Add tests for Nullish Coalesce Expression

test/language/expressions/coalesce/abrupt-is-a-short-circuit.js

@@ -0,0 +1,58 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Abrupt completions are also a Short circuit and prevent evaluation of the right-side expressions
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+function poison() {
+    throw new Test262Error('poison handled');
+}
+
+function morePoison() {
+    throw 'poison!!!!';
+}
+
+x = undefined;
+assert.throws(Test262Error, function() {
+    undefined ?? poison() ?? morePoison();
+}, 'undefined ?? poison() ?? morePoison();');
+
+x = undefined;
+assert.throws(Test262Error, function() {
+    null ?? poison() ?? morePoison();
+}, 'null ?? poison() ?? morePoison();');
+
+assert.throws(Test262Error, function() {
+    poison() ?? morePoison();
+}, 'poison() ?? morePoison();');

test/language/expressions/coalesce/cannot-chain-head-with-logical-and.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Cannot immediately contain, or be contained within, an && or || operation.
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+features: [coalesce-expression]
+negative:
+    phase: early
+    type: SyntaxError
+---*/
+
+0 && 0 ?? true;

test/language/expressions/coalesce/cannot-chain-head-with-logical-or.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Cannot immediately contain, or be contained within, an && or || operation.
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+features: [coalesce-expression]
+negative:
+    phase: early
+    type: SyntaxError
+---*/
+
+0 || 0 ?? true;

test/language/expressions/coalesce/cannot-chain-tail-with-logical-and.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    If the CoalesceExpressionHead is undefined or null, follow return the right-side value.
+    Otherwise, return the left-side value.
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+features: [coalesce-expression]
+negative:
+    phase: early
+    type: SyntaxError
+---*/
+
+0 ?? 0 && true;

test/language/expressions/coalesce/cannot-chain-tail-with-logical-or.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    If the CoalesceExpressionHead is undefined or null, follow return the right-side value.
+    Otherwise, return the left-side value.
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+features: [coalesce-expression]
+negative:
+    phase: early
+    type: SyntaxError
+---*/
+
+0 ?? 0 || true;

test/language/expressions/coalesce/chainable-with-bitwise-and.js

@@ -0,0 +1,49 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    CoalesceExpression is chainable with the BitwiseANDExpression
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = null ?? 42 & 43;
+assert.sameValue(x, 42, 'null ?? 42 & 43');
+
+x = undefined ?? 42 & 43;
+assert.sameValue(x, 42, 'null ?? 42 & 43');
+
+x = false ?? 42 & 43;
+assert.sameValue(x, false, 'false ?? 42 & 43');
+
+x = true ?? 42 & 43;
+assert.sameValue(x, true, 'true ?? 42 & 43');

test/language/expressions/coalesce/chainable-with-bitwise-or.js

@@ -0,0 +1,49 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    CoalesceExpression is chainable with the BitwiseORExpression
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = null ?? 1 | 42;
+assert.sameValue(x, 43, 'null ?? 1 | 42');
+
+x = undefined ?? 1 | 42;
+assert.sameValue(x, 43, 'null ?? 1 | 42');
+
+x = false ?? 1 | 42;
+assert.sameValue(x, false, 'false ?? 1 | 42');
+
+x = true ?? 1 | 42;
+assert.sameValue(x, true, 'true ?? 1 | 42');

test/language/expressions/coalesce/chainable-with-bitwise-xor.js

@@ -0,0 +1,49 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    CoalesceExpression is chainable with the BitwiseXORExpression
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = null ?? 1 ^ 42;
+assert.sameValue(x, 43, 'null ?? 1 ^ 42');
+
+x = undefined ?? 1 ^ 42;
+assert.sameValue(x, 43, 'null ?? 1 ^ 42');
+
+x = false ?? 1 ^ 42;
+assert.sameValue(x, false, 'false ?? 1 ^ 42');
+
+x = true ?? 1 ^ 42;
+assert.sameValue(x, true, 'true ?? 1 ^ 42');

