Octal escape sequences should be a lexical/syntactic error in strict mode and ES5

The following code should be disallowed in strict mode and ES5:

"\5";
"\05";
"\55";
"\055";

This is disallowed by Annex B.1.2 of the EcmaScript 5 spec.

This has become an a problem since 1.8 release. I had ANSI escape codes in my TypeScript files, which were compiled to JS just fine, but 1.8 started adding use strict and all of a sudden node started freaking out.

I think a compiler error is due here if use strict is inserted.

Artem Basov (@basart)

I don't quite understand the status of this issue? It is still present in 2.1.4. Is the TypeScript leaving this for the community to fix? (if so, fine...I just want to know).

I've run into this a number of times when using Artem Basov (@basart)'s typestyle package to import raw css via template strings. It is very unintuitive that template strings allow embedded octal literals (since the contents of the template string are NOT TypeScript or Javascript). Nevertheless, that is the standard behavior. As such, the TypeScript compiler shouldn't be outputting invalid template strings (i.e., in my opinion the TypeScript compiler should consider an invalidate template string as an error and not emit it). It is particularly nasty when you run this gets passed through both tsc and webpack only to throw an error in the browser. At that point, it is so far downstream it is often difficult for people to trace things back to the original issue.

Yes, that is what the 'Accepting PRs' label means.

Nathan Shively-Sanders (@sandersn)

Nathan Shively-Sanders (@sandersn) What's the process for adding new error messages? Just make something up?

how would you test the change then?

I could add a test for #24209 and verify that x as "\1" is assignable to y as "\x01", or something like that. I don't actually care about that type, but I do care about the text field in the AST being correct.

Note that octals are disallowed completely (SyntaxError) in template literal strings, whether in strict mode or not. They're technically only deprecated in normal ES5 code. So it should definitely be an error in template literals, and possibly just a warning outside of them.

Also this may be obvious but '\0' is not an octal sequence while all other one, two, or three-digit forms are, ie '\00' and '\1'.

Here's a RegEx that includes all valid octals and excludes all invalid ones with the notable exception of \0: /\\[0-3]?[0-7]{1,2}/g. Try it.

List of things to do for resolving this:

parser.ts:
- Not really needed, but there is a comment here that is no longer relevant and should be removed:
  // Octal literals are not allowed...

scanner.ts:

At the end of scanEscapeSequence() should add:

if (isDigit(ch)) tokenFlags |= TokenFlags.ContainsInvalidEscape;

but...

types.ts:
- ContainsInvalidEscape = 1 << 11 is defined here but it's unused!
- TemplateLiteralLikeFlags = ContainsInvalidEscape ⇒ this is fishy, probably should be its own value
binder.ts:
- See checkStrictModeNumericLiteral and make a similar checker for strings with the ContainsInvalidEscape flag.

One decision to make is whether to allow octal escapes in TS when not producing strict-mode code. It would probably be easier to forbid them anyway (especially since they're never allowed in template strings) but if not, then the scanner mode should also parse the octal escapes in case the output is not strict.

Eli Barzilay (@elibarzilay)

Eli Barzilay (@elibarzilay)
Can I work on this issue?
Am I correct in understanding that I should work on the to-do list that you have written?
This is my first time contributing to Typescript and I'm looking forward to working on it!

Yeah, just give it a shot and see how it goes 👍🏻

Thank you! I'll try!

Eli Barzilay (@elibarzilay)

Eli Barzilay (@elibarzilay) Orta Therox (@orta)
Can I consider a fix to disallow octal escaping even if it is not strict-mode?
Do you have any concerns about this?

(Is this a topic that should be discussed in PR rather than in this Issue?)

I'm afraid that would be over-stepping, as they are allowed in those modes: #396 (comment)

I see, too much.
Thanks for the quick reply!

One decision to make is whether to allow octal escapes in TS when not producing strict-mode code. It would probably be easier to forbid them anyway (especially since they're never allowed in template strings)

#396 (comment)
↑I was just trying to make sure about this.

So, is it the policy that octal escaping is allowed (or left allowed) when not in strict-mode?
I'm sorry if I misunderstood.

Orta Therox (@orta)

Orta Therox (@orta)
#396 (comment)
If you could confirm this, it would be greatly appreciated!

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Octal escape sequences should be a lexical/syntactic error in strict mode and ES5 #396

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Octal escape sequences should be a lexical/syntactic error in strict mode and ES5 #396

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alexgorbatchev commented on Apr 1, 2016

xogeny commented on Jan 12, 2017

sandersn commented on Jan 12, 2017

masaeedu commented on May 16, 2017

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