Next gen style: Prettier

[cwillisf]

Resolves

• Closes chore(deps): update dependency eslint to v9 #171
• Replaces Next gen style: ESLint Stylistic #212
• Resolves POD-186

Proposed Changes

Primary change: implement new style rules for eslint and prettier, similar to those already being used for NGP work

Supporting changes:

• Upgrade to eslint@^9
• Use new flat format required by eslint@^9
• Move flattened legacy configs into legacy/
• Make a new interface for more flexibly making eslint configurations (see README.md)

Bonus changes:

• The new configurations can lint JS/TS embedded in MD and HTML files

Reason for Changes

• Modernize our style rules
• Reduce maintenance effort by leaning on recommended rule sets more than we did previously

Test Coverage

Tested on the files in this repository. I also created a temporary HTML file to verify that those rules work.

[Copilot]

Pull Request Overview

This PR modernizes the ESLint and Prettier configurations by upgrading to ESLint v9, switching to the new flat format, refactoring legacy configurations into a dedicated folder, and enhancing the documentation and examples.

• Upgrade to ESLint v9 and adapt to its new flat configuration format
• Refactor legacy configuration files into the "legacy/" folder and remove deprecated JS config files
• Introduce a new interface for generating ESLint and Prettier configurations alongside updated README examples

Reviewed Changes

Copilot reviewed 20 out of 22 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
release.config.js	Formatting tweaks in the branch configuration
react.js, node.js, es6.js	Removal of old configuration files
prettier.config.mjs, lib/prettier.mjs	Addition of Prettier configuration with modern settings
lib/**/*.mjs	New and refactored ESLint configurations, including legacy support
README.md	Updated documentation and usage examples
.github/workflows/*.yml	Minor formatting adjustments in workflow files
commitlint.config.mjs	Small formatting update

Files not reviewed (2)

• .prettierignore: Language not supported
• package.json: Language not supported

Comments suppressed due to low confidence (1)

lib/eslint.mjs:43

• Avoid shadowing the outer 'globalsIn' parameter by renaming this variable (e.g., to 'globalValue') to improve clarity.

const globalsIn = globals[objOrKey]

[cwillisf]

Turn on "Hide whitespace" or add "w=1" to the URL to ignore indenting changes :)

[georgyangelov]

Looks great!

Maybe on the NGP side we should eventually update scratch-platform to use this one?

[cwillisf]

Maybe on the NGP side we should eventually update scratch-platform to use this one?

I think that would make sense: using this configuration in more places means more opportunities for us to find improvements 😁

The first place I'll be using this is in the "Scratchium" work, and it seems likely that I'll run into issues of some sort there. If so, I hope to find non-disruptive ways to resolve those issues. That's why makePrettierConfig is a function, for example, even though it doesn't (yet?) take any arguments. This potential for an initially bumpy road is the main reason I can think of that you might want to hold off for a minute or two before adopting this.