[Qemu-devel] [PATCH v5 12/28] qapi: Introduce 'alternate' to replace anonymous union

[Eric Blake <eblake@redhat.com>]

Rather than special-casing "'union':'foo','alternate':{}" as an
unusual union that can represent a non-dictionary, it is nicer
to designate a separate meta-type "'alternate':'foo'" for the
purpose.  This involves a lot of documentation tweaks and fallout
from .json files, but I already split as much as possible into
earlier commits.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 docs/qapi-code-gen.txt                             | 63 +++++++++++-----------
 qapi/block-core.json                               |  6 +--
 scripts/qapi-types.py                              | 26 ++++++---
 scripts/qapi-visit.py                              | 17 +++---
 scripts/qapi.py                                    | 41 +++++++-------
 tests/qapi-schema/alternate-array.err              |  2 +-
 tests/qapi-schema/alternate-array.json             |  3 +-
 tests/qapi-schema/alternate-base.err               |  2 +-
 tests/qapi-schema/alternate-base.json              |  5 +-
 tests/qapi-schema/alternate-clash.err              |  2 +-
 tests/qapi-schema/alternate-clash.json             |  5 +-
 tests/qapi-schema/alternate-conflict-dict.err      |  2 +-
 tests/qapi-schema/alternate-conflict-dict.json     |  5 +-
 tests/qapi-schema/alternate-conflict-string.err    |  2 +-
 tests/qapi-schema/alternate-conflict-string.json   |  3 +-
 tests/qapi-schema/alternate-good.json              |  5 +-
 tests/qapi-schema/alternate-good.out               |  4 +-
 tests/qapi-schema/alternate-nested.err             |  2 +-
 tests/qapi-schema/alternate-nested.json            |  8 ++-
 tests/qapi-schema/alternate-unknown.err            |  2 +-
 tests/qapi-schema/alternate-unknown.json           |  3 +-
 tests/qapi-schema/flat-union-bad-base.err          |  2 +-
 tests/qapi-schema/flat-union-bad-discriminator.err |  2 +-
 .../qapi-schema/flat-union-bad-discriminator.json  |  5 +-
 tests/qapi-schema/flat-union-base-union.err        |  2 +-
 tests/qapi-schema/flat-union-base-union.json       |  2 +-
 tests/qapi-schema/flat-union-no-base.err           |  2 +-
 tests/qapi-schema/qapi-schema-test.json            |  3 +-
 tests/qapi-schema/qapi-schema-test.out             |  2 +-
 tests/qapi-schema/union-invalid-base.err           |  2 +-
 30 files changed, 117 insertions(+), 113 deletions(-)

diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
index ce9c4b9..8792b94 100644
--- a/docs/qapi-code-gen.txt
+++ b/docs/qapi-code-gen.txt
@@ -79,16 +79,16 @@ the definition of complex structs that can have mutually recursive
 types, and allows for indefinite nesting of QMP that satisfies the
 schema.  A type name should not be defined more than once.

-There are six top-level expressions recognized by the parser:
-'include', 'command', 'type', 'enum', 'union', and 'event'.  There are
-several built-in types, such as 'int' and 'str'; additionally, the
-top-level expressions can define complex types, enumeration types, and
-several flavors of union types.  The 'command' expression can refer to
-existing types by name, or list an anonymous type as a dictionary.
-Listing a type name inside an array refers to a single-dimension array
-of that type; multi-dimension arrays are not directly supported
-(although an array of a complex struct that contains an array member
-is possible).
+There are seven top-level expressions recognized by the parser:
+'include', 'command', 'type', 'enum', 'union', 'alternate', and
+'event'.  There are several built-in types, such as 'int' and 'str';
+additionally, the top-level expressions can define complex types,
+enumeration types, two flavors of union types, and an alternate type.
+The 'command' expression can refer to existing types by name, or list
+an anonymous type as a dictionary.  Listing a type name inside an
+array refers to a single-dimension array of that type; multi-dimension
+arrays are not directly supported (although an array of a complex
+struct that contains an array member is possible).

