qapi: Permit omitting all flat union branches

Absent flat union branches default to the empty struct (since commit
800877bb16 "qapi: allow empty branches in flat unions").  But an
attempt to omit all of them is rejected with "Union 'FOO' has no
branches".  Harmless oddity, but it's easy to avoid, so do that.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190913201349.24332-11-armbru@redhat.com>
[Commit message typo fixed]
This commit is contained in:
Markus Armbruster 2019-09-13 22:13:43 +02:00
parent f03255362a
commit 0ced9531f1
8 changed files with 27 additions and 14 deletions

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@ -436,8 +436,7 @@ Union types are used to let the user choose between several different
variants for an object. There are two flavors: simple (no
discriminator or base), and flat (both discriminator and base). A union
type is defined using a data dictionary as explained in the following
paragraphs. The data dictionary for either type of union must not
be empty.
paragraphs. Unions must have at least one branch.
A simple union type defines a mapping from automatic discriminator
values to data types like in this example:

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@ -852,7 +852,7 @@ def check_union(expr, info):
# With no discriminator it is a simple union.
if discriminator is None:
enum_define = None
enum_values = members.keys()
allow_metas = ['built-in', 'union', 'alternate', 'struct', 'enum']
if base is not None:
raise QAPISemError(info, "Simple union '%s' must not have a base" %
@ -885,16 +885,17 @@ def check_union(expr, info):
'must not be conditional' %
(base, discriminator, name))
enum_define = enum_types.get(discriminator_value['type'])
allow_metas = ['struct']
# Do not allow string discriminator
if not enum_define:
raise QAPISemError(info,
"Discriminator '%s' must be of enumeration "
"type" % discriminator)
enum_values = enum_get_names(enum_define)
allow_metas = ['struct']
if (len(enum_values) == 0):
raise QAPISemError(info, "Union '%s' has no branches" % name)
# Check every branch; don't allow an empty union
if len(members) == 0:
raise QAPISemError(info, "Union '%s' cannot have empty 'data'" % name)
for (key, value) in members.items():
check_name(info, "Member of union '%s'" % name, key)
@ -907,8 +908,8 @@ def check_union(expr, info):
# If the discriminator names an enum type, then all members
# of 'data' must also be members of the enum type.
if enum_define:
if key not in enum_get_names(enum_define):
if discriminator is not None:
if key not in enum_values:
raise QAPISemError(info,
"Discriminator value '%s' is not found in "
"enum '%s'"
@ -1578,7 +1579,6 @@ class QAPISchemaObjectTypeVariants(object):
assert bool(tag_member) != bool(tag_name)
assert (isinstance(tag_name, str) or
isinstance(tag_member, QAPISchemaObjectTypeMember))
assert len(variants) > 0
for v in variants:
assert isinstance(v, QAPISchemaObjectTypeVariant)
self._tag_name = tag_name

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@ -1 +1 @@
tests/qapi-schema/flat-union-empty.json:4: Union 'Union' cannot have empty 'data'
tests/qapi-schema/flat-union-empty.json:4: Union 'Union' has no branches

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@ -1,4 +1,4 @@
# flat unions cannot be empty
# flat union discriminator cannot be empty
{ 'enum': 'Empty', 'data': [ ] }
{ 'struct': 'Base', 'data': { 'type': 'Empty' } }
{ 'union': 'Union', 'base': 'Base', 'discriminator': 'type', 'data': { } }

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@ -25,6 +25,11 @@
{ 'struct': 'Empty1', 'data': { } }
{ 'struct': 'Empty2', 'base': 'Empty1', 'data': { } }
# Likewise for an empty flat union
{ 'union': 'Union',
'base': { 'type': 'EnumOne' }, 'discriminator': 'type',
'data': { } }
{ 'command': 'user_def_cmd0', 'data': 'Empty2', 'returns': 'Empty2' }
# for testing override of default naming heuristic

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@ -23,6 +23,15 @@ enum MyEnum
object Empty1
object Empty2
base Empty1
object q_obj_Union-base
member type: EnumOne optional=False
object Union
base q_obj_Union-base
tag type
case value1: q_empty
case value2: q_empty
case value3: q_empty
case value4: q_empty
command user_def_cmd0 Empty2 -> Empty2
gen=True success_response=True boxed=False oob=False preconfig=False
enum QEnumTwo

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@ -1 +1 @@
tests/qapi-schema/union-empty.json:2: Union 'Union' cannot have empty 'data'
tests/qapi-schema/union-empty.json:2: Union 'Union' has no branches

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@ -1,2 +1,2 @@
# unions cannot be empty
# simple unions cannot be empty
{ 'union': 'Union', 'data': { } }