Give a diagnostic when creating a function in a class and not specifying the first argument as self

[CTrando]

Waiting on #1273 before I can merge this one.

e.g

class Test:
    def hello(x, y, z):
         pass

[jakebailey]

I don't think we should merge this one, at least not for now. Although calling the first argument "self" is convention, it's not a runtime-requirement and code which doesn't say self will still work if the first variable is used correctly.

(Arguably, we should be trying to rely on the name self less and less, but that's another issue.)

[MikhailArkhipov]

It is an error per http://pylint-messages.wikidot.com/messages:e0213. As in big VS, one can always suppress it via settings/pragmas. By default though, VS shows violations or common conventions although said violations may not always translate to crashes.

https://legacy.python.org/dev/peps/pep-0008/#function-and-method-arguments
Always use self for the first argument to instance methods.
Always use cls for the first argument to class methods.

[CTrando]

WIP until I can add no class argument and no method argument.

[brettcannon]

Not using self as the name of the first parameter of an instance method is not an error and potentially done on purpose (e.g. if you are using **kwargs and you don't want self to be captured as a positional or keyword argument). It also won't work if you use staticmethod (where it doesn't make sense), or classmethod (which is traditionally cls). This also doesn't cover other clever decorators, metaclasses, etc.

If this being done as a stylistic thing then I would leave to a style linter like Pylint. If the worry is someone mis-typed self then the preexisting check for undefined variables should catch that. And if it's due to someone simply forgetting to include self then tests should capture that, but on its own I would say that since this isn't an obvious run-time error that this is going to be difficult to get right like the redefinition check.

[MikhailArkhipov]

Per links above it is considered an error in pylint which then refers to https://legacy.python.org/dev/peps/pep-0008/#function-and-method-arguments. Tests may be useful, but in C# I's rather see that I mistyped this to ths before I even get to compilation. VS editor does not require even to build to see issues.

Besides, some people never write tests and that is their choice. We can't really insist on 'write tests and that will catch the error'.

The question is a) how to classify the message. By default it is a warning, not an error. And b) how to let people to suppress categories easily. Like in VS I have 600 info messages from C# and Resharper which I suppress with a single click.

[CTrando]

Need to check for Type in the Mro, don't know an easy way besides this

[CTrando]

I looked at this for the abstract check

[CTrando]

Very similar to the one in PythonFunctionExtensions, any idea how to remove the duplication?

[MikhailArkhipov]

Instead of passing type, pass actual flags. I.e. HasValidDecorators(bool isAbstract, bool isClassMethod, ...)

[CTrando]

Diagnostics on function params:

Gives diagnostics on:

• Not usingself in a regular function

class A: 
  def tmp(x, y, z): ...

• Not using cls in a class method or an abstract class method

class A: 
  @classmethod / @abstractclassmethod
  def tmp(x, y, z): ...

• Not using cls in an automatic class method, I have __new__, __init_subclass__, __class_getitem__.

class A: 
  def __new__(x, y, z): ...

No diagnostics on:

• Methods declared with @staticmethod
• Methods declared in a class that is in a metaclass chain, (has type in its Mro)

What I don't handle:
Decorators with somewhat unorthodox behavior such as singledispatch.

I could add something that checks if there are any unknown decorators on the function, don't give any diagnostics on the parameters.

Diagnostics on decorator combinations:

Properties:

• Static method + property is not allowed

class A:
  @property  
  @staticmethod 
  def tmp(self): ...

• Class method + property is not allowed

class A:
  @property  
  @classmethod 
  def tmp(self): ...

Functions:

• Static method + Class method is not allowed

class A:
  @staticmethod  
  @classmethod 
  def tmp(self): ...

Note: Important to note that if there are any errors found in evaluating decorator combinations, no diagnostics are given on the parameters of the given property or function.

[MikhailArkhipov]

Check #1401, it has a null ref around similar __init__ check.

[CTrando]

Removing because was unused and does not check for declaration type and null check for name.