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=4.9.5&sourceType=module&code=MYewdgzgLgBCBGArAXDA3jADgJxJg-KgNpgCuAtvAKbYC6MAvjALzoMDcAUJwGaljAoAS3AwIVKAHkBVABQA3AIYAbUlVRlKNAJTFN1Ouk4wY2CaWxg4SAHQ48MfPlZElqqrXYwA9N5gBCGAABKABPTCoIYGwhTCgAWkjlITAobzAQeP4wKmBIiEVsUPjQMAATIWFwVAAiAFUwHLyIAqKYUoqqsBUAGhgqAA8IwSoymGUqHgSAC0VysSEyqjgeGAADJzW4COxFKBBsGH2YaiwQFqF4ZVCYMmVlOEP+JZ4U0ZsazgZOIA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6Jge1tiacTJTIAhtEK0yHJgBNK+SpPRRE0aB2iRwYAL4gtQA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoAkNZOgB4CG0euBxTqACprIljwBPACpCBZSnkwBXdABpwEKCWnJWAORmpUAYQAW6aAGtJYaXKUBfEFaA

Repro Code

constobj:{prop?:[number]}={};functionsetOnce(value:number):[number]{returnobj.prop??=[value];// ! @typescript-eslint/no-unnecessary-condition: "Unnecessary conditional, expected left-hand side of `??` operator to be possibly null or undefined."}

ESLint Config

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

tsconfig

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

Expected Result

I expected the expressionobj.prop ??= [value] to not report an error.

Since the property hasn’t been set yet, it is actually undefined at runtime.

Actual Result

The expressionobj.prop ??= [value] is reported as an error.

typescript-eslint thinksobj.prop is non-nullish sinceexactOptionalPropertyTypes is on. We don’t want to turn it off because we still don’t want to allow statements likeobj.prop = undefined;.

Additional Info

Related:#3553,#5344,#6632