Re: [PATCH] qapi: Fix code generation with Python 3.5

[John Snow <jsnow@redhat.com>]

On 1/17/20 2:07 AM, Markus Armbruster wrote:
> John Snow <jsnow@redhat.com> writes:
> 
>> On 1/16/20 3:25 PM, Markus Armbruster wrote:
>>> Recent commit 3e7fb5811b "qapi: Fix code generation for empty modules"
>>> modules" switched QAPISchema.visit() from
>>>
>>>     for entity in self._entity_list:
>>>
>>> effectively to
>>>
>>>     for mod in self._module_dict.values():
>>>         for entity in mod._entity_list:
>>>
>>> Visits in the same order as long as .values() is in insertion order.
>>> That's the case only for Python 3.6 and later.  Before, it's in some
>>> arbitrary order, which results in broken generated code.
>>>
>>> Fix by making self._module_dict an OrderedDict rather than a dict.
>>>
>>> Fixes: 3e7fb5811baab213dcc7149c3aa69442d683c26c
>>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>>> ---
>>>  scripts/qapi/schema.py | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
>>> index 0bfc5256fb..5100110fa2 100644
>>> --- a/scripts/qapi/schema.py
>>> +++ b/scripts/qapi/schema.py
>>> @@ -795,7 +795,7 @@ class QAPISchema(object):
>>>          self.docs = parser.docs
>>>          self._entity_list = []
>>>          self._entity_dict = {}
>>> -        self._module_dict = {}
>>> +        self._module_dict = OrderedDict()
>>>          self._schema_dir = os.path.dirname(fname)
>>>          self._make_module(None) # built-ins
>>>          self._make_module(fname)
>>>
>>
>> This problem has bitten me *many* times. I'm wondering if there's a
>> prescription that isn't just "Wait until we can stipulate 3.6+".
> 
> No clue.
> 
> 3.5 EOL is scheduled for 2020-09-13.
> https://devguide.python.org/#status-of-python-branches
> 
> We support 3.5 because we support Debian 9.
> 
> We'd normally drop support for Debian 9 two years after Debian 10,
> i.e. July 2021.  Assuming Debian supports it that far.  Whether they can
> truly support Python 3.5 after uptstream EOL seems doubtful.
> 

We should decide whether we consider Debian LTS to be adequately
supported, yes-or-no.

We should use a rule of "two years after successor, or End-of-Support,
whichever comes first."

For Debian, is end of support three years after it comes out, or is it
when the LTS is EOL?

In this specific case, do we trust that Debian 9 LTS will continue to
patch Python3.5 all the way up until July 2021?

--js