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qapi: Permit alternates with just one branch

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A union or alternate without branches makes no sense and doesn't work:
it can't be instantiated.  A union or alternate with just one branch
works, but is degenerate.  We accept the former, but reject the
latter.  Weird.  docs/devel/qapi-code-gen.txt doesn't mention the
difference.  It claims an alternate definition is "is similar to a
simple union type".

Permit degenerate alternates to make them consistent with unions.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190913201349.24332-10-armbru@redhat.com>
This commit is contained in:
Markus Armbruster 2019-09-13 22:13:42 +02:00
parent 675b214bc6
commit f03255362a
5 changed files with 12 additions and 10 deletions
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6
scripts/qapi/common.py
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@ -920,11 +920,9 @@ def check_alternate(expr, info):
members = expr['data']
types_seen = {}
# Check every branch; require at least two branches
if len(members) < 2:
if len(members) == 0:
raise QAPISemError(info,
"Alternate '%s' should have at least two branches "
"in 'data'" % name)
"Alternate '%s' cannot have empty 'data'" % name)
for (key, value) in members.items():
check_name(info, "Member of alternate '%s'" % name, key)
check_known_keys(info,

2
tests/qapi-schema/alternate-empty.err
View File

@ -1 +1 @@
tests/qapi-schema/alternate-empty.json:2: Alternate 'Alt' should have at least two branches in 'data'
tests/qapi-schema/alternate-empty.json:2: Alternate 'Alt' cannot have empty 'data'

4
tests/qapi-schema/alternate-empty.json
View File

@ -1,2 +1,2 @@
# alternates must list at least two types to be useful
{ 'alternate': 'Alt', 'data': { 'i': 'int' } }
# alternates cannot be empty
{ 'alternate': 'Alt', 'data': { } }

4
tests/qapi-schema/qapi-schema-test.json
View File

@ -186,19 +186,21 @@
# test that we correctly compile downstream extensions, as well as munge
# ticklish names
# also test union and alternate with just one branch
{ 'enum': '__org.qemu_x-Enum', 'data': [ '__org.qemu_x-value' ] }
{ 'struct': '__org.qemu_x-Base',
'data': { '__org.qemu_x-member1': '__org.qemu_x-Enum' } }
{ 'struct': '__org.qemu_x-Struct', 'base': '__org.qemu_x-Base',
'data': { '__org.qemu_x-member2': 'str', '*wchar-t': 'int' } }
{ 'union': '__org.qemu_x-Union1', 'data': { '__org.qemu_x-branch': 'str' } }
{ 'alternate': '__org.qemu_x-Alt1', 'data': { '__org.qemu_x-branch': 'str' } }
{ 'struct': '__org.qemu_x-Struct2',
'data': { 'array': ['__org.qemu_x-Union1'] } }
{ 'union': '__org.qemu_x-Union2', 'base': '__org.qemu_x-Base',
'discriminator': '__org.qemu_x-member1',
'data': { '__org.qemu_x-value': '__org.qemu_x-Struct2' } }
{ 'alternate': '__org.qemu_x-Alt',
'data': { '__org.qemu_x-branch': 'str', 'b': '__org.qemu_x-Base' } }
'data': { '__org.qemu_x-branch': '__org.qemu_x-Base' } }
{ 'event': '__ORG.QEMU_X-EVENT', 'data': '__org.qemu_x-Struct' }
{ 'command': '__org.qemu_x-command',
'data': { 'a': ['__org.qemu_x-Enum'], 'b': ['__org.qemu_x-Struct'],

6
tests/qapi-schema/qapi-schema-test.out
View File

@ -274,6 +274,9 @@ object __org.qemu_x-Union1
member type: __org.qemu_x-Union1Kind optional=False
tag type
case __org.qemu_x-branch: q_obj_str-wrapper
alternate __org.qemu_x-Alt1
tag type
case __org.qemu_x-branch: str
array __org.qemu_x-Union1List __org.qemu_x-Union1
object __org.qemu_x-Struct2
member array: __org.qemu_x-Union1List optional=False
@ -283,8 +286,7 @@ object __org.qemu_x-Union2
case __org.qemu_x-value: __org.qemu_x-Struct2
alternate __org.qemu_x-Alt
tag type
case __org.qemu_x-branch: str
case b: __org.qemu_x-Base
case __org.qemu_x-branch: __org.qemu_x-Base
event __ORG.QEMU_X-EVENT __org.qemu_x-Struct
boxed=False
array __org.qemu_x-EnumList __org.qemu_x-Enum