MarkInfo class is misused for collection of MarkInfo objects

[JanBednarik]

MarkInfo class ( https://github.com/pytest-dev/pytest/blob/master/_pytest/mark.py#L286 ) is used for two purposes:

• store MarkInfo (args and kwargs) of one object
• iterable collection of MarkInfo objects (list of args and kwargs)

This unclear usage leads to nasty bugs like #751 and makes requests like #759 too hard to implement. MarkInfo should be refactored into two classes one for each purpose.

[chmeldax]

@JanBednarik Well, did you start working on it or what is the progress of this "enhacement"? I just wonder if I should somehow reopen #759 :)

[JanBednarik]

@chmeldax I started working on it, but looks like deeper issue.

@RonnyPfannschmidt Should I work on this? Or you will deal with this in issue #891 ?

[RonnyPfannschmidt]

@JanBednarik for easing #891 some toolings to delcare/use and merge collections of marks seem handy - more communication needed, are you by chance on irc, or is another medium better

[RonnyPfannschmidt]

the underlying refactorings are done, the other facade will get a new api