test/language/expressions/coalesce/chainable.js

@@ -0,0 +1,50 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    If the CoalesceExpressionHead is undefined or null, follow return the right-side value.
+    Otherwise, return the left-side value.
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = null ?? undefined ?? 42;
+assert.sameValue(x, 42, 'null ?? undefined ?? 42');
+
+x = undefined ?? null ?? 42;
+assert.sameValue(x, 42, 'undefined ?? null ?? 42');
+
+x = null ?? null ?? 42;
+assert.sameValue(x, 42, 'null ?? null ?? 42');
+
+x = undefined ?? undefined ?? 42;
+assert.sameValue(x, 42, 'null ?? null ?? 42');

test/language/expressions/coalesce/follows-null.js

@@ -0,0 +1,49 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    If the CoalesceExpressionHead is null, follow return the right-side eval.
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = null ?? 42;
+assert.sameValue(x, 42, 'null ?? 42');
+
+x = null ?? undefined;
+assert.sameValue(x, undefined, 'null ?? undefined');
+
+x = null ?? null;
+assert.sameValue(x, null, 'null ?? null');
+
+x = null ?? false;
+assert.sameValue(x, false, 'null ?? false');

test/language/expressions/coalesce/follows-undefined.js

@@ -0,0 +1,49 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    If the CoalesceExpressionHead is undefined, follow return the right-side eval.
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = undefined ?? 42;
+assert.sameValue(x, 42, 'undefined ?? 42');
+
+x = undefined ?? undefined;
+assert.sameValue(x, undefined, 'undefined ?? undefined');
+
+x = undefined ?? null;
+assert.sameValue(x, null, 'undefined ?? null');
+
+x = undefined ?? false;
+assert.sameValue(x, false, 'undefined ?? false');

test/language/expressions/coalesce/short-circuit-number-0.js

@@ -0,0 +1,81 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit if the CoalesceExpressionHead is not undefined or null (0)
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = undefined;
+x = 0 ?? 1;
+assert.sameValue(x, 0, '0 ?? 1');
+
+x = undefined;
+x = 0 ?? null;
+assert.sameValue(x, 0, '0 ?? null');
+
+x = undefined;
+x = 0 ?? undefined;
+assert.sameValue(x, 0, '0 ?? undefined');
+
+x = undefined;
+x = 0 ?? null ?? undefined;
+assert.sameValue(x, 0, '0 ?? null ?? undefined');
+
+x = undefined;
+x = 0 ?? undefined ?? null;
+assert.sameValue(x, 0, '0 ?? undefined ?? null');
+
+x = undefined;
+x = 0 ?? null ?? null;
+assert.sameValue(x, 0, '0 ?? null ?? null');
+
+x = undefined;
+x = 0 ?? undefined ?? undefined;
+assert.sameValue(x, 0, '0 ?? null ?? null');
+
+x = undefined;
+x = null ?? 0 ?? null;
+assert.sameValue(x, 0, 'null ?? 0 ?? null');
+
+x = undefined;
+x = null ?? 0 ?? undefined;
+assert.sameValue(x, 0, 'null ?? 0 ?? undefined');
+
+x = undefined;
+x = undefined ?? 0 ?? null;
+assert.sameValue(x, 0, 'undefined ?? 0 ?? null');
+
+x = undefined;
+x = undefined ?? 0 ?? undefined;
+assert.sameValue(x, 0, 'undefined ?? 0 ?? undefined');

