Ensure getTabletState() in TabletMetadata does not allow a null extent (

#4438)

Previously the private reference for the extent inside TabletMetadata
was passed to the TabletLocationState constructor inside of
getTabletState(). The extent may not have been loaded at this point as
it is lazy loaded by the getExtent() method and requires PREV_ROW to
have been fetched. This change now uses the getter to make sure we do
not inadvertently pass a null extent which is invalid.

core/src/main/java/org/apache/accumulo/core/metadata/TabletLocationState.java

@@ -22,6 +22,7 @@
 
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Objects;
 import java.util.Set;
 
 import org.apache.accumulo.core.dataImpl.KeyExtent;
@@ -58,7 +59,7 @@ public Text getEncodedEndRow() {
   public TabletLocationState(KeyExtent extent, Location future, Location current, Location last,
       SuspendingTServer suspend, Collection<Collection<String>> walogs, boolean chopped)
       throws BadLocationStateException {
-    this.extent = extent;
+    this.extent = Objects.requireNonNull(extent);
     this.future = validateLocation(future, TabletMetadata.LocationType.FUTURE);
     this.current = validateLocation(current, TabletMetadata.LocationType.CURRENT);
     this.last = validateLocation(last, TabletMetadata.LocationType.LAST);

core/src/main/java/org/apache/accumulo/core/metadata/schema/TabletMetadata.java

@@ -373,7 +373,9 @@ public TabletState getTabletState(Set<TServerInstance> liveTServers) {
         future = location;
       }
       // only care about the state so don't need walogs and chopped params
-      var tls = new TabletLocationState(extent, future, current, last, suspend, null, false);
+      // Use getExtent() when passing the extent as the private reference may not have been
+      // initialized yet. This will also ensure PREV_ROW was fetched
+      var tls = new TabletLocationState(getExtent(), future, current, last, suspend, null, false);
       return tls.getState(liveTServers);
     } catch (TabletLocationState.BadLocationStateException blse) {
       throw new IllegalArgumentException("Error creating TabletLocationState", blse);

core/src/test/java/org/apache/accumulo/core/metadata/schema/TabletMetadataTest.java

@@ -26,6 +26,7 @@
 import static org.apache.accumulo.core.metadata.schema.MetadataSchema.TabletsSection.ServerColumnFamily.TIME_COLUMN;
 import static org.apache.accumulo.core.metadata.schema.TabletMetadata.ColumnType.LAST;
 import static org.apache.accumulo.core.metadata.schema.TabletMetadata.ColumnType.LOCATION;
+import static org.apache.accumulo.core.metadata.schema.TabletMetadata.ColumnType.PREV_ROW;
 import static org.apache.accumulo.core.metadata.schema.TabletMetadata.ColumnType.SUSPEND;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -196,6 +197,13 @@ public void testLocationStates() {
         .put(ser1.getHostPort());
     SortedMap<Key,Value> rowMap = toRowMap(mutation);
 
+    // PREV_ROW was not fetched
+    final var missingPrevRow =
+        TabletMetadata.convertRow(rowMap.entrySet().iterator(), colsToFetch, false);
+    assertThrows(IllegalStateException.class, () -> missingPrevRow.getTabletState(tservers));
+
+    // This should now work as PREV_ROW has been included
+    colsToFetch = EnumSet.of(LOCATION, LAST, SUSPEND, PREV_ROW);
     TabletMetadata tm = TabletMetadata.convertRow(rowMap.entrySet().iterator(), colsToFetch, false);
     TabletState state = tm.getTabletState(tservers);