Re: [PATCH 12/22] qapi/parser: add type hint annotations

[John Snow <jsnow@redhat.com>]

On 4/25/21 8:34 AM, Markus Armbruster wrote:
> John Snow <jsnow@redhat.com> writes:
> 
>> Annotations do not change runtime behavior.
>> This commit *only* adds annotations.
>>
>> (Annotations for QAPIDoc are in a later commit.)
>>
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> ---
>>   scripts/qapi/parser.py | 61 ++++++++++++++++++++++++++++--------------
>>   1 file changed, 41 insertions(+), 20 deletions(-)
>>
>> diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
>> index d02a134aae9..f2b57d5642a 100644
>> --- a/scripts/qapi/parser.py
>> +++ b/scripts/qapi/parser.py
>> @@ -17,16 +17,29 @@
>>   from collections import OrderedDict
>>   import os
>>   import re
>> -from typing import List
>> +from typing import (
>> +    Dict,
>> +    List,
>> +    Optional,
>> +    Set,
>> +    Union,
>> +)
>>   
>>   from .common import match_nofail
>>   from .error import QAPISemError, QAPISourceError
>>   from .source import QAPISourceInfo
>>   
>>   
>> +#: Represents a parsed JSON object; semantically: one QAPI schema expression.
>> +Expression = Dict[str, object]
> 
> I believe you use this for what qapi-code-gen.txt calls a top-level
> expression.  TopLevelExpression is rather long, but it's used just once,
> and once more in RFC PATCH 13.  What do you think?
> 

Yeah, I left a comment on gitlab about this -- Sorry for splitting the 
stream, I didn't expect you to reply on-list without at least clicking 
the link ;)

You're right, this is TOP LEVEL EXPR. I actually do mean to start using 
it in expr.py as well too, in what will become (I think) pt5c: 
non-immediately-necessary parser cleanups.

I can use TopLevelExpression as the type name if you'd like, but if you 
have a suggestion for something shorter I am open to suggestions if 
"Expression" is way too overloaded/confusing.

>> +
>> +# Return value alias for get_expr().
>> +_ExprValue = Union[List[object], Dict[str, object], str, bool]
> 
> This is essentially a node in our pidgin-JSON parser's abstract syntax
> tree.  Tree roots use the Dict branch of this Union.
> 
> See also my review of PATCH 06.
> 

OK, I skimmed that one for now but I'll get back to it.

>> +
>> +
>>   class QAPIParseError(QAPISourceError):
>>       """Error class for all QAPI schema parsing errors."""
>> -    def __init__(self, parser, msg):
>> +    def __init__(self, parser: 'QAPISchemaParser', msg: str):
> 
> Forward reference needs quotes.  Can't be helped.
> 
>>           col = 1
>>           for ch in parser.src[parser.line_pos:parser.pos]:
>>               if ch == '\t':
>> @@ -38,7 +51,10 @@ def __init__(self, parser, msg):
>>   
>>   class QAPISchemaParser:
>>   
>> -    def __init__(self, fname, previously_included=None, incl_info=None):
>> +    def __init__(self,
>> +                 fname: str,
>> +                 previously_included: Optional[Set[str]] = None,
> 
> This needs to be Optional[] because using the empty set as default
> parameter value would be a dangerous trap.  Python's choice to evaluate
> the default parameter value just once has always been iffy.  Stirring
> static typing into the language makes it iffier.  Can't be helped.
> 

We could force it to accept a tuple and convert it into a set 
internally. It's just that we seem to use it for sets now.

Or ... in pt5c I float the idea of just passing the parent parser in, 
and I reach up and grab the previously-included stuff directly.

>> +                 incl_info: Optional[QAPISourceInfo] = None):
>>           self._fname = fname
>>           self._included = previously_included or set()
>>           self._included.add(os.path.abspath(self._fname))
>> @@ -46,20 +62,20 @@ def __init__(self, fname, previously_included=None, incl_info=None):
>>   
>>           # Lexer state (see `accept` for details):
>>           self.info = QAPISourceInfo(self._fname, incl_info)
>> -        self.tok = None
>> +        self.tok: Optional[str] = None
> 
> Would
> 
>             self.tok: str
> 
> work?
> 

Not without modifications, because the Token being None is used to 
represent EOF.