 Types, commands, and events share a common namespace.  Therefore,
 generally speaking, type definitions should always use CamelCase for
@@ -159,8 +159,8 @@ Usage: { 'type': 'str', 'data': 'dict', '*base': 'complex-type-name' }
 A complex type 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
-complex, enum, union, or built-in type, or a one-element array
-containing a type name.  An example of a complex type is:
+complex, enum, union, alternate, or built-in type, or a one-element
+array containing a type name.  An example of a complex type is:

  { 'type': 'MyType',
    'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } }
@@ -246,14 +246,12 @@ open-coding the field to be type 'str'.
 Usage: { 'union': 'str', 'data': 'dict' }
 or:    { 'union': 'str', 'data': 'dict', 'base': 'complex-type-name',
          'discriminator': 'enum-member-of-base' }
-or:    { 'union': 'str', 'data': 'dict', 'discriminator': {} }

 Union types are used to let the user choose between several different
-data types.  There are three flavors: simple (no discriminator), flat
-(a base type is mandatory, and discriminator is the name of an enum
-field within that base type), and anonymous (discriminator is an
-empty dictionary).  A union type is defined using a data dictionary as
-explained in the following paragraphs.
+data types.  There are two flavors: simple (no discriminator or base),
+and flat (a base type is mandatory, and discriminator is the name of
+an enum field within that base type).  A union type is defined using a
+data dictionary as explained in the following paragraphs.

 A simple union type defines a mapping from automatic discriminator
 values to data types like in this example:
@@ -321,22 +319,23 @@ Resulting in this JSON object:
    "lazy-refcounts": true }


-The final flavor of unions is an anonymous union. While the other two
-union types are always passed as a dictionary in the wire format, an
-anonymous union instead allows the direct use of different types in
-its place. As they aren't structured, they don't have any explicit
-discriminator but use the (QObject) data type of their value as an
-implicit discriminator. This means that they are restricted to using
-only one discriminator value per QObject type. For example, you cannot
-have two different complex types in an anonymous union, or two
-different integer types.
+=== Alternate types ===

-Anonymous unions are declared using an empty dictionary as their discriminator.
-The discriminator values never appear on the wire, they are only used in the
-generated C code. Anonymous unions cannot have a base type.
+Usage: { 'alternate: 'str', 'data': 'dict' }

- { 'union': 'BlockRef',
-   'discriminator': {},
+An alternate type is one that allows a choice between two or more
+QObject data types (string, integer, number, or dictionary, but not
+array) on the wire.  The definition is similar to a simple union type,
+where each branch of the dictionary names a type, and where an
+implicit C enum NameKind is created for the alternate Name.  But
+unlike a union, the discriminator string is never passed on the wire
+for QMP, instead appearing only in the generated C code.  The type on
+the wire serves an implicit discriminator, which in turn means that an
+alternate can express a choice between a string and a single complex
+type (passed as a dictionary), but cannot distinguish between two
+different complex types.  For example:
+
+ { 'alternate': 'BlockRef',
    'data': { 'definition': 'BlockdevOptions',
              'reference': 'str' } }

diff --git a/qapi/block-core.json b/qapi/block-core.json
index f525b04..581c448 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1419,8 +1419,7 @@
 #
 # Since: 2.2
 ##
-{ 'union': 'Qcow2OverlapChecks',
-  'discriminator': {},
+{ 'alternate': 'Qcow2OverlapChecks',
   'data': { 'flags': 'Qcow2OverlapCheckFlags',
             'mode':  'Qcow2OverlapCheckMode' } }

@@ -1711,8 +1710,7 @@
 #
 # Since: 1.7
 ##
-{ 'union': 'BlockdevRef',
-  'discriminator': {},
+{ 'alternate': 'BlockdevRef',
   'data': { 'definition': 'BlockdevOptions',
             'reference': 'str' } }

diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index c9e0201..9c8d68c 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -172,7 +172,7 @@ typedef enum %(name)s

 def generate_alternate_qtypes(expr):

-    name = expr['union']
+    name = expr['alternate']
     members = expr['data']

     ret = mcgen('''
@@ -182,7 +182,7 @@ const int %(name)s_qtypes[QTYPE_MAX] = {

     for key in members:
         qtype = find_alternate_member_qtype(members[key])
-        assert qtype, "Invalid anonymous union member"
+        assert qtype, "Invalid alternate member"

         ret += mcgen('''
     [ %(qtype)s ] = %(abbrev)s_KIND_%(enum)s,
@@ -197,9 +197,9 @@ const int %(name)s_qtypes[QTYPE_MAX] = {
     return ret


