Fix await using double lookahead edge case

[adams85]

In the double lookahead to determine whether it's an await using declaration, the check for the using keyword is not correct. Adding a Unicode escaped identifier character fools the parser logic:

async () => { await using\\u0061 b = c }

This incorrectly parses without an error.

I made an attempt at fixing the issue. (This way we should be consistent with the readWord1 function of the tokenizer.)

BTW, it seems like there are similar issues here:

• acorn/acorn/src/statement.js

  Line 73 in ad66d00

  !(isIdentifierChar(after = this.input.charCodeAt(next + 8)) || after > 0xd7ff && after < 0xdc00))

• acorn/acorn/src/statement.js

  Line 45 in ad66d00

  if (nextCh === 91 || nextCh === 92) return true // '[', '\'

[baseballyama]

Thank you!

[marijnh]

Thanks for fixing that!

[adams85]

My pleasure.

However, how about the other similar cases of lookaheads I mentioned above, in the PR description?

Shall I submit another PR and shall we discuss those there?

[marijnh]

Either works. I don't have time to look into them today but I could also have a look later this week.

[marijnh]

Attached patch adjusts isAsyncFunction to handle a backslash directly after function. I wasn't able to find an actual input on which that changed the parser's behavior, but it does make the function return the right thing, which counts for something.

I don't think there's an issue in isLet. If there's a backslash directly after let, that will have been tokenized as part of an identifier token, and isContextual("let") will already return false.

[adams85]

Attached patch adjusts isAsyncFunction to handle a backslash directly after function. I wasn't able to find an actual input on which that changed the parser's behavior, but it does make the function return the right thing, which counts for something.

Thank you. This will report the error at the correct position BTW.

However, it's still not completely correct as it doesn't account for astral identifier characters. (My original fix was incorrect too.) EDIT: see the description of the linked PR

I submitted another PR, which hopefully sorts this out once and for all.