Support negative offsets in SQL string::slice() function

Closes #1490

lib/src/fnc/args.rs

@@ -45,6 +45,12 @@ impl FromArg for i64 {
 	}
 }
 
+impl FromArg for isize {
+	fn from_arg(arg: Value) -> Result<Self, Error> {
+		Ok(arg.as_int() as isize)
+	}
+}
+
 impl FromArg for usize {
 	fn from_arg(arg: Value) -> Result<Self, Error> {
 		Ok(arg.as_int() as usize)

lib/src/fnc/string.rs

@@ -51,8 +51,18 @@ pub fn reverse((string,): (String,)) -> Result<Value, Error> {
 	Ok(string.chars().rev().collect::<String>().into())
 }
 
-pub fn slice((val, beg, lim): (String, usize, usize)) -> Result<Value, Error> {
+pub fn slice((val, beg, lim): (String, Option<isize>, Option<isize>)) -> Result<Value, Error> {
-	Ok(val.chars().skip(beg).take(lim).collect::<String>().into())
+	let val = match beg {
+		Some(v) if v < 0 => val.chars().skip(val.len() - v.unsigned_abs()).collect::<String>(),
+		Some(v) => val.chars().skip(v as usize).collect::<String>(),
+		None => val,
+	};
+	let val = match lim {
+		Some(v) if v < 0 => val.chars().take(val.len() - v.unsigned_abs()).collect::<String>(),
+		Some(v) => val.chars().take(v as usize).collect::<String>(),
+		None => val,
+	};
+	Ok(val.into())
 }
 
 pub fn slug((string,): (String,)) -> Result<Value, Error> {

lib/tests/function.rs

@@ -6,12 +6,12 @@ use surrealdb::Error;
 use surrealdb::Session;
 
 #[tokio::test]
-async fn array_distinct() -> Result<(), Error> {
+async fn function_array_distinct() -> Result<(), Error> {
 	let sql = r#"
-		SELECT * FROM array::distinct([1, 3, 2, 1, 3, 3, 4]);
+		RETURN array::distinct([1, 3, 2, 1, 3, 3, 4]);
-		SELECT * FROM array::distinct([]);
+		RETURN array::distinct([]);
-		SELECT * FROM array::distinct("something");
+		RETURN array::distinct("something");
-		SELECT * FROM array::distinct(["something"]);
+		RETURN array::distinct(["something"]);
 	"#;
 	let dbs = Datastore::new("memory").await?;
 	let ses = Session::for_kv().with_ns("test").with_db("test");
@@ -27,7 +27,7 @@ async fn array_distinct() -> Result<(), Error> {
 	assert_eq!(tmp, val);
 	//
 	let tmp = res.remove(0).result?;
-	let val = Value::parse("[NONE]");
+	let val = Value::None;
 	assert_eq!(tmp, val);
 	//
 	let tmp = res.remove(0).result?;
@@ -36,3 +36,45 @@ async fn array_distinct() -> Result<(), Error> {
 	//
 	Ok(())
 }
+
+#[tokio::test]
+async fn function_string_slice() -> Result<(), Error> {
+	let sql = r#"
+		RETURN string::slice("the quick brown fox jumps over the lazy dog.");
+		RETURN string::slice("the quick brown fox jumps over the lazy dog.", 16);
+		RETURN string::slice("the quick brown fox jumps over the lazy dog.", 0, 60);
+		RETURN string::slice("the quick brown fox jumps over the lazy dog.", 0, -1);
+		RETURN string::slice("the quick brown fox jumps over the lazy dog.", 16, -1);
+		RETURN string::slice("the quick brown fox jumps over the lazy dog.", -9, -1);
+	"#;
+	let dbs = Datastore::new("memory").await?;
+	let ses = Session::for_kv().with_ns("test").with_db("test");
+	let res = &mut dbs.execute(&sql, &ses, None, false).await?;
+	assert_eq!(res.len(), 6);
+	//
+	let tmp = res.remove(0).result?;
+	let val = Value::parse("'the quick brown fox jumps over the lazy dog.'");
+	assert_eq!(tmp, val);
+	//
+	let tmp = res.remove(0).result?;
+	let val = Value::parse("'fox jumps over the lazy dog.'");
+	assert_eq!(tmp, val);
+	//
+	let tmp = res.remove(0).result?;
+	let val = Value::parse("'the quick brown fox jumps over the lazy dog.'");
+	assert_eq!(tmp, val);
+	//
+	let tmp = res.remove(0).result?;
+	let val = Value::parse("'the quick brown fox jumps over the lazy dog'");
+	assert_eq!(tmp, val);
+	//
+	let tmp = res.remove(0).result?;
+	let val = Value::parse("'fox jumps over the lazy dog'");
+	assert_eq!(tmp, val);
+	//
+	let tmp = res.remove(0).result?;
+	let val = Value::parse("'lazy dog'");
+	assert_eq!(tmp, val);
+	//
+	Ok(())
+}