[PATCH] qapi: allow unions to contain further unions

["Daniel P. Berrangé" <berrange@redhat.com>]

This extends the QAPI schema validation to permit unions inside unions,
provided the checks for clashing fields pass.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---

This patch comes out of the discussion on Het's migration series
starting at this patch:

  https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg02111.html

Markus had described his desired improved architecture

  https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg02719.html

but I don't think I have enough knowledge of the QAPI code to attempt
to fuse the handling of structs/unions as mentioned. This patch does
what looks to be the bare minimum to permit unions in unions, while
keeping validation checks for clashing fields.

I've not tested beyond the unit tests, but if this is acceptable
from Markus' POV, I'd expect Het to insert this patch at the
start of his migration series and thus test it more fully.

 scripts/qapi/schema.py                        |  6 +--
 .../union-invalid-union-subfield.err          |  2 +
 .../union-invalid-union-subfield.json         | 27 +++++++++++++
 .../union-invalid-union-subfield.out          |  0
 .../union-invalid-union-subtype.err           |  2 +
 .../union-invalid-union-subtype.json          | 26 +++++++++++++
 .../union-invalid-union-subtype.out           |  0
 tests/qapi-schema/union-union-branch.err      |  0
 tests/qapi-schema/union-union-branch.json     | 26 +++++++++++++
 tests/qapi-schema/union-union-branch.out      | 38 +++++++++++++++++++
 10 files changed, 124 insertions(+), 3 deletions(-)
 create mode 100644 tests/qapi-schema/union-invalid-union-subfield.err
 create mode 100644 tests/qapi-schema/union-invalid-union-subfield.json
 create mode 100644 tests/qapi-schema/union-invalid-union-subfield.out
 create mode 100644 tests/qapi-schema/union-invalid-union-subtype.err
 create mode 100644 tests/qapi-schema/union-invalid-union-subtype.json
 create mode 100644 tests/qapi-schema/union-invalid-union-subtype.out
 create mode 100644 tests/qapi-schema/union-union-branch.err
 create mode 100644 tests/qapi-schema/union-union-branch.json
 create mode 100644 tests/qapi-schema/union-union-branch.out

diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index cd8661125c..062c6bbb00 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -465,9 +465,10 @@ def check(self, schema):
     # on behalf of info, which is not necessarily self.info
     def check_clash(self, info, seen):
         assert self._checked
-        assert not self.variants       # not implemented
         for m in self.members:
             m.check_clash(info, seen)
+        if self.variants:
+            self.variants.check_clash(info, seen)
 
