Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I havesearched for related issues and found none that matched my issue.
• I haveread the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=5.8.2&fileType=.ts&code=CYUwxgNghgTiAEYD2A7AzgF3gWygTwCMQAueAcijPgB9yCyBuAKFElgWXSwDMoIICUMAGtSAbTJgyAXWatoceNwCuKMBgCWqRHCgYQANT7KQaABQBKUphgaUAczHSa8VaG52QwZkxVrN2sjYAA7K%2BgDKGLYO5lbwNnaOzgDeTPCIqJjwdvow2F4aeggAvDj4RPDFVeSU8ABkdTogRUYQJrE%2B6ZxZAG7GJdkoufnAhfo0tLz8giKd8HAYyjAo8H1tIMwAvkxAA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6Y6RAM0WlqYSNkAC1pkA9gEMkyMswDm6KL2jjokcGAC%2BILUA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false

Repro Code

declareconstmaybe:'a'|'b';declareconstfallback:['c'];declarefunctioncreateValues():string[]|undefined;functioncomputeStrings():string[]{constintermediate=maybe==='a'&&createValues();constvalue=intermediate||fallback;returnvalue;}

ESLint Config

module.exports={"rules":{"@typescript-eslint/prefer-nullish-coalescing":"error"}}

tsconfig

{"compilerOptions": {"strictNullChecks":true  }}

Expected Result

intermediate isfalse | string[] | undefined and its parent function returnsstring[]. The|| is the right operator to use to makevalue astring[], not astring[] | false.

Actual Result

Prefer using nullish coalescing operator (`??`) instead of a logical or (`||`), as it is a safer operator. 8:30 - 8:32

Additional Info

Related:#7055,#10356, and probably others, searching gives a lot of false positive results...

#10356 notes that this gets suggested a good amount. I personally was surprised to re-discover that the default behavior of the rule is to report in a way that is sometimes incorrect/unnecessary.

Proposal: I think we should switch the rule to ignorefalse | undefined | (always-truthy)s by default.

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