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=5.8.3&fileType=.tsx&code=C4TwDgpgBAYgdlAvFA3gWAFBSgHgEpQQAewEcAJgM5SXABOAlnAOZQA%2BUArhRAGZMRyAPgAUASgBcUPAG5MAX0wBjAPZxaUYFPhIo4pEK49%2BcQXIyZe3JcAZqoAGxWUIAeToAZZxHFTajFnYoOE4AWwAjCDpUTGwGXj0AWQBDYAALADo6ZIoVUP0hZAAGDIBWMRisbCg6CGBOOgRgfWTqfyZmc2x5QgcXSuqauoam8S6oRQxJoA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6Jge1tiacTJTIAhtEK0ipWkOTJE0fJQ5N0UOdA7RI4MAF8QOoA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eFYDArugDTg10NM8AOXapUAYQAW6aAGsylDul4BfECqA&tokens=false

Repro Code

typeFn={<Rextendsstring|undefined>():R;}constt:Fn=()=>undefined;functionloseOrLose():string|number{if(Math.random()>=0.5){// no-unnecessary-type-assertion thinks the "as string" is unnecessaryreturnt()asstring;}else{// but without `as string` typescript failsreturnt();}}

ESLint Config

module.exports={parser:"@typescript-eslint/parser",rules:{"@typescript-eslint/no-unnecessary-type-assertion":"error"},};

tsconfig

{"compilerOptions": {"strict":true,"strictNullChecks":true  }}

Expected Result

I expected thatas string would be allowed, since TypeScript fails without it.

Actual Result

no-unnecessary-type-assertion claims theas string is unnecessary

Additional Info

This is similar to#11054, but I do not know if it has the same root cause.