test/language/expressions/coalesce/short-circuit-number-42.js

@@ -0,0 +1,81 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit if the CoalesceExpressionHead is not undefined or null (42)
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = undefined;
+x = 42 ?? 1;
+assert.sameValue(x, 42, '42 ?? 1');
+
+x = undefined;
+x = 42 ?? null;
+assert.sameValue(x, 42, '42 ?? null');
+
+x = undefined;
+x = 42 ?? undefined;
+assert.sameValue(x, 42, '42 ?? undefined');
+
+x = undefined;
+x = 42 ?? null ?? undefined;
+assert.sameValue(x, 42, '42 ?? null ?? undefined');
+
+x = undefined;
+x = 42 ?? undefined ?? null;
+assert.sameValue(x, 42, '42 ?? undefined ?? null');
+
+x = undefined;
+x = 42 ?? null ?? null;
+assert.sameValue(x, 42, '42 ?? null ?? null');
+
+x = undefined;
+x = 42 ?? undefined ?? undefined;
+assert.sameValue(x, 42, '42 ?? null ?? null');
+
+x = undefined;
+x = null ?? 42 ?? null;
+assert.sameValue(x, 42, 'null ?? 42 ?? null');
+
+x = undefined;
+x = null ?? 42 ?? undefined;
+assert.sameValue(x, 42, 'null ?? 42 ?? undefined');
+
+x = undefined;
+x = undefined ?? 42 ?? null;
+assert.sameValue(x, 42, 'undefined ?? 42 ?? null');
+
+x = undefined;
+x = undefined ?? 42 ?? undefined;
+assert.sameValue(x, 42, 'undefined ?? 42 ?? undefined');

test/language/expressions/coalesce/short-circuit-number-empty-string.js

@@ -0,0 +1,82 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit if the CoalesceExpressionHead is not undefined or null (the empty string)
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+var str = '';
+
+x = undefined;
+x = str ?? 1;
+assert.sameValue(x, str, 'str ?? 1');
+
+x = undefined;
+x = str ?? null;
+assert.sameValue(x, str, 'str ?? null');
+
+x = undefined;
+x = str ?? undefined;
+assert.sameValue(x, str, 'str ?? undefined');
+
+x = undefined;
+x = str ?? null ?? undefined;
+assert.sameValue(x, str, 'str ?? null ?? undefined');
+
+x = undefined;
+x = str ?? undefined ?? null;
+assert.sameValue(x, str, 'str ?? undefined ?? null');
+
+x = undefined;
+x = str ?? null ?? null;
+assert.sameValue(x, str, 'str ?? null ?? null');
+
+x = undefined;
+x = str ?? undefined ?? undefined;
+assert.sameValue(x, str, 'str ?? null ?? null');
+
+x = undefined;
+x = null ?? str ?? null;
+assert.sameValue(x, str, 'null ?? str ?? null');
+
+x = undefined;
+x = null ?? str ?? undefined;
+assert.sameValue(x, str, 'null ?? str ?? undefined');
+
+x = undefined;
+x = undefined ?? str ?? null;
+assert.sameValue(x, str, 'undefined ?? str ?? null');
+
+x = undefined;
+x = undefined ?? str ?? undefined;
+assert.sameValue(x, str, 'undefined ?? str ?? undefined');

test/language/expressions/coalesce/short-circuit-number-false.js

@@ -0,0 +1,81 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit if the CoalesceExpressionHead is not undefined or null (false)
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = undefined;
+x = false ?? 1;
+assert.sameValue(x, false, 'false ?? 1');
+
+x = undefined;
+x = false ?? null;
+assert.sameValue(x, false, 'false ?? null');
+
+x = undefined;
+x = false ?? undefined;
+assert.sameValue(x, false, 'false ?? undefined');
+
+x = undefined;
+x = false ?? null ?? undefined;
+assert.sameValue(x, false, 'false ?? null ?? undefined');
+
+x = undefined;
+x = false ?? undefined ?? null;
+assert.sameValue(x, false, 'false ?? undefined ?? null');
+
+x = undefined;
+x = false ?? null ?? null;
+assert.sameValue(x, false, 'false ?? null ?? null');
+
+x = undefined;
+x = false ?? undefined ?? undefined;
+assert.sameValue(x, false, 'false ?? null ?? null');
+
+x = undefined;
+x = null ?? false ?? null;
+assert.sameValue(x, false, 'null ?? false ?? null');
+
+x = undefined;
+x = null ?? false ?? undefined;
+assert.sameValue(x, false, 'null ?? false ?? undefined');
+
+x = undefined;
+x = undefined ?? false ?? null;
+assert.sameValue(x, false, 'undefined ?? false ?? null');
+
+x = undefined;
+x = undefined ?? false ?? undefined;
+assert.sameValue(x, false, 'undefined ?? false ?? undefined');

