Paolo Bonzini <[email protected]> writes: > From: Marc-André Lureau <[email protected]> > > Generate Rust #[cfg(...)] guards from QAPI 'if' conditions.
Please mention that this isn't used, yet. I commonly write something like "The next commit will put it to use." > Signed-off-by: Marc-André Lureau <[email protected]> > Link: > https://lore.kernel.org/r/[email protected] > Signed-off-by: Paolo Bonzini <[email protected]> > --- > scripts/qapi/common.py | 16 ++++++++++++++++ > scripts/qapi/schema.py | 4 ++++ > 2 files changed, 20 insertions(+) > > diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py > index d7c8aa3365c..f16b9568bb9 100644 > --- a/scripts/qapi/common.py > +++ b/scripts/qapi/common.py > @@ -199,6 +199,22 @@ def guardend(name: str) -> str: > name=c_fname(name).upper()) > > > +def rsgen_ifcond(ifcond: Optional[Union[str, Dict[str, Any]]]) -> str: This is the Rust-generating cousin of cgen_ifcond(). The argument is None or a tree. The tree's leaves are str, and its inner nodes look like {'all': [sub-tree, ...]} {'any': [sub-tree, ...]} {'not': sub-tree} mypy doesn't do recursive types, so we approximate the tree as Union[str, Dict[str, Any]]. > + > + def cfg(ifcond: Union[str, Dict[str, Any]]) -> str: The argument's type is wrong. It should be Union[str, List[Dict[str, Any]], Dict[str, Any]] We'll see below why mypy doesn't complain, and where the List[...] comes from. The name @ifcond is misleading. This isn't an if condition, it's the union of if condition and list of if conditions. I needed John Snow's help to figure this out. Thanks, John! Case 1: the code for str, i.e. a tree leaf: > + if isinstance(ifcond, str): > + return ifcond Case 2: the code for List[Dict[str, Any]]: > + if isinstance(ifcond, list): > + return ', '.join([cfg(c) for c in ifcond]) Case 3: the code for Dict[str, Any]: gen_ifcond() below has assert isinstance(ifcond, dict) and len(ifcond) == 1 right here to make this crystal clear. > + oper, operands = next(iter(ifcond.items())) Recall @ifcond is either {'all': [sub-tree, ...]} {'any': [sub-tree, ...]} {'not': sub-tree} The next(...) wizardry returns the first element of the @ifcond dictionary. Actually *the* element, since @ifcond has just one. Thus: @oper is 'all', 'any', or 'not' @operands is a sub-tree when @oper is 'not', else a [sub-tree, ...], i.e. Dict[str, Any] or List[Dict[str, Any]] > + operands = cfg(operands) We pass @operands to cfg(). That's where the List[...] comes from. > + return f'{oper}({operands})' > + > + if not ifcond: > + return '' > + return '#[cfg(%s)]' % cfg(ifcond) So, cfg(ifcond) returns the argument to interpolate into '#[cfg(%s)]'. When @ifcond is str, it's @ifcond itself. This is case 1. When @ifcond is {'not': COND}, it's 'not(CC)', where CC is cfg(COND). This is case 3 and case 2 with a non-list argument. When @ifcond is {'all': [COND, ...]}, it's 'all(CC, ...)', where the CC are cfg(COND). This is case 3 and case 2 with a list argument. Likewise for {'any': [COND, ...]}. Okay apart from the incorrect type hint and the misleading name. Less clever code would've saved me quite some review time. But why doesn't mypy scream? Consider again oper, operands = next(iter(ifcond.items())) @ifcond's static type is Dict[str, Any]. Therefore @oper's static type is str, and @operands is Any. Any suppresses type checking! The call cfg(operands) is therefore *not* checked, and we get away with passing a list to cfg() even though its type hint doesn't allow it. > + > + > def gen_ifcond(ifcond: Optional[Union[str, Dict[str, Any]]], > cond_fmt: str, not_fmt: str, > all_operator: str, any_operator: str) -> str: > diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py > index 8d88b40de2e..848a7401251 100644 > --- a/scripts/qapi/schema.py > +++ b/scripts/qapi/schema.py > @@ -37,6 +37,7 @@ > docgen_ifcond, > gen_endif, > gen_if, > + rsgen_ifcond, > ) > from .error import QAPIError, QAPISemError, QAPISourceError > from .expr import check_exprs > @@ -63,6 +64,9 @@ def gen_endif(self) -> str: > def docgen(self) -> str: > return docgen_ifcond(self.ifcond) > > + def rsgen(self) -> str: > + return rsgen_ifcond(self.ifcond) > + > def is_present(self) -> bool: > return bool(self.ifcond)
