Support @dataclass classes

[jakebailey]

Classes decorated as @dataclass get a slew of methods added to them, which we currently cannot detect: https://docs.python.org/3/library/dataclasses.html

For example, if I declared a Point class as a dataclass, I'd expect to see some extra info when trying to instantiate one:

It should look the same as:

(Where I've explicitly defined __init__ as the Python docs do.)

Unfortunately, it's not as simple as "see @dataclass, add these methods", since the decorator allows for customizing which methods get added. I expect this will need to operate a lot like namedtuple and need to look at the call to determine what to add. Also note the rules like "if __init__ exists, it's not overridden" which will need to be considered.

[munael]

One point for completely 'vanilla' dataclasses:

Initialized variables of a dataclass type offer correct completions (usually even better sorted than completions for a manually-created class with the same members, which can show several __blah members before normal members), but type hints don't always show when hovering over a member name (but a member is consistent; it either shows the type or doesn't).

Like this:

Here^ I was hovering over dirs in app.dirs. app's type is correctly inferred and shows on hover, its members show in autocomplete, but members' types don't show on hover.

[brettcannon]

microsoft/vscode-python#3598 discovered that dataclasses currently have their attributes flagged as use-before-def. Do you want that reported as a separate issue?

[jakebailey]

No, that's probably #395. The new LS hasn't reimplemented that diagnostic yet, either way, so I'd be hoping to implement it without these bugs (in a less hacky way).

[erezsh]

Hi, any idea if there's any progress on this?

jedi (in vscode) has pretty good support for it (dataclass autocomplete). Perhaps you can look at their solution for inspiration?

[alphacentauri12]

@jakebailey I also had this problem and I think I might have solved it by adding a docstring. If it is still not working delete the folder __pycache__.

[mahmoudajawad]

@alphacentauri12, what do you add to the docstring? full definition of the args used?