@@ -590,7 +590,10 @@ 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)
@@ -613,7 +616,11 @@ def check_alternate(expr, expr_info):
members = expr['data']
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)
@@ -1059,6 +1066,7 @@ 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
@@ -187,11 +187,11 @@ 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' } }
@@ -288,9 +288,10 @@ or: { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME,
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
+discriminator or base), and 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:
@@ -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' } }
@@ -1,5 +0,0 @@
-object :empty
-alternate Alt
- case i: int
-enum QType ['none', 'qnull', 'qint', 'qstring', 'qdict', 'qlist', 'qfloat', 'qbool']
- prefix QTYPE
@@ -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': { } }
@@ -1,9 +0,0 @@
-object :empty
-object Base
- member type: Empty optional=False
-enum Empty []
-enum QType ['none', 'qnull', 'qint', 'qstring', 'qdict', 'qlist', 'qfloat', 'qbool']
- prefix QTYPE
-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': { } }
@@ -1,6 +0,0 @@
-object :empty
-enum QType ['none', 'qnull', 'qint', 'qstring', 'qdict', 'qlist', 'qfloat', 'qbool']
- prefix QTYPE
-object Union
- member type: UnionKind optional=False
-enum UnionKind []
Empty unions serve no purpose, and while we compile with gcc which permits them, strict C99 forbids them. We happen to inject a dummy 'void *data' member into the C unions that represent QAPI unions and alternates, but we want to get rid of that member (it pollutes the namespace for no good reason), which would leave us with an empty union if the user didn't provide any branches. 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. Note that the documentation already mentioned that alternates should have "two or more JSON data types"; so this also fixes the code to enforce that. However, we have existing uses of a union type with only one branch, so the 2-or-more strictness is intentionally limited to alternates. Signed-off-by: Eric Blake <eblake@redhat.com> --- v11: improve commit message v10: hoist into earlier series [no v7, v8, or v9] v6: rebase to earlier qapi.py cleanups --- scripts/qapi.py | 12 ++++++++++-- docs/qapi-code-gen.txt | 15 ++++++++------- 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 | 5 ----- 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 | 9 --------- 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 | 6 ------ 14 files changed, 27 insertions(+), 35 deletions(-)