SOLR-6594 Mark old schema APIs as deprecated

solr/CHANGES.txt

@@ -319,6 +319,8 @@ Upgrading from Solr 5.4
 * Clearing up stored async collection api responses via REQUESTSTATUS call is now deprecated and would be
   removed in 6.0. See SOLR-8648 for more details.
 
+* SOLR-6594: Deprecated the old schema API which will be removed in a later major release
+
 Detailed Change List
 ----------------------
 

solr/core/src/java/org/apache/solr/rest/BaseSolrResource.java

@@ -175,12 +175,18 @@ public abstract class BaseSolrResource extends ServerResource {
     
     // TODO: should status=0 (success?) be left as-is in the response header?
     SolrCore.postDecorateResponse(null, solrRequest, solrResponse);
+    addDeprecatedWarning();
 
     if (log.isInfoEnabled() && solrResponse.getToLog().size() > 0) {
       log.info(solrResponse.getToLogAsString(solrCore.getLogId()));
     }
   }
 
+  protected void addDeprecatedWarning(){
+    solrResponse.add("warn","This API is deprecated");
+
+  }
+
   /**
    * If there is an exception on the SolrResponse:
    * <ul>

solr/core/src/java/org/apache/solr/rest/RestManager.java

@@ -432,6 +432,11 @@ public class RestManager {
       }
       return parsedJson;
     }
+
+    @Override
+    protected void addDeprecatedWarning() {
+      //this is not deprecated
+    }
   } // end ManagedEndpoint class
   
   /**