Annotate that no changes happen through pointer component.

* collSpec is meant to be a dumb data collection, none of its member should
  be subject to change.

src/pio_client.c

@@ -294,7 +294,7 @@ cdiPioStreamDefDecomposedVlist(int streamID, int vlistID, const Xt_idxlist partD
   struct collSpec cspec = { .numClients = rup.numClients,
                             .numServers = rup.numColl,
                             .sendRPCData = rup.sendRPCData,
-                            .partDesc = (Xt_idxlist *) partDesc,
+                            .partDesc = partDesc,
                             .conversion = (int *) conversion };
   cdiPioClientStreamWinCreate(streamID, &cspec);
 }

src/pio_rpc.c

@@ -43,7 +43,7 @@ computeClientStreamBufSize(int streamID, const struct collSpec *collector)
       /* the distribution of data is fully prescribed in this case,
        * i.e. memory needed can be computed exactly for the double
        * precision case */
-      Xt_idxlist *partDesc = collector->partDesc;
+      const Xt_idxlist *partDesc = collector->partDesc;
       const int *conversion = collector->conversion;
       for (size_t varID = 0; varID < nvars; ++varID)
         {

src/pio_rpc.h

@@ -130,7 +130,7 @@ struct clientBufSize
 
 struct collSpec
 {
-  Xt_idxlist *partDesc;
+  const Xt_idxlist *partDesc;
   int *conversion;
   int numClients;
   int numServers;