Bug 201615 – [JSC] Add missing syntax errors for await in function parameter default expressions

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Ross Kirsling]

Arrow function parameter default expressions should not permit await keyword

[Ross Kirsling]

Created attachment 378411 [details]
Patch

[Ross Kirsling]

Comment on attachment 378411 [details]
Patch

Ugh, guess this solution is too naive since it breaks, e.g., `await => {}` at the top level (which evidently neither we nor test262 have tests for...).

Also the problem description is a bit off.

We need to prohibit await in default expressions of:
- async arrow and non-arrow functions
- non-async arrow functions in an async context

So these need to become errors:
    async function f(x = await => {}) {}
    async (x = await => {}) => {};

    async function f() { (x = await => {}) => {}; }
    async () => { (x = await => {}) => {}; };

And these must not become errors:
    async function f() { function g(x = await => {}) {} }
    (x = await => {}) => {};

[Ross Kirsling]

Created attachment 378591 [details]
Patch

[Yusuke Suzuki]

Comment on attachment 378591 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=378591&action=review

> Source/JavaScriptCore/parser/Parser.cpp:350
> +        semanticFailIfTrue(!m_parserState.allowAwait && match(AWAIT), "Cannot use 'await' as a parameter name in an async function");

What is the difference between this check and isDisallowedIdentifierAwait?

[Ross Kirsling]

(In reply to Yusuke Suzuki from comment #4)
> Comment on attachment 378591 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=378591&action=review
> 
> > Source/JavaScriptCore/parser/Parser.cpp:350
> > +        semanticFailIfTrue(!m_parserState.allowAwait && match(AWAIT), "Cannot use 'await' as a parameter name in an async function");
> 
> What is the difference between this check and isDisallowedIdentifierAwait?

Hmm, I (In reply to Yusuke Suzuki from comment #4)
> Comment on attachment 378591 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=378591&action=review
> 
> > Source/JavaScriptCore/parser/Parser.cpp:350
> > +        semanticFailIfTrue(!m_parserState.allowAwait && match(AWAIT), "Cannot use 'await' as a parameter name in an async function");
> 
> What is the difference between this check and isDisallowedIdentifierAwait?

Hmm, I didn't consciously avoid `isDisallowedIdentifierAwait` here, but the observable difference I can see would be in module code: namely, that `await => 3` in a module would change from `Cannot use 'await' as a parameter name in a module.` to `Cannot use 'await' as a parameter name in an async function.`, which would be incorrect.

[Ross Kirsling]

Created attachment 378883 [details]
Patch

[Ross Kirsling]

Comment on attachment 378883 [details]
Patch

Added even more tests (for all the things I was implicitly expecting).

Any further concerns here?

[Ross Kirsling]

Created attachment 378887 [details]
Patch

[Ross Kirsling]

Created attachment 378888 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 378888 [details]
Patch

Clearing flags on attachment: 378888

Committed r249925: <https://trac.webkit.org/changeset/249925>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/55418472>