Integrate weights into simplified RRF retriever syntax (elastic#132680)

* Made changes to include simplified weights to PR:

* Add basic changes to include the feature

* implemented changes

* [CI] Auto commit changes from spotless

* Work in progress

* WIP

* WIP

* Modified changes to include the simplified rrf

* Clean the mess

* Fixed the failing tests

* Removed the it
nit*

* refactored component

* Fixed issues

* Improved the parsing tests

* Modified code

* Refactored code'

* Update and rename 133400.yaml to 132680.yaml

* cleaned up code

* Merge conflicts

* Update LinearRetrieverBuilderTests.java

* RRFBuilder checkstyle issue

* fix failing test

* [CI] Auto commit changes from spotless

* Resolved merge conflict

* [CI] Auto commit changes from spotless

* Parsing and yaml changes

* Cleaned uo the builder

* cleanedup

* Unnecessary comments

* cleaned up

* Cleanup

* Cleanup

* removed duplicate

---------

Co-authored-by: elasticsearchmachine <[email protected]>

Author: 2 people

docs/changelog/132680.yaml

@@ -0,0 +1,5 @@
+pr: 132680
+summary: Add support for per-field weights in simplified RRF retriever syntax
+area: Search
+type: enhancement
+issues: []

x-pack/plugin/rank-rrf/src/main/java/org/elasticsearch/xpack/rank/RankRRFFeatures.java

@@ -39,6 +39,7 @@ public Set<NodeFeature> getTestFeatures() {
             LinearRetrieverBuilder.MULTI_FIELDS_QUERY_FORMAT_SUPPORT,
             RRFRetrieverBuilder.MULTI_FIELDS_QUERY_FORMAT_SUPPORT,
             RRFRetrieverBuilder.WEIGHTED_SUPPORT,
+            RRFRetrieverBuilder.SIMPLIFIED_WEIGHTED_SUPPORT,
             LINEAR_RETRIEVER_TOP_LEVEL_NORMALIZER,
             LinearRetrieverBuilder.MULTI_INDEX_SIMPLIFIED_FORMAT_SUPPORT,
             RRFRetrieverBuilder.MULTI_INDEX_SIMPLIFIED_FORMAT_SUPPORT

x-pack/plugin/rank-rrf/src/main/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverBuilder.java

@@ -30,6 +30,7 @@
 import org.elasticsearch.xcontent.XContentParser;
 import org.elasticsearch.xpack.core.XPackPlugin;
 import org.elasticsearch.xpack.rank.MultiFieldsInnerRetrieverUtils;
+import org.elasticsearch.xpack.rank.MultiFieldsInnerRetrieverUtils.WeightedRetrieverSource;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -46,10 +47,14 @@
  * meaning it has a set of child retrievers that each return a set of
  * top docs that will then be combined and ranked according to the rrf
  * formula.
+ *
+ * Supports both explicit retriever configuration and simplified field-based
+ * syntax with optional per-field weights (e.g., "field^2.0").
  */
 public final class RRFRetrieverBuilder extends CompoundRetrieverBuilder<RRFRetrieverBuilder> {
     public static final NodeFeature MULTI_FIELDS_QUERY_FORMAT_SUPPORT = new NodeFeature("rrf_retriever.multi_fields_query_format_support");
     public static final NodeFeature WEIGHTED_SUPPORT = new NodeFeature("rrf_retriever.weighted_support");
+    public static final NodeFeature SIMPLIFIED_WEIGHTED_SUPPORT = new NodeFeature("rrf_retriever.simplified_weighted_support");
     public static final NodeFeature MULTI_INDEX_SIMPLIFIED_FORMAT_SUPPORT = new NodeFeature(
         "rrf_retriever.multi_index_simplified_format_support"
     );
@@ -265,23 +270,8 @@ protected RetrieverBuilder doRewrite(QueryRewriteContext ctx) {
                 fields,
                 query,
                 localIndicesMetadata.values(),
-                r -> {
-                    List<RetrieverSource> retrievers = new ArrayList<>(r.size());
-                    float[] weights = new float[r.size()];
-                    for (int i = 0; i < r.size(); i++) {
-                        var retriever = r.get(i);
-                        retrievers.add(retriever.retrieverSource());
-                        weights[i] = retriever.weight();
-                    }
-                    return new RRFRetrieverBuilder(retrievers, null, null, rankWindowSize, rankConstant, weights);
-                },
-                w -> {
-                    if (w != 1.0f) {
-                        throw new IllegalArgumentException(
-                            "[" + NAME + "] does not support per-field weights in [" + FIELDS_FIELD.getPreferredName() + "]"
-                        );
-                    }
-                }
+                r -> createRRFFromWeightedRetrievers(r, rankWindowSize, rankConstant),
+                w -> validateNonNegativeWeight(w)
             ).stream().map(RetrieverSource::from).toList();
 
             if (fieldsInnerRetrievers.isEmpty() == false) {
@@ -295,7 +285,6 @@ protected RetrieverBuilder doRewrite(QueryRewriteContext ctx) {
                 rewritten = new StandardRetrieverBuilder(new MatchNoneQueryBuilder());
             }
         }
-
         return rewritten;
     }
 
