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Libraries Rule Set

Rules in this rule set report issues related to libraries API exposure.

ForbiddenPublicDataClass​

Data classes are bad for binary compatibility in public APIs. Avoid using them.

This rule is aimed at library maintainers. If you are developing a final application you can ignore this issue.

More info: Public API challenges in Kotlin

Active by default: Yes - Since v1.16.0

Debt: 20min

Configuration options:​

  • ignorePackages (default: ['*.internal', '*.internal.*'])

    ignores classes in the specified packages.

Noncompliant Code:​

data class C(val a: String) // violation: public data class

Compliant Code:​

internal data class C(val a: String)

LibraryCodeMustSpecifyReturnType​

Functions/properties exposed as public APIs of a library should have an explicit return type. Inferred return type can easily be changed by mistake which may lead to breaking changes.

See also: Kotlin 1.4 Explicit API

Active by default: Yes - Since v1.2.0

Requires Type Resolution

Debt: 5min

Noncompliant Code:​

// code from a library
val strs = listOf("foo, bar")
fun bar() = 5
class Parser {
    fun parse() = ...
}

Compliant Code:​

// code from a library
val strs: List<String> = listOf("foo, bar")
fun bar(): Int = 5

class Parser {
    fun parse(): ParsingResult = ...
}

LibraryEntitiesShouldNotBePublic​

Library typealias and classes should be internal or private.

Active by default: Yes - Since v1.16.0

Debt: 5min

Noncompliant Code:​

// code from a library
class A

Compliant Code:​

// code from a library
internal class A