-def generate_union(expr):
+def generate_union(expr, meta):

-    name = expr['union']
+    name = expr[meta]
     typeinfo = expr['data']

     base = expr.get('base')
@@ -243,7 +243,7 @@ struct %(name)s
     ret += mcgen('''
 };
 ''')
-    if discriminator == {}:
+    if meta == 'alternate':
         ret += mcgen('''
 extern const int %(name)s_qtypes[];
 ''',
@@ -407,8 +407,12 @@ for expr in exprs:
             ret += generate_enum('%sKind' % expr['union'], expr['data'].keys())
             fdef.write(generate_enum_lookup('%sKind' % expr['union'],
                                             expr['data'].keys()))
-        if expr.get('discriminator') == {}:
-            fdef.write(generate_alternate_qtypes(expr))
+    elif expr.has_key('alternate'):
+        ret += generate_fwd_struct(expr['alternate'], expr['data']) + "\n"
+        ret += generate_enum('%sKind' % expr['alternate'], expr['data'].keys())
+        fdef.write(generate_enum_lookup('%sKind' % expr['alternate'],
+                                        expr['data'].keys()))
+        fdef.write(generate_alternate_qtypes(expr))
     else:
         continue
     fdecl.write(ret)
@@ -438,11 +442,17 @@ for expr in exprs:
         ret += generate_type_cleanup_decl(expr['type'])
         fdef.write(generate_type_cleanup(expr['type']) + "\n")
     elif expr.has_key('union'):
-        ret += generate_union(expr)
+        ret += generate_union(expr, 'union')
         ret += generate_type_cleanup_decl(expr['union'] + "List")
         fdef.write(generate_type_cleanup(expr['union'] + "List") + "\n")
         ret += generate_type_cleanup_decl(expr['union'])
         fdef.write(generate_type_cleanup(expr['union']) + "\n")
+    elif expr.has_key('alternate'):
+        ret += generate_union(expr, 'alternate')
+        ret += generate_type_cleanup_decl(expr['alternate'] + "List")
+        fdef.write(generate_type_cleanup(expr['alternate'] + "List") + "\n")
+        ret += generate_type_cleanup_decl(expr['alternate'])
+        fdef.write(generate_type_cleanup(expr['alternate']) + "\n")
     elif expr.has_key('enum'):
         ret += generate_type_cleanup_decl(expr['enum'] + "List")
         fdef.write(generate_type_cleanup(expr['enum'] + "List") + "\n")
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 77b0a1f..3e11089 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -256,7 +256,7 @@ void visit_type_%(name)s(Visitor *m, %(name)s **obj, const char *name, Error **e
 ''',
     name=name)

-    # For anon union, always use the default enum type automatically generated
+    # For alternate, always use the default enum type automatically generated
     # as "'%sKind' % (name)"
     disc_type = '%sKind' % (name)

@@ -264,7 +264,7 @@ void visit_type_%(name)s(Visitor *m, %(name)s **obj, const char *name, Error **e
         assert (members[key] in builtin_types.keys()
             or find_struct(members[key])
             or find_union(members[key])
-            or find_enum(members[key])), "Invalid anonymous union member"
+            or find_enum(members[key])), "Invalid alternate member"

         enum_full_value = generate_enum_full_value(disc_type, key)
         ret += mcgen('''
@@ -300,10 +300,6 @@ def generate_visit_union(expr):
     base = expr.get('base')
     discriminator = expr.get('discriminator')

-    if discriminator == {}:
-        assert not base
-        return generate_visit_alternate(name, members)
-
     enum_define = discriminator_find_enum_define(expr)
     if enum_define:
         # Use the enum type as discriminator
@@ -572,6 +568,15 @@ for expr in exprs:
                                      expr['data'].keys())
         ret += generate_declaration(expr['union'], expr['data'])
         fdecl.write(ret)
+    elif expr.has_key('alternate'):
+        ret = generate_visit_alternate(expr['alternate'], expr['data'])
+        ret += generate_visit_list(expr['alternate'], expr['data'])
+        fdef.write(ret)
+
+        ret = generate_decl_enum('%sKind' % expr['alternate'],
+                                 expr['data'].keys())
+        ret += generate_declaration(expr['alternate'], expr['data'])
+        fdecl.write(ret)
     elif expr.has_key('enum'):
         ret = generate_visit_list(expr['enum'], expr['data'])
         ret += generate_visit_enum(expr['enum'], expr['data'])
diff --git a/scripts/qapi.py b/scripts/qapi.py
index 17252e9..018ec45 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -273,11 +273,10 @@ def check_union(expr, expr_info):
     values = { 'MAX': '(automatic)' }

