# Pull Request

## 🤨 Rationale

Adopts eslint v9 🎉

## 👩‍💻 Implementation

- Switches to ni eslint config packages using flat config
- Removes `prettier-eslint` which is in [alpha
builds](https://github.com/prettier/prettier-eslint/releases?q=v17&expanded=true)
for eslint v9 support, significantly hurt lint performance, and had
[major conflicts with
eslint](#2718 (comment)).
Now that eslint libraries like [stylistic](https://eslint.style/) are
dedicated to style rules and eslint supports more formats such as
[markdown syntax](https://github.com/eslint/markdown) and [markdown
style](https://github.com/ota-meshi/eslint-plugin-markdown-preferences?tab=readme-ov-file)
it's possible we don't need to rely on prettier long term. Either way we
remove prettier for now to unblock eslint upgrades and can reconsider in
the future
- Linting performance was significantly improved so simplified the
`validate` concurrency scripts to run all lint sequentially in parallel
to tests. Now `validate` completes ~100s faster. It's also possible we
will get another speed bump enabling [multithreaded
eslint](https://eslint.org/blog/2025/08/multithread-linting/) but will
save for a follow-up PR.
- In the nimble private `eslint-config-nimble` package:
- Created a shared `lintNimbleConfig` configuration that is used in each
eslint config to make sure the eslint config file itself is linted and
to give a spot for very general shared config in follow-up PRs (like
markdown or json linting)
- Created an angular lint similar to our typescript / component configs
as shared config for the angular projects. This resolves issues where
extending from a base config in the angular workspace is technically
crossing a library boundary and triggered lint errors about reaching
across package boundaries. Now we explicitly depend on a shared package.
- Angular workspace changes:
- The angular workspace root config is now for the config file in root,
not the angular projects.
- Each angular project uses the shared `angularTypescriptNimbleConfig`
and `angularTemplateNimbleConfig`
- Root workspace changes:
- Added a top-level eslint config file for the config in root (the
config file itself and beachball) but could also be used for linting
markdown, etc. in the future.
- Having a root eslint config also prevents the eslint vscode plugin
from getting confused (errors in extension output logs) searching for
the eslint config for files in root.

## 🧪 Testing

Note, see #2774 for CI results and source changes resulting from this
config change.

## ✅ Checklist

- [x] I have updated the project documentation to reflect my changes or
determined no changes are needed. **A follow-up PR will remove prettier
references and docs**

---------

Signed-off-by: gokulprasanth-ni <131153319+gokulprasanth-ni@users.noreply.github.com>
Co-authored-by: gokulprasanth-ni <131153319+gokulprasanth-ni@users.noreply.github.com>
Co-authored-by: rajsite <1588923+rajsite@users.noreply.github.com>