SOLR-14040: restore legacy Collection auto-creation

solr/core/src/java/org/apache/solr/cloud/CloudConfigSetService.java

@@ -18,8 +18,11 @@ package org.apache.solr.cloud;
 
 import java.lang.invoke.MethodHandles;
 
+import org.apache.solr.cloud.api.collections.CreateCollectionCmd;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.cloud.ZkConfigManager;
+import org.apache.solr.common.cloud.ZkStateReader;
+import org.apache.solr.common.cloud.ZooKeeperException;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.core.ConfigSetProperties;
 import org.apache.solr.core.ConfigSetService;
@@ -46,7 +49,33 @@ public class CloudConfigSetService extends ConfigSetService {
 
   @Override
   public SolrResourceLoader createCoreResourceLoader(CoreDescriptor cd) {
-    return new ZkSolrResourceLoader(cd.getInstanceDir(), cd.getConfigSet(), parentLoader.getClassLoader(),
+    final String colName = cd.getCollectionName();
+
+    // For back compat with cores that can create collections without the collections API
+    try {
+      if (!zkController.getZkClient().exists(ZkStateReader.COLLECTIONS_ZKNODE + "/" + colName, true)) {
+        // TODO remove this functionality or maybe move to a CLI mechanism
+        log.warn("Auto-creating collection (in ZK) from core descriptor (on disk).  This feature may go away!");
+        CreateCollectionCmd.createCollectionZkNode(zkController.getSolrCloudManager().getDistribStateManager(), colName, cd.getCloudDescriptor().getParams());
+      }
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+      throw new ZooKeeperException(SolrException.ErrorCode.SERVER_ERROR, "Interrupted auto-creating collection", e);
+    } catch (KeeperException e) {
+      throw new ZooKeeperException(SolrException.ErrorCode.SERVER_ERROR, "Failure auto-creating collection", e);
+    }
+
+    // The configSet is read from ZK and populated.  Ignore CD's pre-existing configSet; only populated in standalone
+    final String configSetName;
+    try {
+      //TODO readConfigName() also validates the configSet exists but seems needless.  We'll get errors soon enough.
+      configSetName = zkController.getZkStateReader().readConfigName(colName);
+      cd.setConfigSet(configSetName);
+    } catch (KeeperException ex) {
+      throw new ZooKeeperException(SolrException.ErrorCode.SERVER_ERROR, "Trouble resolving configSet for collection " + colName + ": " + ex.getMessage());
+    }
+
+    return new ZkSolrResourceLoader(cd.getInstanceDir(), configSetName, parentLoader.getClassLoader(),
         cd.getSubstitutableProperties(), zkController);
   }
 

solr/core/src/java/org/apache/solr/cloud/CloudDescriptor.java

@@ -21,15 +21,10 @@ import java.util.Map;
 import java.util.Properties;
 
 import com.google.common.base.Strings;
-import org.apache.solr.common.SolrException;
 import org.apache.solr.common.StringUtils;
 import org.apache.solr.common.cloud.Replica;
-import org.apache.solr.common.cloud.ZooKeeperException;
 import org.apache.solr.core.CoreDescriptor;
 import org.apache.solr.util.PropertiesUtil;
-import org.apache.zookeeper.KeeperException;
-
-import static org.apache.solr.core.CoreDescriptor.CORE_CONFIGSET;
 
 /**
  * SolrCloud metadata attached to a {@link CoreDescriptor}.
@@ -61,7 +56,7 @@ public class CloudDescriptor {
    */
   private final Replica.Type replicaType;
 
-  public CloudDescriptor(CoreDescriptor cd, String coreName, Properties props, ZkController zkController) {
+  public CloudDescriptor(CoreDescriptor cd, String coreName, Properties props) {
     this.cd = cd;
     this.shardId = props.getProperty(CoreDescriptor.CORE_SHARD, null);
     if (Strings.isNullOrEmpty(shardId))
@@ -84,19 +79,6 @@ public class CloudDescriptor {
         collectionParams.put(propName.substring(ZkController.COLLECTION_PARAM_PREFIX.length()), props.getProperty(propName));
       }
     }
-    // The configSet comes from ZK, not from CD's properties like it does in standalone.
-    // But we want to put it on CD because CD has getConfigSet() which is sensible; don't want that to return null.
-    if (zkController != null) { // there's a test where we pass null 'cause it wanted a dummy instance.  Yuck?
-      try {
-        //TODO readConfigName() also validates the configSet exists but seems needless.  We'll get errors soon enough.
-        String configSetName = zkController.getZkStateReader().readConfigName(collectionName);
-        props.setProperty(CORE_CONFIGSET, configSetName);
-        //noinspection StringEquality
-        assert cd.getConfigSet() == configSetName;
-      } catch (KeeperException ex) {
-        throw new ZooKeeperException(SolrException.ErrorCode.SERVER_ERROR, "Trouble resolving configSet for collection " + collectionName + ": " + ex.getMessage());
-      }
-    }
   }
   
   public boolean requiresTransactionLog() {

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

@@ -211,7 +211,7 @@ public class CoreDescriptor {
 
     // TODO maybe make this a CloudCoreDescriptor subclass?
     if (zkController != null) {
-      cloudDesc = new CloudDescriptor(this, name, coreProperties, zkController);
+      cloudDesc = new CloudDescriptor(this, name, coreProperties);
     } else {
       cloudDesc = null;
     }
@@ -371,6 +371,11 @@ public class CoreDescriptor {
     return coreProperties.getProperty(CORE_CONFIGSET);
   }
 
+  /** TODO remove mutability or at least make this non-public? */
+  public void setConfigSet(String configSetName) {
+    coreProperties.setProperty(CORE_CONFIGSET, configSetName);
+  }
+
   public String getConfigSetPropertiesName() {
     return coreProperties.getProperty(CORE_CONFIGSET_PROPERTIES);
   }

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

@@ -128,7 +128,7 @@ public class CoreSorterTest extends SolrTestCaseJ4 {
       p.setProperty(CoreDescriptor.CORE_SHARD, "shard_" + slice);
       p.setProperty(CoreDescriptor.CORE_COLLECTION, "coll_" + slice);
       p.setProperty(CoreDescriptor.CORE_NODE_NAME, replicaName);
-      cd = new CloudDescriptor(null, replicaName, p, null);
+      cd = new CloudDescriptor(null, replicaName, p);
     }
 
     @Override