     # Two types of unions, determined by discriminator.
-    assert discriminator != {}

     # If the union object has no member 'discriminator', it's an
     # ordinary union.  For now, it must not have a base.
-    if not discriminator:
+    if discriminator is None:
         enum_define = None
         if base:
             raise QAPIExprError(expr_info,
@@ -287,18 +286,22 @@ def check_union(expr, expr_info):
     # Else, it's a flat union.
     else:
         # The object must have a member 'base'.
-        if not base:
+        if not isinstance(base, str):
             raise QAPIExprError(expr_info,
-                                "Flat union '%s' must have a base field"
+                                "Flat union '%s' must have a string base field"
                                 % name)
         base_fields = find_base_fields(base)
         if not base_fields:
             raise QAPIExprError(expr_info,
-                                "Base '%s' is not a valid type"
+                                "Base '%s' is not a valid base type"
                                 % base)

         # The value of member 'discriminator' must name a member of the
         # base type.
+        if not isinstance(discriminator, str):
+            raise QAPIExprError(expr_info,
+                                "Flat union '%s' must have a string "
+                                "discriminator field" % name)
         discriminator_type = base_fields.get(discriminator)
         if not discriminator_type:
             raise QAPIExprError(expr_info,
@@ -333,17 +336,15 @@ def check_union(expr, expr_info):
             values[c_key] = key

 def check_alternate(expr, expr_info):
-    name = expr['union']
-    base = expr.get('base')
-    discriminator = expr.get('discriminator')
+    name = expr['alternate']
     members = expr['data']
     values = { 'MAX': '(automatic)' }
     types_seen = {}

-    assert discriminator == {}
+    base = expr.get('base')
     if base:
         raise QAPIExprError(expr_info,
-                            "Anonymous union '%s' must not have a base"
+                            "Alternate '%s' must not have a base"
                             % name)

     # Check every branch
@@ -352,23 +353,23 @@ def check_alternate(expr, expr_info):
         c_key = _generate_enum_string(key)
         if c_key in values:
             raise QAPIExprError(expr_info,
-                                "Union '%s' member '%s' clashes with '%s'"
+                                "Alternate '%s' member '%s' clashes with '%s'"
                                 % (name, key, values[c_key]))
         values[c_key] = key

         # Ensure alternates have no type conflicts.
         if isinstance(value, list):
             raise QAPIExprError(expr_info,
-                                "Anonymous union '%s' member '%s' must "
+                                "Alternate '%s' member '%s' must "
                                 "not be array type" % (name, key))
         qtype = find_alternate_member_qtype(value)
         if not qtype:
             raise QAPIExprError(expr_info,
-                                "Anonymous union '%s' member '%s' has "
+                                "Alternate '%s' member '%s' has "
                                 "invalid type '%s'" % (name, key, value))
         if qtype in types_seen:
             raise QAPIExprError(expr_info,
-                                "Anonymous union '%s' member '%s' has "
+                                "Alternate '%s' member '%s' has "
                                 "same QObject type as member '%s'"
                                 % (name, key, types_seen[qtype]))
         types_seen[qtype] = key
@@ -401,10 +402,9 @@ def check_exprs(schema):
         if expr.has_key('enum'):
             check_enum(expr, info)
         elif expr.has_key('union'):
-            if expr.get('discriminator') == {}:
-                check_alternate(expr, info)
-            else:
-                check_union(expr, info)
+            check_union(expr, info)
+        elif expr.has_key('alternate'):
+            check_alternate(expr, info)
         elif expr.has_key('event'):
             check_event(expr, info)

@@ -436,6 +436,8 @@ def parse_schema(input_file):
             if expr.has_key('union'):
                 if not discriminator_find_enum_define(expr):
                     add_enum('%sKind' % expr['union'])
+            elif expr.has_key('alternate'):
+                add_enum('%sKind' % expr['alternate'])

