[Qemu-devel] [PATCH v9 27/27] 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>

---
v9: no change
v8: no change
v7: rebase to no member.c_name()
v6: rebase onto earlier testsuite and gen_err_check() improvements
---
 include/qapi/visitor-impl.h |  5 ++---
 include/qapi/visitor.h      | 10 ++++++++--
 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             |  7 +------
 7 files changed, 17 insertions(+), 19 deletions(-)

diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 370935a..fd2e905 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -44,9 +44,8 @@ struct Visitor
     void (*type_any)(Visitor *v, QObject **obj, const char *name,
                      Error **errp);

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

     bool (*start_union)(Visitor *v, bool data_present, Error **errp);
     void (*end_union)(Visitor *v, bool data_present, Error **errp);
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index 67ddd83..e52ad39 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -36,8 +36,14 @@ 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_optional(Visitor *v, bool *present, const char *name,
-                    Error **errp);
+
+/**
+ * Check if an optional member @name of an object needs visiting.
+ * For input visitors, set *@present according to whether the
+ * corresponding visit_type_*() needs calling; for other visitors,
+ * leave *@present unchanged.  Return *@present for convenience.
+ */
+bool visit_optional(Visitor *v, bool *present, const char *name);

 /**
  * Determine the qtype of the item @name in the current object visit.
diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
index cd10392..ef5fb8b 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 cbf7780..2594147 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -73,12 +73,12 @@ void visit_end_union(Visitor *v, bool data_present, Error **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 60be2ff..ced0569 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -304,8 +304,7 @@ 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 9a1f0ac..e60b72c 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -1620,15 +1620,10 @@ def gen_visit_fields(members, prefix='', need_cast=False, skiperr=False):
     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(skiperr=skiperr)
-            ret += mcgen('''
-    if (%(prefix)shas_%(c_name)s) {
-''',
-                         prefix=prefix, c_name=c_name(memb.name))
             push_indent()

         # Ugly: sometimes we need to cast away const
-- 
2.4.3