Re: [Qemu-devel] [PATCH v2 23/54] qapi-commands: add #if conditions to commands

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

Hi

----- Original Message -----
> Marc-André Lureau <marcandre.lureau@redhat.com> writes:
> 
> > Wrap generated code with #if/#endif using the ifcond_decorator.
> >
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> >  scripts/qapi-commands.py  | 2 ++
> >  tests/test-qmp-commands.c | 4 ++--
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
> > index 5eb96b2d95..db45415c41 100644
> > --- a/scripts/qapi-commands.py
> > +++ b/scripts/qapi-commands.py
> > @@ -228,6 +228,7 @@ class QAPISchemaGenCommandVisitor(QAPISchemaVisitor):
> >          self.defn = None
> >          self._regy = None
> >          self._visited_ret_types = None
> > +        self.if_members = ['decl', 'defn', '_regy']
> >  
> >      def visit_begin(self, schema):
> >          self.decl = ''
> > @@ -240,6 +241,7 @@ class QAPISchemaGenCommandVisitor(QAPISchemaVisitor):
> >          self._regy = None
> >          self._visited_ret_types = None
> >  
> > +    @ifcond_decorator
> >      def visit_command(self, name, info, arg_type, ret_type,
> >                        gen, success_response, boxed, ifcond):
> >          if not gen:
> > diff --git a/tests/test-qmp-commands.c b/tests/test-qmp-commands.c
> > index 9b9a7ffee7..ad7b6e4e1d 100644
> > --- a/tests/test-qmp-commands.c
> > +++ b/tests/test-qmp-commands.c
> > @@ -10,11 +10,11 @@
> >  
> >  static QmpCommandList qmp_commands;
> >  
> > -/* #if defined(TEST_IF_CMD) */
> > +#if defined(TEST_IF_CMD)
> >  void qmp_TestIfCmd(TestIfStruct *foo, Error **errp)
> >  {
> >  }
> > -/* #endif */
> > +#endif
> >  
> >  void qmp_user_def_cmd(Error **errp)
> >  {
> 
> To find out whether the clever decorator is worth its keep, I replaced
> it with the dumbest, most obvious code I could think of (appended).
> Does this make visit_command() easier or harder to understand?
> 
> 
> 
> diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
> index db45415c41..13d37d2ac2 100644
> --- a/scripts/qapi-commands.py
> +++ b/scripts/qapi-commands.py
> @@ -228,7 +228,6 @@ class QAPISchemaGenCommandVisitor(QAPISchemaVisitor):
>          self.defn = None
>          self._regy = None
>          self._visited_ret_types = None
> -        self.if_members = ['decl', 'defn', '_regy']
>  
>      def visit_begin(self, schema):
>          self.decl = ''
> @@ -241,18 +240,21 @@ class QAPISchemaGenCommandVisitor(QAPISchemaVisitor):
>          self._regy = None
>          self._visited_ret_types = None
>  
> -    @ifcond_decorator
>      def visit_command(self, name, info, arg_type, ret_type,
>                        gen, success_response, boxed, ifcond):
>          if not gen:
>              return
> -        self.decl += gen_command_decl(name, arg_type, boxed, ret_type)
> +        decl = gen_command_decl(name, arg_type, boxed, ret_type)
> +        defn = ''
>          if ret_type and ret_type not in self._visited_ret_types:
>              self._visited_ret_types.add(ret_type)
> -            self.defn += gen_marshal_output(ret_type)
> -        self.decl += gen_marshal_decl(name)
> -        self.defn += gen_marshal(name, arg_type, boxed, ret_type)
> -        self._regy += gen_register_command(name, success_response)
> +            defn += gen_marshal_output(ret_type)
> +        decl += gen_marshal_decl(name)
> +        defn += gen_marshal(name, arg_type, boxed, ret_type)
> +        self.decl += gen_ifcond(ifcond, decl)
> +        self.defn += gen_ifcond(ifcond, defn)
> +        self._regy += gen_ifcond(ifcond,
> +                                 gen_register_command(name,
> success_response))

This is one of the most simple case, and it is already very intrusive. If you have more branches / early return it becomes awful.

Do it for all the places where we have @ifcond_decorator and you will probably prefer the concise decorated version. For me this case is one of the reason why decorators exist: to wrap enter/exit of a function.

>  
>  
>  (input_file, output_dir, do_c, do_h, prefix, opts) = parse_command_line()
> diff --git a/scripts/qapi.py b/scripts/qapi.py
> index 52099332f1..3de5b8b8f0 100644
> --- a/scripts/qapi.py
> +++ b/scripts/qapi.py
> @@ -1918,29 +1918,10 @@ def gen_endif(ifcond):
>      return ret
>  
>  
> -# 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_ifcond(ifcond, ctext):
> +    if ifcond:
> +        return gen_if(ifcond) + ctext + gen_endif(ifcond)
> +    return ctext
>  
>  
>  def gen_enum_lookup(name, values, prefix=None):
>