make knn query not pushable

Author: carlosdelest

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/lucene/LuceneQueryEvaluator.java

@@ -184,7 +184,8 @@ private class ShardState {
         private final List<SegmentState> perSegmentState;
 
         ShardState(ShardConfig config) throws IOException {
-            weight = config.searcher.createWeight(config.query, scoreMode(), 1.0f);
+            Query rewritten = config.searcher.rewrite(config.query);
+            weight = config.searcher.createWeight(rewritten, scoreMode(), 1.0f);
             searcher = config.searcher;
             perSegmentState = new ArrayList<>(Collections.nCopies(searcher.getLeafContexts().size(), null));
         }

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/plugin/KnnFunctionIT.java

@@ -78,6 +78,24 @@ public void testKnnOptions() {
         }
     }
 
+    public void testKnnNonPushedDown() {
+        var query = """
+            FROM test METADATA _score
+            | WHERE knn(vector, [1.0, 1.0, 1.0], {"k": 5}) OR id % 2 == 0
+            | KEEP id, floats, _score, vector
+            | SORT _score DESC
+            """;
+
+        try (var resp = run(query)) {
+            assertColumnNames(resp.columns(), List.of("id", "floats", "_score", "vector"));
+            assertColumnTypes(resp.columns(), List.of("integer", "double", "double", "dense_vector"));
+
+            List<List<Object>> valuesList = EsqlTestUtils.getValuesList(resp);
+            // K = 5, 2 more for % operator, total 7
+            assertEquals(7, valuesList.size());
+        }
+    }
+
     @Before
     public void setup() throws IOException {
         var indexName = "test";

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/vector/Knn.java

@@ -146,7 +146,13 @@ private Map<String, Object> queryOptions() throws InvalidArgumentException {
 
     @Override
     public Expression replaceChildren(List<Expression> newChildren) {
-        return new Knn(source(), newChildren.get(0), newChildren.get(1), newChildren.size() > 2 ? newChildren.get(2) : null);
+        return new Knn(
+            source(),
+            newChildren.get(0),
+            newChildren.get(1),
+            newChildren.size() > 2 ? newChildren.get(2) : null,
+            queryBuilder()
+        );
     }
 
     @Override