qapi script: support enum type as discriminator in union

By default, any union will automatically generate a enum type as
"[UnionName]Kind" in C code, and it is duplicated when the discriminator
is specified as a pre-defined enum type in schema. After this patch,
the pre-defined enum type will be really used as the switch case
condition in generated C code, if discriminator is an enum field.

Signed-off-by: Wenchao Xia <wenchaoqemu@gmail.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

3 files changed, 60 insertions, 14 deletions

diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index 5885bac5ba..10864efc58 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -201,14 +201,21 @@ def generate_union(expr):
     base = expr.get('base')
     discriminator = expr.get('discriminator')
 
+    enum_define = discriminator_find_enum_define(expr)
+    if enum_define:
+        discriminator_type_name = enum_define['enum_name']
+    else:
+        discriminator_type_name = '%sKind' % (name)
+
     ret = mcgen('''
 struct %(name)s
 {
-    %(name)sKind kind;
+    %(discriminator_type_name)s kind;
     union {
         void *data;
 ''',
-                name=name)
+                name=name,
+                discriminator_type_name=discriminator_type_name)
 
     for key in typeinfo:
         ret += mcgen('''
@@ -389,8 +396,11 @@ for expr in exprs:
         fdef.write(generate_enum_lookup(expr['enum'], expr['data']))
     elif expr.has_key('union'):
         ret += generate_fwd_struct(expr['union'], expr['data']) + "\n"
-        ret += generate_enum('%sKind' % expr['union'], expr['data'].keys())
-        fdef.write(generate_enum_lookup('%sKind' % expr['union'], expr['data'].keys()))
+        enum_define = discriminator_find_enum_define(expr)
+        if not enum_define:
+            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_anon_union_qtypes(expr))
     else:
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 0baaf606dc..45ce3a957a 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -259,10 +259,16 @@ def generate_visit_union(expr):
         assert not base
         return generate_visit_anon_union(name, members)
 
-    # There will always be a discriminator in the C switch code, by default it
-    # is an enum type generated silently as "'%sKind' % (name)"
-    ret = generate_visit_enum('%sKind' % name, members.keys())
-    disc_type = '%sKind' % (name)
+    enum_define = discriminator_find_enum_define(expr)
+    if enum_define:
+        # Use the enum type as discriminator
+        ret = ""
+        disc_type = enum_define['enum_name']
+    else:
+        # There will always be a discriminator in the C switch code, by default it
+        # is an enum type generated silently as "'%sKind' % (name)"
+        ret = generate_visit_enum('%sKind' % name, members.keys())
+        disc_type = '%sKind' % (name)
 
     if base:
         base_fields = find_struct(base)['data']
@@ -298,15 +304,16 @@ void visit_type_%(name)s(Visitor *m, %(name)s ** obj, const char *name, Error **
     pop_indent()
 
     if not discriminator:
-        desc_type = "type"
+        disc_key = "type"
     else:
-        desc_type = discriminator
+        disc_key = discriminator
     ret += mcgen('''
-        visit_type_%(name)sKind(m, &(*obj)->kind, "%(type)s", &err);
+        visit_type_%(disc_type)s(m, &(*obj)->kind, "%(disc_key)s", &err);
         if (!err) {
             switch ((*obj)->kind) {
 ''',
-                 name=name, type=desc_type)
+                 disc_type = disc_type,
+                 disc_key = disc_key)
 
     for key in members:
         if not discriminator:
@@ -517,7 +524,11 @@ for expr in exprs:
         ret += generate_visit_list(expr['union'], expr['data'])
         fdef.write(ret)
 
-        ret = generate_decl_enum('%sKind' % expr['union'], expr['data'].keys())
+        enum_define = discriminator_find_enum_define(expr)
+        ret = ""
+        if not enum_define:
+            ret = generate_decl_enum('%sKind' % expr['union'],
+                                     expr['data'].keys())
         ret += generate_declaration(expr['union'], expr['data'])
         fdecl.write(ret)
     elif expr.has_key('enum'):
diff --git a/scripts/qapi.py b/scripts/qapi.py
index eebc8a7061..2b43ad2f1b 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -180,6 +180,25 @@ def find_base_fields(base):
         return None
     return base_struct_define['data']
 
+# Return the discriminator enum define if discriminator is specified as an
+# enum type, otherwise return None.
+def discriminator_find_enum_define(expr):
+    base = expr.get('base')
+    discriminator = expr.get('discriminator')
+
+    if not (discriminator and base):
+        return None
+
+    base_fields = find_base_fields(base)
+    if not base_fields:
+        return None
+
+    discriminator_type = base_fields.get(discriminator)
+    if not discriminator_type:
+        return None
+
+    return find_enum(discriminator_type)
+
 def check_union(expr, expr_info):
     name = expr['union']
     base = expr.get('base')
@@ -254,11 +273,17 @@ def parse_schema(fp):
             add_enum(expr['enum'], expr['data'])
         elif expr.has_key('union'):
             add_union(expr)
-            add_enum('%sKind' % expr['union'])
         elif expr.has_key('type'):
             add_struct(expr)
         exprs.append(expr)
 
+    # Try again for hidden UnionKind enum
+    for expr_elem in schema.exprs:
+        expr = expr_elem['expr']
+        if expr.has_key('union'):
+            if not discriminator_find_enum_define(expr):
+                add_enum('%sKind' % expr['union'])
+
     try:
         check_exprs(schema)
     except QAPIExprError, e: