Forbid group.query and group.func

solr/core/src/java/org/apache/solr/search/grouping/GroupingSpecification.java

@@ -76,10 +76,16 @@ private void validateSkipSecondGroupingStep() {
           GroupParams.GROUP_LIMIT + " != 1 ("+GroupParams.GROUP_LIMIT+" is "+limit+")");
     }
 
+    // group.func not supported
     if (functions.length > 0){
       throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
               GroupParams.GROUP_SKIP_DISTRIBUTED_SECOND + " does not support "+ GroupParams.GROUP_FUNC);
     }
+    // group.query not supported
+    if (queries.length > 0){
+      throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
+              GroupParams.GROUP_SKIP_DISTRIBUTED_SECOND + " does not support "+ GroupParams.GROUP_QUERY);
+    }
 
     if (offset != 0) {
       throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,

solr/core/src/test/org/apache/solr/TestDistributedGrouping.java

@@ -517,6 +517,10 @@ private void doTestGroupSkipSecondStep() throws Exception {
     assertSimpleQueryThrows("q", "{!func}id_i1", "rows", 3, "group.skip.second.step", true,  "fl",  "id," + i1, "group", "true",
             "group.func", i1);
 
+    // check that the requests fails if group.query is used with group.skip.second.step instead of group.field
+    assertSimpleQueryThrows("q", "{!func}id_i1", "rows", 3, "group.skip.second.step", true,  "fl",  "id," + i1, "group", "true",
+            "group.query", "{!func}id_1");
+
     /// check that group.skip.second.step works properly with group.main == true (using a different
     //  EndResultTransformer but still sharing the skipping logic)
     query("q", "{!func}id_i1", "rows", 3, "group.skip.second.step", true,  "fl",  "id," + i1, "group", "true",
@@ -533,6 +537,7 @@ private void doTestGroupSkipSecondStep() throws Exception {
     query("q", "{!func}id_i1", "rows", "3", "group.skip.second.step", "true", "fl", "id," + i1+",id_i1,score", "group", "true", "group.field", i1, "group.limit", "1");
     query("q", "{!func}id_i1", "rows", "3", "group.skip.second.step", "false", "fl", "id," + i1+",id_i1,score", "group", "true", "group.field", i1, "group.limit", "1");
 
+
     assertNumFoundWithSkipSecondGroupingStep("q", "kings", "group.skip.second.step", "true", "fl", "id," + i1, "group", "true", "group.field", i1);
     assertNumFoundWithSkipSecondGroupingStep( "q", "{!func}id_i1", "rows", "3", "fl", "id," + i1+",id_i1", "group", "true", "group.field", i1, "group.limit", "1","sort", tlong+" desc");
     assertNumFoundWithSkipSecondGroupingStep("q", "{!func}id_i1", "rows", "3", "fl", "id," + i1+",id_i1,score", "group", "true", "group.field", i1, "group.limit", "1");

solr/solr-ref-guide/src/result-grouping.adoc

@@ -115,7 +115,7 @@ Setting this parameter to a number greater than 0 enables caching for result gro
 Testing has shown that group caching only improves search time with Boolean, wildcard, and fuzzy queries. For simple queries like term or "match all" queries, group caching degrades performance.
 
 `group.skip.second.step`::
-This parameter can be set to `true` if only one document per group needs to be retrieved. Result Grouping executes two searches; if enabled this option will disable the second search improving the performance. By default the value is set to `false`. It can be set to `true` if `group.limit` is 1, and `group.sort` fields list is absent or is a prefix of `sort` fields list (e.g., if `sort=price asc,name desc` and `group.sort=price asc` is fine, but `sort=price asc,name desc` and `group.sort=name desc` is not). When enabled it will not be possible to know `numFound` for each group - `numFound` will be set to one. It cannot be used together with <<other-parsers.adoc#re-ranking-query-parser,Re-ranking Query Parser>>, and together with `group.func` - group based on function (not supported in distribute mode).
+This parameter can be set to `true` if only one document per group needs to be retrieved. Result Grouping executes two searches; if enabled this option will disable the second search improving the performance. By default the value is set to `false`. It can be set to `true` if `group.limit` is 1, and `group.sort` fields list is absent or is a prefix of `sort` fields list (e.g., if `sort=price asc,name desc` and `group.sort=price asc` is fine, but `sort=price asc,name desc` and `group.sort=name desc` is not). When grouping only grouping by field is supported (`group.field`), grouping by function (`group.func`) or query (`group.query`) are not supported. The actual `numFound` for each group will not be available, `numFound` will be set to 1. It cannot be used together with <<other-parsers.adoc#re-ranking-query-parser,Re-ranking Query Parser>>.
 +
 More details on `group.skip.second.step` in https://www.youtube.com/watch?v=eMuepJpjUjI&t=1591[Learning to Rank: From Theory to Production].