[Qemu-devel] [PATCH RFC 4/5] qapi: Simplify visits of optional fields

[Eric Blake <eblake@redhat.com>]

None of the visitor callbacks would set an error when testing
if an optional field was present; make this part of the interface
contract by eliminating the errp argument.  Then, for less code,
reflect the determined boolean value back to the caller instead
of making the caller read the boolean after the fact.

The resulting generated code has a nice diff:

|-    visit_optional(v, &has_fdset_id, "fdset-id", &err);
|-    if (err) {
|-        goto out;
|-    }
|-    if (has_fdset_id) {
|+    if (visit_optional(v, &has_fdset_id, "fdset-id")) {
|         visit_type_int(v, &fdset_id, "fdset-id", &err);
|         if (err) {
|             goto out;
|         }
|     }

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 include/qapi/visitor-impl.h | 3 +--
 include/qapi/visitor.h      | 5 ++---
 qapi/opts-visitor.c         | 2 +-
 qapi/qapi-visit-core.c      | 6 +++---
 qapi/qmp-input-visitor.c    | 3 +--
 qapi/string-input-visitor.c | 3 +--
 scripts/qapi.py             | 9 ++-------
 7 files changed, 11 insertions(+), 20 deletions(-)

diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 7e8f728..6feb654 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -69,8 +69,7 @@ struct Visitor
                      Error **errp);

     /* May be NULL; most useful for input visitors. */
-    void (*optional)(Visitor *v, bool *present, const char *name,
-                     Error **errp);
+    void (*optional)(Visitor *v, bool *present, const char *name);

     /* Only required to visit uint64 differently than (*type_int)().  */
     void (*type_uint64)(Visitor *v, uint64_t *obj, const char *name,
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index cd1431a..ef1105b 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -118,10 +118,9 @@ void visit_end_list(Visitor *v, Error **errp);
  * Check if an optional member @name of a QDict needs visiting.
  * For input visitors, set *@present according to whether the
  * corresponding visit_type_*() needs calling; for other visitors,
- * leave *@present unchanged.
+ * leave *@present unchanged.  Return *@present for convenience.
  */
-void visit_optional(Visitor *v, bool *present, const char *name,
-                    Error **errp);
+bool visit_optional(Visitor *v, bool *present, const char *name);

 /**
  * Determine the qtype of the item @name in the current QDict visit.
diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
index 7ae33b3..b2cd5b3 100644
--- a/qapi/opts-visitor.c
+++ b/qapi/opts-visitor.c
@@ -488,7 +488,7 @@ opts_type_size(Visitor *v, uint64_t *obj, const char *name, Error **errp)


 static void
-opts_optional(Visitor *v, bool *present, const char *name, Error **errp)
+opts_optional(Visitor *v, bool *present, const char *name)
 {
     OptsVisitor *ov = DO_UPCAST(OptsVisitor, visitor, v);

diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 9cd17f8..d885347 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -62,12 +62,12 @@ void visit_end_list(Visitor *v, Error **errp)
     v->end_list(v, errp);
 }

-void visit_optional(Visitor *v, bool *present, const char *name,
-                    Error **errp)
+bool visit_optional(Visitor *v, bool *present, const char *name)
 {
     if (v->optional) {
-        v->optional(v, present, name, errp);
+        v->optional(v, present, name);
     }
+    return *present;
 }

 void visit_get_next_type(Visitor *v, qtype_code *type, bool promote_int,
diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 5310db5..f714dfc 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -300,8 +300,7 @@ static void qmp_input_type_any(Visitor *v, QObject **obj, const char *name,
     *obj = qobj;
 }

-static void qmp_input_optional(Visitor *v, bool *present, const char *name,
-                               Error **errp)
+static void qmp_input_optional(Visitor *v, bool *present, const char *name)
 {
     QmpInputVisitor *qiv = to_qiv(v);
     QObject *qobj = qmp_input_get_object(qiv, name, true);
diff --git a/qapi/string-input-visitor.c b/qapi/string-input-visitor.c
index bbd6a54..dee780a 100644
--- a/qapi/string-input-visitor.c
+++ b/qapi/string-input-visitor.c
@@ -299,8 +299,7 @@ static void parse_type_number(Visitor *v, double *obj, const char *name,
     *obj = val;
 }

-static void parse_optional(Visitor *v, bool *present, const char *name,
-                           Error **errp)
+static void parse_optional(Visitor *v, bool *present, const char *name)
 {
     StringInputVisitor *siv = DO_UPCAST(StringInputVisitor, visitor, v);

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 063d299..9af310f 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -1475,15 +1475,10 @@ def gen_visit_fields(members, prefix, errarg):
     for memb in members:
         if memb.optional:
             ret += mcgen('''
-visit_optional(v, &%(prefix)shas_%(c_name)s, "%(name)s", %(errp)s);
+if (visit_optional(v, &%(prefix)shas_%(c_name)s, "%(name)s")) {
 ''',
                          prefix=prefix, c_name=c_name(memb.name),
-                         name=memb.name, errp=errparg)
-            ret += gen_err_check(errarg)
-            ret += mcgen('''
-if (%(prefix)shas_%(c_name)s) {
-''',
-                         prefix=prefix, c_name=c_name(memb.name))
+                         name=memb.name)
             push_indent()

         ret += mcgen('''
-- 
2.4.3