typing.Generic does not correctly call super().__init_subclass__

[wrmsr]

BPO	33207
Nosy	@gvanrossum, @ilevkivskyi, @wrmsr
PRs	bpo-33207: Call super in Generic.__init_subclass__ #6356 [3.7] bpo-33207: Call super in Generic.__init_subclass__ (GH-6356) #6372
Files	generic_init_subclass.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-04-04.16:55:29.967>
created_at = <Date 2018-04-02.22:01:55.103>
labels = ['3.7', 'type-bug', 'library']
title = 'typing.Generic does not correctly call super().__init_subclass__'
updated_at = <Date 2018-04-04.16:55:29.966>
user = 'https://github.com/wrmsr'

bugs.python.org fields:

activity = <Date 2018-04-04.16:55:29.966>
actor = 'levkivskyi'
assignee = 'none'
closed = True
closed_date = <Date 2018-04-04.16:55:29.967>
closer = 'levkivskyi'
components = ['Library (Lib)']
creation = <Date 2018-04-02.22:01:55.103>
creator = 'wrmsr'
dependencies = []
files = ['47513']
hgrepos = []
issue_num = 33207
keywords = ['patch']
message_count = 1.0
messages = ['314828']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'levkivskyi', 'wrmsr']
pr_nums = ['6356', '6372']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33207'
versions = ['Python 3.7']

[wrmsr]

Per the docs ( https://docs.python.org/3/reference/datamodel.html#object.\_\_init_subclass__ ) this should be chain-calling super but currently doesn't, and thus breaks base classes listed after it which depend on this functionality. Attached a test for a real-world usecase of mine. Originally noted in https://bugs.python.org/issue32162? but on a new ticket as requested. Thanks :)