qapi: Segregate anonymous unions into alternates in generator

Special-casing 'discriminator == {}' for handling anonymous unions
is getting awkward; since this particular type is not always a
dictionary on the wire, it is easier to treat it as a completely
different class of type, "alternate", so that if a type is listed
in the union_types array, we know it is not an anonymous union.

This patch just further segregates union handling, to make sure that
anonymous unions are not stored in union_types, and splitting up
check_union() into separate functions.  A future patch will change
the qapi grammar, and having the segregation already in place will
make it easier to deal with the distinct meta-type.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi-types.py

@@ -170,7 +170,7 @@ def generate_enum(name, values):
 
     return lookup_decl + enum_decl
 
-def generate_anon_union_qtypes(expr):
+def generate_alternate_qtypes(expr):
 
     name = expr['union']
     members = expr['data']
@@ -181,7 +181,7 @@ def generate_anon_union_qtypes(expr):
     name=name)
 
     for key in members:
-        qtype = find_anonymous_member_qtype(members[key])
+        qtype = find_alternate_member_qtype(members[key])
         assert qtype, "Invalid anonymous union member"
 
         ret += mcgen('''
@@ -408,7 +408,7 @@ def maybe_open(really, name, opt):
             fdef.write(generate_enum_lookup('%sKind' % expr['union'],
                                             expr['data'].keys()))
         if expr.get('discriminator') == {}:
-            fdef.write(generate_anon_union_qtypes(expr))
+            fdef.write(generate_alternate_qtypes(expr))
     else:
         continue
     fdecl.write(ret)

scripts/qapi-visit.py

@@ -237,7 +237,7 @@ def generate_visit_enum(name, members):
 ''',
                  name=name)
 
-def generate_visit_anon_union(name, members):
+def generate_visit_alternate(name, members):
     ret = mcgen('''
 
 void visit_type_%(name)s(Visitor *m, %(name)s **obj, const char *name, Error **errp)
@@ -302,7 +302,7 @@ def generate_visit_union(expr):
 
     if discriminator == {}:
         assert not base
-        return generate_visit_anon_union(name, members)
+        return generate_visit_alternate(name, members)
 
     enum_define = discriminator_find_enum_define(expr)
     if enum_define:

scripts/qapi.py

@@ -224,21 +224,16 @@ def find_base_fields(base):
         return None
     return base_struct_define['data']
 
-# Return the qtype of an anonymous union branch, or None on error.
-def find_anonymous_member_qtype(qapi_type):
+# Return the qtype of an alternate branch, or None on error.
+def find_alternate_member_qtype(qapi_type):
     if builtin_types.has_key(qapi_type):
         return builtin_types[qapi_type]
     elif find_struct(qapi_type):
         return "QTYPE_QDICT"
     elif find_enum(qapi_type):
         return "QTYPE_QSTRING"
-    else:
-        union = find_union(qapi_type)
-        if union:
-            discriminator = union.get('discriminator')
-            if discriminator == {}:
-                return None
-            return "QTYPE_QDICT"
+    elif find_union(qapi_type):
+        return "QTYPE_QDICT"
     return None
 
 # Return the discriminator enum define if discriminator is specified as an
@@ -276,7 +271,6 @@ def check_union(expr, expr_info):
     discriminator = expr.get('discriminator')
     members = expr['data']
     values = { 'MAX': '(automatic)' }
-    types_seen = {}
 
     # If the object has a member 'base', its value must name a complex type,
     # and there must be a discriminator.
@@ -286,13 +280,15 @@ def check_union(expr, expr_info):
                                 "Union '%s' requires a discriminator to go "
                                 "along with base" %name)
 
-    # If the union object has no member 'discriminator', it's a
-    # simple union. If 'discriminator' is {}, it is an anonymous union.
-    if discriminator is None or discriminator == {}:
+    # Two types of unions, determined by discriminator.
+    assert discriminator != {}
+
+    # With no discriminator it is a simple union.
+    if discriminator is None:
         enum_define = None
         if base is not None:
             raise QAPIExprError(expr_info,
-                                "Union '%s' must not have a base"
+                                "Simple union '%s' must not have a base"
                                 % name)
 
     # Else, it's a flat union.
@@ -347,24 +343,46 @@ def check_union(expr, expr_info):
                                     % (name, key, values[c_key]))
             values[c_key] = key
 
-        # Ensure anonymous unions have no type conflicts.
-        if discriminator == {}:
-            if isinstance(value, list):
-                raise QAPIExprError(expr_info,
-                                    "Anonymous union '%s' member '%s' must "
-                                    "not be array type" % (name, key))
-            qtype = find_anonymous_member_qtype(value)
-            if not qtype:
-                raise QAPIExprError(expr_info,
-                                    "Anonymous union '%s' member '%s' has "
-                                    "invalid type '%s'" % (name, key, value))
-            if qtype in types_seen:
-                raise QAPIExprError(expr_info,
-                                    "Anonymous union '%s' member '%s' can't "
-                                    "be distinguished from member '%s'"
-                                    % (name, key, types_seen[qtype]))
-            types_seen[qtype] = key
+def check_alternate(expr, expr_info):
+    name = expr['union']
+    base = expr.get('base')
+    discriminator = expr.get('discriminator')
+    members = expr['data']
+    values = { 'MAX': '(automatic)' }
+    types_seen = {}
+
+    assert discriminator == {}
+    if base is not None:
+        raise QAPIExprError(expr_info,
+                            "Anonymous union '%s' must not have a base"
+                            % name)
+
+    # Check every branch
+    for (key, value) in members.items():
+        # Check for conflicts in the generated enum
+        c_key = _generate_enum_string(key)
+        if c_key in values:
+            raise QAPIExprError(expr_info,
+                                "Anonymous union '%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 "
+                                "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 "
+                                "invalid type '%s'" % (name, key, value))
+        if qtype in types_seen:
+            raise QAPIExprError(expr_info,
+                                "Anonymous union '%s' member '%s' can't "
+                                "be distinguished from member '%s'"
+                                % (name, key, types_seen[qtype]))
+        types_seen[qtype] = key
 
 def check_enum(expr, expr_info):
     name = expr['enum']
@@ -394,7 +412,10 @@ def check_exprs(schema):
         if expr.has_key('enum'):
             check_enum(expr, info)
         elif expr.has_key('union'):
-            check_union(expr, info)
+            if expr.get('discriminator') == {}:
+                check_alternate(expr, info)
+            else:
+                check_union(expr, info)
         elif expr.has_key('event'):
             check_event(expr, info)
 
@@ -536,7 +557,8 @@ def find_struct(name):
 
 def add_union(definition):
     global union_types
-    union_types.append(definition)
+    if definition.get('discriminator') != {}:
+        union_types.append(definition)
 
 def find_union(name):
     global union_types

tests/qapi-schema/alternate-base.err

@@ -1 +1 @@
-tests/qapi-schema/alternate-base.json:4: Union 'MyUnion' must not have a base
+tests/qapi-schema/alternate-base.json:4: Anonymous union 'MyUnion' must not have a base

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: Anonymous union 'Union1' member 'ONE' clashes with 'one'