[smart pipes] Add support for question-mark tokens

[js-choi]

Q	A
Fixed Issues?	No
Patch: Bug Fix?	No
Major: Breaking Change?	No
Minor: New Feature?	Yes
Tests Added + Pass?	Yes
Documentation PR Link	[pending on 7.2.0 docs]
Any Dependency Changes?	No
License	MIT

This pull request builds on #8289, which initially implemented parsing of the stage-0 smart-pipeline proposal. #8289 uses # as its “topic token” (aka the “placeholder token”), but this is only a preliminary choice, and the actual token has not yet been actually decided. This present pull request adds support for switching to the question mark ? as the topic token using a new topicToken configuration option on the pipelineOperator parser plugin. Future pull requests will add support for other good possibilities, namely % and @.

See also #9122 and #9179. CC @mAAdhaTTah, @littledan, @thiagoarrais.

[thiagoarrais]

You might want to update babel-generator too. It currently hardcodes # as the topic token.

The relevant code is at types.js/PipelinePrimaryTopicReference.

[js-choi]

Will do. Thanks for the heads up.

[js-choi]

On the other hand, it might be worth implementing generator support in a separate pull request, since, to my understanding, babel-generator is decoupled from babel-parser. I’ll work on it later today, in any case.

[js-choi]

How should the configuration option for generated topic tokens (default # but also may be ?) be designed? There doesn’t seem to be a plugin-option system in babel-generator, unlike babel-parser and the transform plugins.

[nicolo-ribaudo]

You can add a top-level option, like I did for decorators:

babel/packages/babel-generator/src/index.js

Line 55 in c586d4e

decoratorsBeforeExport: !!opts.decoratorsBeforeExport,

I understand that this is sub-optimal, but @babel/generator has just a few options and is almost never used directly, so a plugin system might be overkill.

[nicolo-ribaudo]

Could you add a parameter to the getPluginOption function for the default value? Then it would be enough to do

this.getPluginOption("pipelineOperator", "topicToken", "#") !== topicToken

and it wouldn't be necessary to use this separate function (that check could directly go in the if statement).

[js-choi]

Understood; I’ll replace this.

[nicolo-ribaudo]

I think that having functions like this one is overkill: it has a name so long that it doesn't gain anything in readability neither in typing. Also, the name is basically the same as getPluginOption("pipelineOperator", "topicToken") but with less punctation, it doesn't abstract anything more.

[js-choi]

Understood; I’ll inline this.

[js-choi]

You can add a top-level option, like I did for decorators:

babel/packages/babel-generator/src/index.js
Line 55 in c586d4e
decoratorsBeforeExport: !!opts.decoratorsBeforeExport,
I understand that this is sub-optimal, but @babel/generator has just a few options and is almost never used directly, so a plugin system might be overkill.

Yes, sounds good. Should I put this functionality in this pull request, or should I put it in a new pull request?

[nicolo-ribaudo]

Yes please! 👍

EDIT: I just noticed that "Yes" isn't an answer to your question lol. It is ok to put it in this pull request.

[JLHwung]

Closing this as the smart pipeline proposal is not proposed. As of May 2021, the smart pipeline is replaced by hack pipeline. See also #13191.