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

[John Snow <jsnow@redhat.com>]

On 4/27/21 2:13 AM, Markus Armbruster wrote:
> 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?
> 

Oh, yes.