Implementation of `instanceof` operator (#908)

Co-authored-by: Andrej Onufrák <andrej.onufrak@student.tuke.sk>

boa/src/builtins/symbol/mod.rs

@@ -113,7 +113,7 @@ impl WellKnownSymbols {
     /// Called by the semantics of the instanceof operator.
     #[inline]
     pub fn has_instance_symbol(&self) -> RcSymbol {
-        self.async_iterator.clone()
+        self.has_instance.clone()
     }
 
     /// The `Symbol.isConcatSpreadable` well known symbol.

boa/src/object/gcobject.rs

@@ -676,6 +676,67 @@ impl GcObject {
     pub fn is_native_object(&self) -> bool {
         self.borrow().is_native_object()
     }
+
+    /// Retrieves value of specific property, when the value of the property is expected to be a function.
+    ///
+    /// More information:
+    /// - [EcmaScript reference][spec]
+    ///
+    /// [spec]: https://tc39.es/ecma262/#sec-getmethod
+    #[inline]
+    pub fn get_method<K>(&self, context: &mut Context, key: K) -> Result<Option<GcObject>>
+    where
+        K: Into<PropertyKey>,
+    {
+        let key = key.into();
+        let value = self.get(&key);
+
+        if value.is_null_or_undefined() {
+            return Ok(None);
+        }
+
+        match value.as_object() {
+            Some(object) if object.is_callable() => Ok(Some(object)),
+            _ => Err(context
+                .construct_type_error("value returned for property of object is not a function")),
+        }
+    }
+
+    /// Determines if `value` inherits from the instance object inheritance path.
+    ///
+    /// More information:
+    /// - [EcmaScript reference][spec]
+    ///
+    /// [spec]: https://tc39.es/ecma262/#sec-ordinaryhasinstance
+    #[inline]
+    pub fn ordinary_has_instance(&self, context: &mut Context, value: &Value) -> Result<bool> {
+        if !self.is_callable() {
+            return Ok(false);
+        }
+
+        // TODO: If C has a [[BoundTargetFunction]] internal slot, then
+        //           Let BC be C.[[BoundTargetFunction]].
+        //           Return ? InstanceofOperator(O, BC).
+
+        if let Some(object) = value.as_object() {
+            if let Some(prototype) = self.get(&"prototype".into()).as_object() {
+                let mut object = object.get_prototype_of();
+                while let Some(object_prototype) = object.as_object() {
+                    if GcObject::equals(&prototype, &object_prototype) {
+                        return Ok(true);
+                    }
+                    object = object_prototype.get_prototype_of();
+                }
+
+                Ok(false)
+            } else {
+                Err(context
+                    .construct_type_error("function has non-object prototype in instanceof check"))
+            }
+        } else {
+            Ok(false)
+        }
+    }
 }
 
 impl AsRef<GcCell<Object>> for GcObject {

boa/src/object/mod.rs

@@ -22,6 +22,9 @@ use std::{
     ops::{Deref, DerefMut},
 };
 
+#[cfg(test)]
+mod tests;
+
 mod gcobject;
 mod internal_methods;
 mod iter;

boa/src/object/tests.rs

@@ -0,0 +1,19 @@
+use crate::exec;
+
+#[test]
+fn ordinary_has_instance_nonobject_prototype() {
+    let scenario = r#"
+        try {
+          function C() {}
+          C.prototype = 1
+          String instanceof C
+        } catch (err) {
+          err.toString()
+        }
+        "#;
+
+    assert_eq!(
+        &exec(scenario),
+        "\"TypeError: function has non-object prototype in instanceof check\""
+    );
+}

boa/src/syntax/ast/node/operator/bin_op/mod.rs

@@ -125,17 +125,28 @@ impl Executable for BinOp {
                         interpreter.has_property(&y, &key)
                     }
                     CompOp::InstanceOf => {
-                        if !y.is_object() {
+                        if let Some(object) = y.as_object() {
+                            let key = interpreter.well_known_symbols().has_instance_symbol();
+
+                            match object.get_method(interpreter, key)? {
+                                Some(instance_of_handler) => instance_of_handler
+                                    .call(&y, &[x], interpreter)?
+                                    .to_boolean(),
+                                None if object.is_callable() => {
+                                    object.ordinary_has_instance(interpreter, &x)?
+                                }
+                                None => {
+                                    return interpreter.throw_type_error(
+                                        "right-hand side of 'instanceof' is not callable",
+                                    );
+                                }
+                            }
+                        } else {
                             return interpreter.throw_type_error(format!(
                                 "right-hand side of 'instanceof' should be an object, got {}",
                                 y.get_type().as_str()
                             ));
                         }
-
-                        // TODO: implement the instanceof operator
-                        // spec: https://tc39.es/ecma262/#sec-instanceofoperator
-
-                        false
                     }
                 }))
             }

boa/src/syntax/ast/node/operator/tests.rs

@@ -26,3 +26,37 @@ fn assignmentoperator_rhs_throws_error() {
 
     assert_eq!(&exec(scenario), "\"ReferenceError: b is not defined\"");
 }
+
+#[test]
+fn instanceofoperator_rhs_not_object() {
+    let scenario = r#"
+        try {
+          let s = new String();
+          s instanceof 1
+        } catch (err) {
+          err.toString()
+        }
+        "#;
+
+    assert_eq!(
+        &exec(scenario),
+        "\"TypeError: right-hand side of 'instanceof' should be an object, got number\""
+    );
+}
+
+#[test]
+fn instanceofoperator_rhs_not_callable() {
+    let scenario = r#"
+        try {
+          let s = new String();
+          s instanceof {}
+        } catch (err) {
+          err.toString()
+        }
+        "#;
+
+    assert_eq!(
+        &exec(scenario),
+        "\"TypeError: right-hand side of 'instanceof' is not callable\""
+    );
+}