[New] async-server-action: Add rule to require that server actions be async

[jorgezreik]

Adds a new rule to require that a server actions (functions with the 'use server' directive) be async as specified by the server actions spec. Suggests fixes for server actions that aren't async by adding the async keyword.

Note: It is my first time contributing so let me know if I missed anything!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.59%. Comparing base (a944aa5) to head (7f9a2bd).

❗ Current head 7f9a2bd differs from pull request most recent head 4d1e087

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3729      +/-   ##
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+ Coverage   94.47%   97.59%   +3.11%     
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  Files         134      134              
  Lines        9613     9479     -134     
  Branches     3486     3468      -18     
==========================================
+ Hits         9082     9251     +169     
+ Misses        531      228     -303     

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[ljharb]

I see some examples using single and double quotes - great! - but none using backticks. Can we add some? (whether it's supported or not)

[ljharb]

is this actually released yet?

despite vercel's usage of it prior to it being fully released, i don't think we should ship a rule until that's the case.

[jorgezreik]

So the feature is still in canary. I understand not wanting to ship a rule for a canary feature, and if that's the final policy then I'm happy to wait until it's out of canary to merge this in.

That being said, Server Components are definitely seeing widespread use, mainly through Vercel, with less stable implementations elsewhere. Additionally, the React team confirmed that they're officially shipping the feature with React 19 (when that comes out is anyone's guess).

Because of this, I think adding this rule (as an optional rule outside of the recommended config) would be very helpful to users using server components, while not impacting users who are not yet using them.

[jorgezreik]

I see some examples using single and double quotes - great! - but none using backticks. Can we add some? (whether it's supported or not)

I knew I'd miss a few things 😅 Thanks for the feedback, really appreciate it!

Backticks don't work with use server, but great idea to test them. Adding now.

[jorgezreik]

A semi-related question that came to mind that I'd like advice on:

Other ESLint rules like eslint/require-await and typescript-eslint/require-await report async functions that do not have an await operator as incorrect. Any ideas on how we can make rules like these not report on "use server"? Adding options to these rules to ignore functions with certain directives would do the trick, but an option like that is React-specific enough that it's unlikely to get merged.

[ljharb]

The require-await rules are harmful and bad and should never have existed in the first place. An async function without any awaits is perfectly acceptable (unlike a generator without a yield).

As such, the solution there is to just disable those horrifically foolish rules.

[ljharb]

Rebased. I'd love to see lots more test cases, and I'm not going to merge this until the feature is available in a non-canary full release, so I'll mark it as a draft until then.