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CouldBeSequence.kt
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CouldBeSequence.kt
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package io.gitlab.arturbosch.detekt.rules.performance
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 io.gitlab.arturbosch.detekt.api.config
import io.gitlab.arturbosch.detekt.api.internal.Configuration
import io.gitlab.arturbosch.detekt.api.internal.RequiresTypeResolution
import org.jetbrains.kotlin.name.FqName
import org.jetbrains.kotlin.psi.KtCallExpression
import org.jetbrains.kotlin.psi.KtExpression
import org.jetbrains.kotlin.psi.psiUtil.getQualifiedExpressionForReceiver
import org.jetbrains.kotlin.psi.psiUtil.getQualifiedExpressionForSelectorOrThis
import org.jetbrains.kotlin.resolve.BindingContext
import org.jetbrains.kotlin.resolve.calls.util.getResolvedCall
import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameOrNull
/**
* Long chains of collection operations will have a performance penalty due to a new list being created for each call. Consider using sequences instead. Read more about this in the [documentation](https://kotlinlang.org/docs/sequences.html)
*
* <noncompliant>
* listOf(1, 2, 3, 4).map { it*2 }.filter { it < 4 }.map { it*it }
* </noncompliant>
*
* <compliant>
* listOf(1, 2, 3, 4).asSequence().map { it*2 }.filter { it < 4 }.map { it*it }
*
* listOf(1, 2, 3, 4).map { it*2 }
* </compliant>
*/
@RequiresTypeResolution
class CouldBeSequence(config: Config = Config.empty) : Rule(config) {
override val issue: Issue = Issue(
"CouldBeSequence",
Severity.Performance,
"Several chained collection operations that should be a sequence.",
Debt.FIVE_MINS
)
@Configuration("the number of chained collection operations required to trigger rule")
private val threshold: Int by config(defaultValue = 3)
private var visitedCallExpressions = mutableListOf<KtExpression>()
@Suppress("ReturnCount")
override fun visitCallExpression(expression: KtCallExpression) {
super.visitCallExpression(expression)
if (bindingContext == BindingContext.EMPTY) return
if (visitedCallExpressions.contains(expression)) return
if (!expression.isCalling(operationsFqNames)) return
var counter = 1
var nextCall = expression.nextChainedCall()
while (counter < threshold && nextCall != null) {
visitedCallExpressions += nextCall
if (!nextCall.isCalling(operationsFqNames)) {
break
}
counter++
nextCall = nextCall.nextChainedCall()
}
if (counter >= threshold) {
val message = "${expression.text} could be .asSequence().${expression.text}"
report(CodeSmell(issue, Entity.from(expression), message))
}
}
private fun KtExpression.nextChainedCall(): KtExpression? {
val expression = this.getQualifiedExpressionForSelectorOrThis()
return expression.getQualifiedExpressionForReceiver()?.selectorExpression
}
private fun KtExpression.isCalling(fqNames: List<FqName>): Boolean {
val calleeText = (this as? KtCallExpression)?.calleeExpression?.text ?: this.text
val targetFqNames = fqNames.filter { it.shortName().asString() == calleeText }
if (targetFqNames.isEmpty()) return false
return getResolvedCall(bindingContext)?.resultingDescriptor?.fqNameOrNull() in targetFqNames
}
companion object {
private val operationsFqNames = listOf(
FqName("kotlin.collections.filter"),
FqName("kotlin.collections.filterIndexed"),
FqName("kotlin.collections.map"),
FqName("kotlin.collections.mapIndexed"),
FqName("kotlin.collections.flatMap"),
FqName("kotlin.collections.flatMapIndexed"),
FqName("kotlin.collections.reduce"),
FqName("kotlin.collections.zip")
)
}
}