qapi: Change visit_start_implicit_struct to visit_start_alternate

After recent changes, the only remaining use of
visit_start_implicit_struct() is for allocating the space needed
when visiting an alternate.  Since the term 'implicit struct' is
hard to explain, rename the function to its current usage.  While
at it, we can merge the functionality of visit_get_next_type()
into the same function, making it more like visit_start_struct().

Generated code is now slightly smaller:

| {
|     Error *err = NULL;
|
|-    visit_start_implicit_struct(v, (void**) obj, sizeof(BlockdevRef), &err);
|+    visit_start_alternate(v, name, (GenericAlternate **)obj, sizeof(**obj),
|+                          true, &err);
|     if (err) {
|         goto out;
|     }
|-    visit_get_next_type(v, name, &(*obj)->type, true, &err);
|-    if (err) {
|-        goto out_obj;
|-    }
|     switch ((*obj)->type) {
|     case QTYPE_QDICT:
|         visit_start_struct(v, name, NULL, 0, &err);
...
|     }
|-out_obj:
|-    visit_end_implicit_struct(v);
|+    visit_end_alternate(v);
| out:
|     error_propagate(errp, err);
| }

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1455778109-6278-16-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 3 insertions, 7 deletions

diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 3a3918f952..2308268a62 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -182,14 +182,11 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, Error
 {
     Error *err = NULL;
 
-    visit_start_implicit_struct(v, (void**) obj, sizeof(%(c_name)s), &err);
+    visit_start_alternate(v, name, (GenericAlternate **)obj, sizeof(**obj),
+                          %(promote_int)s, &err);
     if (err) {
         goto out;
     }
-    visit_get_next_type(v, name, &(*obj)->type, %(promote_int)s, &err);
-    if (err) {
-        goto out_obj;
-    }
     switch ((*obj)->type) {
 ''',
                  c_name=c_name(name), promote_int=promote_int)
@@ -227,8 +224,7 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, Error
         error_setg(&err, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
                    "%(name)s");
     }
-out_obj:
-    visit_end_implicit_struct(v);
+    visit_end_alternate(v);
 out:
     error_propagate(errp, err);
 }