@@ -340,4 +329,26 @@ public boolean doEquals(Object o) {
     public int doHashCode() {
         return Objects.hash(super.doHashCode(), fields, query, rankConstant, Arrays.hashCode(weights));
     }
+
+    private static RRFRetrieverBuilder createRRFFromWeightedRetrievers(
+        List<WeightedRetrieverSource> r,
+        int rankWindowSize,
+        int rankConstant
+    ) {
+        int size = r.size();
+        List<RetrieverSource> retrievers = new ArrayList<>(size);
+        float[] weights = new float[size];
+        for (int i = 0; i < size; i++) {
+            var retriever = r.get(i);
+            retrievers.add(retriever.retrieverSource());
+            weights[i] = retriever.weight();
+        }
+        return new RRFRetrieverBuilder(retrievers, null, null, rankWindowSize, rankConstant, weights);
+    }
+
+    private static void validateNonNegativeWeight(float w) {
+        if (w < 0) {
+            throw new IllegalArgumentException("[" + NAME + "] per-field weights must be non-negative");
+        }
+    }
 }

x-pack/plugin/rank-rrf/src/test/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverBuilderParsingTests.java

@@ -51,7 +51,14 @@ public static RRFRetrieverBuilder createRandomRRFRetrieverBuilder() {
         List<String> fields = null;
         String query = null;
         if (randomBoolean()) {
-            fields = randomList(1, 10, () -> randomAlphaOfLengthBetween(1, 10));
+            fields = randomList(1, 10, () -> {
+                String field = randomAlphaOfLengthBetween(1, 10);
+                if (randomBoolean()) {
+                    float weight = randomFloatBetween(0.0f, 10.1f, true);
+                    field = field + "^" + weight;
+                }
+                return field;
+            });
             query = randomAlphaOfLengthBetween(1, 10);
         }
 
@@ -359,6 +366,36 @@ public void testRRFRetrieverComponentErrorCases() throws IOException {
         expectParsingException(retrieverAsStringContent, "retriever must be an object");
     }
 
+    public void testSimplifiedWeightedFieldsParsing() throws IOException {
+        String restContent = """
+            {
+              "retriever": {
+                "rrf": {
+                  "retrievers": [
+                    {
+                      "test": {
+                        "value": "foo"
+                      }
+                    },
+                    {
+                      "test": {
+                        "value": "bar"
+                      }
+                    }
+                  ],
+                  "fields": ["name^2.0", "description^0.5"],
+                  "query": "test",
+                  "rank_window_size": 100,
+                  "rank_constant": 10,
+                  "min_score": 20.0,
+                  "_name": "foo_rrf"
+                }
+              }
+            }
+            """;
+        checkRRFRetrieverParsing(restContent);
+    }
+
     private void expectParsingException(String restContent, String expectedMessageFragment) throws IOException {
         SearchUsageHolder searchUsageHolder = new UsageService().getSearchUsageHolder();
         try (XContentParser jsonParser = createParser(JsonXContent.jsonXContent, restContent)) {

x-pack/plugin/rank-rrf/src/test/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverBuilderTests.java

@@ -200,11 +200,29 @@ public void testMultiFieldsParamsRewrite() {
             Map.of("semantic_field_1", 1.0f, "semantic_field_2", 1.0f),
             "foo2"
         );
+    }
 
-        // Glob matching on inference and non-inference fields
-        rrfRetrieverBuilder = new RRFRetrieverBuilder(
+    public void testMultiFieldsParamsRewriteWithWeights() {
+        final String indexName = "test-index";
+        final List<String> testInferenceFields = List.of("semantic_field_1", "semantic_field_2");
+        final ResolvedIndices resolvedIndices = createMockResolvedIndices(Map.of(indexName, testInferenceFields), null, Map.of());
+        final QueryRewriteContext queryRewriteContext = new QueryRewriteContext(
+            parserConfig(),
+            null,
             null,
-            List.of("field_*", "*_field_1"),
+            TransportVersion.current(),
+            RemoteClusterAware.LOCAL_CLUSTER_GROUP_KEY,
+            resolvedIndices,
+            new PointInTimeBuilder(new BytesArray("pitid")),
+            null,
+            null,
+            false
+        );
+
+        // Simple per-field boosting
+        RRFRetrieverBuilder rrfRetrieverBuilder = new RRFRetrieverBuilder(
+            null,
+            List.of("field_1", "field_2^1.5", "semantic_field_1", "semantic_field_2^2"),
             "bar",
             DEFAULT_RANK_WINDOW_SIZE,
             RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
@@ -213,15 +231,16 @@ public void testMultiFieldsParamsRewrite() {
         assertMultiFieldsParamsRewrite(
             rrfRetrieverBuilder,
             queryRewriteContext,
-            Map.of("field_*", 1.0f, "*_field_1", 1.0f),
-            Map.of("semantic_field_1", 1.0f),
-            "bar"
+            Map.of("field_1", 1.0f, "field_2", 1.5f),
+            Map.of("semantic_field_1", 1.0f, "semantic_field_2", 2.0f),
+            "bar",
+            null
         );
 
