An issue about constant

[YiWen-y]

Version

chakra-1.11.24

Test case

const x = 'const x';
this.x = 20;
delete this.x;
print(this.x);
print(x);
x = 1;
print(x);

Execution steps

./ChakraCore/out/Release/ch testcase.js

Output

undefined
const x
1

Expected behavior

undefined
const x
testcase.js:6:1 TypeError: invalid assignment to const 'x'

Description

In the above test case, the value of the constant x cannot be modified, but chakra did successfully modify the value of x(line 6). Maybe this is a problem with chakra.

[ljharb]

In this case, the this.x assignment creates a global variable, but the const x is supposed to be shadowing that in the Script scope, so the x assignment should indeed never reach the global.

[rhuanjl]

Definitely a bug - though it's specifically an issue to do with global scope outside of any block, if you do this:

{
  const x = 'const x';
  this.x = 20;
  delete this.x;
  print(this.x);
  print(x);
  x = 1;
  print(x);
}

It errors correctly.

Going to be weird edge case somewhere - probably in the parser, I'll try and take a look shortly.

EDIT, this case also errors correctly - so it's something to do with delete:

  const x = 'const x';
  this.x = 20;
  print(this.x);
  print(x);
  x = 1;
  print(x);

[ljharb]

Presumably it's an issue with the global contour in chakra - ie, the difference between global variables that are properties of the global object (var/function declarations), and global variables that are not (const/let).

[pleath]

I'd say the problem is going to be in the type system rather than the parser. It has to do with what the delete does to the global object's type. If the delete is commented out, or if it's "delete x" rather than "delete this.x", or if the assignment to const happens before the delete, then we get the right error.

[rhuanjl]

I'd say the problem is going to be in the type system rather than the parser. It has to do with what the delete does to the global object's type. If the delete is commented out, or if it's "delete x" rather than "delete this.x", or if the assignment to const happens before the delete, then we get the right error.

Stepped through it in the debugger and can confirm - thanks for the pointer. At the time the property is being deleted it's aware that it's shadowed, when the set is occurring it doesn't find that.