         # Final pass - validate that exprs make sense
         check_exprs(schema)
@@ -546,8 +548,7 @@ def find_struct(name):

 def add_union(definition):
     global union_types
-    if definition.get('discriminator') != {}:
-        union_types.append(definition)
+    union_types.append(definition)

 def find_union(name):
     global union_types
diff --git a/tests/qapi-schema/alternate-array.err b/tests/qapi-schema/alternate-array.err
index 2638b85..5721ed2 100644
--- a/tests/qapi-schema/alternate-array.err
+++ b/tests/qapi-schema/alternate-array.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-array.json:4: Anonymous union 'MyUnion' member 'two' must not be array type
+tests/qapi-schema/alternate-array.json:4: Alternate 'Alt' member 'two' must not be array type
diff --git a/tests/qapi-schema/alternate-array.json b/tests/qapi-schema/alternate-array.json
index e330d57..86d8fa0 100644
--- a/tests/qapi-schema/alternate-array.json
+++ b/tests/qapi-schema/alternate-array.json
@@ -1,7 +1,6 @@
 # FIXME: we do not support array branches of anonymous unions yet
 { 'type': 'One',
   'data': { 'name': 'str' } }
-{ 'union': 'MyUnion',
-  'discriminator': {},
+{ 'alternate': 'Alt',
   'data': { 'one': 'One',
 	    'two': [ 'int' ] } }
diff --git a/tests/qapi-schema/alternate-base.err b/tests/qapi-schema/alternate-base.err
index a2486b8..4a2566e 100644
--- a/tests/qapi-schema/alternate-base.err
+++ b/tests/qapi-schema/alternate-base.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-base.json:4: Anonymous union 'MyUnion' must not have a base
+tests/qapi-schema/alternate-base.json:4: Alternate 'Alt' must not have a base
diff --git a/tests/qapi-schema/alternate-base.json b/tests/qapi-schema/alternate-base.json
index dad7f02..66edc89 100644
--- a/tests/qapi-schema/alternate-base.json
+++ b/tests/qapi-schema/alternate-base.json
@@ -1,7 +1,6 @@
-# we reject anonymous union with base type
+# we reject alternate with base type
 { 'type': 'Base',
   'data': { 'string': 'str' } }
-{ 'union': 'MyUnion',
+{ 'alternate': 'Alt',
   'base': 'Base',
-  'discriminator': {},
   'data': { 'number': 'int' } }
diff --git a/tests/qapi-schema/alternate-clash.err b/tests/qapi-schema/alternate-clash.err
index 1130c12..51bea3e 100644
--- a/tests/qapi-schema/alternate-clash.err
+++ b/tests/qapi-schema/alternate-clash.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-clash.json:2: Union 'Union1' member 'ONE' clashes with 'one'
+tests/qapi-schema/alternate-clash.json:2: Alternate 'Alt1' member 'ONE' clashes with 'one'
diff --git a/tests/qapi-schema/alternate-clash.json b/tests/qapi-schema/alternate-clash.json
index fa2d27e..3947935 100644
--- a/tests/qapi-schema/alternate-clash.json
+++ b/tests/qapi-schema/alternate-clash.json
@@ -1,4 +1,3 @@
-# we detect C enum collisions in an anonymous union
-{ 'union': 'Union1',
-  'discriminator': {},
+# we detect C enum collisions in an alternate
+{ 'alternate': 'Alt1',
   'data': { 'one': 'str', 'ONE': 'int' } }
diff --git a/tests/qapi-schema/alternate-conflict-dict.err b/tests/qapi-schema/alternate-conflict-dict.err
index f256d51..c535332 100644
--- a/tests/qapi-schema/alternate-conflict-dict.err
+++ b/tests/qapi-schema/alternate-conflict-dict.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-conflict-dict.json:6: Anonymous union 'MyUnion' member 'two' has same QObject type as member 'one'
+tests/qapi-schema/alternate-conflict-dict.json:6: Alternate 'Alt' member 'two' has same QObject type as member 'one'
diff --git a/tests/qapi-schema/alternate-conflict-dict.json b/tests/qapi-schema/alternate-conflict-dict.json
index 177c163..eaac5b3 100644
--- a/tests/qapi-schema/alternate-conflict-dict.json
+++ b/tests/qapi-schema/alternate-conflict-dict.json
@@ -1,9 +1,8 @@
-# we reject anonymous unions with multiple object branches
+# we reject alternates with multiple object branches
 { 'type': 'One',
   'data': { 'name': 'str' } }
 { 'type': 'Two',
   'data': { 'value': 'int' } }
-{ 'union': 'MyUnion',
-  'discriminator': {},
+{ 'alternate': 'Alt',
   'data': { 'one': 'One',
 	    'two': 'Two' } }
diff --git a/tests/qapi-schema/alternate-conflict-string.err b/tests/qapi-schema/alternate-conflict-string.err
index a3b7b6d..18ef0d3 100644
--- a/tests/qapi-schema/alternate-conflict-string.err
+++ b/tests/qapi-schema/alternate-conflict-string.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-conflict-string.json:4: Anonymous union 'MyUnion' member 'two' has same QObject type as member 'one'
+tests/qapi-schema/alternate-conflict-string.json:4: Alternate 'Alt' member 'two' has same QObject type as member 'one'
diff --git a/tests/qapi-schema/alternate-conflict-string.json b/tests/qapi-schema/alternate-conflict-string.json
index a1b0bea..ce00307 100644
--- a/tests/qapi-schema/alternate-conflict-string.json
+++ b/tests/qapi-schema/alternate-conflict-string.json
@@ -1,8 +1,7 @@
 # we reject anonymous unions with multiple string-like branches
 { 'enum': 'Enum',
   'data': [ 'hello', 'world' ] }
-{ 'union': 'MyUnion',
-  'discriminator': {},
+{ 'alternate': 'Alt',
   'data': { 'one': 'str',
 	    'two': 'Enum' } }

