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

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> ----- Original Message -----
>> Hi
>> 
>> ----- Original Message -----
>> > Marc-André Lureau <address@hidden> writes:
>> > 
>> > > Wrap generated code with #if/#endif using the ifcond_decorator.
>> > >
>> > > Signed-off-by: Marc-André Lureau <address@hidden>
>> > > ---
>> > >  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.

This is just a quick experiment.  We certainly have to compare complete
solutions to decide whether the decorator is worthwhile.

> Oh and your version looks inferior, since it will generate empty #if/#endif 
> blocks. You seemed to be quite strict about having the generated output be 
> nicely formatted & human friendly, so I thought clearing those empty block 
> was a must for you.

Yes, it is a must for me.  Should be easy enough to fix: in
gen_ifcond(), replace "if ifcond" by "if ifcond and text is not blank".

>> >  
>> >  
>> >  (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):
>> > 
>>