Fix enumerable attribute on string length property (#974)

* Fix enumerable attribute on string length property

* Remove unnecessary conversion

* Fix length for string value

Co-authored-by: tofpie <tofpie@users.noreply.github.com>

boa/src/builtins/string/mod.rs

@@ -13,6 +13,7 @@ pub mod string_iterator;
 #[cfg(test)]
 mod tests;
 
+use crate::property::DataDescriptor;
 use crate::{
     builtins::{string::string_iterator::StringIterator, BuiltIn, RegExp},
     object::{ConstructorBuilder, Object, ObjectData},
@@ -140,9 +141,11 @@ impl String {
             None => RcString::default(),
         };
 
-        let length = string.encode_utf16().count();
-
-        this.set_field("length", Value::from(length as i32));
+        let length = DataDescriptor::new(
+            Value::from(string.encode_utf16().count()),
+            Attribute::NON_ENUMERABLE,
+        );
+        this.set_property("length", length);
 
         this.set_data(ObjectData::String(string.clone()));
 

boa/src/builtins/string/tests.rs

@@ -39,6 +39,20 @@ fn new_string_has_length() {
     assert_eq!(forward(&mut context, "a.length"), "4");
 }
 
+#[test]
+fn new_string_has_length_not_enumerable() {
+    let mut context = Context::new();
+    let init = r#"
+        let a = new String("1234");
+        "#;
+
+    forward(&mut context, init);
+    assert_eq!(
+        forward(&mut context, "a.propertyIsEnumerable('length')"),
+        "false"
+    );
+}
+
 #[test]
 fn new_utf8_string_has_length() {
     let mut context = Context::new();

boa/src/value/mod.rs

@@ -664,7 +664,11 @@ impl Value {
                     ObjectData::String(string.clone()),
                 ));
                 // Make sure the correct length is set on our new string object
-                object.set("length".into(), string.chars().count().into());
+                object.insert_property(
+                    PropertyKey::String("length".into()),
+                    Value::from(string.encode_utf16().count()),
+                    Attribute::NON_ENUMERABLE,
+                );
                 Ok(object)
             }
             Value::Symbol(ref symbol) => {

boa/src/value/tests.rs

@@ -251,6 +251,37 @@ fn to_string() {
     assert_eq!(f64_to_str(3e50), "3e+50");
 }
 
+#[test]
+fn string_length_is_not_enumerable() {
+    let mut context = Context::new();
+
+    let object = Value::from("foo").to_object(&mut context).unwrap();
+    let length_desc = object
+        .get_own_property(&PropertyKey::from("length"))
+        .unwrap();
+    assert!(!length_desc.enumerable());
+}
+
+#[test]
+fn string_length_is_in_utf16_codeunits() {
+    let mut context = Context::new();
+
+    // 😀 is one Unicode code point, but 2 UTF-16 code units
+    let object = Value::from("😀").to_object(&mut context).unwrap();
+    let length_desc = object
+        .get_own_property(&PropertyKey::from("length"))
+        .unwrap();
+    assert_eq!(
+        length_desc
+            .as_data_descriptor()
+            .unwrap()
+            .value()
+            .to_integer_or_infinity(&mut context)
+            .unwrap(),
+        IntegerOrInfinity::Integer(2)
+    );
+}
+
 #[test]
 fn add_number_and_number() {
     let mut context = Context::new();