Bug in exponential operator

[nzakas]

When using Acorn 3.0.2 and ecmaVersion 7, the following code throws an error but should not:

a++ ** 2;

The grammar specifically allows both ++ and -- in the base position:

The grammar is as follows (per this comment):

ExponentiationExpression :
  UnaryExpression
  UpdateExpression `**` ExponentiationExpression

UpdateExpression :
  LeftHandSideExpression `++`
  LeftHandSideExpression `--`
  `++` UnaryExpression
  `--` UnaryExpression

UnaryExpression :
  UpdateExpression
  `delete` UnaryExpression
  `void` UnaryExpression
  `typeof` UnaryExpression
  `+` UnaryExpression
  `-` UnaryExpression
  `~` UnaryExpression
  `!` UnaryExpression

[nzakas]

I'm going to take a look at this, will see how far I get.

[nzakas]

Gave this a shot and couldn't get very far. It seems like sawUnary needs to end up false whenever there's ++ or --, but when I do that, then I get an error "Assigning to rvalue". I can't seem to track down where that's coming from.

[ljharb]

Does (a++) ** 2 have the same error, or does that parse?

[nzakas]

That parses just fine because of the parens (same escape hatch for all other unary operators).

[marijnh]

I think attached patch should take care of this. Take a look.

[nzakas]

Thanks!

[ljharb]

@marijnh Thanks, when is a release planned that includes this fix?

[marijnh]

I just published 3.0.4.

[ljharb]

👍 thank you!