LUCENE-5500: SortingMergePolicy should error if the Sort refers to the score

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1575306 13f79535-47bb-0310-9956-ffa450edef68

lucene/core/src/java/org/apache/lucene/search/Sort.java

@@ -202,8 +202,8 @@ public class Sort {
     return 0x45aaf665 + Arrays.hashCode(fields);
   }
 
-  /** Whether the relevance score is needed to sort documents. */
-  boolean needsScores() {
+  /** Returns true if the relevance score is needed to sort documents. */
+  public boolean needsScores() {
     for (SortField sortField : fields) {
       if (sortField.needsScores()) {
         return true;

lucene/misc/src/java/org/apache/lucene/index/sorter/Sorter.java

@@ -39,6 +39,9 @@ final class Sorter {
   
   /** Creates a new Sorter to sort the index with {@code sort} */
   Sorter(Sort sort) {
+    if (sort.needsScores()) {
+      throw new IllegalArgumentException("Cannot sort an index with a Sort that refers to the relevance score");
+    }
     this.sort = sort;
   }
 

lucene/misc/src/test/org/apache/lucene/index/sorter/SortingAtomicReaderTest.java

@@ -62,5 +62,14 @@ public class SortingAtomicReaderTest extends SorterTestBase {
     
     TestUtil.checkReader(reader);
   }
+  
+  public void testBadSort() throws Exception {
+    try {
+      SortingAtomicReader.wrap(reader, Sort.RELEVANCE);
+      fail("Didn't get expected exception");
+    } catch (IllegalArgumentException e) {
+      assertEquals("Cannot sort an index with a Sort that refers to the relevance score", e.getMessage());
+    }
+  }
 
 }

lucene/misc/src/test/org/apache/lucene/index/sorter/TestSortingMergePolicy.java

@@ -172,5 +172,14 @@ public class TestSortingMergePolicy extends LuceneTestCase {
     
     assertReaderEquals("", sortedReader1, sortedReader2);
   }
+  
+  public void testBadSort() throws Exception {
+    try {
+      new SortingMergePolicy(newMergePolicy(), Sort.RELEVANCE);
+      fail("Didn't get expected exception");
+    } catch (IllegalArgumentException e) {
+      assertEquals("Cannot sort an index with a Sort that refers to the relevance score", e.getMessage());
+    }
+  }
 
 }