Re: [Qemu-devel] [PATCH v6 04/15] qapi: leave the ifcond attribute undefined until check()

[Markus Armbruster <armbru@redhat.com>]

Marc-André Lureau <marcandre.lureau@redhat.com> writes:

> We commonly initialize attributes to None in .init(), then set their
> real value in .check().  Accessing the attribute before .check()
> yields None.  If we're lucky, the code that accesses the attribute
> prematurely chokes on None.
>
> It won't for .ifcond, because None is a legitimate value.
>
> Leave the ifcond attribute undefined until check().
>
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>

Note to self: consider squashing into previous patch.

> ---
>  scripts/qapi/common.py | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
> index 4f4014b387..46e33e23e4 100644
> --- a/scripts/qapi/common.py
> +++ b/scripts/qapi/common.py
> @@ -1021,13 +1021,19 @@ class QAPISchemaEntity(object):
>          # such place).
>          self.info = info
>          self.doc = doc
> -        self.ifcond = listify_cond(ifcond)
> +        self._ifcond = ifcond  # self.ifcond is set only after .check()
>  
>      def c_name(self):
>          return c_name(self.name)
>  
>      def check(self, schema):
> -        pass
> +        if isinstance(self._ifcond, QAPISchemaType):
> +            # inherit the condition from a type
> +            typ = self._ifcond
> +            typ.check(schema)
> +            self.ifcond = typ.ifcond
> +        else:
> +            self.ifcond = listify_cond(self._ifcond)
>  
>      def is_implicit(self):
>          return not self.info

One of the questions I had on v5 of this patch is still open.  I asked
whether we can restrict the inheritance feature to array elements.  You
pointed to implicit object types.  I asked for an example (because I
couldn't figure out what you meant).  Please reply in that thread.

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