[BG(1)]     binding: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\collections\abc.pyi ...
[BG(1)]       parsing: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\_collections_abc.pyi [fs read 1ms] (1ms)
[BG(1)]       binding: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\_collections_abc.pyi (1ms)
[BG(1)]     binding: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\collections\abc.pyi (2ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\param_functions.py [fs read 0ms] (6ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\fastapi\param_functions.py (1ms)
[BG(1)]     parsing: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\pydantic\fields.py [fs read 1ms] (19ms)
[BG(1)]     binding: c:\Users\D\AppData\Roaming\Python\Python39\site-packages\pydantic\fields.py (13ms)
[BG(1)]   checking: c:\Users\D\code\random\test.py (254ms)
[BG(1)] analyzing: c:\Users\D\code\random\test.py (397ms)
Background analysis message: resumeAnalysis
Background analysis message: markFilesDirty
Background analysis message: markFilesDirty
Background analysis message: markFilesDirty
Background analysis message: analyze
Background analysis message: getDiagnosticsForRange
Background analysis message: getDiagnosticsForRange
[FG] parsing: c:\Users\D\code\random\test.py (83ms)
[FG] parsing: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\builtins.pyi [fs read 0ms] (44ms)
[FG] binding: c:\Users\D\.vscode\extensions\ms-python.vscode-pylance-2021.11.0\dist\typeshed-fallback\stdlib\builtins.pyi (15ms)
[FG] binding: c:\Users\D\code\random\test.py (0ms)

Code Snippet / Additional information

Defaults are always shown as Unknown (not even autocomplete works)

Pylance knows about the variables

Type-checking still occurs

[jakebailey]

This seems like a bug in the hover provider; hovering works in the context outside of the default values, but not when inside a default value (and everything else works).

[jakebailey]

Just to quick test, if you remove the decorator from the function, do you see that hover works?

[erictraut]

Which version of fastapi do you have installed? I just installed the latest published version (0.70.0), and I'm seeing a different behavior than you.

Here's the code that I typed in from your screen shot, for reference:

import fastapi

app = fastapi.FastAPI()

@app.route("/echo")
async def echo(text: str = fastapi.Query()):
    return {"message": text}

And here's what I see in the hover text.

Unrelated to the issue you're reporting, I'm curious whether it's really your intent to use a function call inside of a default argument expression. That's generally a very dangerous thing to do because of the way default arguments work in Python. They are evaluated only once at the time the function definition is processed, not once for each time the function is called like in other languages.

[thesadru]

Just to quick test, if you remove the decorator from the function, do you see that hover works?

The issue persists no matter the decorator. I have also tried it with other libraries which use the same kind of behavior (typer and disnake). Both have the same problem.

[thesadru]

Which version of fastapi do you have installed? I just installed the latest published version (0.70.0), and I'm seeing a different behavior than you.

Also 0.70.0. this issue is not even specific to fastapi

And here's what I see in the hover text.

At times the hover also works for me. However only when I have just typed the default value and haven't provided any arguments. After I do things like type arguments and then click elsewhere the hover always stops recognizing anything in the default value.
To add to this, when trying to go to the definition or declaration of anything in the default value it will always say it could not be found.

Unrelated to the issue you're reporting, I'm curious whether it's really your intent to use a function call inside of a default argument expression. That's generally a very dangerous thing to do because of the way default arguments work in Python. They are evaluated only once at the time the function definition is processed, not once for each time the function is called like in other languages.

Yes I am completely aware of the risk. The default value being shared is actually ideal in my case. Recently a lot of libraries have been using this kind of syntax as a sort of parameter descriptor. I simply chose fastapi as it's the most known library with this syntax.

[erictraut]

Thanks for the additional context. I was able to repro the problem and find the underlying cause. This will be fixed in the next release.

[heejaechang]

fixed in 2021.11.2