qapi: Detect base class loops

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 the
old check_member_clash() parser function was not prepared to
check for this, and entered an infinite recursion (at least
until Python gives up, complaining about nesting too deep).

Now that check_member_clash() has been recently removed,
attempts at self-inheritance trigger an assertion failure
introduced by commit ac88219a.  The obvious fix is to turn
the assertion into a conditional.

This patch includes both the tests (base-cycle-direct and
base-cycle-indirect) and the fix, since the .err file output
for the unfixed case is not useful (particularly when it was
warning about unbounded recursion, as that limit may be
platform-specific).

We don't need to worry about cycles in flat unions (neither
the base type nor the type of a variant can be a union) nor
in alternates (alternate branches cannot themselves be an
alternate).  But if we later allow a union type as a variant,
we will still be okay, as QAPISchemaObjectTypeVariants.check()
triggers the same QAPISchemaObjectType.check() that will
detect any loops.

Likewise, we need not worry about the case of diamond
inheritance where the same class is used for a flat union base
class and one of its variants; either both uses will introduce
a collision in trying to insert the same member name twice, or
the shared type is empty and changes nothing.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1449033659-25497-16-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 8edfd79c5220865fc76604e387ac2ef8ff595eda..7dec611d0981487018f673b68d16c792460454bb 100644 (file)
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -940,7 +940,9 @@ 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
+            raise QAPIExprError(self.info,
+                                "Object %s contains itself" % self.name)
         if self.members:
             return
         self.members = False                    # mark as being checked

diff --git a/tests/Makefile b/tests/Makefile
index 69cef7760d7c8f64a0abbc01da4a3c8c06103c7b..053c1ae481334f4feff08d490f0554a5c0c06123 100644 (file)
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -257,6 +257,8 @@ 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-direct.json
+qapi-schema += base-cycle-indirect.json
 qapi-schema += command-int.json
 qapi-schema += comments.json
 qapi-schema += double-data.json

diff --git a/tests/qapi-schema/base-cycle-direct.err b/tests/qapi-schema/base-cycle-direct.err
new file mode 100644 (file)
index 0000000..9c68f65
--- /dev/null
+++ b/tests/qapi-schema/base-cycle-direct.err
@@ -0,0 +1 @@
+tests/qapi-schema/base-cycle-direct.json:2: Object Loopy contains itself

diff --git a/tests/qapi-schema/base-cycle-direct.exit b/tests/qapi-schema/base-cycle-direct.exit
new file mode 100644 (file)
index 0000000..d00491f
--- /dev/null
+++ b/tests/qapi-schema/base-cycle-direct.exit
@@ -0,0 +1 @@
+1

diff --git a/tests/qapi-schema/base-cycle-direct.json b/tests/qapi-schema/base-cycle-direct.json
new file mode 100644 (file)
index 0000000..4fc66d0
--- /dev/null
+++ b/tests/qapi-schema/base-cycle-direct.json
@@ -0,0 +1,2 @@
+# we reject a loop in base classes
+{ 'struct': 'Loopy', 'base': 'Loopy', 'data': {} }

diff --git a/tests/qapi-schema/base-cycle-direct.out b/tests/qapi-schema/base-cycle-direct.out
new file mode 100644 (file)
index 0000000..e69de29

diff --git a/tests/qapi-schema/base-cycle-indirect.err b/tests/qapi-schema/base-cycle-indirect.err
new file mode 100644 (file)
index 0000000..fc92fe4
--- /dev/null
+++ b/tests/qapi-schema/base-cycle-indirect.err
@@ -0,0 +1 @@
+tests/qapi-schema/base-cycle-indirect.json:2: Object Base1 contains itself

diff --git a/tests/qapi-schema/base-cycle-indirect.exit b/tests/qapi-schema/base-cycle-indirect.exit
new file mode 100644 (file)
index 0000000..d00491f
--- /dev/null
+++ b/tests/qapi-schema/base-cycle-indirect.exit
@@ -0,0 +1 @@
+1

diff --git a/tests/qapi-schema/base-cycle-indirect.json b/tests/qapi-schema/base-cycle-indirect.json
new file mode 100644 (file)
index 0000000..2866772
--- /dev/null
+++ b/tests/qapi-schema/base-cycle-indirect.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-indirect.out b/tests/qapi-schema/base-cycle-indirect.out
new file mode 100644 (file)
index 0000000..e69de29