src/main/kotlin/io/github/mkohm/detekt/hint/rules/LackOfCohesionMethods.kt
package io.github.mkohm.detekt.hint.rules
import io.gitlab.arturbosch.detekt.api.CodeSmell
import io.gitlab.arturbosch.detekt.api.Config
import io.gitlab.arturbosch.detekt.api.Debt
import io.gitlab.arturbosch.detekt.api.Entity
import io.gitlab.arturbosch.detekt.api.Issue
import io.gitlab.arturbosch.detekt.api.Rule
import io.gitlab.arturbosch.detekt.api.Severity
import org.jetbrains.kotlin.js.resolve.diagnostics.findPsi
import org.jetbrains.kotlin.psi.KtCallExpression
import org.jetbrains.kotlin.psi.KtClass
import org.jetbrains.kotlin.psi.KtExpression
import org.jetbrains.kotlin.psi.KtNamedDeclaration
import org.jetbrains.kotlin.psi.KtNamedFunction
import org.jetbrains.kotlin.psi.KtParameter
import org.jetbrains.kotlin.psi.KtProperty
import org.jetbrains.kotlin.psi.KtReferenceExpression
import org.jetbrains.kotlin.psi.psiUtil.collectDescendantsOfType
import org.jetbrains.kotlin.psi.psiUtil.containingClass
import org.jetbrains.kotlin.psi.psiUtil.isProtected
import org.jetbrains.kotlin.psi.psiUtil.isPublic
import org.jetbrains.kotlin.resolve.BindingContext
import org.jetbrains.kotlin.resolve.calls.callUtil.getResolvedCall
/**
* A rule that notifies if there is too much lack of cohesion. Remember to configure it correctly in the detekt.yml.
*
* LCOM for a class will range between 0 and 1, with 0 being totally cohesive and 1 being totally non-cohesive.
* This makes sense since a low “lack of cohesion” score would mean a lot of cohesion.
*
* For each property in the class, you count the methods that reference it, and then you add all of those up across all properties. This value is called referencesCount.
* You then divide that by the count of methods times the count of properties, and you subtract the result from one.
*
* LCOM = 1 - referencesCount / ( methodsCount * propertyCount)
*/
class LackOfCohesionMethods(config: Config = Config.empty) : Rule(config) {
override val issue = Issue(
javaClass.simpleName,
Severity.CodeSmell,
"This rule reports a file with low LCOM value.",
Debt.TWENTY_MINS
)
private val memoizedResults = mutableMapOf<KtExpression, List<KtExpression>>()
private var propertyCount: Int = 0
private var referencesCount = 0
override fun visitNamedDeclaration(declaration: KtNamedDeclaration) {
super.visitNamedDeclaration(declaration)
if (bindingContext == BindingContext.EMPTY) return
if ((propertyIsMember(declaration) || isPropertyInitializedInPrimaryConstructor(declaration)) && hasContainingClass(declaration)) {
propertyCount++
// We know that the containing class exist, because of the above check hasContainingClass().
// Landmine operator is therefore okay.
@Suppress("UnsafeCallOnNullableType")
val containingClass = declaration.containingClass()!!
searchForReferences(declaration, containingClass)
}
}
override fun visitClass(klass: KtClass) {
// Skip interfaces, enums and inner classes.
if (klass.isInterface() || klass.isEnum() || klass.isInner()) return
propertyCount = 0
referencesCount = 0
val publicAndProtectedMethods = getPublicAndProtectedMethods(klass)
/*
* methodsCount is the number of methods that can reference properties in the class. Since constructors count as methods we have to add those as well.
*
* Initializer blocks can reference properties.
* Primary constructors can initialize properties with the concise Kotlin syntax. We add 1 if the current class uses this syntax.
* Secondary constructors can reference properties.
*/
val methodsCount =
publicAndProtectedMethods.size +
klass.getAnonymousInitializers().size +
klass.secondaryConstructors.size +
if (initializesPropertiesFromPrimaryConstructor(klass)) 1 else 0
super.visitClass(klass)
// If there is no methods or properties, there is no point of calculating LCOM, we will therefore return without reporting any value
if (methodsCount == 0 || propertyCount == 0) {
return
}
val lcom = calculateLCOMvalue(methodsCount, propertyCount, referencesCount)
val thresholdValue = valueOrNull<String>("threshold")?.toDouble() ?: error("You must specify a threshold value in detekt.yml")
if (lcom >= thresholdValue) {
report(
CodeSmell(issue, Entity.from(klass), "${klass.name} have a too high LCOM value: $lcom. Number of methods: $methodsCount, number of properties: $propertyCount, number of references: $referencesCount")
)
}
}
private fun hasContainingClass(declaration: KtNamedDeclaration) = declaration.containingClass() != null
private fun propertyIsMember(declaration: KtNamedDeclaration): Boolean {
return try {
// We only want to return true if the declaration is a true member of the class we are calculating LCOM for.
