Collection Add To Self

kotlin.collection_add_to_self

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Kotlin

Description

Reports add(self) and addAll(self) calls where the receiver and the sole argument are the same identifier. Adding a collection to itself produces undefined behaviour at runtime.

Rationale

val list = mutableListOf<Any>()
list.add(list)        // FLAW — infinite recursion on toString/hashCode/equals
list.addAll(list)     // FLAW — usually ConcurrentModificationException

add(self) stores a reference to the collection inside itself. The very next call to toString, hashCode, or equals recurses indefinitely and crashes with StackOverflowError. addAll(self) iterates the collection while mutating it; most JDK implementations detect the mid-iteration resize and throw ConcurrentModificationException.

Remediation

Add the right collection — usually a copy of the receiver, or the contents of a different collection:

val list = mutableListOf<Any>()

// If you wanted to duplicate the contents:
list.addAll(list.toList())   // OK — toList() snapshots first

// If you wanted to merge from another source:
val other = listOf("a", "b")
list.addAll(other)           // OK

References

Kotlin — MutableCollection