test/language/expressions/coalesce/short-circuit-number-object.js

@@ -0,0 +1,89 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit if the CoalesceExpressionHead is not undefined or null (object)
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+var obj = {
+    toString() {
+        return null;
+    },
+    valueOf() {
+        return null;
+    }
+};
+
+x = undefined;
+x = obj ?? 1;
+assert.sameValue(x, obj, 'obj ?? 1');
+
+x = undefined;
+x = obj ?? null;
+assert.sameValue(x, obj, 'obj ?? null');
+
+x = undefined;
+x = obj ?? undefined;
+assert.sameValue(x, obj, 'obj ?? undefined');
+
+x = undefined;
+x = obj ?? null ?? undefined;
+assert.sameValue(x, obj, 'obj ?? null ?? undefined');
+
+x = undefined;
+x = obj ?? undefined ?? null;
+assert.sameValue(x, obj, 'obj ?? undefined ?? null');
+
+x = undefined;
+x = obj ?? null ?? null;
+assert.sameValue(x, obj, 'obj ?? null ?? null');
+
+x = undefined;
+x = obj ?? undefined ?? undefined;
+assert.sameValue(x, obj, 'obj ?? null ?? null');
+
+x = undefined;
+x = null ?? obj ?? null;
+assert.sameValue(x, obj, 'null ?? obj ?? null');
+
+x = undefined;
+x = null ?? obj ?? undefined;
+assert.sameValue(x, obj, 'null ?? obj ?? undefined');
+
+x = undefined;
+x = undefined ?? obj ?? null;
+assert.sameValue(x, obj, 'undefined ?? obj ?? null');
+
+x = undefined;
+x = undefined ?? obj ?? undefined;
+assert.sameValue(x, obj, 'undefined ?? obj ?? undefined');

test/language/expressions/coalesce/short-circuit-number-string.js

@@ -0,0 +1,82 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit if the CoalesceExpressionHead is not undefined or null (string)
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+var str = 'undefined';
+
+x = undefined;
+x = str ?? 1;
+assert.sameValue(x, str, 'str ?? 1');
+
+x = undefined;
+x = str ?? null;
+assert.sameValue(x, str, 'str ?? null');
+
+x = undefined;
+x = str ?? undefined;
+assert.sameValue(x, str, 'str ?? undefined');
+
+x = undefined;
+x = str ?? null ?? undefined;
+assert.sameValue(x, str, 'str ?? null ?? undefined');
+
+x = undefined;
+x = str ?? undefined ?? null;
+assert.sameValue(x, str, 'str ?? undefined ?? null');
+
+x = undefined;
+x = str ?? null ?? null;
+assert.sameValue(x, str, 'str ?? null ?? null');
+
+x = undefined;
+x = str ?? undefined ?? undefined;
+assert.sameValue(x, str, 'str ?? null ?? null');
+
+x = undefined;
+x = null ?? str ?? null;
+assert.sameValue(x, str, 'null ?? str ?? null');
+
+x = undefined;
+x = null ?? str ?? undefined;
+assert.sameValue(x, str, 'null ?? str ?? undefined');
+
+x = undefined;
+x = undefined ?? str ?? null;
+assert.sameValue(x, str, 'undefined ?? str ?? null');
+
+x = undefined;
+x = undefined ?? str ?? undefined;
+assert.sameValue(x, str, 'undefined ?? str ?? undefined');

