Re: [Qemu-devel] [PATCH v2 19/54] qapi: add #if/#endif helpers

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> Add helpers to generate #if/#endif and wrap visitor methods generating
> code. Used in the following patches.
>
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  scripts/qapi.py | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
>
> diff --git a/scripts/qapi.py b/scripts/qapi.py
> index 86845a28f9..52099332f1 100644
> --- a/scripts/qapi.py
> +++ b/scripts/qapi.py
> @@ -1892,6 +1892,57 @@ def guardend(name):
>                   name=guardname(name))
>  
>  
> +def gen_if(ifcond):
> +    if not ifcond:
> +        return ''
> +    if isinstance(ifcond, str):
> +        ifcond = [ifcond]
> +    # Not using mcgen() because we don't want indent or \n stipped

s/stipped/stripped/ I guess.

Which newline exactly don't you want to strip?

Here's what mcgen() currently does:

* Strip one leading newline, so that this works:

      mcgen('''
  line 1
  line 2
  ''')

* Interpolate keywords

* Indent by @indent_level spaces

* Strip @eatspace.

> +    ret = '\n'
> +    for ifc in ifcond:
> +        ret += '#if %s\n' % ifc
> +    ret += '\n'
> +    return ret
> +
> +
> +def gen_endif(ifcond):
> +    if not ifcond:
> +        return ''
> +    if isinstance(ifcond, str):
> +        ifcond = [ifcond]
> +    # Not using mcgen() because we don't want indent or \n stipped

Likewise.

> +    ret = '\n'
> +    for ifc in reversed(ifcond):
> +        ret += '#endif /* %s */\n' % ifc
> +    ret += '\n'
> +    return ret

I guess factoring out the common parts of gen_if() and gen_endif() would
make the code longer and more complex.

> +
> +
> +# Wrap a method to add #if / #endif to generated code, only if some
> +# code was generated.
> +# self must have 'if_members' listing the attributes to wrap.
> +# The last argument of the wrapped function must be the 'ifcond'.
> +def ifcond_decorator(func):
> +
> +    def func_wrapper(self, *args, **kwargs):
> +        ifcond = args[-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):]
> +                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 "too clever by half", but i'm reserving judgement
until after review of its use.