qom: Clean up fragile use of error_is_set() in set() methods

Using error_is_set(ERRP) to find out whether a function failed is
either wrong, fragile, or unnecessarily opaque.  It's wrong when ERRP
may be null, because errors go undetected when it is.  It's fragile
when proving ERRP non-null involves a non-local argument.  Else, it's
unnecessarily opaque (see commit 84d18f0).

I guess the error_is_set(errp) in the ObjectProperty set() methods are
merely fragile right now, because I can't find a call chain that
passes a null errp argument.

Make the code more robust and more obviously correct: receive the
error in a local variable, then propagate it through the parameter.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/hw/misc/tmp105.c b/hw/misc/tmp105.c
index 63aa3d6..636ee97 100644
--- a/hw/misc/tmp105.c
+++ b/hw/misc/tmp105.c
@@ -68,10 +68,12 @@ static void tmp105_set_temperature(Object *obj, Visitor *v, void *opaque,
                                    const char *name, Error **errp)
 {
     TMP105State *s = TMP105(obj);
+    Error *local_err = NULL;
     int64_t temp;
 
-    visit_type_int(v, &temp, name, errp);
-    if (error_is_set(errp)) {
+    visit_type_int(v, &temp, name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         return;
     }
     if (temp >= 128000 || temp < -128000) {