test/language/expressions/coalesce/short-circuit-number-symbol.js

@@ -0,0 +1,82 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit if the CoalesceExpressionHead is not undefined or null (Symbol)
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+var s = Symbol();
+
+x = undefined;
+x = s ?? 1;
+assert.sameValue(x, s, 's ?? null');
+
+x = undefined;
+x = s ?? null;
+assert.sameValue(x, s, 's ?? null');
+
+x = undefined;
+x = s ?? undefined;
+assert.sameValue(x, s, 's ?? undefined');
+
+x = undefined;
+x = s ?? null ?? undefined;
+assert.sameValue(x, s, 's ?? null ?? undefined');
+
+x = undefined;
+x = s ?? undefined ?? null;
+assert.sameValue(x, s, 's ?? undefined ?? null');
+
+x = undefined;
+x = s ?? null ?? null;
+assert.sameValue(x, s, 's ?? null ?? null');
+
+x = undefined;
+x = s ?? undefined ?? undefined;
+assert.sameValue(x, s, 's ?? null ?? null');
+
+x = undefined;
+x = null ?? s ?? null;
+assert.sameValue(x, s, 'null ?? s ?? null');
+
+x = undefined;
+x = null ?? s ?? undefined;
+assert.sameValue(x, s, 'null ?? s ?? undefined');
+
+x = undefined;
+x = undefined ?? s ?? null;
+assert.sameValue(x, s, 'undefined ?? s ?? null');
+
+x = undefined;
+x = undefined ?? s ?? undefined;
+assert.sameValue(x, s, 'undefined ?? s ?? undefined');

test/language/expressions/coalesce/short-circuit-number-true.js

@@ -0,0 +1,81 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit if the CoalesceExpressionHead is not undefined or null (true)
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = undefined;
+x = true ?? 1;
+assert.sameValue(x, true, 'true ?? null');
+
+x = undefined;
+x = true ?? null;
+assert.sameValue(x, true, 'true ?? null');
+
+x = undefined;
+x = true ?? undefined;
+assert.sameValue(x, true, 'true ?? undefined');
+
+x = undefined;
+x = true ?? null ?? undefined;
+assert.sameValue(x, true, 'true ?? null ?? undefined');
+
+x = undefined;
+x = true ?? undefined ?? null;
+assert.sameValue(x, true, 'true ?? undefined ?? null');
+
+x = undefined;
+x = true ?? null ?? null;
+assert.sameValue(x, true, 'true ?? null ?? null');
+
+x = undefined;
+x = true ?? undefined ?? undefined;
+assert.sameValue(x, true, 'true ?? null ?? null');
+
+x = undefined;
+x = null ?? true ?? null;
+assert.sameValue(x, true, 'null ?? true ?? null');
+
+x = undefined;
+x = null ?? true ?? undefined;
+assert.sameValue(x, true, 'null ?? true ?? undefined');
+
+x = undefined;
+x = undefined ?? true ?? null;
+assert.sameValue(x, true, 'undefined ?? true ?? null');
+
+x = undefined;
+x = undefined ?? true ?? undefined;
+assert.sameValue(x, true, 'undefined ?? true ?? undefined');

test/language/expressions/coalesce/short-circuit-prevents-evaluation.js

@@ -0,0 +1,56 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    Short circuit can prevent evaluation of the right-side expressions
+esid: sec-conditional-operator
+info: |
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    Runtime Semantics: Evaluation
+
+    CoalesceExpression:CoalesceExpressionHead??BitwiseORExpression
+
+    1. Let lref be the result of evaluating CoalesceExpressionHead.
+    2. Let lval be ? GetValue(lref).
+    3. If lval is undefined or null,
+        a. Let rref be the result of evaluating BitwiseORExpression.
+        b. Return ? GetValue(rref).
+    4. Otherwise, return lval.
+features: [coalesce-expression]
+---*/
+
+var x;
+function poison() {
+    throw new Test262Error('should not evaluate poison');
+}
+
+x = undefined;
+x = undefined ?? 42 ?? undefined ?? poison();
+assert.sameValue(x, 42);
+
+x = undefined;
+x = 42 ?? undefined ?? poison();
+assert.sameValue(x, 42);
+
+x = undefined;
+x = undefined ?? 42 ?? poison();
+assert.sameValue(x, 42);
+
+x = undefined;
+x = 42 ?? poison();
+assert.sameValue(x, 42);

