SOLR-15017: Core's lib/ dir was ignored sometimes (#2107)

A core's lib/ folder was ignored when the core's configuration did not define any <lib> element.  This is a regression introduced in 8.6 by SOLR-14197.

solr/CHANGES.txt

@@ -210,6 +210,9 @@ Bug Fixes
 
 * SOLR-15009: Correctly propogate exceptions from DirectoryFactory.exists (Mike Drob)
 
+* SOLR-15017: Core lib directories were not being recognized unless the solrconfig included a <lib> directive.
+  (Thomas Mortagne)
+
 Other Changes
 ---------------------
 

solr/core/src/java/org/apache/solr/core/SolrConfig.java

@@ -765,43 +765,47 @@ public class SolrConfig extends XmlConfigFile implements MapSerializable {
     }
 
     NodeList nodes = (NodeList) evaluate("lib", XPathConstants.NODESET);
-    if (nodes == null || nodes.getLength() == 0) return;
-    if (!isConfigsetTrusted) {
-      throw new SolrException(ErrorCode.UNAUTHORIZED, "The configset for this collection was uploaded without any authentication in place,"
-          + " and use of <lib> is not available for collections with untrusted configsets. To use this component, re-upload the configset"
-          + " after enabling authentication and authorization.");
-    }
+    if (nodes != null && nodes.getLength() > 0) {
+      if (!isConfigsetTrusted) {
+        throw new SolrException(ErrorCode.UNAUTHORIZED,
+          "The configset for this collection was uploaded without any authentication in place,"
+            + " and use of <lib> is not available for collections with untrusted configsets. To use this component, re-upload the configset"
+            + " after enabling authentication and authorization.");
+      }
 
-    for (int i = 0; i < nodes.getLength(); i++) {
-      Node node = nodes.item(i);
-      String baseDir = DOMUtil.getAttr(node, "dir");
-      String path = DOMUtil.getAttr(node, PATH);
-      if (null != baseDir) {
-        // :TODO: add support for a simpler 'glob' mutually exclusive of regex
-        Path dir = instancePath.resolve(baseDir);
-        String regex = DOMUtil.getAttr(node, "regex");
-        try {
-          if (regex == null)
-            urls.addAll(SolrResourceLoader.getURLs(dir));
-          else
-            urls.addAll(SolrResourceLoader.getFilteredURLs(dir, regex));
-        } catch (IOException e) {
-          log.warn("Couldn't add files from {} filtered by {} to classpath: {}", dir, regex, e);
+      for (int i = 0; i < nodes.getLength(); i++) {
+        Node node = nodes.item(i);
+        String baseDir = DOMUtil.getAttr(node, "dir");
+        String path = DOMUtil.getAttr(node, PATH);
+        if (null != baseDir) {
+          // :TODO: add support for a simpler 'glob' mutually exclusive of regex
+          Path dir = instancePath.resolve(baseDir);
+          String regex = DOMUtil.getAttr(node, "regex");
+          try {
+            if (regex == null)
+              urls.addAll(SolrResourceLoader.getURLs(dir));
+            else
+              urls.addAll(SolrResourceLoader.getFilteredURLs(dir, regex));
+          } catch (IOException e) {
+            log.warn("Couldn't add files from {} filtered by {} to classpath: {}", dir, regex, e);
+          }
+        } else if (null != path) {
+          final Path dir = instancePath.resolve(path);
+          try {
+            urls.add(dir.toUri().toURL());
+          } catch (MalformedURLException e) {
+            log.warn("Couldn't add file {} to classpath: {}", dir, e);
+          }
+        } else {
+          throw new RuntimeException("lib: missing mandatory attributes: 'dir' or 'path'");
         }
-      } else if (null != path) {
-        final Path dir = instancePath.resolve(path);
-        try {
-          urls.add(dir.toUri().toURL());
-        } catch (MalformedURLException e) {
-          log.warn("Couldn't add file {} to classpath: {}", dir, e);
-        }
-      } else {
-        throw new RuntimeException("lib: missing mandatory attributes: 'dir' or 'path'");
       }
     }
 
-    loader.addToClassLoader(urls);
-    loader.reloadLuceneSPI();
+    if (!urls.isEmpty()) {
+      loader.addToClassLoader(urls);
+      loader.reloadLuceneSPI();
+    }
   }
 
   public int getMultipartUploadLimitKB() {

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

@@ -0,0 +1,45 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.core;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import org.apache.solr.SolrTestCaseJ4;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class TestMinimalConfig extends SolrTestCaseJ4 {
+
+  @BeforeClass
+  public static void beforeClass() throws Exception {
+    initCore("solrconfig-minimal.xml","schema-minimal.xml");
+  }
+
+  // Make sure the content of the lib/ core subfolder is loaded even if there is no <lib> node in the solrconfig
+  @Test
+  public void testLib() throws IOException {
+    SolrResourceLoader loader = h.getCore().getResourceLoader();
+    InputStream data = null;
+    String[] expectedFiles = new String[] { "empty-file-main-lib.txt"};
+    for (String f : expectedFiles) {
+      data = loader.openResource(f);
+      assertNotNull("Should have found file " + f, data);
+      data.close();
+    }
+  }
+}