fix: allow to use {wildcards} for group jobs in cluster config (#1555)

* Add merged wildcards to group job formatting rule

* fixes, as suggested by @twillis209

snakemake/jobs.py

@@ -1437,15 +1437,27 @@ def priority(self):
     def is_local(self):
         return all(job.is_local for job in self.jobs)
 
+    def merged_wildcards(self):
+        jobs = iter(self.jobs)
+        merged_wildcards = Wildcards(toclone=next(jobs).wildcards)
+        for job in jobs:
+            for name, value in job.wildcards.items():
+                if name not in merged_wildcards.keys():
+                    merged_wildcards.append(value)
+                    merged_wildcards._add_name(name)
+        return merged_wildcards
+
     def format_wildcards(self, string, **variables):
         """Format a string with variables from the job."""
+
         _variables = dict()
         _variables.update(self.dag.workflow.globals)
         _variables.update(
             dict(
                 input=self.input,
                 output=self.output,
                 threads=self.threads,
+                wildcards=self.merged_wildcards(),
                 jobid=self.jobid,
                 name=self.name,
                 rule="GROUP",