Re: [Qemu-devel] [PATCH v3 09/50] qapi: add #if/#endif helpers

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> Add helpers to wrap generated code with #if/#endif lines.
>
> Add a function decorator that will be used to wrap visitor methods.
> The decorator will check if code was generated before adding #if/#endif
> lines. Used in the following patches.
>
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  scripts/qapi.py | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
>
> diff --git a/scripts/qapi.py b/scripts/qapi.py
> index 2a8e60e975..94b735d8d6 100644
> --- a/scripts/qapi.py
> +++ b/scripts/qapi.py
> @@ -1897,6 +1897,61 @@ def guardend(name):
>                   name=guardname(name))
>  
>  
> +def gen_if(ifcond):
> +    if not ifcond:
> +        return ''
> +    if isinstance(ifcond, str):
> +        ifcond = [ifcond]

Perhaps we should take this normalization step in the QAPISchema
constructors.

> +    ret = ''
> +    for ifc in ifcond:
> +        ret += mcgen('''
> +#if %(cond)s
> +''', cond=ifc)
> +    return ret
> +
> +
> +def gen_endif(ifcond):
> +    if not ifcond:
> +        return ''
> +    if isinstance(ifcond, str):
> +        ifcond = [ifcond]
> +    ret = ''
> +    for ifc in reversed(ifcond):
> +        ret += mcgen('''
> +#endif /* %(cond)s */
> +''', cond=ifc)
> +    return ret
> +
> +
> +# Wrap a method to add #if / #endif to generated code, only if some
> +# code was generated. The method must have an 'ifcond' argument.
> +# self must have 'if_members' listing the attributes to wrap.
> +def ifcond_decorator(func):
> +
> +    def func_wrapper(self, *args, **kwargs):
> +        import inspect

Is hiding imports in function a good idea?

> +        idx = inspect.getargspec(func).args.index('ifcond')
> +        ifcond = args[idx - 1]
> +        save = {}
> +        for mem in self.if_members:
> +            save[mem] = getattr(self, mem)
> +        func(self, *args, **kwargs)
> +        for mem, val in save.items():
> +            newval = getattr(self, mem)
> +            if newval != val:
> +                assert newval.startswith(val)
> +                newval = newval[len(val):]
> +                if newval[0] == '\n':
> +                    val += '\n'
> +                    newval = newval[1:]
> +                val += gen_if(ifcond)
> +                val += newval
> +                val += gen_endif(ifcond)
> +            setattr(self, mem, val)
> +
> +    return func_wrapper
> +
> +
>  def gen_enum_lookup(name, values, prefix=None):
>      ret = mcgen('''

My gut feeling is still "too clever by half", but i'm reserving
judgement until after review of its use, and exploration of
alternatives.