Implement `Symbol.prototype[ @@toPrimitive ]` (#1634)

boa/src/builtins/symbol/mod.rs

@@ -99,6 +99,12 @@ impl BuiltIn for Symbol {
 
         let attribute = Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::PERMANENT;
 
+        let to_primitive = FunctionBuilder::native(context, Self::to_primitive)
+            .name("[Symbol.toPrimitive]")
+            .length(1)
+            .constructable(false)
+            .build();
+
         let get_description = FunctionBuilder::native(context, Self::get_description)
             .name("get description")
             .constructable(false)
@@ -123,7 +129,7 @@ impl BuiltIn for Symbol {
         .static_property("search", symbol_search, attribute)
         .static_property("species", symbol_species, attribute)
         .static_property("split", symbol_split, attribute)
-        .static_property("toPrimitive", symbol_to_primitive, attribute)
+        .static_property("toPrimitive", symbol_to_primitive.clone(), attribute)
         .static_property("toStringTag", symbol_to_string_tag.clone(), attribute)
         .static_property("unscopables", symbol_unscopables, attribute)
         .method(Self::to_string, "toString", 0)
@@ -141,6 +147,11 @@ impl BuiltIn for Symbol {
             Self::NAME,
             Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE,
         )
+        .property(
+            symbol_to_primitive,
+            to_primitive,
+            Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE,
+        )
         .build();
 
         symbol_object.into()
@@ -316,4 +327,25 @@ impl Symbol {
             context.throw_type_error("Symbol.keyFor: sym is not a symbol")
         }
     }
+
+    /// `Symbol.prototype [ @@toPrimitive ]`
+    ///
+    /// This function is called by ECMAScript language operators to convert a Symbol object to a primitive value.
+    /// NOTE: The argument is ignored
+    ///
+    /// More information:
+    /// - [MDN documentation][mdn]
+    /// - [ECMAScript reference][spec]
+    ///
+    /// [spec]: https://tc39.es/ecma262/multipage/#sec-symbol.prototype-@@toprimitive
+    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/@@toPrimitive
+    pub(crate) fn to_primitive(
+        this: &JsValue,
+        _: &[JsValue],
+        context: &mut Context,
+    ) -> JsResult<JsValue> {
+        let sym = Self::this_symbol_value(this, context)?;
+        // 1. Return ? thisSymbolValue(this value).
+        Ok(sym.into())
+    }
 }

boa/src/object/mod.rs

@@ -1227,7 +1227,7 @@ impl<'context> FunctionBuilder<'context> {
         self
     }
 
-    /// Specify the whether the object function object can be called with `new` keyword.
+    /// Specify whether the object function object can be called with `new` keyword.
     ///
     /// The default is `false`.
     #[inline]