qapi: Fix code generation for empty modules

When a sub-module doesn't contain any definitions, we don't generate
code for it, but we do generate the #include.

We generate code only for modules that get visited.
QAPISchema.visit() visits only modules that have definitions.  It can
visit modules multiple times.

Clean this up as follows.  Collect entities in their QAPISchemaModule.
Have QAPISchema.visit() call QAPISchemaModule.visit() for each module.
Have QAPISchemaModule.visit() call .visit_module() for itself, and
QAPISchemaEntity.visit() for each of its entities.  This way, we visit
each module exactly once.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20191120182551.23795-6-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

scripts/qapi/schema.py

@@ -68,6 +68,7 @@ class QAPISchemaEntity(object):
     def _set_module(self, schema, info):
         assert self._checked
         self._module = schema.module_by_fname(info and info.fname)
+        self._module.add_entity(self)
 
     def set_module(self, schema):
         self._set_module(schema, self.info)
@@ -77,11 +78,6 @@ class QAPISchemaEntity(object):
         assert self._checked
         return self._ifcond
 
-    @property
-    def module(self):
-        assert self._module or not self.info
-        return self._module
-
     def is_implicit(self):
         return not self.info
 
@@ -142,6 +138,16 @@ class QAPISchemaVisitor(object):
 class QAPISchemaModule(object):
     def __init__(self, name):
         self.name = name
+        self._entity_list = []
+
+    def add_entity(self, ent):
+        self._entity_list.append(ent)
+
+    def visit(self, visitor):
+        visitor.visit_module(self.name)
+        for entity in self._entity_list:
+            if visitor.visit_needed(entity):
+                entity.visit(visitor)
 
 
 class QAPISchemaInclude(QAPISchemaEntity):
@@ -1093,10 +1099,6 @@ class QAPISchema(object):
     def visit(self, visitor):
         visitor.visit_begin(self)
         module = None
-        for entity in self._entity_list:
-            if visitor.visit_needed(entity):
-                if entity.module != module:
-                    module = entity.module
-                    visitor.visit_module(module.name)
-                entity.visit(visitor)
+        for mod in self._module_dict.values():
+            mod.visit(visitor)
         visitor.visit_end()

tests/qapi-schema/empty.out

@@ -9,3 +9,4 @@ enum QType
     member qdict
     member qlist
     member qbool
+module empty.json

tests/qapi-schema/include-repetition.out

@@ -11,15 +11,13 @@ enum QType
     member qbool
 module include-repetition.json
 include comments.json
+include include-repetition-sub.json
+include comments.json
 module comments.json
 enum Status
     member good
     member bad
     member ugly
-module include-repetition.json
-include include-repetition-sub.json
 module include-repetition-sub.json
 include comments.json
 include comments.json
-module include-repetition.json
-include comments.json

tests/qapi-schema/qapi-schema-test.out

@@ -153,9 +153,6 @@ object q_obj_sizeList-wrapper
     member data: sizeList optional=False
 object q_obj_anyList-wrapper
     member data: anyList optional=False
-module sub-sub-module.json
-array StatusList Status
-module qapi-schema-test.json
 object q_obj_StatusList-wrapper
     member data: StatusList optional=False
 enum UserDefListUnionKind
@@ -193,17 +190,6 @@ object UserDefListUnion
     case any: q_obj_anyList-wrapper
     case user: q_obj_StatusList-wrapper
 include include/sub-module.json
-module include/sub-module.json
-include sub-sub-module.json
-module sub-sub-module.json
-enum Status
-    member good
-    member bad
-    member ugly
-module include/sub-module.json
-object SecondArrayRef
-    member s: StatusList optional=False
-module qapi-schema-test.json
 command user_def_cmd None -> None
     gen=True success_response=True boxed=False oob=False preconfig=False
 object q_obj_user_def_cmd1-arg
@@ -435,3 +421,13 @@ command test-command-cond-features3 None -> None
     gen=True success_response=True boxed=False oob=False preconfig=False
     feature feature1
         if ['defined(TEST_IF_COND_1)', 'defined(TEST_IF_COND_2)']
+module include/sub-module.json
+include sub-sub-module.json
+object SecondArrayRef
+    member s: StatusList optional=False
+module sub-sub-module.json
+array StatusList Status
+enum Status
+    member good
+    member bad
+    member ugly