diff --git a/tests/qapi-schema/alternate-good.json b/tests/qapi-schema/alternate-good.json
index 1068e2f..74f338c 100644
--- a/tests/qapi-schema/alternate-good.json
+++ b/tests/qapi-schema/alternate-good.json
@@ -1,10 +1,9 @@
-# Working example of anonymous union
+# Working example of alternate
 { 'type': 'Data',
   'data': { '*number': 'int', '*name': 'str' } }
 { 'enum': 'Enum',
   'data': [ 'hello', 'world' ] }
-{ 'union': 'MyUnion',
-  'discriminator': {},
+{ 'alternate': 'Alt',
   'data': { 'value': 'int',
 	    'string': 'Enum',
 	    'struct': 'Data' } }
diff --git a/tests/qapi-schema/alternate-good.out b/tests/qapi-schema/alternate-good.out
index b5117d1..c3a6b77 100644
--- a/tests/qapi-schema/alternate-good.out
+++ b/tests/qapi-schema/alternate-good.out
@@ -1,6 +1,6 @@
 [OrderedDict([('type', 'Data'), ('data', OrderedDict([('*number', 'int'), ('*name', 'str')]))]),
  OrderedDict([('enum', 'Enum'), ('data', ['hello', 'world'])]),
- OrderedDict([('union', 'MyUnion'), ('discriminator', OrderedDict()), ('data', OrderedDict([('value', 'int'), ('string', 'Enum'), ('struct', 'Data')]))])]
+ OrderedDict([('alternate', 'Alt'), ('data', OrderedDict([('value', 'int'), ('string', 'Enum'), ('struct', 'Data')]))])]
 [{'enum_name': 'Enum', 'enum_values': ['hello', 'world']},
- {'enum_name': 'MyUnionKind', 'enum_values': None}]
+ {'enum_name': 'AltKind', 'enum_values': None}]
 [OrderedDict([('type', 'Data'), ('data', OrderedDict([('*number', 'int'), ('*name', 'str')]))])]
diff --git a/tests/qapi-schema/alternate-nested.err b/tests/qapi-schema/alternate-nested.err
index 59df96e..00b05c6 100644
--- a/tests/qapi-schema/alternate-nested.err
+++ b/tests/qapi-schema/alternate-nested.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-nested.json:5: Anonymous union 'Union2' member 'nested' has invalid type 'Union1'
+tests/qapi-schema/alternate-nested.json:4: Alternate 'Alt2' member 'nested' has invalid type 'Alt1'
diff --git a/tests/qapi-schema/alternate-nested.json b/tests/qapi-schema/alternate-nested.json
index ed2b6b7..2a115b9 100644
--- a/tests/qapi-schema/alternate-nested.json
+++ b/tests/qapi-schema/alternate-nested.json
@@ -1,7 +1,5 @@
 # we reject a nested anonymous union branch
-{ 'union': 'Union1',
-  'discriminator': {},
+{ 'alternate': 'Alt1',
   'data': { 'name': 'str', 'value': 'int' } }
-{ 'union': 'Union2',
-  'discriminator': {},
-  'data': { 'nested': 'Union1' } }
+{ 'alternate': 'Alt2',
+  'data': { 'nested': 'Alt1' } }
diff --git a/tests/qapi-schema/alternate-unknown.err b/tests/qapi-schema/alternate-unknown.err
index bf8e9ae..7af1b4c 100644
--- a/tests/qapi-schema/alternate-unknown.err
+++ b/tests/qapi-schema/alternate-unknown.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-unknown.json:2: Anonymous union 'Union' member 'unknown' has invalid type 'MissingType'
+tests/qapi-schema/alternate-unknown.json:2: Alternate 'Alt' member 'unknown' has invalid type 'MissingType'
diff --git a/tests/qapi-schema/alternate-unknown.json b/tests/qapi-schema/alternate-unknown.json
index 0c305c2..d7b217e 100644
--- a/tests/qapi-schema/alternate-unknown.json
+++ b/tests/qapi-schema/alternate-unknown.json
@@ -1,4 +1,3 @@
 # we reject an anonymous union with unknown type in branch
-{ 'union': 'Union',
-  'discriminator': {},
+{ 'alternate': 'Alt',
   'data': { 'unknown': 'MissingType' } }
