[Qemu-block] [PATCH v4 04/14] qapi: Allow optional discriminators

[Max Reitz]

Optional discriminators are fine, as long as there is a default value.

Signed-off-by: Max Reitz <mre...@redhat.com>
---
 scripts/qapi/common.py | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
index 8c57d0c67a..203623795b 100644
--- a/scripts/qapi/common.py
+++ b/scripts/qapi/common.py
@@ -1052,11 +1052,21 @@ def check_union(expr, info):
         base_members = find_base_members(base)
         assert base_members is not None
 
-        # The value of member 'discriminator' must name a non-optional
-        # member of the base struct.
+        # The value of member 'discriminator' must name a member of
+        # the base struct.  (Optional members are allowed, but the
+        # discriminator name must not start with '*', so keep
+        # allow_optional=False.)
         check_name(info, "Discriminator of flat union '%s'" % name,
                    discriminator)
+
         discriminator_value = base_members.get(discriminator)
+        if not discriminator_value:
+            discriminator_value = base_members.get('*' + discriminator)
+            if discriminator_value and 'default' not in discriminator_value:
+                raise QAPISemError(info,
+                    "Optional discriminator '%s' has no default value" %
+                    discriminator)
+
         if not discriminator_value:
             raise QAPISemError(info,
                                "Discriminator '%s' is not a member of base "
-- 
2.21.0