qapi: Simplify gen_visit_fields() error handling

Since we have consolidated all generated code to use 'err' as
the name of the local variable for error detection, we can
simplify the decision on whether to skip error detection (useful
for deallocation paths) to be a boolean.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1443565276-4535-18-git-send-email-eblake@redhat.com>
[Change to gen_visit_fields() simplified]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi-commands.py

@@ -101,19 +101,17 @@ def gen_marshal_input_visit(arg_type, dealloc=False):
         return ret
 
     if dealloc:
-        errarg = None
         ret += mcgen('''
     qmp_input_visitor_cleanup(qiv);
     qdv = qapi_dealloc_visitor_new();
     v = qapi_dealloc_get_visitor(qdv);
 ''')
     else:
-        errarg = 'err'
         ret += mcgen('''
     v = qmp_input_get_visitor(qiv);
 ''')
 
-    ret += gen_visit_fields(arg_type.members, errarg=errarg)
+    ret += gen_visit_fields(arg_type.members, skiperr=dealloc)
 
     if dealloc:
         ret += mcgen('''

scripts/qapi.py

@@ -1537,23 +1537,23 @@ def gen_params(arg_type, extra):
     return ret
 
 
-def gen_err_check(err='err', label='out'):
-    if not err:
+def gen_err_check(label='out', skiperr=False):
+    if skiperr:
         return ''
     return mcgen('''
-    if (%(err)s) {
+    if (err) {
         goto %(label)s;
     }
 ''',
-                 err=err, label=label)
+                 label=label)
 
 
-def gen_visit_fields(members, prefix='', need_cast=False, errarg='err'):
+def gen_visit_fields(members, prefix='', need_cast=False, skiperr=False):
     ret = ''
-    if errarg:
-        errparg = '&' + errarg
-    else:
+    if skiperr:
         errparg = 'NULL'
+    else:
+        errparg = '&err'
 
     for memb in members:
         if memb.optional:
@@ -1562,7 +1562,7 @@ def gen_visit_fields(members, prefix='', need_cast=False, errarg='err'):
 ''',
                          prefix=prefix, c_name=c_name(memb.name),
                          name=memb.name, errp=errparg)
-            ret += gen_err_check(err=errarg)
+            ret += gen_err_check(skiperr=skiperr)
             ret += mcgen('''
     if (%(prefix)shas_%(c_name)s) {
 ''',
@@ -1581,7 +1581,7 @@ def gen_visit_fields(members, prefix='', need_cast=False, errarg='err'):
                      c_type=memb.type.c_name(), prefix=prefix, cast=cast,
                      c_name=c_name(memb.name), name=memb.name,
                      errp=errparg)
-        ret += gen_err_check(err=errarg)
+        ret += gen_err_check(skiperr=skiperr)
 
         if memb.optional:
             pop_indent()