FEAT: Implement ??

rhino/src/main/java/org/mozilla/javascript/IRFactory.java

@@ -2038,6 +2038,27 @@ private static Node createBinary(int nodeType, Node left, Node right) {
                     }
                     break;
                 }
+
+            case Token.NULLISH_COALESCING:
+                {
+                    // foo ?? default =>
+                    //     (foo == undefined || foo == null) ? foo (left) : default (right)
+
+                    Node undefinedNode = new Name(0, "undefined");
+                    Node nullNode = new Node(Token.NULL);
+
+                    Node conditional =
+                            new Node(
+                                    Token.OR,
+                                    new Node(Token.SHEQ, nullNode, left),
+                                    new Node(Token.SHEQ, undefinedNode, left));
+
+                    return new Node(
+                            Token.HOOK,
+                            /* left= */ conditional,
+                            /* mid= */ right,
+                            /* right= */ left);
+                }
         }
 
         return new Node(nodeType, left, right);

rhino/src/main/java/org/mozilla/javascript/Parser.java

@@ -2370,7 +2370,7 @@ private AstNode assignExpr() throws IOException {
     }
 
     private AstNode condExpr() throws IOException {
-        AstNode pn = orExpr();
+        AstNode pn = nullishCoalescingExpr();
         if (matchToken(Token.HOOK, true)) {
             int line = ts.lineno;
             int qmarkPos = ts.tokenBeg, colonPos = -1;
@@ -2402,6 +2402,25 @@ private AstNode condExpr() throws IOException {
         return pn;
     }
 
+    private AstNode nullishCoalescingExpr() throws IOException {
+        AstNode pn = orExpr();
+        if (matchToken(Token.NULLISH_COALESCING, true)) {
+            int opPos = ts.tokenBeg;
+            AstNode rn = nullishCoalescingExpr();
+
+            // Cannot immediately contain, or be contained within, an && or || operation.
+            if (pn.getType() == Token.OR
+                    || pn.getType() == Token.AND
+                    || rn.getType() == Token.OR
+                    || rn.getType() == Token.AND) {
+                reportError("msg.nullish.bad.token");
+            }
+
+            pn = new InfixExpression(Token.NULLISH_COALESCING, pn, rn, opPos);
+        }
+        return pn;
+    }
+
     private AstNode orExpr() throws IOException {
         AstNode pn = andExpr();
         if (matchToken(Token.OR, true)) {

rhino/src/main/java/org/mozilla/javascript/Token.java

@@ -229,7 +229,8 @@ public static enum CommentType {
             TEMPLATE_LITERAL_SUBST = 175, // template literal - substitution
             TAGGED_TEMPLATE_LITERAL = 176, // template literal - tagged/handler
             DOTDOTDOT = 177, // spread/rest ...
-            LAST_TOKEN = 177;
+            NULLISH_COALESCING = 178, // nullish coalescing (??)
+            LAST_TOKEN = 178;
 
     /**
      * Returns a name for the token. If Rhino is compiled with certain hardcoded debugging flags in
@@ -468,6 +469,8 @@ public static String typeToName(int token) {
                 return "COLON";
             case OR:
                 return "OR";
+            case NULLISH_COALESCING:
+                return "NULLISH_COALESCING";
             case AND:
                 return "AND";
             case INC:

rhino/src/main/java/org/mozilla/javascript/TokenStream.java

@@ -1146,6 +1146,9 @@ && peekChar() == '!'
                 case ',':
                     return Token.COMMA;
                 case '?':
+                    if (matchChar('?')) {
+                        return Token.NULLISH_COALESCING;
+                    }
                     return Token.HOOK;
                 case ':':
                     if (matchChar(':')) {

rhino/src/main/java/org/mozilla/javascript/ast/AstNode.java

@@ -82,6 +82,7 @@ public abstract class AstNode extends Node implements Comparable<AstNode> {
         operatorNames.put(Token.COMMA, ",");
         operatorNames.put(Token.COLON, ":");
         operatorNames.put(Token.OR, "||");
+        operatorNames.put(Token.NULLISH_COALESCING, "??");
         operatorNames.put(Token.AND, "&&");
         operatorNames.put(Token.INC, "++");
         operatorNames.put(Token.DEC, "--");

rhino/src/main/resources/org/mozilla/javascript/resources/Messages.properties

@@ -122,6 +122,9 @@ msg.bad.yield =\
 msg.yield.parenthesized =\
     yield expression must be parenthesized.
 
+msg.nullish.bad.token =\
+    Syntax Error: Unexpected token.
+
 # NativeGlobal
 msg.cant.call.indirect =\
     Function "{0}" must be called directly, and not by way of a \

rhino/src/main/resources/org/mozilla/javascript/resources/Messages_fr.properties

@@ -87,6 +87,9 @@ msg.bad.yield =\
 msg.yield.parenthesized =\
     L''expression suivant ''yield'' doit \u00eatre entre parenth\u00e8ses.
 