-        // All-fields wildcard
+        // Glob matching on inference and non-inference fields with per-field boosting
         rrfRetrieverBuilder = new RRFRetrieverBuilder(
             null,
-            List.of("*"),
+            List.of("field_*^1.5", "*_field_1^2.5"),
             "baz",
             DEFAULT_RANK_WINDOW_SIZE,
             RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
@@ -230,10 +249,117 @@ public void testMultiFieldsParamsRewrite() {
         assertMultiFieldsParamsRewrite(
             rrfRetrieverBuilder,
             queryRewriteContext,
-            Map.of("*", 1.0f),
-            Map.of("semantic_field_1", 1.0f, "semantic_field_2", 1.0f),
-            "baz"
+            Map.of("field_*", 1.5f, "*_field_1", 2.5f),
+            Map.of("semantic_field_1", 2.5f),
+            "baz",
+            null
+        );
+
+        // Multiple boosts defined on the same field
+        rrfRetrieverBuilder = new RRFRetrieverBuilder(
+            null,
+            List.of("field_*^1.5", "field_1^3.0", "*_field_1^2.5", "semantic_*^1.5"),
+            "baz2",
+            DEFAULT_RANK_WINDOW_SIZE,
+            RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
+            new float[0]
+        );
+        assertMultiFieldsParamsRewrite(
+            rrfRetrieverBuilder,
+            queryRewriteContext,
+            Map.of("field_*", 1.5f, "field_1", 3.0f, "*_field_1", 2.5f, "semantic_*", 1.5f),
+            Map.of("semantic_field_1", 3.75f, "semantic_field_2", 1.5f),
+            "baz2",
+            null
+        );
+
+        // All-fields wildcard with weights
+        rrfRetrieverBuilder = new RRFRetrieverBuilder(
+            null,
+            List.of("*^2.0"),
+            "qux",
+            DEFAULT_RANK_WINDOW_SIZE,
+            RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
+            new float[0]
+        );
+        assertMultiFieldsParamsRewrite(
+            rrfRetrieverBuilder,
+            queryRewriteContext,
+            Map.of("*", 2.0f),
+            Map.of("semantic_field_1", 2.0f, "semantic_field_2", 2.0f),
+            "qux",
+            null
+        );
+
+        // Zero weights (testing that zero is allowed as non-negative)
+        rrfRetrieverBuilder = new RRFRetrieverBuilder(
+            null,
+            List.of("field_1^0", "field_2^1.0"),
+            "zero_test",
+            DEFAULT_RANK_WINDOW_SIZE,
+            RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
+            new float[0]
+        );
+        assertMultiFieldsParamsRewrite(
+            rrfRetrieverBuilder,
+            queryRewriteContext,
+            Map.of("field_1", 0.0f, "field_2", 1.0f),
+            Map.of(),
+            "zero_test",
+            null
+        );
+
+        // Mixed weighted and unweighted fields in simplified syntax
+        rrfRetrieverBuilder = new RRFRetrieverBuilder(
+            null,
+            List.of("title^2.5", "content", "tags^1.5", "description"),
+            "test query",
+            DEFAULT_RANK_WINDOW_SIZE,
+            RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
+            new float[0]
+        );
+        assertMultiFieldsParamsRewrite(
+            rrfRetrieverBuilder,
+            queryRewriteContext,
+            Map.of("title", 2.5f, "content", 1.0f, "tags", 1.5f, "description", 1.0f),
+            Map.of(),
+            "test query",
+            null
+        );
+
+        // Decimal weight precision handling
+        rrfRetrieverBuilder = new RRFRetrieverBuilder(
+            null,
+            List.of("field1^0.1", "field2^2.75", "field3^10.999"),
+            "test query",
+            DEFAULT_RANK_WINDOW_SIZE,
+            RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
+            new float[0]
+        );
+        assertMultiFieldsParamsRewrite(
+            rrfRetrieverBuilder,
+            queryRewriteContext,
+            Map.of("field1", 0.1f, "field2", 2.75f, "field3", 10.999f),
+            Map.of(),
+            "test query",
+            null
+        );
+
+        // Test negative weight validation
+        RRFRetrieverBuilder negativeWeightBuilder = new RRFRetrieverBuilder(
+            null,
+            List.of("field_1^-1.0"),
+            "negative_test",
+            DEFAULT_RANK_WINDOW_SIZE,
+            RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
+            new float[0]
+        );
+
+        IllegalArgumentException iae = expectThrows(
+            IllegalArgumentException.class,
+            () -> negativeWeightBuilder.doRewrite(queryRewriteContext)
         );
+        assertEquals("[rrf] per-field weights must be non-negative", iae.getMessage());
     }
 
     public void testMultiIndexMultiFieldsParamsRewrite() {