[v2,10/19] qapi-visit: Factor out gen_visit_members_call()

Upcoming patches will be adding several contexts where we want
to handle the visit of an implicit type (an anonymous base type,
or an anonymous branch of a flat union) by directly inlining
the visit of each member of the implicit type. The work is made
easier by factoring out a new helper, gen_visit_members_call(),
so that the caller doesn't need to care whether the type it is
visiting is implicit or normal.

For now, the only implicit type we encounter are the branches
of a simple union; the initial implementation of the helper
method is hard-coded to that usage, but it gets us one step
closer to completely dropping the hack of simple_union_type().

Generated output is unchanged.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v2: retitle, rebase to s/fields/members/ changes
---
 scripts/qapi-visit.py | 42 ++++++++++++++++++++++++------------------
 1 file changed, 24 insertions(+), 18 deletions(-)

Eric Blake <eblake@redhat.com> writes:

> Upcoming patches will be adding several contexts where we want
> to handle the visit of an implicit type (an anonymous base type,
> or an anonymous branch of a flat union) by directly inlining
> the visit of each member of the implicit type. The work is made
> easier by factoring out a new helper, gen_visit_members_call(),
> so that the caller doesn't need to care whether the type it is
> visiting is implicit or normal.
>
> For now, the only implicit type we encounter are the branches
> of a simple union; the initial implementation of the helper
> method is hard-coded to that usage, but it gets us one step
> closer to completely dropping the hack of simple_union_type().
>
> Generated output is unchanged.
>
> Signed-off-by: Eric Blake <eblake@redhat.com>
>
> ---
> v2: retitle, rebase to s/fields/members/ changes
> ---
>  scripts/qapi-visit.py | 42 ++++++++++++++++++++++++------------------
>  1 file changed, 24 insertions(+), 18 deletions(-)
>
> diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
> index a712e9a..dbae00c 100644
> --- a/scripts/qapi-visit.py
> +++ b/scripts/qapi-visit.py
> @@ -34,6 +34,25 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp);
>                   c_name=c_name(name))
>
>
> +def gen_visit_members_call(typ, c_name):

The actual arguments of c_name are C expressions, not names.

> +    ret = ''
> +    assert isinstance(typ, QAPISchemaObjectType)
> +    if typ.is_implicit():
> +        # TODO ugly special case for simple union
> +        assert len(typ.members) == 1
> +        assert not typ.variants

This is an inlined and simplified version of simple_union_type().
Violation of DRY, acceptable if temporary, but could use a comment.

> +        ret += mcgen('''
> +    visit_type_%(c_type)s(v, "data", %(c_name)s, &err);
> +''',
> +                     c_type=typ.members[0].type.c_name(), c_name=c_name)
> +    else:
> +        ret += mcgen('''
> +    visit_type_%(c_type)s_members(v, %(c_name)s, &err);
> +''',
> +                     c_type=typ.c_name(), c_name=c_name)
> +    return ret
> +
> +
>  def gen_visit_object_members(name, base, members, variants):
>      ret = mcgen('''
>
> @@ -45,10 +64,7 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
>                  c_name=c_name(name))
>
>      if base:
> -        ret += mcgen('''
> -    visit_type_%(c_type)s_members(v, (%(c_type)s *)obj, &err);
> -''',
> -                     c_type=base.c_name())
> +        ret += gen_visit_members_call(base, '(%s *)obj' % base.c_name())
>          ret += gen_err_check()
>
>      ret += gen_visit_members(members, prefix='obj->')
> @@ -60,26 +76,16 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
>                       c_name=c_name(variants.tag_member.name))
>
>          for var in variants.variants:
> -            # TODO ugly special case for simple union
> -            simple_union_type = var.simple_union_type()
>              ret += mcgen('''
>      case %(case)s:
>  ''',
>                           case=c_enum_const(variants.tag_member.type.name,
>                                             var.name,
>                                             variants.tag_member.type.prefix))
> -            if simple_union_type:
> -                ret += mcgen('''
> -        visit_type_%(c_type)s(v, "data", &obj->u.%(c_name)s, &err);
> -''',
> -                             c_type=simple_union_type.c_name(),
> -                             c_name=c_name(var.name))
> -            else:
> -                ret += mcgen('''
> -        visit_type_%(c_type)s_members(v, &obj->u.%(c_name)s, &err);
> -''',
> -                             c_type=var.type.c_name(),
> -                             c_name=c_name(var.name))
> +            push_indent()
> +            ret += gen_visit_members_call(var.type,
> +                                          '&obj->u.' + c_name(var.name))
> +            pop_indent()
>              ret += mcgen('''
>          break;
>  ''')

Not an improvement on its own.  Need to review more patches before I can
more.