[wanjinhao1]

Resolves #16368.

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Description

What is the purpose of this pull request?

This pull request:

• Adds unexport ESLINT_FLAGS to tools/make/lib/lint/javascript/eslint.mk so that the make variable ESLINT_FLAGS is not leaked into the environment of the invoked ESLint process.

Background: GNU make exports command-line variables as environment variables to recipes. Since ESLint 9.39+, the ESLINT_FLAGS environment variable is read to enable ESLint feature flags (e.g., unstable_native_nodejs_ts_config) and any unrecognized value throws Unknown flag '<value>'. Consequently, when the CI lint retry runs make lint-javascript-files ... ESLINT_FLAGS='--quiet' (see .github/workflows/scripts/common/lint_javascript_files_error_log), ESLint received ESLINT_FLAGS=--quiet in its environment, treated --quiet as a feature flag, and crashed with Error: Unknown flag '--quiet'. for every linted file — masking the actual lint results. Unexporting the variable keeps it as a pure make variable used only to build the ESLint command-line options (where --quiet is valid).

Reproduction (ESLint 9.39.5):

$ make check ESLINT_FLAGS=--quiet   # without this fix
Error: Unknown flag '--quiet'.
$ make check ESLINT_FLAGS=--quiet   # with `unexport ESLINT_FLAGS`
$ echo $?
0

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• Fix JavaScript lint errors #16368

Reference Packages

Did the content of this pull request follow one or more existing packages? Answering is optional.

This pull request followed these packages:

• none

What carried over from the reference(s)?

• none

What differed, or what did you have to work out yourself?

• Diagnosed the root cause by reproducing the collision between GNU make's command-line variable export behavior and ESLint 9.39+'s new ESLINT_FLAGS environment variable for feature flags.

Questions

Any questions for reviewers of this pull request?

No.

---

Verification: reproduced the failure locally with ESLint 9.39.5 using a minimal Makefile mirroring the eslint_flags pattern (make check ESLINT_FLAGS=--quiet fails with Error: Unknown flag '--quiet'. before the fix and passes after adding unexport ESLINT_FLAGS). Could not run the repository's full lint target locally without a full development-environment install; the change is limited to make variable export semantics.

This PR was prepared with AI assistance (agent operating on behalf of @wanjinhao1).

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[kgryte]

I am not sure this is the right fix. If --quiet is not supported, maybe we should not be using the flag in the first place.

cc @Planeshifter

[Planeshifter]

@kgryte, I believe this to be a good and correct fix for the regression.

--quiet option is still supported in ESLint. Problem arises because ESLint introduced reading a ESLINT_FLAGS environment variable in v9.27.0, released May 16, 2025, according to its release notes.

Before that, Make could export ESLINT_FLAGS=--quiet harmlessly because ESLint ignored the environment variable. But now it is interpreted as a feature flag and rejected: https://eslint.org/docs/latest/flags#enable-feature-flags-with-environment-variables.

Other options would be to rename our ESLINT_FLAGS variable to say ESLINT_CLI_FLAGS, which would be a breaking change, or to unset it each time when invoking ESLint. Both arguably worse than the solution offered in this PR.

[kgryte]

@Planeshifter Except no other environment variable defined in our make recipes is accommodated like this.

While *_CLI_* also goes against convention, I am not sure I'd call it a "breaking change", as this is purely for developer usage, not downstream consumers.

[Planeshifter]

I did a search and looks like we only have four occurrences of ESLINT_FLAGS across 2 files:

• .github/workflows/scripts/common/lint_javascript_files_error_log
• tools/make/lib/lint/javascript/eslint.mk

I expected many more. So to make it cleaner, renaming instead to say ESLINT_CLI_FLAGS seems fine, too. And it would have the advantage of retaining ability of passing feature flags, should that ever be necessary, via ESLINT_FLAGS.

Granted, no breakage for end-users, but contributors will need to update Bash aliases, scripts, or shell functions that used the old variable name.