1339123 - Hoisted block-level function named "arguments" not initialized with undefined per B.3.3.1

Status: NEW

(Core :: JavaScript Engine, defect, P3)

Description

[André Bargull [:anba]]

Test case:
---
(function(a = (print(arguments))) {
  print(arguments);
  { function arguments() {} }
  print(arguments);
})();
---

Expected output:
[object Arguments]
undefined
function arguments() {}

Actual output:
[object Arguments]
[object Arguments]
function arguments() {}


Spec
https://tc39.github.io/ecma262/#sec-web-compat-functiondeclarationinstantiation initializes the block functions which apply for B.3.3.1 with |undefined| in step 1.a.ii.2 if their names aren't included in the |instantiatedVarNames| list.

Comment 1

[Shu-yu Guo [:shu]]

Recapping some IRC conversation below.

Per current spec text of Annex B that uses |parameterList| to test if Annex B behavior should apply, when a function has |argumentsObjectNeede = true|, Annex B behavior would *not* apply to functions named "arguments".

However, Waldo says this was an unintended normative change from his editorial PR https://github.com/tc39/ecma262/pull/677

I'll go ahead and fix it according to the ES2015 behavior (anba's test case above). Waldo, could you file an upstream PR?

Comment 2

[Shu-yu Guo [:shu]]

Attachment: Fix 'arguments' handling in parameter expressions when there is also a var binding of 'arguments'.

Turns out our in-tree test was wrong. The bug is that if parameter exprs needed
the arguments object and didn't have a formal named 'parameter', we weren't
treating var bindings of 'arguments' like
regular var bindings.

Comment 3

[Shu-yu Guo [:shu]]

Comment on attachment 8836916 [details] [diff] [review]
Fix 'arguments' handling in parameter expressions when there is also a var binding of 'arguments'.

I'm not sure what the intended semantics are anymore. Retracting patch.

Comment 4

[Shu-yu Guo [:shu]]

Filed https://github.com/tc39/ecma262/issues/815

Comment 5

[Leo Balter]

On test262:

test/annexB/language/function-code/block-decl-func-skip-arguments.js

Comment 6

[Matthew Gaudet (he/him) [:mgaudet]]

See https://github.com/tc39/ecma262/issues/991 as well (this probably should be fixed in spec is my reading)