error: don't delay error message construction

Today, the error message is only constructed when it's used. This commit
changes that to construct the error message when the error object is
built (ie. when the error is reported).

This simplifies the Error object.
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>

error.c

@@ -20,7 +20,6 @@
 struct Error
 {
     QDict *obj;
-    const char *fmt;
     char *msg;
 };
 
@@ -39,7 +38,7 @@ void error_set(Error **errp, const char *fmt, ...)
     va_start(ap, fmt);
     err->obj = qobject_to_qdict(qobject_from_jsonv(fmt, &ap));
     va_end(ap);
-    err->fmt = fmt;
+    err->msg = qerror_format(fmt, err->obj);
 
     *errp = err;
 }
@@ -50,7 +49,6 @@ Error *error_copy(const Error *err)
 
     err_new = g_malloc0(sizeof(*err));
     err_new->msg = g_strdup(err->msg);
-    err_new->fmt = err->fmt;
     err_new->obj = err->obj;
     QINCREF(err_new->obj);
 
@@ -64,10 +62,6 @@ bool error_is_set(Error **errp)
 
 const char *error_get_pretty(Error *err)
 {
-    if (err->msg == NULL) {
-        err->msg = qerror_format(err->fmt, err->obj);
-    }
-
     return err->msg;
 }
 

qerror.c

@@ -543,7 +543,6 @@ void qerror_report(const char *fmt, ...)
 struct Error
 {
     QDict *obj;
-    const char *fmt;
     char *msg;
 };
 
@@ -555,8 +554,7 @@ void qerror_report_err(Error *err)
     loc_save(&qerr->loc);
     QINCREF(err->obj);
     qerr->error = err->obj;
-
-    qerr->err_msg = qerror_format(err->fmt, qerr->error);
+    qerr->err_msg = g_strdup(err->msg);
 
     if (monitor_cur_is_qmp()) {
         monitor_set_error(cur_mon, qerr);