+msg.nullish.bad.token =\
+    Erreur de syntaxe: Jeton inattendu.
+
 # NativeGlobal
 msg.cant.call.indirect =\
     La fonction "{0}" doit \u00EAtre appel\u00E9e directement et non par l''interm\u00E9diaire \

tests/src/test/java/org/mozilla/javascript/tests/NullishCoalescingOpTest.java

@@ -0,0 +1,59 @@
+package org.mozilla.javascript.tests;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.mozilla.javascript.Context;
+import org.mozilla.javascript.Scriptable;
+
+public class NullishCoalescingOpTest {
+
+    @Test
+    public void testNullishColascingBasic() {
+        Utils.runWithAllOptimizationLevels(
+                cx -> {
+                    Scriptable scope = cx.initStandardObjects();
+                    cx.setLanguageVersion(Context.VERSION_ES6);
+
+                    String script = "null ?? 'default string'";
+                    Assert.assertEquals(
+                            "default string",
+                            cx.evaluateString(scope, script, "nullish coalescing basic", 0, null));
+
+                    String script2 = "undefined ?? 'default string'";
+                    Assert.assertEquals(
+                            "default string",
+                            cx.evaluateString(scope, script2, "nullish coalescing basic", 0, null));
+                    return null;
+                });
+    }
+
+    @Test
+    public void testNullishColascingShortCircuit() {
+        String script = "0 || 0 ?? true";
+        Utils.assertEvaluatorExceptionES6("Syntax Error: Unexpected token. (test#1)", script);
+
+        String script2 = "0 && 0 ?? true";
+        Utils.assertEvaluatorExceptionES6("Syntax Error: Unexpected token. (test#1)", script2);
+
+        String script3 = "0 ?? 0 && true;";
+        Utils.assertEvaluatorExceptionES6("Syntax Error: Unexpected token. (test#1)", script3);
+
+        String script4 = "0 ?? 0 || true;";
+        Utils.assertEvaluatorExceptionES6("Syntax Error: Unexpected token. (test#1)", script4);
+    }
+
+    @Test
+    public void testNullishColascingPrecedence() {
+        Utils.runWithAllOptimizationLevels(
+                cx -> {
+                    Scriptable scope = cx.initStandardObjects();
+                    cx.setLanguageVersion(Context.VERSION_ES6);
+
+                    String script1 = "3 == 3 ? 'yes' ?? 'default string' : 'no'";
+                    Assert.assertEquals(
+                            "yes",
+                            cx.evaluateString(scope, script1, "nullish coalescing basic", 0, null));
+                    return null;
+                });
+    }
+}

tests/testsrc/test262.properties

@@ -4470,7 +4470,9 @@ language/expressions/call 60/92 (65.22%)
 
 ~language/expressions/class
 
-~language/expressions/coalesce
+language/expressions/coalesce 2/24 (8.33%)
+    tco-pos-null.js {unsupported: [tail-call-optimization]}
+    tco-pos-undefined.js {unsupported: [tail-call-optimization]}
 
 language/expressions/comma 1/6 (16.67%)
     tco-final.js {unsupported: [tail-call-optimization]}
@@ -4616,8 +4618,7 @@ language/expressions/compound-assignment 137/454 (30.18%)
 
 language/expressions/concatenation 0/5 (0.0%)
 
-language/expressions/conditional 3/22 (13.64%)
-    coalesce-expr-ternary.js
+language/expressions/conditional 2/22 (9.09%)
     tco-cond.js {unsupported: [tail-call-optimization]}
     tco-pos.js {unsupported: [tail-call-optimization]}
 
@@ -5271,7 +5272,7 @@ language/expressions/new 41/59 (69.49%)
 
 ~language/expressions/new.target
 
-language/expressions/object 864/1169 (73.91%)
+language/expressions/object 865/1169 (73.99%)
     dstr/async-gen-meth-ary-init-iter-close.js {unsupported: [async-iteration, async]}
     dstr/async-gen-meth-ary-init-iter-get-err.js {unsupported: [async-iteration]}
     dstr/async-gen-meth-ary-init-iter-get-err-array-prototype.js {unsupported: [async-iteration]}
@@ -6077,7 +6078,6 @@ language/expressions/object 864/1169 (73.91%)
     cpn-obj-lit-computed-property-name-from-assignment-expression-coalesce.js
     cpn-obj-lit-computed-property-name-from-async-arrow-function-expression.js
     cpn-obj-lit-computed-property-name-from-await-expression.js {unsupported: [module, async]}
-    cpn-obj-lit-computed-property-name-from-expression-coalesce.js
     cpn-obj-lit-computed-property-name-from-yield-expression.js
     fn-name-accessor-get.js
     fn-name-accessor-set.js