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[backport] [CNA] use linter preference (#83194) #84087

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merged 1 commit into from
Sep 22, 2025
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[backport] [CNA] use linter preference (#83194) #84087

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10 changes: 9 additions & 1 deletion packages/create-next-app/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -291,6 +291,11 @@ async function run(): Promise<void> {
opts.biome = preferredLinter === 'biome'
// No need to set noLinter flag since we check args at runtime
} else {
const linterIndexMap = {
eslint: 0,
biome: 1,
none: 2,
}
const { linter } = await prompts({
onState: onPromptState,
type: 'select',
Expand All @@ -313,7 +318,10 @@ async function run(): Promise<void> {
description: 'Skip linter configuration',
},
],
initial: 0,
initial:
linterIndexMap[
getPrefOrDefault('linter') as keyof typeof linterIndexMap
],
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Suggested change
],
] ?? 0,

The code could fail if the user's linter preference contains an unexpected value, causing undefined to be passed as the initial prompt selection.

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Analysis

Undefined initial value passed to prompts when linter preference is invalid

What fails: The linterIndexMap lookup in packages/create-next-app/index.ts:321-324 returns undefined when getPrefOrDefault('linter') returns a value not in the map ('eslint', 'biome', 'none'), causing the prompts library to receive initial: undefined.

How to trigger:

  1. Create or modify the create-next-app config with an invalid linter preference:
# Edit ~/.config/create-next-app/config.json to contain:
{"preferences": {"linter": "invalid-value"}}
  1. Run create-next-app without CLI linter flags to trigger the interactive prompt

Result: The prompts library receives initial: undefined instead of a valid array index, leading to unpredictable default selection behavior.

Expected: Should default to a valid index (0 = ESLint) when the preference value is not recognized, ensuring consistent user experience.

Fix applied: Added nullish coalescing operator ?? 0 to provide fallback to first option (ESLint) when lookup returns undefined.

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We will get at least a default value so wouldn't be undefined

})

opts.eslint = linter === 'eslint'
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