// If a property is declared inside an anonymous class, it is a member, but the fqname will be null, and we can therefore discard it.
return (declaration as KtProperty).isMember && declaration.fqName != null
} catch (e: ClassCastException) {
false
}
}
private fun calculateLCOMvalue(
methodsCount: Int,
propertyCount: Int,
referencesCount: Int
) = 1 - (referencesCount.toDouble() / (methodsCount * propertyCount))
private fun initializesPropertiesFromPrimaryConstructor(klass: KtClass): Boolean {
return klass.primaryConstructorParameters.any { it.hasValOrVar() }
}
private fun isPropertyInitializedInPrimaryConstructor(declaration: KtNamedDeclaration) =
(declaration is KtParameter) && declaration.hasValOrVar()
private fun searchForReferences(property: KtNamedDeclaration, containingClass: KtClass) {
// Properties can be referenced from public methods, protected methods?, initializer blocks and in secondary constructors.
val expressionsToLookForReferences =
getPublicAndProtectedMethods(containingClass).mapNotNull { it.bodyExpression } +
containingClass.getAnonymousInitializers().mapNotNull { it.body } +
containingClass.secondaryConstructors.mapNotNull { it.bodyExpression }
// If the property is initialized in the primary constructor it is automatically counted as a reference.
if (isPropertyInitializedInPrimaryConstructor(property)) {
referencesCount++
}
for (expression in expressionsToLookForReferences) {
val referenceExpression = getReferencesOfProperty(expression, property)
if (referenceExpression.isNotEmpty()) {
referencesCount++
continue
}
// Fetch all expressions that is reachable from the current expression (public method), recursively.
val allReachableExpressionsFromPublicMethod = getReachableExpressions(property, expression, arrayListOf(expression))
// We look for references of the property, and as soon as we find it, we increase mf_sum and break so that we can look for references in other public methods.
for (subExpression in allReachableExpressionsFromPublicMethod) {
// Get references in this private function
val references = getReferencesOfProperty(subExpression, property)
if (references.isNotEmpty()) {
referencesCount++
break
}
}
}
}
private fun getPublicAndProtectedMethods(klass: KtClass): List<KtNamedFunction> {
return klass.collectDescendantsOfType<KtNamedFunction> { it.isPublic || it.isProtected() }
}
private fun getReferencesOfProperty(
expression: KtExpression,
property: KtNamedDeclaration
): List<KtReferenceExpression> {
return expression.collectDescendantsOfType { reference ->
isReferenceOfPropertyClass(reference, expression) && reference.text == property.name
}
}
/**
* We need to ensure that the found reference not only have the same name as the property, but if it is a member of the correct class as well.
*/
private fun isReferenceOfPropertyClass(
reference: KtReferenceExpression,
expression: KtExpression
) =
reference.getResolvedCall(bindingContext)?.resultingDescriptor?.containingDeclaration?.name.toString() == expression.containingClass()?.name
private fun isCalleeInPropertyClass(
callee: KtExpression,
property: KtNamedDeclaration
) =
callee.containingClass()?.name == property.containingClass()?.name
/*
* From public, protected, initializer methods etc. Calls to private methods can exist.
* We need to find all such calls and look for references there as well.
*/
private fun getReachableExpressions(
property: KtNamedDeclaration,
expression: KtExpression,
foundExpressions: List<KtExpression>
): ArrayList<KtExpression> {
val reachableExpressionsFromThisExpressions =
ArrayList(expression.collectDescendantsOfType<KtCallExpression>()
.mapNotNull {
try {
(it.getResolvedCall(bindingContext)?.resultingDescriptor?.findPsi() as KtNamedFunction).bodyExpression
} catch (e: java.lang.ClassCastException) {
null
}
}.filter {
!foundExpressions.contains(it) && isCalleeInPropertyClass(
it,
property
)
}.distinct().ifEmpty {
return arrayListOf()
})
reachableExpressionsFromThisExpressions.addAll(foundExpressions)
// We need to dig further down into all the found expressions.
// There may be an unlimited amount of reachable expressions inside found expression.
// For performance reasons, the results are memoized.
for (reachableExpression in reachableExpressionsFromThisExpressions) {
// Memoize the results of the calculation to speed things up
var newResult = listOf<KtExpression>()
if (memoizedResults.containsKey(reachableExpression)) {
// After each call we put the result into the map, we therefore know that the key exists.
// Landmine operator is therefore okay in this case.
@Suppress("UnsafeCallOnNullableType")
newResult = memoizedResults[reachableExpression]!!
} else {
newResult = getReachableExpressions(property, reachableExpression, reachableExpressionsFromThisExpressions)
memoizedResults[reachableExpression] = newResult
}
reachableExpressionsFromThisExpressions + newResult
}
return reachableExpressionsFromThisExpressions
}
}