Add ES|QL bit_length function

docs/changelog/115792.yaml

@@ -0,0 +1,5 @@
+pr: 115792
+summary: Add ES|QL `bit_length` function
+area: ES|QL
+type: enhancement
+issues: []

docs/reference/esql/functions/string-functions.asciidoc

@@ -8,6 +8,7 @@
 {esql} supports these string functions:
 
 // tag::string_list[]
+* <<esql-bit_length>>
 * <<esql-concat>>
 * <<esql-ends_with>>
 * <<esql-from_base64>>
@@ -30,6 +31,7 @@
 * <<esql-trim>>
 // end::string_list[]
 
+include::layout/bit_length.asciidoc[]
 include::layout/concat.asciidoc[]
 include::layout/ends_with.asciidoc[]
 include::layout/from_base64.asciidoc[]

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

@@ -656,3 +656,21 @@ FROM sample_data
 
 @timestamp:date | client_ip:ip | event_duration:long | message:keyword
 ;
+
+docsBitLength
+// tag::bitLength[]
+FROM employees
+| KEEP first_name, last_name
+| EVAL fn_bit_length = BIT_LENGTH(first_name)
+// end::bitLength[]
+| SORT first_name
+| LIMIT 3
+;
+
+// tag::bitLength-result[]
+first_name:keyword   | last_name:keyword   | fn_bit_length:integer
+Alejandro      |McAlpine       |72              
+Amabile        |Gomatam        |56              
+Anneke         |Preusig        |48
+// end::bitLength-result[]
+;

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

@@ -38,6 +38,56 @@ emp_no:integer | l:integer
 10003 | 5
 ;
 
+bitLength
+required_capability: fn_bit_length
+row a = "hello", b = "" | eval y = bit_length(a) + bit_length(b);
+
+a:keyword | b:keyword | y:integer
+hello | | 40
+;
+
+bitLengthWithNonAsciiChars
+required_capability: fn_bit_length
+row a = "¡", b = "❗️" | eval y = bit_length(a) | eval z = bit_length(b);
+
+a:keyword | b:keyword | y:integer | z:integer
+¡ | ❗️ | 16 | 48
+;
+
+foldBitLength
+required_capability: fn_bit_length
+row a = 1 | eval b = bit_length("hello");
+
+a:integer | b:integer
+1 | 40
+;
+
+bitLengthAndSourceQuoting
+required_capability: fn_bit_length
+from "employees" | sort emp_no | limit 3 | eval l = bit_length(first_name) | keep emp_no, l;
+
+emp_no:integer | l:integer
+10001 | 48
+10002 | 56
+10003 | 40
+;
+
+bitLengthInsideOtherFunction
+required_capability: fn_bit_length
+row a = "abc", b = "de" | eval g = greatest(bit_length(a), bit_length(b), bit_length("fghi"));
+
+a:keyword | b:keyword | g:integer
+abc | de | 32
+;
+
+bitLengthNull
+required_capability: fn_bit_length
+row a = "abc" | eval l = bit_length(null);
+
+a:string | l:integer
+abc | null
+;
+
 startsWithConstant
 from employees | sort emp_no | limit 10 | eval f_S = starts_with(first_name, "S") | keep emp_no, first_name, f_S;
 

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -27,6 +27,12 @@
  */
 public class EsqlCapabilities {
     public enum Cap {
+
+        /**
+         * Support for function {@code BIT_LENGTH}. Done in #115792
+         */
+        FN_BIT_LENGTH,
+
         /**
          * Support for function {@code REVERSE}.
          */

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

@@ -117,6 +117,7 @@
 import org.elasticsearch.xpack.esql.expression.function.scalar.spatial.StDistance;
 import org.elasticsearch.xpack.esql.expression.function.scalar.spatial.StX;
 import org.elasticsearch.xpack.esql.expression.function.scalar.spatial.StY;
+import org.elasticsearch.xpack.esql.expression.function.scalar.string.BitLength;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.Concat;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.EndsWith;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.LTrim;
@@ -305,6 +306,7 @@ private FunctionDefinition[][] functions() {
                 def(Tau.class, Tau::new, "tau") },
             // string
             new FunctionDefinition[] {
+                def(BitLength.class, BitLength::new, "bit_length"),
                 def(Concat.class, Concat::new, "concat"),
                 def(EndsWith.class, EndsWith::new, "ends_with"),
                 def(LTrim.class, LTrim::new, "ltrim"),

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

@@ -38,6 +38,7 @@
 import org.elasticsearch.xpack.esql.expression.function.scalar.math.Tau;
 import org.elasticsearch.xpack.esql.expression.function.scalar.nulls.Coalesce;
 import org.elasticsearch.xpack.esql.expression.function.scalar.spatial.BinarySpatialFunction;
+import org.elasticsearch.xpack.esql.expression.function.scalar.string.BitLength;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.Concat;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.EndsWith;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.Left;
@@ -74,6 +75,7 @@ public static List<NamedWriteableRegistry.Entry> getNamedWriteables() {
         List<NamedWriteableRegistry.Entry> entries = new ArrayList<>();
         entries.add(And.ENTRY);
         entries.add(Atan2.ENTRY);
+        entries.add(BitLength.ENTRY);
         entries.add(Bucket.ENTRY);
         entries.add(Case.ENTRY);
         entries.add(Categorize.ENTRY);