feat: adding tests for optional chaining proposal

features.txt

@@ -133,6 +133,10 @@ import.meta
 WeakRef
 FinalizationGroup
 
+# Optional Chaining
+# https://github.com/tc39/proposal-optional-chaining
+optional-chaining
+
 ## Standard language features
 #
 # Language features that have been included in a published version of the

test/language/expressions/optional-chaining/call-expression.js

@@ -0,0 +1,20 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  optional chain on call expression
+info: |
+  Left-Hand-Side Expressions
+    OptionalExpression:
+      CallExpression OptionalChain
+features: [optional-chaining]
+---*/
+
+function fn () {
+  return {a: 33};
+};
+
+// CallExpression Arguments
+assert.sameValue(33, fn()?.a);
+assert.sameValue(undefined, fn()?.b);

test/language/expressions/optional-chaining/early-errors-tail-position-template-string-esi.js

@@ -0,0 +1,25 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  template string passed to tail position of optional chain
+info: |
+  Static Semantics: Early Errors
+    OptionalChain:
+      ?.TemplateLiteral
+      OptionalChain TemplateLiteral
+features: [optional-chaining]
+negative:
+  type: SyntaxError
+  phase: parse
+---*/
+
+$DONOTEVALUATE();
+
+const a = {fn() {}};
+
+// This production exists in order to prevent automatic semicolon
+// insertion rules.
+a?.fn
+  `hello`

test/language/expressions/optional-chaining/early-errors-tail-position-template-string.js

@@ -0,0 +1,24 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  template string passed to tail position of optional chain
+info: |
+  Static Semantics: Early Errors
+    OptionalChain:
+      ?.TemplateLiteral
+      OptionalChain TemplateLiteral
+features: [optional-chaining]
+negative:
+  type: SyntaxError
+  phase: parse
+---*/
+
+$DONOTEVALUATE();
+
+const a = {fn() {}};
+
+// This production exists in order to prevent automatic semicolon
+// insertion rules.
+a?.fn`hello`;

test/language/expressions/optional-chaining/member-expression.js

@@ -0,0 +1,56 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  optional chain on member expression
+info: |
+  Left-Hand-Side Expressions
+    OptionalExpression:
+      MemberExpression OptionalChain
+features: [optional-chaining]
+---*/
+
+// PrimaryExpression
+//   IdentifierReference
+
+const arr = [10, 11];
+const fn = (arg1, arg2) => {
+  return arg1 + arg2;
+}
+const i = 0;
+const obj = {
+  a: 'hello',
+  b: {val: 13},
+  c(arg1) {
+    return arg1 * 2;
+  },
+  arr: [11, 12]
+};
+
+// OptionalChain: ?.[Expression]
+assert.sameValue(11, arr?.[i + 1]);
+
+// OptionalChain: ?.IdentifierName
+assert.sameValue('hello', obj?.a);
+
+// OptionalChain: ?.Arguments
+assert.sameValue(30, fn?.(10, 20));
+
+// OptionalChain: OptionalChain [Expression]
+assert.sameValue(12, obj?.arr[i + 1]);
+assert.throws(TypeError, function() {
+  obj?.d[i + 1];
+});
+
+// OptionalChain: OptionalChain .IdentifierName
+assert.sameValue(13, obj?.b.val);
+assert.throws(TypeError, function() {
+  obj?.d.e;
+});
+
+// OptionalChain: OptionalChain Arguments
+assert.sameValue(20, obj?.c(10));
+assert.throws(TypeError, function() {
+  obj?.d();
+});

test/language/expressions/optional-chaining/optional-expression.js

@@ -0,0 +1,27 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  optional chain on recursive optional expression
+info: |
+  Left-Hand-Side Expressions
+    OptionalExpression:
+      OptionalExpression OptionalChain
+features: [optional-chaining]
+---*/
+
+const obj = {
+  a: {
+    b: 22
+  }
+};
+
+function fn () {
+  return {};
+}
+
+// MemberExpression
+assert.sameValue(22, (obj?.a)?.b);
+// CallExpression
+assert.sameValue(undefined, (fn()?.a)?.b);

test/language/expressions/optional-chaining/punctuator-decimal-lookahead.js

@@ -0,0 +1,15 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  ternary operation with decimal does not evaluate as optional chain 
+info: |
+  Punctuators
+    OptionalChainingPunctuator::
+      ?.[lookahead ∉ DecimalDigit]
+features: [optional-chaining]
+---*/
+
+const value = true ?.30 : false;
+assert.sameValue(.30, value);

test/language/expressions/optional-chaining/runtime-semantics-evaluation.js

@@ -0,0 +1,18 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  accessing optional value on undefined or null returns undefined.
+info: |
+  If baseValue is undefined or null, then
+    Return undefined.
+features: [optional-chaining]
+---*/
+
+const nul = null;
+const undf = undefined;
+assert.sameValue(undefined, nul?.a);
+assert.sameValue(undefined, undf?.b);
+assert.sameValue(undefined, null?.a);
+assert.sameValue(undefined, undefined?.b);

test/language/expressions/optional-chaining/short-circuiting.js

@@ -0,0 +1,22 @@
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  demonstrate syntax-based short-circuiting.
+info: |
+  If the expression on the LHS of ?. evaluates to null/undefined, the RHS is
+  not evaluated
+features: [optional-chaining]
+---*/
+
+const a = undefined;
+let x = 1;
+
+a?.[++x] // short-circuiting.
+a?.b.c(++x).d; // long short-circuiting.
+
+undefined?.[++x] // short-circuiting.
+undefined?.b.c(++x).d; // long short-circuiting.
+
+assert.sameValue(1, x);

test/language/expressions/optional-chaining/static-semantics-simple-assignment.js

@@ -0,0 +1,23 @@
+
+// Copyright 2019 Google, Inc.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: prod-OptionalExpression
+description: >
+  an optional expression cannot be target of assignment
+info: |
+  Static Semantics: IsValidSimpleAssignmentTarget
+    LeftHandSideExpression:
+      OptionalExpression
+    Return false.
+features: [optional-chaining]
+negative:
+  type: SyntaxError
+  phase: parse
+---*/
+
+$DONOTEVALUATE();
+
+const obj = {};
+
+obj?.a = 33;