ESLint v9 contains breaking API changes

[james-yeoman]

Is there an existing issue for this?

• I have searched the existing issues and my issue is unique
• My issue appears in the command-line and not only in the text editor

Description Overview

Upon bumping to the ESLint beta for v9, I was met with several errors in my monorepo during the linting test-run.

Namely:

• Error: context.getScope is not a function
  • Rule: "react/no-string-refs"
• Error: context.getFirstTokens is not a function
  • Rule: "react/display-name"

I get that it's still only a beta, but these API changes were announced in september 2023.

Additionally, there are some rule structure changes outlined separately that may be worth ensuring are in compliance.

Expected Behavior

Given that ESLint v9 is now in beta, I wasn't expecting to find any plugins that haven't yet addressed the API changes

eslint-plugin-react version

v7.34.0

eslint version

v9.0.0-beta.1

node version

v18.12.0

[ljharb]

That expectation is flawed; the point of it being in beta is for plugins to begin to address the changes - announcements are irrelevant. Thanks for the report.

A fix for this will also need to add eslint 9 into the test matrix.

[ljharb]

I put up a branch running tests on eslint 9; https://github.com/ljharb/eslint-plugin-react/actions/runs/8147742013/job/22269131527#step:5:21 is failing because the jsx-no-undef and jsx-uses-react and jsx-uses-vars tests call linter.defineRule. @bmish, any thoughts on an approach here?

[ljharb]

Additionally, when I comment out those 3 lines, i get 22166 failures because Error: ESLint configuration in rule-tester is invalid: Key "parserOptions": This appears to be in eslintrc format rather than flat config format.. Does this mean eslint 9 drops support for eslintrc, or it's just no longer the default?

If the former, how can we run the same tests with both normal eslintrc stuff on eslint 8, and also with flat config on eslint 9?

[james-yeoman]

ESLint 9 makes the flat config the default. It renames the ESLintRC style classes to be LegacyESLint and the Linter requires an option of {configType: "eslintrc"}, and in ESLint 10, they plan on dropping the legacy config altogether.

There's a migration guide that might be a good place to start in terms of compiling a list of required tasks for this

[ljharb]

Awesome, thanks for the pointers.

That will help get us unblocked for eslint 9, but we'll still have a lot of work to support eslint 10.

[james-yeoman]

Is there any update on this yet? Or is this still quite far off? The first release candidate for v9 released last week

[ljharb]

@james-yeoman it is almost never the case that all the plugins in the eslint ecosystem support a new major until awhile after the final release is out. It'd be great to beat that, but if there'd been any update, it'd be in this issue :-)

[JstnMcBrd]

Eslint officially released v9.0.0 today. Hope this plugin will support it soon!

[nodegin]

Getting TypeError: context.getScope is not a function here

[chelsea6502]

I'd like to continue using this plugin, but this bug is unfortunately stopping me.

I hope we get to see a fix soon!

[ljharb]

Nobody’s forcing you to upgrade to eslint 9 right away ¯\_(ツ)_/¯ new eslint majors always take months before everything supports them, and this one will take longer because it’s changing the default config format.

[Standard8]

and this one will take longer because it’s changing the default config format.

Having worked on a couple of other plugins, I want to elaborate that I think there's two parts to this upgrade.

The real breaking change for v9 is the fact that v9 has removed APIs - it looks like this is being covered in #3727.

The second change is flat config compatibility. Consumers can use the plugin as-is (as long as the API issues are resolved). It is slightly more work, but it is possible. Of course, supporting the flat config natively makes it easier, and ESLint has a good migration guide should anyone wanting to upgrade to v9 feel like contributing a patch (I might eventually, but I have several other plugins that I'm focussing on).

[MirKml]

yay, big step #3759 is done/merged. So I hope we see finish line 🏁, 🏃

Edit - I'm not package maintainer/developer :-), just spreading the message.

[targumon]

When can we expect the next release? Do you intend to accumulate a few more merges before it? Thanks in advance!

[ljharb]

@targumon yes, i'm trying to gather as many semver-minors as i can before a release.

[ljharb]

Fixed in #3759.