fix: only warn about literals and undefined on no-return-await

[clshortfuse]

In async functions, returning awaited promises no longer has any performance penalty and is now faster than returning promises directly.

Because we cannot detect what the result type of a CallExpression or the type of a MemberExpression, or the type of an Identifier, warnings related to whether an actual Promise is being returned cannot be processed. Strictly from at an AST level, we can detect Literal node types and undefined.

• Detect await being used on Literal node type
• Detect await being used on an Identifier named undefined
• Detect await being used on a ConditionalExpression that returns either a Literal type or undefined.
• Detect await being used on a void operation (results in undefined)

Futher changes can be made to detect syntaxes where a Literal type would be returned, such as

• await (4 + 3)
• await ('foo' + 'bar')

Future changes may also, suggest rewriting awaited CondtionExpression nodes such as:

• async function foo(value) { return await (value ? true : bar()) }

This would require more extensive testing.

Fixes #17345

See: https://v8.dev/blog/fast-async

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[x] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

(see commit message)

Is there anything you'd like reviewers to focus on?

It's impossible to properly assess the return type, but we can at least check for Literal nodes and undefined.

This keeps the rule being a suggestion, but relaxes type-related checks.

[eslint-github-bot]

Hi @clshortfuse!, thanks for the Pull Request

The first commit message isn't properly formatted. We ask that you update the message to match this format, as we use it to generate changelogs and automate releases.

• The commit message tag wasn't recognized. Did you mean "docs", "fix", or "feat"?
• There should be a space following the initial tag and colon, for example 'feat: Message'.

To Fix: You can fix this problem by running git commit --amend, editing your commit message, and then running git push -f to update this pull request.

Read more about contributing to ESLint here

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: clshortfuse / name: Carlos Lopez (4faa777)

[netlify]

✅ Deploy Preview for docs-eslint canceled.

Name	Link
🔨 Latest commit	4faa777
🔍 Latest deploy log	https://app.netlify.com/sites/docs-eslint/deploys/64b012b42b47440008aa5568

[nzakas]

@clshortfuse thanks for the PR. In the issue you reference (#17345) it was agreed to make a documentation change, not a change to how the rule works. We'd happily accept a documentation change explaining the points you made. Please revert the changes to the rule itself and update the docs accordingly.

[github-actions]

Hi everyone, it looks like we lost track of this pull request. Please review and see what the next steps are. This pull request will auto-close in 7 days without an update.

[mdjermanovic]

Closing in favor of #17417