job-list: split up R parsing function

Problem: In the near future, R may be updated and may need to be
parsed multiple times.  R parsing code sits in a function that is called
only when R is initially loaded.

Split R parsing into two functions, one for loading R and one for
parsing R.  That way parsing R can be done multiple times without the
additional call to json_loads().

src/modules/job-list/job_data.c

@@ -385,7 +385,20 @@ int job_parse_jobspec_fatal (struct job *job, const char *s, json_t *updates)
     return job_jobspec_update (job, updates);
 }
 
-static int parse_R (struct job *job, const char *s, bool allow_nonfatal)
+static int load_R (struct job *job, const char *s, bool allow_nonfatal)
+{
+    json_error_t error;
+
+    if (!(job->R = json_loads (s, 0, &error))) {
+        flux_log (job->h, LOG_ERR,
+                  "%s: job %s invalid R: %s",
+                  __FUNCTION__, idf58 (job->id), error.text);
+        return allow_nonfatal ? 0 : -1;
+    }
+    return 0;
+}
+
+static int parse_R (struct job *job, bool allow_nonfatal)
 {
     struct rlist *rl = NULL;
     struct idset *idset = NULL;
@@ -396,13 +409,6 @@ static int parse_R (struct job *job, const char *s, bool allow_nonfatal)
     struct rnode *rnode;
     int saved_errno, rc = -1;
 
-    if (!(job->R = json_loads (s, 0, &error))) {
-        flux_log (job->h, LOG_ERR,
-                  "%s: job %s invalid R: %s",
-                  __FUNCTION__, idf58 (job->id), error.text);
-        goto nonfatal_error;
-    }
-
     if (!(rl = rlist_from_json (job->R, &error))) {
         flux_log_error (job->h, "rlist_from_json: %s", error.text);
         goto nonfatal_error;
@@ -456,12 +462,16 @@ static int parse_R (struct job *job, const char *s, bool allow_nonfatal)
 
 int job_parse_R (struct job *job, const char *s)
 {
-    return parse_R (job, s, true);
+    if (load_R (job, s, true) < 0)
+        return -1;
+    return parse_R (job, true);
 }
 
 int job_parse_R_fatal (struct job *job, const char *s)
 {
-    return parse_R (job, s, false);
+    if (load_R (job, s, false) < 0)
+        return -1;
+    return parse_R (job, false);
 }
 
 int job_jobspec_update (struct job *job, json_t *updates)