test/language/expressions/coalesce/tco-cond.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+description: Expression is a candidate for tail-call optimization.
+esid: sec-static-semantics-hascallintailposition
+flags: [onlyStrict]
+features: [tail-call-optimization, coalesce-expression]
+includes: [tcoHelper.js]
+---*/
+
+var callCount = 0;
+(function f(n) {
+  if (n === 0) {
+    callCount += 1
+    return;
+  }
+  return f(n - 1) ?? false;
+}($MAX_ITERATIONS));
+assert.sameValue(callCount, 1);

test/language/expressions/coalesce/tco-pos-null.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+description: Expression is a candidate for tail-call optimization.
+esid: sec-static-semantics-hascallintailposition
+flags: [onlyStrict]
+features: [tail-call-optimization, coalesce-expression]
+includes: [tcoHelper.js]
+---*/
+
+var callCount = 0;
+(function f(n) {
+  if (n === 0) {
+    callCount += 1
+    return;
+  }
+  return null ?? f(n - 1);
+}($MAX_ITERATIONS));
+assert.sameValue(callCount, 1);

test/language/expressions/coalesce/tco-pos-undefined.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+description: Expression is a candidate for tail-call optimization.
+esid: sec-static-semantics-hascallintailposition
+flags: [onlyStrict]
+features: [tail-call-optimization, coalesce-expression]
+includes: [tcoHelper.js]
+---*/
+
+var callCount = 0;
+(function f(n) {
+  if (n === 0) {
+    callCount += 1
+    return;
+  }
+  return undefined ?? f(n - 1);
+}($MAX_ITERATIONS));
+assert.sameValue(callCount, 1);

test/language/expressions/conditional/coalesce-expr-ternary.js

@@ -0,0 +1,73 @@
+// Copyright (C) 2019 Leo Balter. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+    ShortCircuitExpression in the Conditional Expression (? :)
+esid: sec-conditional-operator
+info: |
+    ShortCircuitExpression :
+        LogicalORExpression
+        CoalesceExpression
+
+    CoalesceExpression :
+        CoalesceExpressionHead ?? BitwiseORExpression
+
+    CoalesceExpressionHead :
+        CoalesceExpression
+        BitwiseORExpression
+
+    ConditionalExpression :
+        ShortCircuitExpression
+        ShortCircuitExpression ? AssignmentExpression : AssignmentExpression
+features: [coalesce-expression]
+---*/
+
+var x;
+
+x = undefined ?? true ? 0 : 42;
+assert.sameValue(x, 0, 'undefined ?? true ? 0 : 42');
+
+x = undefined;
+x = null ?? true ? 0 : 42;
+assert.sameValue(x, 0, 'null ?? true ? 0 : 42');
+
+x = undefined;
+x = undefined ?? false ? 0 : 42;
+assert.sameValue(x, 42, 'undefined ?? false ? 0 : 42');
+
+x = undefined;
+x = null ?? false ? 0 : 42;
+assert.sameValue(x, 42, 'null ?? false ? 0 : 42');
+
+x = undefined;
+x = false ?? true ? 0 : 42;
+assert.sameValue(x, 42, 'false ?? true ? 0 : 42');
+
+x = undefined;
+x = 0 ?? true ? 0 : 42;
+assert.sameValue(x, 42, '0 ?? true ? 0 : 42');
+
+x = undefined;
+x = 1 ?? false ? 0 : 42;
+assert.sameValue(x, 0, '1 ?? false ? 0 : 42');
+
+x = undefined;
+x = true ?? false ? 0 : 42;
+assert.sameValue(x, 0, 'true ?? false ? 0 : 42');
+
+x = undefined;
+x = true ?? true ? 0 : 42;
+assert.sameValue(x, 0, 'true ?? true ? 0 : 42');
+
+x = undefined;
+x = '' ?? true ? 0 : 42;
+assert.sameValue(x, 42, '"" ?? true ? 0 : 42');
+
+x = undefined;
+x = Symbol() ?? false ? 0 : 42;
+assert.sameValue(x, 0, 'Symbol() ?? false ? 0 : 42');
+
+x = undefined;
+x = {} ?? false ? 0 : 42;
+assert.sameValue(x, 0, 'object ?? false ? 0 : 42');