Initial Release of ES Lint #22663

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timsmallwood wants to merge 6 commits into pantsbuild:main from timsmallwood:ESLint

timsmallwood commented Sep 17, 2025 •

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Add comprehensive ESLint integration for JavaScript/TypeScript linting and formatting

Why

ESLint is the de facto standard linting tool for JavaScript and TypeScript projects. This PR adds complete ESLint
integration to Pants, filling a significant gap in the JavaScript/TypeScript toolchain support and enabling
consistent code quality enforcement across monorepo projects.

What

New experimental backend: pants.backend.experimental.javascript.lint.eslint
Dual functionality: Supports both pants lint and pants fmt goals
Comprehensive config discovery: Supports all ESLint config file types (flat configs, legacy configs,
package.json)
TypeScript support: Via configurable extra dev dependencies
JSON output mode: With parsed error/warning summaries
Skip field support: skip_eslint=True on individual targets
Extensive test coverage: Integration tests, edge cases, and comprehensive documentation

Usage

# pants.toml
[GLOBAL]
backend_packages.add = [
  "pants.backend.javascript",
  "pants.backend.experimental.javascript.lint.eslint",
]

pants lint src/js/::
pants fmt src/js/::

This implementation provides a solid foundation for JavaScript/TypeScript code quality in Pants-managed projects.

timsmallwood and others added 4 commits

September 17, 2025 15:26


          Initial Release of ES Lint

58fd60b


          Merge branch 'main' into ESLint

7c23820


          Merge branch 'main' into ESLint

42fdc2b


          Merge branch 'main' into ESLint

b3362c1

Contributor

cburroughs commented Sep 25, 2025

Thanks for the contribution! Could you flesh out the "why" and "what" of the PR description?

timsmallwood added 2 commits

September 25, 2025 11:46


          Merge branch 'main' into ESLint

0e68e7e


          Merge branch 'main' into ESLint

d3e5184

sureshjoshi self-requested a review

October 17, 2025 00:29

sureshjoshi self-assigned this

riisi reviewed

View reviewed changes

Contributor

riisi left a comment

@timsmallwood Thanks for submitting this - it would definitely be good to have support for eslint.

I've reviewed it briefly - looking at the implementation mostly and not the tests at all yet. Not a maintainer, but I think I have an idea of what would be expected.

I have further questions about the architecture which I've not had time to look into.

Caching: It looks like this is not implemented. Is it absolutely needed or can it be dropped for now to reduce scope?
Multi-project/resolve handling: How would it work across independent projects with different eslint versions? Does eslint need to operate in a package/project context, or does it just run per-file? In terms of existing goals - is it more like Prettier, or more like Typescript?

docs/docs/javascript/overview/eslint.mdx

+              )
+              ```
+              ## Configuration Files

Contributor

riisi Oct 30, 2025

It might be better here to link to the eslint docs on config file formats and just state that Pants supports them (to avoid re-documenting here, plus this doc is already quite long).

docs/docs/javascript/overview/eslint.mdx


		## Supported File Types

		ESLint in Pants supports:

Contributor

riisi Oct 30, 2025

Are there other types that are currently unsupported? Or is this a generic statement implying that Pants supports all the types one would want to use?

Are .jsx and .tsx files supported?

docs/docs/javascript/overview/eslint.mdx


		### Prettier Integration

		ESLint and Prettier can work together. If you're using both tools, consider:

Contributor

riisi Oct 30, 2025

The numbering implies to me that all of these things should be done in order - I'm not sure that's the case?

Does Pants support running prettier first, then eslint by default, or we need to consider the order of pants fmt lint ... ?

I do think covering this usage is important FWIW - it's been a bit of a minefield in personal past experience to get these working together. I think if we can offer some opinionated guidance, that would be helpful.

docs/docs/javascript/overview/eslint.mdx

+              };
+              ```
+              **Note**: ESLint can lint TypeScript but has limited formatting capabilities for TypeScript-specific syntax. For comprehensive TypeScript formatting, consider using Prettier alongside ESLint.

Contributor

riisi Oct 30, 2025

I wonder if it might make sense to have one docs section on linting and formatting, like with Python - https://www.pantsbuild.org/2.27/docs/python/overview/linters-and-formatters - but we can leave it for now.

docs/docs/javascript/overview/eslint.mdx

+              ```
+              :::tip Cache Location
+              ESLint will create a `.eslintcache` file to store cache data. Consider adding this to your `.gitignore`:

Contributor

riisi Oct 30, 2025

Wondering how this works - wouldn't this be in sandbox and not need to be ignored?

src/python/pants/backend/experimental/javascript/lint/eslint/rules.py

+                  wants_json = False
+                  if getattr(eslint, "json_output", False):
+                      # Only add json format if user did not already specify a formatter

Contributor

riisi Oct 30, 2025

Can json just be a default option instead?

src/python/pants/backend/experimental/javascript/lint/eslint/rules.py

+                  if wants_json:
+                      try:
+                          parsed = json.loads(stdout or "[]")
+                          if isinstance(parsed, list):

Contributor

riisi Oct 30, 2025

No else?

src/python/pants/backend/experimental/javascript/lint/eslint/rules.py

+                              summary = f"ESLint summary: {errors} errors, {warnings} warnings\n\n"
+                              stdout = summary + stdout
+                      except Exception:
+                          pass

Contributor

riisi Oct 30, 2025

Do we need to swallow the exception?

src/python/pants/backend/experimental/javascript/lint/eslint/register.py

		@@ -0,0 +1,25 @@
		# Copyright 2025 Pants project contributors (see CONTRIBUTORS.md).

Contributor

riisi Oct 30, 2025

I think, following the pattern from the other javascript/typescript plugins, that the most of the eslint code should not be located under backend/experimental - only register.py -- see e.g. prettier.

src/python/pants/backend/experimental/javascript/lint/eslint/subsystem.py

+                      ),
+                  )
+                  extra_dev_dependencies = StrListOption(

Contributor

riisi Oct 30, 2025

As far as I can see, this isn't used in the current implementation?

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