Remove unnecessary converters

Author: carlosdelest

x-pack/plugin/esql/qa/testFixtures/src/main/resources/dense_vector.csv-spec

@@ -88,3 +88,16 @@ row doubles = [123.4, 567.8, 901.2]
 vector:dense_vector
 [123.4, 567.8, 901.2]
 ;
+
+convertHexStringToDenseVector
+required_capability: dense_vector_field_type
+required_capability: to_dense_vector_function
+
+row hex_str = "0102030405060708090a0b0c0d0e0f"
+| eval vector = to_dense_vector(hex_str)
+| keep vector
+;
+
+vector:dense_vector
+ [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0]
+;

x-pack/plugin/esql/qa/testFixtures/src/main/resources/knn-function.csv-spec

@@ -327,3 +327,28 @@ navy       | [0.0, 0.0, 128.0]
 gray       | [128.0, 128.0, 128.0]
 chartreuse | [127.0, 255.0, 0.0]
 ;
+
+knnWithHexStringCasting
+required_capability: knn_function_v3
+required_capability: to_dense_vector_function
+
+from colors metadata _score
+| eval query = [0, 120, 0]
+| where knn(rgb_vector, "007800", 10) 
+| sort _score desc, color asc
+| keep color, rgb_vector
+| limit 10
+;
+
+color:text | rgb_vector:dense_vector
+green      | [0.0, 128.0, 0.0]
+black      | [0.0, 0.0, 0.0]
+olive      | [128.0, 128.0, 0.0]
+teal       | [0.0, 128.0, 128.0]
+lime       | [0.0, 255.0, 0.0]
+sienna     | [160.0, 82.0, 45.0]
+maroon     | [128.0, 0.0, 0.0]
+navy       | [0.0, 0.0, 128.0]
+gray       | [128.0, 128.0, 128.0]
+chartreuse | [127.0, 255.0, 0.0]
+;

x-pack/plugin/esql/src/main/generated/org/elasticsearch/xpack/esql/expression/function/scalar/convert/ToDenseVectorFromBooleanEvaluator.java

@@ -2352,6 +2352,8 @@ public void testDenseVectorImplicitCastingKnn() {
         assumeTrue("dense_vector capability not available", EsqlCapabilities.Cap.DENSE_VECTOR_FIELD_TYPE.isEnabled());
         assumeTrue("dense_vector capability not available", EsqlCapabilities.Cap.KNN_FUNCTION_V3.isEnabled());
 
+        checkDenseVectorCastingHexKnn("float_vector");
+        checkDenseVectorCastingHexKnn("byte_vector");
         checkDenseVectorCastingKnn("float_vector");
         checkDenseVectorCastingKnn("byte_vector");
         checkDenseVectorEvalCastingKnn("float_vector");
@@ -2371,6 +2373,19 @@ private static void checkDenseVectorCastingKnn(String fieldName) {
         assertThat(queryVector.value(), equalTo(List.of(0.0f, 1.0f, 2.0f)));
     }
 
+    private static void checkDenseVectorCastingHexKnn(String fieldName) {
+        var plan = analyze(String.format(Locale.ROOT, """
+            from test | where knn(%s, "000102", 10)
+            """, fieldName), "mapping-dense_vector.json");
+
+        var limit = as(plan, Limit.class);
+        var filter = as(limit.child(), Filter.class);
+        var knn = as(filter.condition(), Knn.class);
+        var queryVector = as(knn.query(), Literal.class);
+        assertEquals(DataType.DENSE_VECTOR, queryVector.dataType());
+        assertThat(queryVector.value(), equalTo(List.of(0.0f, 1.0f, 2.0f)));
+    }
+
     private static void checkDenseVectorEvalCastingKnn(String fieldName) {
         var plan = analyze(String.format(Locale.ROOT, """
             from test | eval query = [0, 1, 2] | where knn(%s, query, 10)