Nullish coalescing support

Author: sanex3339

escodegen.js

@@ -85,6 +85,7 @@
         Assignment: 1,
         Conditional: 2,
         ArrowFunction: 2,
+        NullishCoalescing: 3,
         LogicalOR: 3,
         LogicalAND: 4,
         BitwiseOR: 5,
@@ -108,6 +109,7 @@
     };
 
     BinaryPrecedence = {
+        '??': Precedence.NullishCoalescing,
         '||': Precedence.LogicalOR,
         '&&': Precedence.LogicalAND,
         '|': Precedence.BitwiseOR,
@@ -1836,8 +1838,34 @@
         BinaryExpression: function (expr, precedence, flags) {
             var result, leftPrecedence, rightPrecedence, currentPrecedence, fragment, leftSource;
             currentPrecedence = BinaryPrecedence[expr.operator];
-            leftPrecedence = expr.operator === '**' ? Precedence.Postfix : currentPrecedence;
-            rightPrecedence = expr.operator === '**' ? currentPrecedence : currentPrecedence + 1;
+
+            leftPrecedence = currentPrecedence;
+            rightPrecedence = currentPrecedence + 1;
+
+            switch (expr.operator) {
+                case '**':
+                    leftPrecedence = Precedence.Postfix;
+                    rightPrecedence = currentPrecedence;
+                    break;
+
+                case '??':
+                    if (expr.left.operator === '||' || expr.left.operator === '&&') {
+                        leftPrecedence = BinaryPrecedence[expr.left.operator] + 1;
+                    }
+
+                    if (expr.right.operator === '||' || expr.right.operator === '&&') {
+                        rightPrecedence = BinaryPrecedence[expr.right.operator] + 1;
+                    }
+
+                    break;
+
+                case '||':
+                    if (expr.left.operator === '??') {
+                        leftPrecedence = BinaryPrecedence[expr.left.operator] + 1;
+                    }
+
+                    break;
+            }
 
             if (currentPrecedence < precedence) {
                 flags |= F_ALLOW_IN;

test/compare-acorn-es2020/nullish-coalescing.expected.js

@@ -0,0 +1,12 @@
+a ?? b;
+a ?? b ?? c;
+a | b ?? c | d;
+a ?? b ? c : d;
+(a || b) ?? c;
+a || (b ?? c);
+(a && b) ?? c;
+a && (b ?? c);
+(a ?? b) || c;
+a ?? (b || c);
+(a ?? b) && c;
+a ?? (b && c);

test/compare-acorn-es2020/nullish-coalescing.expected.min.js

@@ -0,0 +1 @@
+a??b;a??b??c;a|b??c|d;a??b?c:d;(a||b)??c;a||(b??c);(a&&b)??c;a&&(b??c);(a??b)||c;a??(b||c);(a??b)&&c;a??(b&&c)

test/compare-acorn-es2020/nullish-coalescing.js

@@ -0,0 +1,12 @@
+a ?? b;
+a ?? b ?? c;
+a | b ?? c | d;
+a ?? b ? c : d;
+(a || b) ?? c;
+a || (b ?? c);
+(a && b) ?? c;
+a && (b ?? c);
+(a ?? b) || c;
+a ?? (b || c);
+(a ?? b) && c;
+a ?? (b && c);