SOLR-15156: [child childFilter='...:...'] no longer escapes (#2367)

The query escaping it did was inconsistent with all other places in Solr where a Lucene query may be provided.

solr/CHANGES.txt

@@ -75,6 +75,9 @@ Improvements
 * SOLR-15011: /admin/logging handler will now propagate setLevel (log threshold) to all nodes
 when told to. The admin UI now tells it to. (Nazerke Seidan, David Smiley)
 
+* SOLR-15156: [child] doc transformer's childFilter param no longer applies query syntax
+  escaping. It was inconsistent with other Solr options.  (David Smiley)
+
 Other Changes
 ----------------------
 * SOLR-14656: Autoscaling framework removed (Ishan Chattopadhyaya, noble, Ilan Ginzburg)

solr/core/src/java/org/apache/solr/response/transform/ChildDocTransformerFactory.java

@@ -144,24 +144,24 @@ public class ChildDocTransformerFactory extends TransformerFactory {
     try {
       return QParser.getParser(qstr, req).getQuery();
     } catch (SyntaxError syntaxError) {
-      throw new SolrException(ErrorCode.BAD_REQUEST, "Failed to parse '" + param + "' param.");
+      throw new SolrException(
+              ErrorCode.BAD_REQUEST,
+              "Failed to parse '" + param + "' param: " + syntaxError.getMessage(),
+              syntaxError);
     }
   }
 
-  // NOTE: THIS FEATURE IS PRESENTLY EXPERIMENTAL; WAIT TO SEE IT IN THE REF GUIDE.  FINAL SYNTAX IS TBD.
   protected static String processPathHierarchyQueryString(String queryString) {
     // if the filter includes a path string, build a lucene query string to match those specific child documents.
     // e.g. /toppings/ingredients/name_s:cocoa -> +_nest_path_:/toppings/ingredients +(name_s:cocoa)
     // ingredients/name_s:cocoa -> +_nest_path_:*/ingredients +(name_s:cocoa)
     int indexOfFirstColon = queryString.indexOf(':');
     if (indexOfFirstColon <= 0) {
-      return queryString;// give up
+      return queryString; // regular filter, not hierarchy based.
     }
     int indexOfLastPathSepChar = queryString.lastIndexOf(PATH_SEP_CHAR, indexOfFirstColon);
     if (indexOfLastPathSepChar < 0) {
-      // regular filter, not hierarchy based.
-      return ClientUtils.escapeQueryChars(queryString.substring(0, indexOfFirstColon))
-          + ":" + ClientUtils.escapeQueryChars(queryString.substring(indexOfFirstColon + 1));
+      return queryString; // regular filter, not hierarchy based.
     }
     final boolean isAbsolutePath = queryString.charAt(0) == PATH_SEP_CHAR;
     String path = ClientUtils.escapeQueryChars(queryString.substring(0, indexOfLastPathSepChar));

solr/core/src/test/org/apache/solr/response/transform/TestChildDocTransformerHierarchy.java

@@ -75,6 +75,21 @@ public class TestChildDocTransformerHierarchy extends SolrTestCaseJ4 {
     assertU(commit());
   }
 
+  @Test
+  public void testNonTrivialChildFilter() throws Exception {
+    // just check we don't throw an exception. This used to throw before SOLR-15152
+    assertQ(
+            req(
+                    "q",
+                    "*:*",
+                    "sort",
+                    "id asc",
+                    "fl",
+                    "*, _nest_path_, [child childFilter='type_s:Regular OR type_s:Chocolate']",
+                    "fq",
+                    fqToExcludeNonTestedDocs));
+  }
+
   @Test
   public void testParentFilterJSON() throws Exception {
     indexSampleData(numberOfDocsPerNestedTest);
@@ -111,7 +126,7 @@ public class TestChildDocTransformerHierarchy extends SolrTestCaseJ4 {
   public void testParentFilterLimitJSON() throws Exception {
     indexSampleData(numberOfDocsPerNestedTest);
 
-    try(SolrQueryRequest req = req("q", "type_s:donut", "sort", "id asc", "fl", "id, type_s, toppings, _nest_path_, [child childFilter='_nest_path_:/toppings' limit=1]",
+    try(SolrQueryRequest req = req("q", "type_s:donut", "sort", "id asc", "fl", "id, type_s, toppings, _nest_path_, [child childFilter='{!field f=_nest_path_}/toppings' limit=1]",
         "fq", fqToExcludeNonTestedDocs)) {
       BasicResultContext res = (BasicResultContext) h.queryAndResponse("/select", req).getResponse();
       Iterator<SolrDocument> docsStreamer = res.getProcessedDocuments();
@@ -158,7 +173,7 @@ public class TestChildDocTransformerHierarchy extends SolrTestCaseJ4 {
     assertU(delQ("_nest_path_:\\/toppings"));
     assertU(commit());
 
-    try(SolrQueryRequest req = req("q", "type_s:donut", "sort", "id asc", "fl", "id, type_s, toppings, _nest_path_, [child childFilter='_nest_path_:/toppings' limit=1]",
+    try(SolrQueryRequest req = req("q", "type_s:donut", "sort", "id asc", "fl", "id, type_s, toppings, _nest_path_, [child childFilter='_nest_path_:\\\\/toppings' limit=1]",
         "fq", fqToExcludeNonTestedDocs)) {
       BasicResultContext res = (BasicResultContext) h.queryAndResponse("/select", req).getResponse();
       Iterator<SolrDocument> docsStreamer = res.getProcessedDocuments();

solr/solr-ref-guide/src/major-changes-in-solr-9.adoc

@@ -150,6 +150,9 @@ _(raw; not yet edited)_
 * SOLR-15121: XSLTResponseWriter moved to /contrib/scripting/ package instead
  of shipping as part of Solr, due to security concerns.
 
+* SOLR-15156: Child Doc Transformer's `childFilter` param no longer applies query syntax
+escaping because it's inconsistent with the rest of Solr and was limiting.  This refers to `[child childFilter='field:value']`.
+
 === Upgrade Prerequisites in Solr 9
 
 * Upgrade all collections in stateFormat=1 to stateFormat=2 *before* upgrading to Solr 9, as Solr 9 does not support the