useless postfix expression isn't useless

[jbaron]

Expected Behavior

Detekt should not complain about postfix expression being useless if it increases a value that lives outside the scope of the method it is used.

Observed Behavior

Detekt complaints that the postfix example below is useless, while in fact it does exactly the job it is suppose to do.

Steps to Reproduce

   private var ID = 0

  /**
   * Generate the next order id
   */
  @Synchronized
  private fun nextId(): String {
      return ID++.toString() // this is the line !!!!!
  }

Context

Not a big issue, just a false negative.

Your Environment

Maven build
detekt plugin in IntelliJ 2.3.0
Kotlin 1.9.22

[cortinico]

This is a valid bug. The problem is here:

detekt/detekt-rules-errorprone/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/bugs/UselessPostfixExpression.kt

Lines 69 to 79 in 9cfe9f2

	override fun visitReturnExpression(expression: KtReturnExpression) {
	val postfixExpression = expression.returnedExpression?.asPostFixExpression()
	if (postfixExpression != null && postfixExpression.shouldBeReported()) {
	report(postfixExpression)
	}
	expression.returnedExpression
	?.let(this::getPostfixExpressionChildren)
	?.forEach(this::report)
	}

Basically for return instructions we don't account for properties in the class, which we should.

This is up for grab if someone is looking for an easy contribution