[ES|QL] add reverse function

docs/changelog/113297.yaml

@@ -0,0 +1,5 @@
+pr: 113297
+summary: "[ES|QL] add reverse function"
+area: ES|QL
+type: enhancement
+issues: []

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

@@ -17,6 +17,7 @@
 * <<esql-ltrim>>
 * <<esql-repeat>>
 * <<esql-replace>>
+* <<esql-reverse>>
 * <<esql-right>>
 * <<esql-rtrim>>
 * <<esql-space>>
@@ -38,6 +39,7 @@ include::layout/locate.asciidoc[]
 include::layout/ltrim.asciidoc[]
 include::layout/repeat.asciidoc[]
 include::layout/replace.asciidoc[]
+include::layout/reverse.asciidoc[]
 include::layout/right.asciidoc[]
 include::layout/rtrim.asciidoc[]
 include::layout/space.asciidoc[]

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

@@ -69,6 +69,7 @@ double pi()
 "double pow(base:double|integer|long|unsigned_long, exponent:double|integer|long|unsigned_long)"
 "keyword repeat(string:keyword|text, number:integer)"
 "keyword replace(string:keyword|text, regex:keyword|text, newString:keyword|text)"
+"keyword|text reverse(str:keyword|text)"
 "keyword right(string:keyword|text, length:integer)"
 "double|integer|long|unsigned_long round(number:double|integer|long|unsigned_long, ?decimals:integer)"
 "keyword|text rtrim(string:keyword|text)"
@@ -199,6 +200,7 @@ pi            |null                                |null
 pow           |[base, exponent]                    |["double|integer|long|unsigned_long", "double|integer|long|unsigned_long"]                                                        |["Numeric expression for the base. If `null`\, the function returns `null`.", "Numeric expression for the exponent. If `null`\, the function returns `null`."]
 repeat        |[string, number]                    |["keyword|text", integer]                                                                                                         |[String expression., Number times to repeat.]
 replace       |[string, regex, newString]          |["keyword|text", "keyword|text", "keyword|text"]                                                                                  |[String expression., Regular expression., Replacement string.]
+reverse       |str                                 |"keyword|text"                                                                                                                    |String expression. If `null`, the function returns `null`.
 right         |[string, length]                    |["keyword|text", integer]                                                                                                         |[The string from which to returns a substring., The number of characters to return.]
 round         |[number, decimals]                  |["double|integer|long|unsigned_long", integer]                                                                                    |["The numeric value to round. If `null`\, the function returns `null`.", "The number of decimal places to round to. Defaults to 0. If `null`\, the function returns `null`."]
 rtrim         |string                              |"keyword|text"                                                                                                                    |String expression. If `null`, the function returns `null`.
@@ -329,6 +331,7 @@ pi            |Returns {wikipedia}/Pi[Pi], the ratio of a circle's circumference
 pow           |Returns the value of `base` raised to the power of `exponent`.
 repeat        |Returns a string constructed by concatenating `string` with itself the specified `number` of times.
 replace       |The function substitutes in the string `str` any match of the regular expression `regex` with the replacement string `newStr`.
+reverse       |Returns a new string representing the input string in reverse order.
 right         |Return the substring that extracts 'length' chars from 'str' starting from the right.
 round         |Rounds a number to the specified number of decimal places. Defaults to 0, which returns the nearest integer. If the precision is a negative number, rounds to the number of digits left of the decimal point.
 rtrim         |Removes trailing whitespaces from a string.
@@ -461,6 +464,7 @@ pi            |double
 pow           |double                                                                                                                      |[false, false]              |false           |false
 repeat        |keyword                                                                                                                     |[false, false]              |false           |false
 replace       |keyword                                                                                                                     |[false, false, false]       |false           |false
+reverse       |"keyword|text"                                                                                                              |false                       |false           |false
 right         |keyword                                                                                                                     |[false, false]              |false           |false
 round         |"double|integer|long|unsigned_long"                                                                                         |[false, true]               |false           |false
 rtrim         |"keyword|text"                                                                                                              |false                       |false           |false
@@ -536,5 +540,5 @@ required_capability: meta
 meta functions |  stats  a = count(*), b = count(*), c = count(*) |  mv_expand c;
 
 a:long | b:long | c:long
-119    | 119    | 119
+120    | 120    | 120
 ;

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

@@ -1194,6 +1194,101 @@ a:keyword           | upper:keyword         | lower:keyword
 π/2 + a + B + Λ ºC  | Π/2 + A + B + Λ ºC    | π/2 + a + b + λ ºc
 ;
 
