@@ -182,11 +182,11 @@ prevent incomplete include files.
Usage: { 'struct': STRING, 'data': DICT, '*base': STRUCT-NAME }
-A struct is a dictionary containing a single 'data' key whose
-value is a dictionary. This corresponds to a struct in C or an Object
-in JSON. Each value of the 'data' dictionary must be the name of a
-type, or a one-element array containing a type name. An example of a
-struct is:
+A struct is a dictionary containing a single 'data' key whose value is
+a dictionary; the dictionary may be empty. This corresponds to a
+struct in C or an Object in JSON. Each value of the 'data' dictionary
+must be the name of a type, or a one-element array containing a type
+name. An example of a struct is:
{ 'struct': 'MyType',
'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } }
@@ -277,7 +277,8 @@ 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), flat (both discriminator and base). A union
type is defined using a data dictionary as explained in the following
-paragraphs.
+paragraphs. The data dictionary for either type of union must not
+be empty.
A simple union type defines a mapping from automatic discriminator
values to data types like in this example:
@@ -563,7 +563,10 @@ def check_union(expr, expr_info):
"Discriminator '%s' must be of enumeration "
"type" % discriminator)
- # Check every branch
+ # Check every branch; don't allow an empty union
+ if len(members) == 0:
+ raise QAPIExprError(expr_info,
+ "Union '%s' cannot have empty 'data'" % name)
for (key, value) in members.items():
check_name(expr_info, "Member of union '%s'" % name, key)
@@ -601,7 +604,11 @@ def check_alternate(expr, expr_info):
values = { 'MAX': '(automatic)' }
types_seen = {}
- # Check every branch
+ # Check every branch; require at least two branches
+ if len(members) < 2:
+ raise QAPIExprError(expr_info,
+ "Alternate '%s' should have at least two branches "
+ "in 'data'" % name)
for (key, value) in members.items():
check_name(expr_info, "Member of alternate '%s'" % name, key)
@@ -964,6 +971,7 @@ class QAPISchemaObjectTypeVariants(object):
def __init__(self, tag_name, tag_enum, variants):
assert tag_name is None or isinstance(tag_name, str)
assert tag_enum is None or isinstance(tag_enum, str)
+ assert len(variants) > 0
for v in variants:
assert isinstance(v, QAPISchemaObjectTypeVariant)
self._tag_name = tag_name
@@ -0,0 +1 @@
+tests/qapi-schema/alternate-empty.json:2: Alternate 'Alt' should have at least two branches in 'data'
@@ -1 +1 @@
-0
+1
@@ -1,2 +1,2 @@
-# FIXME - alternates should list at least two types to be useful
+# alternates must list at least two types to be useful
{ 'alternate': 'Alt', 'data': { 'i': 'int' } }
@@ -1,3 +0,0 @@
-object :empty
-alternate Alt
- case i: int
@@ -0,0 +1 @@
+tests/qapi-schema/flat-union-empty.json:4: Union 'Union' cannot have empty 'data'
@@ -1 +1 @@
-0
+1
@@ -1,4 +1,4 @@
-# FIXME - flat unions should not be empty
+# flat unions cannot be empty
{ 'enum': 'Empty', 'data': [ ] }
{ 'struct': 'Base', 'data': { 'type': 'Empty' } }
{ 'union': 'Union', 'base': 'Base', 'discriminator': 'type', 'data': { } }
@@ -1,7 +0,0 @@
-object :empty
-object Base
- member type: Empty optional=False
-enum Empty []
-object Union
- base Base
- tag type
@@ -0,0 +1 @@
+tests/qapi-schema/union-empty.json:2: Union 'Union' cannot have empty 'data'
@@ -1 +1 @@
-0
+1
@@ -1,2 +1,2 @@
-# FIXME - unions should not be empty
+# unions cannot be empty
{ 'union': 'Union', 'data': { } }
@@ -1,4 +0,0 @@
-object :empty
-object Union
- tag type
-enum UnionKind []
Empty unions serve no purpose, and while we compile with gcc which permits them, strict C99 forbids them. We could inject a dummy member (and in fact, we do for empty structs), but while empty structs make sense in qapi, empty unions don't add any expressiveness to the QMP language. So prohibit them at parse time. Update the documentation and testsuite to match. Signed-off-by: Eric Blake <eblake@redhat.com> --- docs/qapi-code-gen.txt | 13 +++++++------ scripts/qapi.py | 12 ++++++++++-- tests/qapi-schema/alternate-empty.err | 1 + tests/qapi-schema/alternate-empty.exit | 2 +- tests/qapi-schema/alternate-empty.json | 2 +- tests/qapi-schema/alternate-empty.out | 3 --- tests/qapi-schema/flat-union-empty.err | 1 + tests/qapi-schema/flat-union-empty.exit | 2 +- tests/qapi-schema/flat-union-empty.json | 2 +- tests/qapi-schema/flat-union-empty.out | 7 ------- tests/qapi-schema/union-empty.err | 1 + tests/qapi-schema/union-empty.exit | 2 +- tests/qapi-schema/union-empty.json | 2 +- tests/qapi-schema/union-empty.out | 4 ---- 14 files changed, 26 insertions(+), 28 deletions(-)