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qapi: Generate a nicer struct for flat unions

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The struct generated for a flat union is weird: the members of its
base are at the end, except for the union tag, which is at the
beginning.

Example: qapi-schema-test.json has

    { 'struct': 'UserDefUnionBase',
      'data': { 'string': 'str', 'enum1': 'EnumOne' } }

    { 'union': 'UserDefFlatUnion',
      'base': 'UserDefUnionBase',
      'discriminator': 'enum1',
      'data': { 'value1' : 'UserDefA',
                'value2' : 'UserDefB',
                'value3' : 'UserDefB' } }

We generate:

    struct UserDefFlatUnion
    {
        EnumOne enum1;
        union {
            void *data;
            UserDefA *value1;
            UserDefB *value2;
            UserDefB *value3;
        };
        char *string;
    };

Change to put all base members at the beginning, unadulterated.  Not
only is this easier to understand, it also permits casting the flat
union to its base, if that should become useful.

We now generate:

    struct UserDefFlatUnion
    {
        /* Members inherited from UserDefUnionBase: */
        char *string;
        EnumOne enum1;
        /* Own members: */
        union { /* union tag is @enum1 */
            void *data;
            UserDefA *value1;
            UserDefB *value2;
            UserDefB *value3;
        };
    };

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Markus Armbruster 2015-06-28 20:05:53 +02:00
parent 0f61af3eb3
commit 1e6c1616a9
1 changed files with 22 additions and 16 deletions
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38
scripts/qapi-types.py
View file

@ -200,13 +200,30 @@ def generate_union(expr, meta):
ret = mcgen('''
struct %(name)s
{
%(discriminator_type_name)s %(discriminator)s;
union {
''',
name=name)
if base:
ret += mcgen('''
/* Members inherited from %(c_name)s: */
''',
c_name=c_name(base))
base_fields = find_struct(base)['data']
ret += generate_struct_fields(base_fields)
ret += mcgen('''
/* Own members: */
''')
else:
assert not discriminator
ret += mcgen('''
%(discriminator_type_name)s kind;
''',
discriminator_type_name=c_name(discriminator_type_name))
ret += mcgen('''
union { /* union tag is @%(c_name)s */
void *data;
''',
name=name,
discriminator=c_name(discriminator or 'kind'),
discriminator_type_name=c_name(discriminator_type_name))
c_name=c_name(discriminator or 'kind'))
for key in typeinfo:
ret += mcgen('''
@ -217,17 +234,6 @@ struct %(name)s
ret += mcgen('''
};
''')
if base:
assert discriminator
base_fields = find_struct(base)['data'].copy()
del base_fields[discriminator]
ret += generate_struct_fields(base_fields)
else:
assert not discriminator
ret += mcgen('''
};
''')
if meta == 'alternate':