kure-potlin

This is a small plugin to detekt tool. The purpose is to report the potential use of impure language elements in kotlin code.

Detected rules

Rule	Detects	Properties with defaults	Requires type resolution
LoopUsage	use of for, while	active: true
ReturnStatement	use of return statement	active: true
VariableUsage	use of var	active: true
ReturnUnit	use of function returning Unit, Nothing, Void; unless annotated with an annotation which name is specified in ignoredAnnotations	active: true ignoreFunctionType: false ignoredAnnotations: [] ignoreDsl: false	☑️
ClassDefinition	use of object-oriented class	active: false
AbstractClassDefinition	use of object-oriented abstract class	active: false
ThrowExpression	use of throw	active: true
MutableCollections	use of mutable collections	active: true	☑️
BranchStatement	use of if or when as statement	active: true
MissingElse	use of if statement without else (which also makes it a statement covered by BranchStatement)	active: false

Usage

a) Use detect plugin in gradle build (.kts syntax). In case of problems refer to detekt documentation.

repositories {
    jcenter()
}

plugins {
    id("io.gitlab.arturbosch.detekt").version("1.16.0")
}

b) add dependency

dependencies {
    detektPlugins("pl.setblack:kure-potlin:0.5.0")
}

c) optionally, you can reconfigure plugin by adding this to your custom detekt.yaml:

impure:
  active: true
  LoopUsage:
    active: true
  ReturnStatement:
    active: true
  VariableUsage:
    active: true
  ReturnUnit:
    active: true
    ignoreFunctionType: false
    ignoredAnnotations: [ ]
    ignoreDsl: false
  ClassDefinition:
    active: false
  AbstractClassDefinition:
    active: false
  ThrowExpression:
    active: true
  MutableCollections:
    active: true
  BranchStatement:
    active: true
  MissingElse:
    active: false

d) run gradle detekt or gradle detektMain to use rules which require type resolution

License

Apache 2.0

text

Examples

fun impure(y: Int): Int {
    var x = 1
    x = x + y
    return x
}

Function above will be reported as impure (uses var and return).

It can be rewritten to a pure version.

fun pure(y: Int): Int = y + 1 

Suppressing

If you need to ignore/suppress issues reported by this plugin. Just annotate function or class with: @Suppress("RULE") where RULE is just a [supported rule name](#Detected rules).

Example:

@Suppress("ReturnStatement")
fun add(a:Int, b:Int) {
    val x  = a+b
    return x
}

(This is a standard detekt feature).

Disclaimer

This plugin will not enforce 100% pure functional programing. It only checks for some keywords. If you use some java libraries it will be easily possible to cheat. For instance: AtomicReference can be used as variable. Use of mutable ( java) objects will not be detected. The existing java/kotlin ecosystem will also force you to write impure code occasionally.

Releases

version 0.5.0:

• improved Unit rule (thanks @krzykrucz)

version 0.4.0:

• improved Unit detection, detects also void, Nothing statements (thanks @krzykrucz)
• introduced BranchStatement
• introduced optional MissingElse rule

version 0.3.0:

• all rules configurable (thanks @krzykrucz)
• class rule (thanks @krzykrucz)
• abstract class rule (thanks @krzykrucz)
• upgraded to dektekt 1.16
• compiled to jvm 1.8

version 0.2.1:

• detects Unit (thanks @MiSikora)
• detects mutable collections (thanks @krzykrucz)
• detects throws (thanks @krzykrucz) and all from version 1.3

version 0.1.3: detects only var, loops and return