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Update eslint 9.39.2 → 10.0.0 (major) #19673

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Update eslint 9.39.2 → 10.0.0 (major) #19673

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2 changes: 1 addition & 1 deletion playgrounds/nextjs/package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@
"@types/node": "catalog:",
"@types/react": "^19.2.14",
"@types/react-dom": "^19.2.3",
"eslint": "^9.39.2",
"eslint": "^10.0.0",
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@coderabbitai coderabbitai bot Feb 18, 2026

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⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
# Check for ESLint config files in playgrounds/nextjs
echo "=== Searching for ESLint configs in playgrounds/nextjs ==="
find playgrounds/nextjs -maxdepth 2 \( -name ".eslintrc*" -o -name "eslint.config.*" -o -name ".eslintignore" \) 2>/dev/null

echo ""
echo "=== Checking root directory for shared ESLint configs ==="
find . -maxdepth 1 \( -name ".eslintrc*" -o -name "eslint.config.*" \) 2>/dev/null

echo ""
echo "=== Listing contents of playgrounds/nextjs ==="
ls -la playgrounds/nextjs/ 2>/dev/null | head -20

Repository: tailwindlabs/tailwindcss

Length of output: 928

🏁 Script executed:

cat -n playgrounds/nextjs/.eslintrc.json

Repository: tailwindlabs/tailwindcss

Length of output: 260

Migrate to flat config before upgrading ESLint to v10.

This playground uses a legacy .eslintrc.json file, which ESLint 10 no longer supports. Upgrading to ^10.0.0 will break the next lint command. Convert the config to eslint.config.js (flat config format) before this upgrade.

The current .eslintrc.json extends next/core-web-vitals and disables two React rules. Verify that the equivalent Next.js 16+ flat config integration supports this setup.

🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@playgrounds/nextjs/package.json` at line 23, The package.json bump to
"eslint": "^10.0.0" will break the legacy .eslintrc.json; convert the repo
ESLint config to a flat config file named eslint.config.js and remove/stop using
.eslintrc.json, migrating the extends "next/core-web-vitals" to the Next.js flat
config integration and re-declare the two disabled React rules (the same rule
names from the .eslintrc.json) as turned off in the new config; after creating
eslint.config.js, verify that running `next lint` works and that Next.js 16+
flat config integration is used instead of the old .eslintrc.json.

"eslint-config-next": "^16.1.6",
"typescript": "^5.9.3"
}
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2 changes: 1 addition & 1 deletion playgrounds/v3/package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@
"@types/react": "^19.2.14",
"@types/react-dom": "^19.2.3",
"autoprefixer": "^10.4.24",
"eslint": "^9.39.2",
"eslint": "^10.0.0",
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@coderabbitai coderabbitai bot Feb 13, 2026

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⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🌐 Web query:

ESLint 10 breaking changes eslintrc flat config migration

💡 Result:

ESLint 10: key breaking changes (esp. .eslintrc → flat config)

  • Legacy .eslintrc is fully removed: .eslintrc.* and .eslintignore are no longer read; ESLINT_USE_FLAT_CONFIG is no longer honored; /* eslint-env */ comments are now errors; and several eslintrc-era CLI flags are removed (--no-eslintrc, --env, --rulesdir, --ignore-path, --resolve-plugins-relative-to). [1]
  • Config lookup changed: ESLint now finds eslint.config.* starting from each linted file’s directory (not just the current working directory). This enables multiple configs in one run (monorepos), but can change which config gets applied. [1]
  • Node.js support floor moved: Node < 20.19.0 (and Node 21/23) are unsupported (see exact supported ranges in the release notes). [1]
  • Integration/API removals related to legacy config: loadESLint() always returns ESLint; Linter’s configType can only be "flat"; LegacyESLint (and some other /use-at-your-own-risk exports) are removed. [1]

Migration: .eslintrc → eslint.config.js (flat config)

  1. Generate a starting flat config automatically:

    npx `@eslint/migrate-config` .eslintrc.json

    (Works best for .eslintrc JSON/YAML; .eslintrc.js is converted from evaluated output and may need more manual cleanup.) [2][3]

  2. Move ignore patterns from .eslintignore into flat config using ignores (top-level in your exported config array/object). [1][2]

  3. Replace env / --env usage with languageOptions.globals (and languageOptions.ecmaVersion / sourceType as needed). [1][2]

  4. Update plugins & shareable configs:

    • Flat config generally expects direct plugin imports (rather than string names + resolver behavior). [1][2]
    • If you depend on shareable configs that are still eslintrc-format, use FlatCompat from @eslint/eslintrc to bridge them during migration. [2]

  5. Monorepos: re-check where you place configs because of the new per-file lookup. You may want a root eslint.config.js plus package-level eslint.config.js files. [1]

Sources

  • [1] ESLint v10.0.0 release notes (eslint.org)
  • [2] ESLint “Configuration Migration Guide” (eslintrc → flat config) (eslint.org)
  • [3] “Introducing the ESLint Configuration Migrator” (@eslint/migrate-config) (eslint.org)

Citations:

🏁 Script executed:

# Search for ESLint config files in playgrounds/v3
find playgrounds/v3 -maxdepth 2 \( -name ".eslintrc*" -o -name "eslint.config.*" -o -name ".eslintignore" \) 2>/dev/null

# Check root directory for ESLint configs that might be inherited
find . -maxdepth 1 \( -name ".eslintrc*" -o -name "eslint.config.*" \) 2>/dev/null

# Look for package.json scripts that reference linting
rg -n "eslint|lint" playgrounds/v3/package.json -A 2

Repository: tailwindlabs/tailwindcss

Length of output: 284

🏁 Script executed:

# Check the .eslintrc.json file
cat playgrounds/v3/.eslintrc.json

# Verify no flat config exists
ls -la playgrounds/v3/eslint.config.* 2>/dev/null || echo "No eslint.config.* found"

Repository: tailwindlabs/tailwindcss

Length of output: 236

Migrate playgrounds/v3 to ESLint flat config before upgrading to v10 (Line 22).

ESLint v10 fully removes legacy .eslintrc.* support. The playground currently uses .eslintrc.json (extending next/core-web-vitals) but has no flat config yet. Upgrading to eslint@^10.0.0 will cause next lint to fail.

Migrate to eslint.config.js using:

npx `@eslint/migrate-config` playgrounds/v3/.eslintrc.json

Then move ignore patterns and ensure the shareable config is correctly imported (or use FlatCompat from @eslint/eslintrc as a bridge if needed).

🤖 Prompt for AI Agents 
In `@playgrounds/v3/package.json` at line 22, Package.json currently pins
"eslint": "^10.0.0" while the playground still uses a legacy .eslintrc.json;
migrate the project to a flat config before upgrading by running the recommended
migration command (npx `@eslint/migrate-config` playgrounds/v3/.eslintrc.json),
then add an eslint.config.js at the repo root that imports or recreates your
existing settings (or use FlatCompat from `@eslint/eslintrc` to bridge shareable
configs like next/core-web-vitals), and ensure ignore patterns from
.eslintignore are moved into the new flat config so that running next lint
succeeds with "eslint": "^10.0.0".

"eslint-config-next": "^16.1.6",
"typescript": "^5.9.3"
}
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