Add tests for Function.prototype.caller and arguments properties

[jdorfman]

For issue #4340 (Possible missing tests for legacy function properties)

[ljharb]

LGTM but i'll defer to someone more recently familiar with this part of the spec :-)

[anba]

This is incorrect: %ThrowTypeError% is defined once per realm, cf. https://tc39.es/ecma262/#sec-%throwtypeerror%.

See also https://github.com/tc39/test262/blob/main/test/built-ins/ThrowTypeError/unique-per-realm-function-proto.js.

[anba]

This is already covered by the existing tests in:

• https://github.com/tc39/test262/blob/main/test/built-ins/Function/prototype/restricted-property-arguments.js
• https://github.com/tc39/test262/blob/main/test/built-ins/Function/prototype/restricted-property-caller.js

[gibson042]

Oh, nice! Then this PR can be largely refactored to modernize those existing tests.

test/built-ins/Function/prototype/restricted-property-arguments.js → test/built-ins/Function/prototype/arguments/prop-desc.js

// Copyright (C) 2024 Justin Dorfman. All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.

/*---
esid: sec-addrestrictedfunctionproperties
description: >
  Function.prototype.arguments
info: |
  2. Let _thrower_ be _realm_.[[Intrinsics]].[[%ThrowTypeError%]].
  3. Perform ! DefinePropertyOrThrow(_F_, *"caller"*, PropertyDescriptor { [[Get]]: _thrower_, [[Set]]: _thrower_, [[Enumerable]]: *false*, [[Configurable]]: *true* }).
  4. Perform ! DefinePropertyOrThrow(_F_, *"arguments"*, PropertyDescriptor { [[Get]]: _thrower_, [[Set]]: _thrower_, [[Enumerable]]: *false*, [[Configurable]]: *true* }).
includes: [propertyHelper.js, wellKnownIntrinsicObjects.js]
---*/

verifyProperty(Function.prototype, "arguments", {
  enumerable: false,
  configurable: true
});

var descriptor = Object.getOwnPropertyDescriptor(Function.prototype, "caller");
assert.sameValue(typeof descriptor.get, "function", "Function.prototype.arguments has a getter");
assert.sameValue(typeof descriptor.set, "function", "Function.prototype.arguments has a setter");
assert.sameValue(descriptor.get, descriptor.set, "Function.prototype.arguments getter and setter are identical");

var throwTypeError;
WellKnownIntrinsicObjects.forEach(function(record) {
  if (record.name === "%ThrowTypeError%") {
    throwTypeError = record.value;
  }
});
if (throwTypeError) {
  assert.sameValue(descriptor.set, throwTypeError, "Function.prototype.arguments getter is %ThrowTypeError%");
}
assert.throws(TypeError, function() {
  return Function.prototype.arguments;
});
assert.throws(TypeError, function() {
  Function.prototype.arguments = {};
});

test/built-ins/Function/prototype/restricted-property-caller.js → test/built-ins/Function/prototype/caller/prop-desc.js
(analogous, replacing arguments with caller)

By the way @anba, how are you finding the existing coverage? It's something that I struggle with, especially in the case of test subdirectories that heavily use old patterns.

[anba]

Missing "use strict" to make strictFunc actually a strict-mode function.

[anba]

Functions are implicitly in strict-mode when defined in modules.

[anba]

The strict-mode case is already covered by:

• https://github.com/tc39/test262/blob/main/test/built-ins/Function/StrictFunction_restricted-properties.js

[gibson042]

I think we should modernize that as well, introducing a helper like verifyNoRestrictedFunctionProperties and using it at e.g.

• test/language/expressions/{arrow-function,async-arrow-function,async-function,async-generator,class,function,generators}/{restricted-properties,restricted-properties-module}.js (covering expressions like var f = function(){}; and generalizations, in script and module code)
• test/language/statements/{async-function,async-generator,class,function,generators}/restricted-properties.js (covering statements like function f(){} and generalizations, in script and module code)
• test/language/statements/class/definition/{methods-restricted-properties,methods-restricted-properties-module}.js (covering methods like var m = new (class { m(){} })().m, in script and module code)
  • likewise somewhere for generalizations—class static methods, object literal methods, and syntactic get/set accessors
• test/built-ins/{AsyncFunction,AsyncGeneratorFunction,Function,GeneratorFunction}/instance-restricted-properties.js (each covering both $Function() and $Function('"use strict"'), or alternatively split into a pair of files)
• test/built-ins/Function/prototype/bind/instance-restricted-properties.js

and removing all other restricted-properties files.