>>           self.pos = 0
>>           self.cursor = 0
>> -        self.val = None
>> +        self.val: Optional[Union[bool, str]] = None
>>           self.line_pos = 0
>>   
>>           # Parser output:
>> -        self.exprs = []
>> -        self.docs = []
>> +        self.exprs: List[Expression] = []
>> +        self.docs: List[QAPIDoc] = []
>>   
>>           # Showtime!
>>           self._parse()
>>   
>> -    def _parse(self):
>> +    def _parse(self) -> None:
>>           cur_doc = None
>>   
>>           with open(self._fname, 'r', encoding='utf-8') as fp:
>> @@ -122,7 +138,7 @@ def _parse(self):
>>           self.reject_expr_doc(cur_doc)
>>   
>>       @staticmethod
>> -    def reject_expr_doc(doc):
>> +    def reject_expr_doc(doc: Optional['QAPIDoc']) -> None:
>>           if doc and doc.symbol:
>>               raise QAPISemError(
>>                   doc.info,
>> @@ -130,10 +146,14 @@ def reject_expr_doc(doc):
>>                   % doc.symbol)
>>   
>>       @staticmethod
>> -    def _include(include, info, incl_fname, previously_included):
>> +    def _include(include: str,
>> +                 info: QAPISourceInfo,
>> +                 incl_fname: str,
>> +                 previously_included: Set[str]
>> +                 ) -> Optional['QAPISchemaParser']:
>>           incl_abs_fname = os.path.abspath(incl_fname)
>>           # catch inclusion cycle
>> -        inf = info
>> +        inf: Optional[QAPISourceInfo] = info
>>           while inf:
>>               if incl_abs_fname == os.path.abspath(inf.fname):
>>                   raise QAPISemError(info, "inclusion loop for %s" % include)
>> @@ -152,9 +172,9 @@ def _include(include, info, incl_fname, previously_included):
>>               ) from err
>>   
>>       @staticmethod
>> -    def _pragma(name, value, info):
>> +    def _pragma(name: str, value: object, info: QAPISourceInfo) -> None:
> 
> value: object isn't wrong, but why not _ExprValue?
> 

I forget; admit this one slipped through from an earlier revision.

Right now: because _ExprValue is too broad. It really wants Dict[str, 
object] but the typing on get_expr() is challenging.

I'll revisit this with better excuses after I digest your patch 6 review.

>>   
>> -        def _check(name, value) -> List[str]:
>> +        def _check(name: str, value: object) -> List[str]:
>>               if (not isinstance(value, list) or
>>                       any([not isinstance(elt, str) for elt in value])):
>>                   raise QAPISemError(
>> @@ -176,7 +196,7 @@ def _check(name, value) -> List[str]:
>>           else:
>>               raise QAPISemError(info, "unknown pragma '%s'" % name)
>>   
>> -    def accept(self, skip_comment=True):
>> +    def accept(self, skip_comment: bool = True) -> None:
>>           while True:
>>               self.tok = self.src[self.cursor]
>>               self.pos = self.cursor
>> @@ -240,8 +260,8 @@ def accept(self, skip_comment=True):
>>                                        self.src[self.cursor-1:])
>>                   raise QAPIParseError(self, "stray '%s'" % match.group(0))
>>   
>> -    def get_members(self):
>> -        expr = OrderedDict()
>> +    def get_members(self) -> 'OrderedDict[str, object]':
>> +        expr: 'OrderedDict[str, object]' = OrderedDict()
>>           if self.tok == '}':
>>               self.accept()
>>               return expr
>> @@ -267,8 +287,8 @@ def get_members(self):
>>               if self.tok != "'":
>>                   raise QAPIParseError(self, "expected string")
>>   
>> -    def get_values(self):
>> -        expr = []
>> +    def get_values(self) -> List[object]:
>> +        expr: List[object] = []
>>           if self.tok == ']':
>>               self.accept()
>>               return expr
>> @@ -284,8 +304,9 @@ def get_values(self):
>>                   raise QAPIParseError(self, "expected ',' or ']'")
>>               self.accept()
>>   
>> -    def get_expr(self, nested):
>> +    def get_expr(self, nested: bool = False) -> _ExprValue:
>>           # TODO: Teach mypy that nested=False means the retval is a Dict.
>> +        expr: _ExprValue
>>           if self.tok != '{' and not nested:
>>               raise QAPIParseError(self, "expected '{'")
>>           if self.tok == '{':
>> @@ -303,7 +324,7 @@ def get_expr(self, nested):
>>                   self, "expected '{', '[', string, or boolean")
>>           return expr
>>   
>> -    def get_doc(self, info):
>> +    def get_doc(self, info: QAPISourceInfo) -> List['QAPIDoc']:
>>           if self.val != '##':
>>               raise QAPIParseError(
>>                   self, "junk after '##' at start of documentation comment")

Thanks!

--js