SOLR-17715: un-deprecate CommonParams.QT and SolrQuery.setRequestHandler have been un-deprecat…

solr/solr-ref-guide/modules/upgrade-notes/pages/major-changes-in-solr-10.adoc

@@ -66,6 +66,8 @@ The `solr.pki.sendVersion` and `solr.pki.acceptVersions` system properties are n
 HttpSolrClient returns; this time as a base class for HttpJettySolrClient and HttpJdkSolrClient.
 Its builder will dynamically detect if solr-jetty is available and use that, otherwise it will use the JDK client.
 
+CommonParams.QT and SolrQuery.setRequestHandler have been un-deprecated.  Nonetheless, if your code makes explicit reference to "qt" when constructing a standard request, there is usually a better way.
+
 == Solr 10.0
 
 === Solr Jetty parameters

solr/solrj/src/java/org/apache/solr/client/solrj/request/SolrQuery.java

@@ -29,6 +29,7 @@
 import org.apache.solr.common.params.HighlightParams;
 import org.apache.solr.common.params.ModifiableSolrParams;
 import org.apache.solr.common.params.MoreLikeThisParams;
+import org.apache.solr.common.params.SolrParams;
 import org.apache.solr.common.params.StatsParams;
 import org.apache.solr.common.params.TermsParams;
 
@@ -1134,22 +1135,22 @@ public Integer getStart() {
   }
 
   /**
-   * The Request Handler to use (see the solrconfig.xml), which is stored in the "qt" parameter.
-   * Normally it starts with a '/' and if so it will be used by {@link
-   * org.apache.solr.client.solrj.request.QueryRequest#getPath()} in the URL instead of the "qt"
-   * parameter. If this is left blank, then the default of "/select" is assumed.
+   * The Request Handler to use (see the solrconfig.xml), starting with a '/'. This isn't passed to
+   * Solr as a parameter; instead {@link QueryRequest} uses it for the path. QueryRequest uses
+   * "/select" if no path or request-handler is provided. Since this isn't <em>really</em> a
+   * parameter in practice, it's preferrable to set this in the constructor of QueryRequest, or the
+   * setter instead.
    *
    * @param qt The Request Handler name corresponding to one in solrconfig.xml on the server.
    * @return this
-   * @deprecated Use {@link SolrRequest#setPath(String)}
+   * @see QueryRequest#QueryRequest(String, SolrParams)
+   * @see SolrRequest#setPath(String)
    */
-  @Deprecated
   public SolrQuery setRequestHandler(String qt) {
     this.set(CommonParams.QT, qt);
     return this;
   }
 
-  @Deprecated
   public String getRequestHandler() {
     return this.get(CommonParams.QT);
   }

solr/solrj/src/java/org/apache/solr/common/params/CommonParams.java

@@ -36,12 +36,13 @@ public interface CommonParams {
   String TZ = "TZ";
 
   /**
-   * the Request Handler (formerly known as the Query Type) - which Request Handler should handle
-   * the request.
+   * the Request Handler (formerly known as the Query Type) to route to as seen in solrconfig.xml.
    *
-   * @deprecated route requests by path instead, not using this parameter
+   * <p>Note: in a standard request, the handler is the last path component of the URL, not this
+   * parameter. This parameter is used for special cases when there is no path like a warming query
+   * or streaming expressions or some other places.
    */
-  @Deprecated String QT = "qt";
+  String QT = "qt";
 
   /** the response writer type - the format of the response */
   String WT = "wt";