Re: [PATCH v2 05/21] qapi/parser: Assert lexer value is a string

[John Snow]

On 5/18/21 6:02 AM, Markus Armbruster wrote:
> John Snow <jsnow@redhat.com> writes:
>
> > The type checker can't narrow the type of the token value to string,
> > because it's only loosely correlated with the return token.
> >
> > We know that a token of '#' should always have a "str" value.
> > Add an assertion.
> >
> > Signed-off-by: John Snow <jsnow@redhat.com>
> > ---
> >   scripts/qapi/parser.py | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
> > index d620706fffb..ba17f1357ad 100644
> > --- a/scripts/qapi/parser.py
> > +++ b/scripts/qapi/parser.py
> > @@ -304,6 +304,7 @@ def get_doc(self, info):
> >           cur_doc = QAPIDoc(self, info)
> >           self.accept(False)
> >           while self.tok == '#':
> > +            assert isinstance(self.val, str)  # comment token MUST have str val
>
> What does the comment add to the assertion?  Isn't it all obvious?  Just
> wondering; if you genuinely think it isn't, I'm not going to argue.
> Except about the long line, which you could easily avoid:

Yeah, I just suppose it's an artifact from when I was first reading this 
code. It wasn't necessarily obvious to me that comment tokens -- which 
are sometimes squelched -- must always have a str val that is non-None.

I felt like adding an assertion here required SOME kind of justification 
for WHY it was true. Since the val can be None *and* the lexer can omit 
comments, it seemed not expressly self-evident at the time.

Less obvious than, say, why 'tf' values will definitely be True/False. 
Maybe just my own brain bug.

I'm not as attached to it as other things at this point anymore, having 
spent more time in this file since I first wrote it.

Remove if you'd like. The commit message can perform the duty of 
explaining more deeply if people need.

>                 assert isinstance(self.val, str)  # comment value MUST be str
>
> >               if self.val.startswith('##'):
> >                   # End of doc comment
> >                   if self.val != '##':