feat: add subqueries feature to builtin features in schema LS

integration/schema-language-server/language-server/src/main/java/ai/vespa/schemals/schemadocument/resolvers/RankExpression/BuiltInFunctions.java

@@ -336,6 +336,17 @@ public class BuiltInFunctions {
         put("onnxModel", new GenericFunction("onnxModel", new FunctionSignature(new SymbolArgument(SymbolType.ONNX_MODEL, "onnx-model"))));
         put("lightgbm", new GenericFunction("lightgbm", new FunctionSignature(new StringArgument("\"/path/to/lightgbm-model.json\""))));
         put("xgboost", new GenericFunction("xgboost", new FunctionSignature(new StringArgument("\"/path/to/xgboost-model.json\""))));
+
+        // TODO: I think this needs to be inside summary-features
+        // https://docs.vespa.ai/en/predicate-fields.html#identifying-subqueries-in-results
+        put("subqueries", new GenericFunction("subqueries", new FunctionSignature(
+            new FieldArgument(FieldType.PREDICATE),
+            Set.of(
+                "",
+                "lsb",
+                "msb"
+            )
+        )));
     }};
 
     // Some features that have not gotten a signature for various reasons

integration/schema-language-server/language-server/src/main/java/ai/vespa/schemals/schemadocument/resolvers/RankExpression/argument/FieldArgument.java

@@ -25,7 +25,8 @@ public static enum FieldType {
         NUMERIC_ARRAY,
         STRING,
         STRING_ARRAY,
-        POSITION
+        POSITION,
+        PREDICATE
     };
 
     public static final EnumSet<FieldType> AnyFieldType = EnumSet.allOf(FieldType.class);

integration/schema-language-server/language-server/src/test/java/ai/vespa/schemals/SchemaParserTest.java

@@ -263,6 +263,7 @@ Stream<DynamicTest> generateGoodFileTests() {
             "src/test/sdfiles/single/structinfieldset.sd",
             "src/test/sdfiles/single/attributeposition.sd",
             "src/test/sdfiles/single/defaultdefault.sd",
+            "src/test/sdfiles/single/subqueries.sd",
         };
 
         return Arrays.stream(filePaths)

integration/schema-language-server/language-server/src/test/sdfiles/single/subqueries.sd

@@ -0,0 +1,16 @@
+schema subqueries {
+    document subqueries {
+        field predicate_field type predicate {
+            indexing: attribute
+            index {
+                arity: 2
+                lower-bound: 3
+                upper-bound: 200
+                dense-posting-list-threshold: 0.25
+            }
+        }
+    }
+    rank-profile default {
+        summary-features: subqueries(predicate_field).lsb subqueries(predicate_field).msb
+    }
+}