qapi: Replace start_optional()/end_optional() by optional()

Semantics of end_optional() differ subtly from the other end_FOO()
callbacks: when start_FOO() succeeds, the matching end_FOO() gets
called regardless of what happens in between.  end_optional() gets
called only when everything in between succeeds as well.  Entirely
undocumented, like all of the visitor API.

The only user of Visitor Callback end_optional() never did anything,
and was removed in commit 9f9ab46.

I'm about to clean up error handling in the generated visitor code,
and end_optional() is in my way.  No users mean no test cases, and
making non-trivial cleanup transformations without test cases doesn't
strike me as a good idea.

Drop end_optional(), and rename start_optional() to optional().  We
can always go back to a pair of callbacks when we have an actual need.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

include/qapi/visitor-impl.h

@@ -42,9 +42,8 @@ struct Visitor
                         Error **errp);
 
     /* May be NULL */
-    void (*start_optional)(Visitor *v, bool *present, const char *name,
-                           Error **errp);
-    void (*end_optional)(Visitor *v, Error **errp);
+    void (*optional)(Visitor *v, bool *present, const char *name,
+                     Error **errp);
 
     void (*type_uint8)(Visitor *v, uint8_t *obj, const char *name, Error **errp);
     void (*type_uint16)(Visitor *v, uint16_t *obj, const char *name, Error **errp);

include/qapi/visitor.h

@@ -39,9 +39,8 @@ void visit_end_implicit_struct(Visitor *v, Error **errp);
 void visit_start_list(Visitor *v, const char *name, Error **errp);
 GenericList *visit_next_list(Visitor *v, GenericList **list, Error **errp);
 void visit_end_list(Visitor *v, Error **errp);
-void visit_start_optional(Visitor *v, bool *present, const char *name,
-                          Error **errp);
-void visit_end_optional(Visitor *v, Error **errp);
+void visit_optional(Visitor *v, bool *present, const char *name,
+                    Error **errp);
 void visit_get_next_type(Visitor *v, int *obj, const int *qtypes,
                          const char *name, Error **errp);
 void visit_type_enum(Visitor *v, int *obj, const char *strings[],

qapi/opts-visitor.c

@@ -484,8 +484,7 @@ opts_type_size(Visitor *v, uint64_t *obj, const char *name, Error **errp)
 
 
 static void
-opts_start_optional(Visitor *v, bool *present, const char *name,
-                       Error **errp)
+opts_optional(Visitor *v, bool *present, const char *name, Error **errp)
 {
     OptsVisitor *ov = DO_UPCAST(OptsVisitor, visitor, v);
 
@@ -528,7 +527,7 @@ opts_visitor_new(const QemuOpts *opts)
     /* type_number() is not filled in, but this is not the first visitor to
      * skip some mandatory methods... */
 
-    ov->visitor.start_optional = &opts_start_optional;
+    ov->visitor.optional = &opts_optional;
 
     ov->opts_root = opts;
 

qapi/qapi-visit-core.c

@@ -69,18 +69,11 @@ void visit_end_list(Visitor *v, Error **errp)
     v->end_list(v, errp);
 }
 
-void visit_start_optional(Visitor *v, bool *present, const char *name,
-                          Error **errp)
+void visit_optional(Visitor *v, bool *present, const char *name,
+                    Error **errp)
 {
-    if (!error_is_set(errp) && v->start_optional) {
-        v->start_optional(v, present, name, errp);
-    }
-}
-
-void visit_end_optional(Visitor *v, Error **errp)
-{
-    if (!error_is_set(errp) && v->end_optional) {
-        v->end_optional(v, errp);
+    if (!error_is_set(errp) && v->optional) {
+        v->optional(v, present, name, errp);
     }
 }
 

qapi/qmp-input-visitor.c

@@ -286,8 +286,8 @@ static void qmp_input_type_number(Visitor *v, double *obj, const char *name,
     }
 }
 
-static void qmp_input_start_optional(Visitor *v, bool *present,
-                                     const char *name, Error **errp)
+static void qmp_input_optional(Visitor *v, bool *present, const char *name,
+                               Error **errp)
 {
     QmpInputVisitor *qiv = to_qiv(v);
     QObject *qobj = qmp_input_get_object(qiv, name, true);
@@ -329,7 +329,7 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj)
     v->visitor.type_bool = qmp_input_type_bool;
     v->visitor.type_str = qmp_input_type_str;
     v->visitor.type_number = qmp_input_type_number;
-    v->visitor.start_optional = qmp_input_start_optional;
+    v->visitor.optional = qmp_input_optional;
     v->visitor.get_next_type = qmp_input_get_next_type;
 
     qmp_input_push(v, obj, NULL);

qapi/string-input-visitor.c

@@ -120,8 +120,8 @@ static void parse_type_number(Visitor *v, double *obj, const char *name,
     *obj = val;
 }
 
-static void parse_start_optional(Visitor *v, bool *present,
-                                 const char *name, Error **errp)
+static void parse_optional(Visitor *v, bool *present, const char *name,
+                           Error **errp)
 {
     StringInputVisitor *siv = DO_UPCAST(StringInputVisitor, visitor, v);
 
@@ -155,7 +155,7 @@ StringInputVisitor *string_input_visitor_new(const char *str)
     v->visitor.type_bool = parse_type_bool;
     v->visitor.type_str = parse_type_str;
     v->visitor.type_number = parse_type_number;
-    v->visitor.start_optional = parse_start_optional;
+    v->visitor.optional = parse_optional;
 
     v->string = str;
     return v;

scripts/qapi-commands.py

@@ -131,7 +131,7 @@ def gen_visitor_input_block(args, dealloc=False):
     for argname, argtype, optional, structured in parse_args(args):
         if optional:
             ret += mcgen('''
-visit_start_optional(v, &has_%(c_name)s, "%(name)s", %(errp)s);
+visit_optional(v, &has_%(c_name)s, "%(name)s", %(errp)s);
 if (has_%(c_name)s) {
 ''',
                          c_name=c_var(argname), name=argname, errp=errparg)
@@ -145,8 +145,7 @@ def gen_visitor_input_block(args, dealloc=False):
             pop_indent()
             ret += mcgen('''
 }
-visit_end_optional(v, %(errp)s);
-''', errp=errparg)
+''')
 
     if dealloc:
         ret += mcgen('''

scripts/qapi-visit.py

@@ -61,7 +61,7 @@ def generate_visit_struct_fields(name, field_prefix, fn_prefix, members, base =
     for argname, argentry, optional, structured in parse_args(members):
         if optional:
             ret += mcgen('''
-visit_start_optional(m, &(*obj)->%(c_prefix)shas_%(c_name)s, "%(name)s", &err);
+visit_optional(m, &(*obj)->%(c_prefix)shas_%(c_name)s, "%(name)s", &err);
 if ((*obj)->%(prefix)shas_%(c_name)s) {
 ''',
                          c_prefix=c_var(field_prefix), prefix=field_prefix,
@@ -82,7 +82,6 @@ def generate_visit_struct_fields(name, field_prefix, fn_prefix, members, base =
             pop_indent()
             ret += mcgen('''
 }
-visit_end_optional(m, &err);
 ''')
 
     pop_indent()