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

[Markus Armbruster <armbru@redhat.com>]

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?

> +
> +# 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.

> +
> +
>  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.

> +                 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?

>          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?

>  
> -        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")