Only allow ECMAScript stage 4 features #22083
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oandregal
requested review from
ajitbohra,
gziolo,
nerrad,
ntwb and
youknowriad
as code owners
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I don't know if using stage-3 was expected. If it was, this PR can be safely closed and I'm sorry for the noise! However, by looking at this PR, I gather that the common thinking was that we can write code in stage-4 (that is enabled by our babel preset). |
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Can you clarify how this actually works? i.e. Where do we configure Stage 4? |
We don't do it directly, but by virtue of using the preset-env. The preset enables all approved changes (stage-4) as stated in the docs (which are a bit lacking on specifics, they only say "preset that allows you to use the latest JavaScript"). While reviewing the docgen PR I've actually looked at the babel-preset code and this is what I've found:
This is all a bit convoluted but that's what I understand we do by using the preset-env. |
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I've traced at least one case where we use syntax enabled by |
As far as I know, this code is run directly through Node and isn't polyfilled in any way. I guess it depends whether this support commitment extends beyond just "features we enable in the Babel configuration" and to also include "any code we write". |
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As noted at #22030 (comment) , this should be considered a breaking change, both for |
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As per this thread and this conversation we're going ahead with this. We'll wait to merge until the beginning of next week, so we have a full plugin cycle to uncover any unexpected errors and bundle it with the CSS support as well. |
oandregal
added
the
[Type] Breaking Change
do we add the CHANGELOG comment here or is it enough to mark this PR as a breaking change and we take care of that in the package release? cc @gziolo |
We should include a note in the CHANGELOG to let people know what has changed so they know how to fix it. In fact, the PR that @aduth is working on #22030 includes a note of how such language features (plugins) can be enabled so it might be a good idea to cross-link. |
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@gziolo I've added a changelog comment here as well, so this is ready for review. |
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Given that the change is applied to @wordpress/babel-preset-default – we should call it a braking change there in the first place. In @wordpress/scripts we probably should only mention that @wordpress/babel-preset had breaking changes that might affect those who use the default config. It's tricky :)
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Added a note in |
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Turns out I misunderstood what I thought that the flag includes proposals that are past-stage-4, approved and scheduled for the next standard release, but the standard is not published yet. But the meaning is different: it includes also stage-3 proposals which are implemented and shipping in browsers and are not yet stable. Every proposal needs the experience and feedback from actual implementation and real-world usage before advancing to stage-4 and beyond. I had a chat with Till Schneidereit from Mozilla, who explained these details to me, and recommended against any blanket rule that includes stage-3 proposals, and recommended using them in production only if there is a real, sizable benefit. |
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@jsnajdr, we get the same explanation in #22030 (comment) from Henry Zhu from Babel :) |
While reviewing #22030 (comment), I realized that we're allowing to write code in ECMAScript stage-3 and above, and not only stage-4.
This was enabled by switching on
shippedProposalsin #19065. At the time, it looks like the thought was that enabling this, will make babel to list feature proposals that were part of stage-4 and already shipped by browsers. However,shippedProposalsmay add stage-3 as per the docs. For example, at the moment, we could theoretically use the numeric separator feature, which is on stage-3.This disables the
shippedProposalsso we only use stage-4.