+reverse
+required_capability: fn_reverse
+from employees | sort emp_no | eval name_reversed = REVERSE(first_name) | keep emp_no, first_name, name_reversed | limit 1;
+
+emp_no:integer  | first_name:keyword    | name_reversed:keyword
+10001           | Georgi                | igroeG
+;
+
+reverseRow
+required_capability: fn_reverse
+// tag::reverse[]
+ROW message = "Some Text" | EVAL message_reversed = REVERSE(message);
+// end::reverse[]
+
+// tag::reverse-result[]
+message:keyword | message_reversed:keyword
+Some Text       | txeT emoS
+// end::reverse-result[]
+;
+
+reverseEmoji
+required_capability: fn_reverse
+// tag::reverseEmoji[]
+ROW message = "😂😁😅😐🥺😢😭" | EVAL message_reversed = REVERSE(message);
+// end::reverseEmoji[]
+
+// tag::reverseEmoji-result[]
+message:keyword | message_reversed:keyword
+😂😁😅😐🥺😢😭 | 😭😢🥺😐😅😁😂
+// end::reverseEmoji-result[]
+;
+
+reverseMultiValue
+required_capability: fn_reverse
+FROM employees | SORT emp_no | EVAL jobs_reversed = REVERSE(job_positions) | KEEP job*, emp_no | LIMIT 5;
+
+warning:Line 1:53: evaluation of [REVERSE(job_positions)] failed, treating result as null. Only first 20 failures recorded.
+warning:Line 1:53: java.lang.IllegalArgumentException: single-value function encountered multi-value
+
+job_positions:keyword                                                   | jobs_reversed:keyword | emp_no:integer
+["Accountant",  "Senior Python Developer"]                              | null                  | 10001
+Senior Team Lead                                                        | daeL maeT roineS      | 10002
+null                                                                    | null                  | 10003
+[Head Human Resources, Reporting Analyst, Support Engineer, Tech Lead]  | null                  | 10004
+null                                                                    | null                  | 10005
+;
+
+reverseNested
+required_capability: fn_reverse
+FROM employees | SORT emp_no | EVAL name_reversed = REVERSE(REVERSE(first_name)), eq = name_reversed == first_name | KEEP first_name, name_reversed, eq, emp_no | LIMIT 5;
+
+first_name:keyword  | name_reversed:keyword | eq:boolean    | emp_no:integer
+Georgi              | Georgi                | true          | 10001
+Bezalel             | Bezalel               | true          | 10002
+Parto               | Parto                 | true          | 10003
+Chirstian           | Chirstian             | true          | 10004
+Kyoichi             | Kyoichi               | true          | 10005
+;
+
+reverseRowNull
+required_capability: fn_reverse
+ROW x = null | EVAL y = REVERSE(x);
+
+x:null      | y:null
+null        | null
+;
+
+
+reverseRowInlineCastWithNull
+required_capability: fn_reverse
+ROW x = 1 | EVAL y = REVERSE((null + 1)::string);
+
+x:integer   | y:string
+1           | null
+;
+
+reverseWithTextFields
+required_capability: fn_reverse
+FROM books 
+| EVAL title_reversed = REVERSE(title), author_reversed_twice = REVERSE(REVERSE(author)), eq = author_reversed_twice == author 
+| KEEP title, title_reversed, author, author_reversed_twice, eq, book_no
+| SORT book_no
+| LIMIT 2;
+
+warning:Line 2:25: evaluation of [REVERSE(title)] failed, treating result as null. Only first 20 failures recorded.
+warning:Line 2:25: java.lang.IllegalArgumentException: single-value function encountered multi-value
+warning:Line 2:73: evaluation of [REVERSE(author)] failed, treating result as null. Only first 20 failures recorded.
+warning:Line 2:73: java.lang.IllegalArgumentException: single-value function encountered multi-value
+
+title:text                                      | title_reversed:text                           | author:text               | author_reversed_twice:text    | eq:boolean    | book_no:keyword
+The brothers Karamazov                          | vozamaraK srehtorb ehT                        | Fyodor Dostoevsky         | Fyodor Dostoevsky             | true          | 1211
+Realms of Tolkien: Images of Middle-earth       | htrae-elddiM fo segamI :neikloT fo smlaeR     | J. R. R. Tolkien          | J. R. R. Tolkien              | true          | 1463
+;
+
+
 values
 required_capability: agg_values