Why is this an issue?

When the return value of a function call contains the operation status code, this value should be tested to make sure the operation completed successfully.

This rule raises an issue when the return values of the following are ignored:

• java.io.File operations that return a status code (except mkdirs)
• Iterator.hasNext()
• Enumeration.hasMoreElements()
• Lock.tryLock()
• non-void Condition.await* methods
• CountDownLatch.await(long, TimeUnit)
• Semaphore.tryAcquire
• BlockingQueue: offer, remove

Noncompliant code example

fun doSomething(file: File, lock: Lock) {
    file.delete() // Noncompliant
    // ...
    lock.tryLock() // Noncompliant
}

Compliant solution

fun doSomething(file: File, lock: Lock) {
    if (!file.delete()) {
        // file delete failed; take appropriate action
    }
    if (!lock.tryLock()) {
        // lock failed; take appropriate action
    }
}

Resources

Although these resources talk about Java, the underlying information concerning the JVM is just as relevant for Kotlin.

• CERT, EXP00-J. - Do not ignore values returned by methods
• CERT, FIO02-J. - Detect and handle file-related errors
• MITRE, CWE-754 - Improper Check for Unusual Exceptional Conditions