Re: [PATCH 07/22] qapi/parser: assert object keys are strings

[Markus Armbruster <armbru@redhat.com>]

John Snow <jsnow@redhat.com> writes:

> On 4/25/21 3:27 AM, Markus Armbruster wrote:
>> John Snow <jsnow@redhat.com> writes:
>> 
>>> The single quote token implies the value is a string. Assert this to be
>>> the case.
>>>
>>> Signed-off-by: John Snow <jsnow@redhat.com>
>>> ---
>>>   scripts/qapi/parser.py | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>
>>> diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
>>> index 6b443b1247e..8d1fe0ddda5 100644
>>> --- a/scripts/qapi/parser.py
>>> +++ b/scripts/qapi/parser.py
>>> @@ -246,6 +246,8 @@ def get_members(self):
>>>               raise QAPIParseError(self, "expected string or '}'")
>>>           while True:
>>>               key = self.val
>>> +            assert isinstance(key, str)  # Guaranteed by tok == "'"
>>> +
>>>               self.accept()
>>>               if self.tok != ':':
>>>                   raise QAPIParseError(self, "expected ':'")
>> 
>> The assertion is correct, but I wonder why mypy needs it.  Can you help?
>> 
>
> The lexer value can also be True/False (Maybe None? I forget) based on 

Yes, None for tokens like '{'.

> the Token returned. Here, since the token was the single quote, we know 
> that value must be a string.
>
> Mypy has no insight into the correlation between the Token itself and 
> the token value, because that relationship is not expressed via the type 
> system.

I understand that mypy can't prove implications like if self.tok == "'",
then self.val is a str.

What I'm curious about is why key needs to be known to be str here.
Hmm, is it so return expr type-checks once you add -> OrderedDict[str,
object] to the function?