[Qemu-devel] [PATCH v8 13/18] qapi: Track owner of each object member

[Eric Blake <eblake@redhat.com>]

Future commits will migrate semantic checking away from parsing
and over to the various QAPISchema*.check() methods.  But to
report an error message about an incorrect semantic use of a
member of an object type, it helps to know which type, command,
or event owns the member.  In particular, when a member is
inherited from a base type, it is desirable to associate the
member name with the base type (and not the type calling
member.check()).

Rather than packing additional information into the seen array
passed to each member.check() (as in seen[m.name] = {'member':m,
'owner':type}), it is easier to have each member track the name
of the owner type in the first place (keeping things simpler
with the existing seen[m.name] = m).  The new member.owner field
is set via a new set_owner() function, called when registering
the members and variants arrays with an object or variant type.
Track only a name, and not the actual type object, to avoid
creating a circular python reference chain.

The source information is intended for human consumption in
error messages, and a new describe() method is added to access
the resulting information.  For example, given the qapi:
  { 'command': 'foo', 'data': { 'string': 'str' } }
an implementation of visit_command() that calls
  arg_type.members[0].describe()
will see "'string' (argument of foo)".

To make the human-readable name of implicit types work without
duplicating efforts, the describe() method has to reverse the
name of implicit types.

No change to generated code.

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

---
v8: don't munge implicit type names [except for event data], and
instead make describe() create nicer messages. Add set_owner(), and
use field 'role' instead of method _describe()
v7: total rewrite: rework implicit object names, assign owner
when initializing owner type rather than when creating member
python object
v6: rebase on new lazy array creation and simple union 'type'
motion; tweak commit message
---
 scripts/qapi.py                        | 48 +++++++++++++++++++++++++++++++---
 tests/qapi-schema/qapi-schema-test.out |  8 +++---
 2 files changed, 49 insertions(+), 7 deletions(-)

diff --git a/scripts/qapi.py b/scripts/qapi.py
index c9ce9ee..8b29e11 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -952,8 +952,10 @@ class QAPISchemaObjectType(QAPISchemaType):
         assert base is None or isinstance(base, str)
         for m in local_members:
             assert isinstance(m, QAPISchemaObjectTypeMember)
-        assert (variants is None or
-                isinstance(variants, QAPISchemaObjectTypeVariants))
+            m.set_owner(name)
+        if variants is not None:
+            assert isinstance(variants, QAPISchemaObjectTypeVariants)
+            variants.set_owner(name)
         self._base_name = base
         self.base = None
         self.local_members = local_members
@@ -1014,8 +1016,14 @@ class QAPISchemaObjectTypeMember(object):
         self._type_name = typ
         self.type = None
         self.optional = optional
+        self.owner = None
+
+    def set_owner(self, name):
+        assert not self.owner
+        self.owner = name

     def check(self, schema, all_members, seen):
+        assert self.owner
         assert self.name not in seen
         self.type = schema.lookup_type(self._type_name)
         assert self.type
@@ -1025,6 +1033,25 @@ class QAPISchemaObjectTypeMember(object):
     def c_name(self):
         return c_name(self.name)

+    def describe(self):
+        owner = self.owner
+        # See QAPISchema._make_implicit_object_type() - reverse the
+        # mapping there to create a nice human-readable description
+        if owner.startswith(':obj-'):
+            owner = owner[5:]
+            if owner.endswith('-arg'):
+                source = '(argument of %s)' % owner[:4]
+            elif owner.endswith('-data'):
+                source = '(data of %s)' % owner[:5]
+            else:
+                assert owner.endswith('-wrapper')
+                source = '(branch of %s)' % owner[:8]
+        else:
+            source = '(%s of %s)' % (self.role, owner)
+        return "'%s' %s" % (self.name, source)
+
+    role = 'member'
+

 # TODO Drop this class once we no longer have the 'type'/'kind' mismatch
 class QAPISchemaObjectTypeUnionTag(QAPISchemaObjectTypeMember):
@@ -1034,6 +1061,11 @@ class QAPISchemaObjectTypeUnionTag(QAPISchemaObjectTypeMember):
         assert self.type.is_implicit()
         return 'kind'

+    def describe(self):
+        # Must override superclass describe() because self.name is 'type'
+        assert self.owner[0] != ':'
+        return "'kind' (implicit tag of %s)" % self.owner
+

 class QAPISchemaObjectTypeVariants(object):
     def __init__(self, tag_name, tag_member, variants):
@@ -1050,6 +1082,12 @@ class QAPISchemaObjectTypeVariants(object):
         self.tag_member = tag_member
         self.variants = variants

+    def set_owner(self, name):
+        if self.tag_member:
+            self.tag_member.set_owner(name)
+        for v in self.variants:
+            v.set_owner(name)
+
     def check(self, schema, members, seen):
         if self.tag_name:
             self.tag_member = seen[self.tag_name]
@@ -1079,12 +1117,15 @@ class QAPISchemaObjectTypeVariant(QAPISchemaObjectTypeMember):
             return self.type.members[0].type
         return None

+    role = 'branch'
+

 class QAPISchemaAlternateType(QAPISchemaType):
     def __init__(self, name, info, variants):
         QAPISchemaType.__init__(self, name, info)
         assert isinstance(variants, QAPISchemaObjectTypeVariants)
         assert not variants.tag_name
+        variants.set_owner(name)
         self.variants = variants

     def check(self, schema):
@@ -1216,6 +1257,7 @@ class QAPISchema(object):
     def _make_implicit_object_type(self, name, info, role, members):
         if not members:
             return None
+        # See also QAPISchemaObjectTypeMember.describe()
         name = ':obj-%s-%s' % (name, role)
         if not self.lookup_entity(name, QAPISchemaObjectType):
             self._def_entity(QAPISchemaObjectType(name, info, None,
@@ -1318,7 +1360,7 @@ class QAPISchema(object):
         data = expr.get('data')
         if isinstance(data, OrderedDict):
             data = self._make_implicit_object_type(
-                name, info, 'arg', self._make_members(data, info))
+                name, info, 'data', self._make_members(data, info))
         self._def_entity(QAPISchemaEvent(name, info, data))

     def _def_exprs(self):
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index a6c80e0..d837475 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -1,9 +1,9 @@
 object :empty
-object :obj-EVENT_C-arg
+object :obj-EVENT_C-data
     member a: int optional=True
     member b: UserDefOne optional=True
     member c: str optional=False
-object :obj-EVENT_D-arg
+object :obj-EVENT_D-data
     member a: EventStructOne optional=False
     member b: str optional=False
     member c: str optional=True
@@ -79,8 +79,8 @@ alternate AltStrNum
 enum AltStrNumKind ['s', 'n']
 event EVENT_A None
 event EVENT_B None
-event EVENT_C :obj-EVENT_C-arg
-event EVENT_D :obj-EVENT_D-arg
+event EVENT_C :obj-EVENT_C-data
+event EVENT_D :obj-EVENT_D-data
 enum EnumOne ['value1', 'value2', 'value3']
 object EventStructOne
     member struct1: UserDefOne optional=False
-- 
2.4.3