qapi: Use predicate callback to determine visit filtering

Previously, qapi-types and qapi-visit filtered out implicit
objects during visit_object_type() by using 'info' (works since
implicit objects do not [yet] have associated info); meanwhile
qapi-introspect filtered out all schema types on the first pass
by returning a python type from visit_begin(), which was then
used at a distance in QAPISchema.visit() to do the filtering.

Rather than keeping these ad hoc approaches, add a new visitor
callback visit_needed() which returns False to skip a given
entity, and which defaults to True unless overridden.  Use the
new mechanism to simplify all three filtering visitors.

No change to the generated code.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1444710158-8723-2-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi-introspect.py

@@ -54,7 +54,6 @@ def visit_begin(self, schema):
         self._jsons = []
         self._used_types = []
         self._name_map = {}
-        return QAPISchemaType   # don't visit types for now
 
     def visit_end(self):
         # visit the types that are actually used
@@ -82,6 +81,10 @@ def visit_end(self):
         self._used_types = None
         self._name_map = None
 
+    def visit_needed(self, entity):
+        # Ignore types on first pass; visit_end() will pick up used types
+        return not isinstance(entity, QAPISchemaType)
+
     def _name(self, name):
         if self._unmask:
             return name

scripts/qapi-types.py

@@ -233,6 +233,10 @@ def visit_end(self):
         self.decl = self._btin + self.decl
         self._btin = None
 
+    def visit_needed(self, entity):
+        # Visit everything except implicit objects
+        return not isinstance(entity, QAPISchemaObjectType) or entity.info
+
     def _gen_type_cleanup(self, name):
         self.decl += gen_type_cleanup_decl(name)
         self.defn += gen_type_cleanup(name)
@@ -254,14 +258,13 @@ def visit_array_type(self, name, info, element_type):
             self._gen_type_cleanup(name)
 
     def visit_object_type(self, name, info, base, members, variants):
-        if info:
-            self._fwdecl += gen_fwd_object_or_array(name)
-            if variants:
-                assert not members      # not implemented
-                self.decl += gen_union(name, base, variants)
-            else:
-                self.decl += gen_struct(name, base, members)
-            self._gen_type_cleanup(name)
+        self._fwdecl += gen_fwd_object_or_array(name)
+        if variants:
+            assert not members      # not implemented
+            self.decl += gen_union(name, base, variants)
+        else:
+            self.decl += gen_struct(name, base, members)
+        self._gen_type_cleanup(name)
 
     def visit_alternate_type(self, name, info, variants):
         self._fwdecl += gen_fwd_object_or_array(name)

scripts/qapi-visit.py

@@ -335,6 +335,10 @@ def visit_end(self):
         self.decl = self._btin + self.decl
         self._btin = None
 
+    def visit_needed(self, entity):
+        # Visit everything except implicit objects
+        return not isinstance(entity, QAPISchemaObjectType) or entity.info
+
     def visit_enum_type(self, name, info, values, prefix):
         self.decl += gen_visit_decl(name, scalar=True)
         self.defn += gen_visit_enum(name)
@@ -351,13 +355,12 @@ def visit_array_type(self, name, info, element_type):
             self.defn += defn
 
     def visit_object_type(self, name, info, base, members, variants):
-        if info:
-            self.decl += gen_visit_decl(name)
-            if variants:
-                assert not members      # not implemented
-                self.defn += gen_visit_union(name, base, variants)
-            else:
-                self.defn += gen_visit_struct(name, base, members)
+        self.decl += gen_visit_decl(name)
+        if variants:
+            assert not members      # not implemented
+            self.defn += gen_visit_union(name, base, variants)
+        else:
+            self.defn += gen_visit_struct(name, base, members)
 
     def visit_alternate_type(self, name, info, variants):
         self.decl += gen_visit_decl(name)

scripts/qapi.py

@@ -811,6 +811,10 @@ def visit_begin(self, schema):
     def visit_end(self):
         pass
 
+    def visit_needed(self, entity):
+        # Default to visiting everything
+        return True
+
     def visit_builtin_type(self, name, info, json_type):
         pass
 
@@ -1304,10 +1308,10 @@ def check(self):
             ent.check(self)
 
     def visit(self, visitor):
-        ignore = visitor.visit_begin(self)
-        for name in sorted(self._entity_dict.keys()):
-            if not ignore or not isinstance(self._entity_dict[name], ignore):
-                self._entity_dict[name].visit(visitor)
+        visitor.visit_begin(self)
+        for (name, entity) in sorted(self._entity_dict.items()):
+            if visitor.visit_needed(entity):
+                entity.visit(visitor)
         visitor.visit_end()