[GR-31950] Improving Value->String conversion in Nashorn compatibility mode.

PullRequest: js/2032

Author: iamstolis

graal-js/src/com.oracle.truffle.js.scriptengine.test/src/com/oracle/truffle/js/scriptengine/test/TestNashornTypeConversion.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * The Universal Permissive License (UPL), Version 1.0
@@ -84,6 +84,15 @@ private static void testToString(Object value, String expectedResult) throws Scr
         assertEquals(expectedResult, holder.getValue());
     }
 
+    private static void testToStringExpressionValue(String expression, String expectedResult) throws ScriptException {
+        ScriptEngine engine = getEngineNashornCompat();
+        ValueHolder holder = new ValueHolder();
+        Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
+        bindings.put("holder", holder);
+        engine.eval("holder.setValue(" + expression + ")");
+        assertEquals(expectedResult, holder.getValue());
+    }
+
     @Test
     public void testNumberToString() throws ScriptException {
         testToString(42, "42");
@@ -100,6 +109,41 @@ public void testObjectToString() throws ScriptException {
         testToString(p, p.toString());
     }
 
+    @Test
+    public void testRegExpToString() throws ScriptException {
+        testToStringExpressionValue("/foo/i", "/foo/i");
+    }
+
+    @Test
+    public void testArrayToString() throws ScriptException {
+        testToStringExpressionValue("[42,211]", "42,211");
+    }
+
+    @Test
+    public void testObjectToStringToString() throws ScriptException {
+        testToStringExpressionValue("({ toString: function() { return 'foo'; } })", "foo");
+    }
+
+    @Test
+    public void testObjectValueOfToString() throws ScriptException {
+        testToStringExpressionValue("Object.setPrototypeOf({ valueOf: function() { return 42; } }, null)", "42");
+    }
+
+    @Test
+    public void testBooleanObjectToString() throws ScriptException {
+        testToStringExpressionValue("Object(true)", "true");
+    }
+
+    @Test
+    public void testNumberObjectToString() throws ScriptException {
+        testToStringExpressionValue("Object(3.14)", "3.14");
+    }
+
+    @Test
+    public void testStringObjectToString() throws ScriptException {
+        testToStringExpressionValue("Object('xyz')", "xyz");
+    }
+
     @Test
     public void testNumberToDouble() throws ScriptException {
         ScriptEngine engine = getEngineNashornCompat();

graal-js/src/com.oracle.truffle.js.scriptengine/src/com/oracle/truffle/js/scriptengine/GraalJSScriptEngine.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * The Universal Permissive License (UPL), Version 1.0
@@ -101,7 +101,7 @@ public final class GraalJSScriptEngine extends AbstractScriptEngine implements C
     private static HostAccess createNashornHostAccess() {
         HostAccess.Builder b = HostAccess.newBuilder(HostAccess.ALL);
         // Last resort conversions similar to those in NashornBottomLinker.
-        b.targetTypeMapping(Value.class, String.class, v -> !v.isNull(), Value::toString, TargetMappingPrecedence.LOWEST);
+        b.targetTypeMapping(Value.class, String.class, v -> !v.isNull(), v -> toString(v), TargetMappingPrecedence.LOWEST);
         b.targetTypeMapping(Number.class, Integer.class, n -> true, n -> n.intValue(), TargetMappingPrecedence.LOWEST);
         b.targetTypeMapping(Number.class, Double.class, n -> true, n -> n.doubleValue(), TargetMappingPrecedence.LOWEST);
         b.targetTypeMapping(Number.class, Long.class, n -> true, n -> n.longValue(), TargetMappingPrecedence.LOWEST);
@@ -110,6 +110,35 @@ private static HostAccess createNashornHostAccess() {
         return b.build();
     }
 
+    // ToString() operation
+    private static String toString(Value value) {
+        return toPrimitive(value).toString();
+    }
+
+    // "Type(result) is not Object" heuristic for the purpose of ToPrimitive() conversion
+    private static boolean isPrimitive(Value value) {
+        return value.isString() || value.isNumber() || value.isBoolean() || value.isNull();
+    }
+
+    // ToPrimitive()/OrdinaryToPrimitive() operation
+    private static Value toPrimitive(Value value) {
+        if (value.hasMembers()) {
+            for (String methodName : new String[]{"toString", "valueOf"}) {
+                if (value.canInvokeMember(methodName)) {
+                    Value maybePrimitive = value.invokeMember(methodName);
+                    if (isPrimitive(maybePrimitive)) {
+                        return maybePrimitive;
+                    }
+                }
+            }
+        }
+        if (isPrimitive(value)) {
+            return value;
+        } else {
+            throw new ClassCastException();
+        }
+    }
+
     private static boolean toBoolean(double d) {
         return d != 0.0 && !Double.isNaN(d);
     }