diff --git a/tests/qapi-schema/flat-union-bad-base.err b/tests/qapi-schema/flat-union-bad-base.err
index 5962ff4..f9c31b2 100644
--- a/tests/qapi-schema/flat-union-bad-base.err
+++ b/tests/qapi-schema/flat-union-bad-base.err
@@ -1 +1 @@
-tests/qapi-schema/flat-union-bad-base.json:9: Base 'OrderedDict([('enum1', 'TestEnum'), ('kind', 'str')])' is not a valid type
+tests/qapi-schema/flat-union-bad-base.json:9: Flat union 'TestUnion' must have a string base field
diff --git a/tests/qapi-schema/flat-union-bad-discriminator.err b/tests/qapi-schema/flat-union-bad-discriminator.err
index 628432f..4f0c798 100644
--- a/tests/qapi-schema/flat-union-bad-discriminator.err
+++ b/tests/qapi-schema/flat-union-bad-discriminator.err
@@ -1 +1 @@
-tests/qapi-schema/flat-union-bad-discriminator.json:10: Simple union 'TestUnion' must not have a base
+tests/qapi-schema/flat-union-bad-discriminator.json:11: Flat union 'TestUnion' must have a string discriminator field
diff --git a/tests/qapi-schema/flat-union-bad-discriminator.json b/tests/qapi-schema/flat-union-bad-discriminator.json
index 1599a59..982f072 100644
--- a/tests/qapi-schema/flat-union-bad-discriminator.json
+++ b/tests/qapi-schema/flat-union-bad-discriminator.json
@@ -1,4 +1,5 @@
-# FIXME: we should require the discriminator to be a string naming a base-type member
+# we require the discriminator to be a string naming a base-type member
+# this tests the old syntax for anonymous unions before we added alternates
 { 'enum': 'TestEnum',
   'data': [ 'value1', 'value2' ] }
 { 'type': 'TestBase',
@@ -9,6 +10,6 @@
   'data': { 'integer': 'int' } }
 { 'union': 'TestUnion',
   'base': 'TestBase',
-  'discriminator': [],
+  'discriminator': {},
   'data': { 'kind1': 'TestTypeA',
             'kind2': 'TestTypeB' } }
diff --git a/tests/qapi-schema/flat-union-base-union.err b/tests/qapi-schema/flat-union-base-union.err
index 185bf51..318c047 100644
--- a/tests/qapi-schema/flat-union-base-union.err
+++ b/tests/qapi-schema/flat-union-base-union.err
@@ -1 +1 @@
-tests/qapi-schema/flat-union-base-union.json:11: Base 'UnionBase' is not a valid type
+tests/qapi-schema/flat-union-base-union.json:11: Base 'UnionBase' is not a valid base type
diff --git a/tests/qapi-schema/flat-union-base-union.json b/tests/qapi-schema/flat-union-base-union.json
index bbaa2da..135332d 100644
--- a/tests/qapi-schema/flat-union-base-union.json
+++ b/tests/qapi-schema/flat-union-base-union.json
@@ -1,4 +1,4 @@
-# FIXME: the error message needs help: we require the base to be a struct
+# we require the base to be a struct
 { 'enum': 'TestEnum',
   'data': [ 'value1', 'value2' ] }
 { 'type': 'TestTypeA',
diff --git a/tests/qapi-schema/flat-union-no-base.err b/tests/qapi-schema/flat-union-no-base.err
index eaf3592..338bff1 100644
--- a/tests/qapi-schema/flat-union-no-base.err
+++ b/tests/qapi-schema/flat-union-no-base.err
@@ -1 +1 @@
-tests/qapi-schema/flat-union-no-base.json:8: Flat union 'TestUnion' must have a base field
+tests/qapi-schema/flat-union-no-base.json:8: Flat union 'TestUnion' must have a string base field
diff --git a/tests/qapi-schema/qapi-schema-test.json b/tests/qapi-schema/qapi-schema-test.json
index e1d35e1..dec8a7c 100644
--- a/tests/qapi-schema/qapi-schema-test.json
+++ b/tests/qapi-schema/qapi-schema-test.json
@@ -53,8 +53,7 @@
   'discriminator': 'enum1',
   'data': { 'value1' : 'UserDefC', 'value2' : 'UserDefB', 'value3' : 'UserDefA' } }