     def connect_doc(self, doc=None):
         super().connect_doc(doc)
@@ -652,8 +653,7 @@ def check(self, schema, seen):
                         self.info,
                         "branch '%s' is not a value of %s"
                         % (v.name, self.tag_member.type.describe()))
-                if (not isinstance(v.type, QAPISchemaObjectType)
-                        or v.type.variants):
+                if not isinstance(v.type, QAPISchemaObjectType):
                     raise QAPISemError(
                         self.info,
                         "%s cannot use %s"
diff --git a/tests/qapi-schema/union-invalid-union-subfield.err b/tests/qapi-schema/union-invalid-union-subfield.err
new file mode 100644
index 0000000000..d3a2e31aff
--- /dev/null
+++ b/tests/qapi-schema/union-invalid-union-subfield.err
@@ -0,0 +1,2 @@
+union-invalid-union-subfield.json: In union 'TestUnion':
+union-invalid-union-subfield.json:22: member 'teeth' of type 'TestTypeFish' collides with base member 'teeth'
diff --git a/tests/qapi-schema/union-invalid-union-subfield.json b/tests/qapi-schema/union-invalid-union-subfield.json
new file mode 100644
index 0000000000..235f76d7da
--- /dev/null
+++ b/tests/qapi-schema/union-invalid-union-subfield.json
@@ -0,0 +1,27 @@
+{ 'enum': 'TestEnum',
+  'data': [ 'animals', 'plants' ] }
+
+{ 'enum': 'TestAnimals',
+  'data': [ 'fish', 'birds'] }
+
+{ 'struct': 'TestTypeFish',
+  'data': { 'scales': 'int', 'teeth': 'int' } }
+
+{ 'struct': 'TestTypeBirds',
+  'data': { 'feathers': 'int' } }
+
+{ 'union': 'TestTypeAnimals',
+  'base': { 'atype': 'TestAnimals' },
+  'discriminator': 'atype',
+  'data': { 'fish': 'TestTypeFish',
+            'birds': 'TestTypeBirds' } }
+
+{ 'struct': 'TestTypePlants',
+  'data': { 'integer': 'int' } }
+
+{ 'union': 'TestUnion',
+  'base': { 'type': 'TestEnum',
+	    'teeth': 'int' },
+  'discriminator': 'type',
+  'data': { 'animals': 'TestTypeAnimals',
+            'plants': 'TestTypePlants' } }
diff --git a/tests/qapi-schema/union-invalid-union-subfield.out b/tests/qapi-schema/union-invalid-union-subfield.out
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/qapi-schema/union-invalid-union-subtype.err b/tests/qapi-schema/union-invalid-union-subtype.err
new file mode 100644
index 0000000000..7b8679c08f
--- /dev/null
+++ b/tests/qapi-schema/union-invalid-union-subtype.err
@@ -0,0 +1,2 @@
+union-invalid-union-subtype.json: In union 'TestUnion':
+union-invalid-union-subtype.json:22: base member 'type' collides with base member 'type'
diff --git a/tests/qapi-schema/union-invalid-union-subtype.json b/tests/qapi-schema/union-invalid-union-subtype.json
new file mode 100644
index 0000000000..59ca4b0385
--- /dev/null
+++ b/tests/qapi-schema/union-invalid-union-subtype.json
@@ -0,0 +1,26 @@
+{ 'enum': 'TestEnum',
+  'data': [ 'value-a', 'value-b' ] }
+
+{ 'enum': 'TestEnumA',
+  'data': [ 'value-a1', 'value-a2' ] }
+
+{ 'struct': 'TestTypeA1',
+  'data': { 'integer': 'int' } }
+
+{ 'struct': 'TestTypeA2',
+  'data': { 'integer': 'int' } }
+
+{ 'union': 'TestTypeA',
+  'base': { 'type': 'TestEnumA' },
+  'discriminator': 'type',
+  'data': { 'value-a1': 'TestTypeA1',
+            'value-a2': 'TestTypeA2' } }
+
+{ 'struct': 'TestTypeB',
+  'data': { 'integer': 'int' } }
+
+{ 'union': 'TestUnion',
+  'base': { 'type': 'TestEnum' },
+  'discriminator': 'type',
+  'data': { 'value-a': 'TestTypeA',
+            'value-b': 'TestTypeB' } }
diff --git a/tests/qapi-schema/union-invalid-union-subtype.out b/tests/qapi-schema/union-invalid-union-subtype.out
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/qapi-schema/union-union-branch.err b/tests/qapi-schema/union-union-branch.err
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/qapi-schema/union-union-branch.json b/tests/qapi-schema/union-union-branch.json
new file mode 100644
index 0000000000..d3d7ce57c6
--- /dev/null
+++ b/tests/qapi-schema/union-union-branch.json
@@ -0,0 +1,26 @@
+{ 'enum': 'TestEnum',
+  'data': [ 'value-a', 'value-b' ] }
+
+{ 'enum': 'TestEnumA',
+  'data': [ 'value-a1', 'value-a2' ] }
+
+{ 'struct': 'TestTypeA1',
+  'data': { 'integer': 'int' } }
+
+{ 'struct': 'TestTypeA2',
+  'data': { 'integer': 'int' } }
+
+{ 'union': 'TestTypeA',
+  'base': { 'type-a': 'TestEnumA' },
+  'discriminator': 'type-a',
+  'data': { 'value-a1': 'TestTypeA1',
+            'value-a2': 'TestTypeA2' } }
+
+{ 'struct': 'TestTypeB',
+  'data': { 'integer': 'int' } }
+
+{ 'union': 'TestUnion',
+  'base': { 'type': 'TestEnum' },
+  'discriminator': 'type',
+  'data': { 'value-a': 'TestTypeA',
+            'value-b': 'TestTypeB' } }
diff --git a/tests/qapi-schema/union-union-branch.out b/tests/qapi-schema/union-union-branch.out
new file mode 100644
index 0000000000..d0c37495c2
--- /dev/null
+++ b/tests/qapi-schema/union-union-branch.out
@@ -0,0 +1,38 @@
+module ./builtin
+object q_empty
+enum QType
+    prefix QTYPE
+    member none
+    member qnull
+    member qnum
+    member qstring
+    member qdict
+    member qlist
+    member qbool
+module union-union-branch.json
+enum TestEnum
+    member value-a
+    member value-b
+enum TestEnumA
+    member value-a1
+    member value-a2
+object TestTypeA1
+    member integer: int optional=False
+object TestTypeA2
+    member integer: int optional=False
+object q_obj_TestTypeA-base
+    member type-a: TestEnumA optional=False
+object TestTypeA
+    base q_obj_TestTypeA-base
+    tag type-a
+    case value-a1: TestTypeA1
+    case value-a2: TestTypeA2
+object TestTypeB
+    member integer: int optional=False
+object q_obj_TestUnion-base
+    member type: TestEnum optional=False
+object TestUnion
+    base q_obj_TestUnion-base
+    tag type
+    case value-a: TestTypeA
+    case value-b: TestTypeB
-- 
2.39.1