GitLab

Move the old code within `parser_main.py` to `parser/__main__.py`
So that rql package can be run with the -m module flag.

When calling `$ python3 -m rql.parser "Any 1+1;"`, the main function
defined inside __main__.py will be executed and the string "Any 1+1;"
will be parsed.

Are those 2 modules really used anywhere within the Cubi-verse ?

- add Op type as a list of all operations
- type hint SelectionMgr class
- should we make NodeOperation class truly abstract?
- type hint NodeOperation class
- add undo method inside NodeOperation class to make Op type more consistent

1. Define a custom type: TranslationFunction:
This depends on `Protocol` which is only available on python >= 3.8.
`typing_extensions` provides it for lower versions.

2. Update get_description function signature:
For `tr` parameter, Use TranslationFunction instead of Callable[[str, str], str]

3. get_description signature redefined, stop ignoring call-arg errors

- variable_ref is a function that should take a Variable or a VariableRef
- type alias VarType was not used (will probably be moved inside rqltypes module)

From version 0.900,
Mypy now only ships with type stubs for stdlib modules.
For some third-party libraries we need to explicitly install stub packages.

See: http://mypy-lang.blogspot.com/2021/06/mypy-0900-released.html

Those 2 methods are called with many other classes (not only BaseNode class), so:

- add a new generic type Y to be used with get_nodes & iget_nodes methods
- rewrite get_nodes & iget_nodes methods to be more generic inside base.py

- update tox configuration, add black environment
- format the whole project
- update Gitlab CI config add a job for black

- Add types within stcheck.py module
- Update the accept & leave methods signatures inside the VisitableMixIn class
- Redefine type (and set a type alias) for Select.vargraph attribute

related: cubicweb#301

- make sure remove method & replace method have the same signature
- make sure to use 'rql.base.BaseNode' instead of 'BaseNode' when typing

- Fix undefined name 'pinput'
- Fix undefined name 'MUL_OP'

with_ used to be a class attribute, shared by all the instances. Some tricks
were used to redefine it as an instance attribute on the fly. It was leading to
an infinite recursion.

Let's simplify all of this, and remove the magic. Instance attributes should be
defined in the __init__.