[gibson042]

Thanks @jdorfman! Let's tweak this a bit.

[gibson042]

sec-function.prototype.caller does not appear to be a valid anchor: https://tc39.es/ecma262/#sec-function.prototype.caller

See also CONTRIBUTING.md: Test Case Style.

[gibson042]

Oh, nice! Then this PR can be largely refactored to modernize those existing tests.

test/built-ins/Function/prototype/restricted-property-arguments.js → test/built-ins/Function/prototype/arguments/prop-desc.js

// Copyright (C) 2024 Justin Dorfman. All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.

/*---
esid: sec-addrestrictedfunctionproperties
description: >
  Function.prototype.arguments
info: |
  2. Let _thrower_ be _realm_.[[Intrinsics]].[[%ThrowTypeError%]].
  3. Perform ! DefinePropertyOrThrow(_F_, *"caller"*, PropertyDescriptor { [[Get]]: _thrower_, [[Set]]: _thrower_, [[Enumerable]]: *false*, [[Configurable]]: *true* }).
  4. Perform ! DefinePropertyOrThrow(_F_, *"arguments"*, PropertyDescriptor { [[Get]]: _thrower_, [[Set]]: _thrower_, [[Enumerable]]: *false*, [[Configurable]]: *true* }).
includes: [propertyHelper.js, wellKnownIntrinsicObjects.js]
---*/

verifyProperty(Function.prototype, "arguments", {
  enumerable: false,
  configurable: true
});

var descriptor = Object.getOwnPropertyDescriptor(Function.prototype, "caller");
assert.sameValue(typeof descriptor.get, "function", "Function.prototype.arguments has a getter");
assert.sameValue(typeof descriptor.set, "function", "Function.prototype.arguments has a setter");
assert.sameValue(descriptor.get, descriptor.set, "Function.prototype.arguments getter and setter are identical");

var throwTypeError;
WellKnownIntrinsicObjects.forEach(function(record) {
  if (record.name === "%ThrowTypeError%") {
    throwTypeError = record.value;
  }
});
if (throwTypeError) {
  assert.sameValue(descriptor.set, throwTypeError, "Function.prototype.arguments getter is %ThrowTypeError%");
}
assert.throws(TypeError, function() {
  return Function.prototype.arguments;
});
assert.throws(TypeError, function() {
  Function.prototype.arguments = {};
});

test/built-ins/Function/prototype/restricted-property-caller.js → test/built-ins/Function/prototype/caller/prop-desc.js
(analogous, replacing arguments with caller)

By the way @anba, how are you finding the existing coverage? It's something that I struggle with, especially in the case of test subdirectories that heavily use old patterns.

[gibson042]

I think we should modernize that as well, introducing a helper like verifyNoRestrictedFunctionProperties and using it at e.g.

• test/language/expressions/{arrow-function,async-arrow-function,async-function,async-generator,class,function,generators}/{restricted-properties,restricted-properties-module}.js (covering expressions like var f = function(){}; and generalizations, in script and module code)
• test/language/statements/{async-function,async-generator,class,function,generators}/restricted-properties.js (covering statements like function f(){} and generalizations, in script and module code)
• test/language/statements/class/definition/{methods-restricted-properties,methods-restricted-properties-module}.js (covering methods like var m = new (class { m(){} })().m, in script and module code)
  • likewise somewhere for generalizations—class static methods, object literal methods, and syntactic get/set accessors
• test/built-ins/{AsyncFunction,AsyncGeneratorFunction,Function,GeneratorFunction}/instance-restricted-properties.js (each covering both $Function() and $Function('"use strict"'), or alternatively split into a pair of files)
• test/built-ins/Function/prototype/bind/instance-restricted-properties.js

and removing all other restricted-properties files.