-{ 'union': 'UserDefAlternate',
-  'discriminator': {},
+{ 'alternate': 'UserDefAlternate',
   'data': { 'uda': 'UserDefA', 's': 'str', 'i': 'int' } }

 # for testing native lists
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index b55ab8d..313ecf3 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -10,7 +10,7 @@
  OrderedDict([('type', 'UserDefUnionBase'), ('data', OrderedDict([('string', 'str'), ('enum1', 'EnumOne')]))]),
  OrderedDict([('union', 'UserDefFlatUnion'), ('base', 'UserDefUnionBase'), ('discriminator', 'enum1'), ('data', OrderedDict([('value1', 'UserDefA'), ('value2', 'UserDefB'), ('value3', 'UserDefB')]))]),
  OrderedDict([('union', 'UserDefFlatUnion2'), ('base', 'UserDefUnionBase'), ('discriminator', 'enum1'), ('data', OrderedDict([('value1', 'UserDefC'), ('value2', 'UserDefB'), ('value3', 'UserDefA')]))]),
- OrderedDict([('union', 'UserDefAlternate'), ('discriminator', OrderedDict()), ('data', OrderedDict([('uda', 'UserDefA'), ('s', 'str'), ('i', 'int')]))]),
+ OrderedDict([('alternate', 'UserDefAlternate'), ('data', OrderedDict([('uda', 'UserDefA'), ('s', 'str'), ('i', 'int')]))]),
  OrderedDict([('union', 'UserDefNativeListUnion'), ('data', OrderedDict([('integer', ['int']), ('s8', ['int8']), ('s16', ['int16']), ('s32', ['int32']), ('s64', ['int64']), ('u8', ['uint8']), ('u16', ['uint16']), ('u32', ['uint32']), ('u64', ['uint64']), ('number', ['number']), ('boolean', ['bool']), ('string', ['str']), ('sizes', ['size'])]))]),
  OrderedDict([('command', 'user_def_cmd'), ('data', OrderedDict())]),
  OrderedDict([('command', 'user_def_cmd1'), ('data', OrderedDict([('ud1a', 'UserDefOne')]))]),
diff --git a/tests/qapi-schema/union-invalid-base.err b/tests/qapi-schema/union-invalid-base.err
index 3cc82c0..bedec06 100644
--- a/tests/qapi-schema/union-invalid-base.err
+++ b/tests/qapi-schema/union-invalid-base.err
@@ -1 +1 @@
-tests/qapi-schema/union-invalid-base.json:8: Base 'int' is not a valid type
+tests/qapi-schema/union-invalid-base.json:8: Base 'int' is not a valid base type
-- 
2.1.0