1382209 - Add new restrictions for "yield" and "await" as binding identifiers per ES2018

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement)

Description

[André Bargull [:anba]]

From https://github.com/tc39/ecma262/commit/925cdc437e0878b36f7ceb7dbecd9036157a6337

"yield" and "await" are now always parsed as binding identifiers, but additional static semantics restrict "yield" to non-generator and "await" to non-async function contexts.


Ecma262 PR: https://github.com/tc39/ecma262/pull/885
Test262 PR: https://github.com/tc39/test262/issues/1084

Comment 1

[André Bargull [:anba]]

Attachment: bug1382209-part1-yield-await-bindingident.patch

We no longer need to take the yield-handling into account when checking if the next token after |let| continues a let-declaration (resp. the await-is-keyword state for "await"). 

Waldo's test cases are superseded by https://github.com/tc39/test262/issues/1084, therefore we can remove them, too.

Comment 2

[André Bargull [:anba]]

Attachment: bug1382209-part2-yield-handling-modules.patch

"yield" is forbidden as an identifier in module contexts, because modules are implicitly strict-mode code, and not because the Module (https://tc39.github.io/ecma262/#prod-Module) production has a [Yield] grammar parameter. So we actually should use YieldIsName instead of YieldIsKeyword for the various module related parser methods.

Comment 3

[Shu-yu Guo [:shu]]

Comment on attachment 8887922 [details] [diff] [review]
bug1382209-part1-yield-await-bindingident.patch

Review of attachment 8887922 [details] [diff] [review]:
-----------------------------------------------------------------

This spec change is awesome.

::: js/src/frontend/Parser.cpp
@@ +7464,5 @@
>      MOZ_ALWAYS_TRUE(tokenStream.peekToken(&verify));
>      MOZ_ASSERT(next == verify);
>  #endif
>  
>      // Destructuring is (for once) the easy case.

Without the gnarly yield/await semantics, the comment now reads odd. I'd replace with

// Destructuring continues a let declaration.

Comment 4

[Shu-yu Guo [:shu]]

Comment on attachment 8887924 [details] [diff] [review]
bug1382209-part2-yield-handling-modules.patch

Review of attachment 8887924 [details] [diff] [review]:
-----------------------------------------------------------------

While you're here, could you update the comment above ParserBase::isValidStrictBinding?

Comment 5

[André Bargull [:anba]]

Attachment: bug1382209-part1-yield-await-bindingident.patch

Update part 1 per review comments, carrying r+.

Comment 6

[André Bargull [:anba]]

Attachment: bug1382209-part2-yield-handling-modules.patch

Update part 2 per review comments, carrying r+.

Comment 7

[André Bargull [:anba]]

Try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=06f70a56db4dbb89f79f68615a7d8817c6357b4a

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/bf1ddf4c1619
Part 1: Add new restrictions for "yield" and "await" as binding identifiers per ES2018 draft spec. r=shu
https://hg.mozilla.org/integration/mozilla-inbound/rev/595d4c0210e2
Part 2: Use correct YieldHandling for module contexts. r=shu

Comment 9

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/bf1ddf4c1619
https://hg.mozilla.org/mozilla-central/rev/595d4c0210e2