arch: Improve errors returned by incorrect combinations of deviceid and visible devices

Author: EdCaunt

devito/arch/archinfo.py

@@ -497,7 +497,7 @@ def get_visible_devices():
     )
     for v in device_vars:
         try:
-            return tuple(int(i) for i in os.environ[v].split(','))
+            return v, tuple(int(i) for i in os.environ[v].split(','))
         except ValueError:
             # Visible devices set via UUIDs or other non-integer identifiers.
             warning("Setting visible devices via UUIDs or other non-integer"
@@ -507,7 +507,7 @@ def get_visible_devices():
             # Environment variable not set
             continue
 
-    return None
+    return None, None
 
 
 @memoized_func

devito/operator/operator.py

@@ -1398,15 +1398,15 @@ def _physical_deviceid(self):
                 rank = self.comm.Get_rank() if self.comm != MPI.COMM_NULL else 0
                 logical_deviceid = rank
 
-            visible_devices = get_visible_devices()
+            visible_device_var, visible_devices = get_visible_devices()
             if visible_devices is None:
                 return logical_deviceid
             else:
                 try:
                     return visible_devices[logical_deviceid]
                 except IndexError:
                     errmsg = (f"A deviceid value of {logical_deviceid} is not valid "
-                              f"with VISIBLE_DEVICES={visible_devices}. Note that "
+                              f"with {visible_device_var}={visible_devices}. Note that "
                               "deviceid corresponds to the logical index within the "
                               "visible devices, not the physical device index.")
                     raise ValueError(errmsg)