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

(BRANCH PLAYGROUND - NOT ON MAIN YET)

Repro Code

functionjoin<Textendsstring|number>(els:T[]){returnels.map(el=>''+el).join(',');}

ESLint Config

module.exports={"rules":{"@typescript-eslint/no-unnecessary-type-parameters":"warn"}}

tsconfig

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

Expected Result

functionjoin(els:(string|number)[]){returnels.map(el=>''+el).join(',');}

Actual Result

functionjoin(els:string|number[]){returnels.map(el=>''+el).join(',');}

Additional Info

This is a followup to#9536 (comment). note that, while this specific report case isn't merged yet,

• I'm pretty sure it will be merged imminently
• I'm pretty sure we could figure out a repro where the parenthesization is wrong on a case the rule already reports on, but I haven't bothered thinking too hard about it