[Qemu-devel] [PATCH v5 16/46] qapi: Detect base class loops

[Eric Blake <eblake@redhat.com>]

It should be fairly obvious that qapi base classes need to
form an acyclic graph, since QMP cannot specify the same
key more than once, while base classes are included as flat
members alongside other members added by the child.  But prior
to Markus' introspection commits (such as commit 75ebcd7f),
the test in isolation would cause python to exit with a
complaint about unbounded nesting; and after his patches (in
particular ac88219a), it triggers an assertion failure. This
patch includes both the test and the fix, since the .err file
output for an assertion failure is too hard to rebase when
other patches cause line number changes.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
"Commit ac88219a" above assumes the commit ids from the pending
pull-qapi-2015-09-21 tag will be preserved
---
 scripts/qapi.py                   | 6 +++++-
 tests/Makefile                    | 1 +
 tests/qapi-schema/base-cycle.err  | 1 +
 tests/qapi-schema/base-cycle.exit | 1 +
 tests/qapi-schema/base-cycle.json | 3 +++
 tests/qapi-schema/base-cycle.out  | 0
 6 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 tests/qapi-schema/base-cycle.err
 create mode 100644 tests/qapi-schema/base-cycle.exit
 create mode 100644 tests/qapi-schema/base-cycle.json
 create mode 100644 tests/qapi-schema/base-cycle.out

diff --git a/scripts/qapi.py b/scripts/qapi.py
index f5f1c60..c6a047b 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -920,7 +920,11 @@ class QAPISchemaObjectType(QAPISchemaType):
         self.members = None

     def check(self, schema):
-        assert self.members is not False        # not running in cycles
+        if self.members is False:               # check for cycles
+            assert self._base_name
+            raise QAPIExprError(self._info,
+                                "Object %s cyclically depends on %s"
+                                % (self.name, self._base_name))
         if self.members:
             return
         self.members = False                    # mark as being checked
diff --git a/tests/Makefile b/tests/Makefile
index df16c9c..20b84b5 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -248,6 +248,7 @@ qapi-schema += bad-ident.json
 qapi-schema += bad-type-bool.json
 qapi-schema += bad-type-dict.json
 qapi-schema += bad-type-int.json
+qapi-schema += base-cycle.json
 qapi-schema += command-int.json
 qapi-schema += comments.json
 qapi-schema += double-data.json
diff --git a/tests/qapi-schema/base-cycle.err b/tests/qapi-schema/base-cycle.err
new file mode 100644
index 0000000..e0221b5
--- /dev/null
+++ b/tests/qapi-schema/base-cycle.err
@@ -0,0 +1 @@
+tests/qapi-schema/base-cycle.json:2: Object Base1 cyclically depends on Base2
diff --git a/tests/qapi-schema/base-cycle.exit b/tests/qapi-schema/base-cycle.exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/qapi-schema/base-cycle.exit
@@ -0,0 +1 @@
+1
diff --git a/tests/qapi-schema/base-cycle.json b/tests/qapi-schema/base-cycle.json
new file mode 100644
index 0000000..2866772
--- /dev/null
+++ b/tests/qapi-schema/base-cycle.json
@@ -0,0 +1,3 @@
+# we reject a loop in base classes
+{ 'struct': 'Base1', 'base': 'Base2', 'data': {} }
+{ 'struct': 'Base2', 'base': 'Base1', 'data': {} }
diff --git a/tests/qapi-schema/base-cycle.out b/tests/qapi-schema/base-cycle.out
new file mode 100644
index 0000000..e69de29
-- 
2.4.3