MissingWhenCase false negative with nulls

[BraisGabin]

Expected Behavior

MissingWhenCase should check for null case if the enum or sealed can be null

Observed Behavior

It doesn't check that.

Steps to Reproduce

fun whenOnEnumPass(c: Color?) {
    when(c) {
        Color.BLUE -> {}
        Color.GREEN -> {}
        Color.RED -> {}
    }
}

Your Environment

• Version of detekt used: master (1.14.2)

[schalkms]

Closed due to the arguments made in the referenced PR.

• Check for presence of null case in MissingWhenCase rule #3194 (comment)
• Check for presence of null case in MissingWhenCase rule #3194 (comment)

[BraisGabin]

Should we create a tag "require smart cast" or something similar to track this issues? I mean, even if we close it to find them if we eventually implement it. Or if we want ro evaluate if it's worth it to implement it.

[schalkms]

An available smart cast detection alone won't solve the problem here. You'll need more sophisticated analysis than that.

[BraisGabin]

🤔 why not?

[schalkms]

I didn't know that we already have dataflow analysis as part of the bindingContext. Great. Thanks for bringing this up.
This issue can be reopened.

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

Lines 66 to 78 in b1269b5

	expression.parent is KtStringTemplateEntry -> {
	val compilerResources = compilerResources ?: return
	val descriptor = expression.descriptor() ?: return
	val originalType = descriptor.returnType ?.takeIf { it.isNullable() } ?: return
	val dataFlowInfo =
	bindingContext[BindingContext.EXPRESSION_TYPE_INFO, expression]?.dataFlowInfo ?: return
	val dataFlowValue = compilerResources.dataFlowValueFactory.createDataFlowValue(
	expression, originalType, bindingContext, descriptor
	)
	val dataFlowTypes =
	dataFlowInfo.getStableTypes(dataFlowValue, compilerResources.languageVersionSettings)
	if (dataFlowTypes.any { !it.isNullable() }) return
	}

[schalkms]

By the way, this has nothing to do with smart casts per se. The enabler here is data flow analysis as part of the Kotlin compiler. With the help of data flow analysis we can detect whether null checks or the necessary casts have been made before the when clause.