io.gitlab.arturbosch.detekt.rules.style.UseLet.kt Maven / Gradle / Ivy

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package io.gitlab.arturbosch.detekt.rules.style

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.rules.isNonNullCheck
import io.gitlab.arturbosch.detekt.rules.isNullCheck
import org.jetbrains.kotlin.psi.KtBinaryExpression
import org.jetbrains.kotlin.psi.KtBlockExpression
import org.jetbrains.kotlin.psi.KtConstantExpression
import org.jetbrains.kotlin.psi.KtExpression
import org.jetbrains.kotlin.psi.KtIfExpression
import org.jetbrains.kotlin.psi.KtPsiUtil

/**
 * `if` expressions that either check for not-null and return `null` in the false case or check for `null` and returns
 * `null` in the truthy case are better represented as `?.let {}` blocks.
 *
 * 
 * if (x != null) { x.transform() } else null
 * if (x == null) null else y
 * 
 *
 * 
 * x?.let { it.transform() }
 * x?.let { y }
 * 
 */
class UseLet(
    config: Config = Config.empty
) : Rule(config) {
    override val issue = Issue(
        javaClass.simpleName,
        Severity.Style,
        "Use `?.let {}` instead of if/else with a null block when checking for nullable values",
        Debt.FIVE_MINS
    )

    private fun isExpressionNull(branch: KtExpression?): Boolean {
        val statement = when (branch) {
            is KtBlockExpression -> if (branch.statements.size == 1) branch.statements.first() else null
            is KtConstantExpression -> branch
            else -> null
        }

        return statement?.let { KtPsiUtil.isNullConstant(it) } ?: false
    }

    override fun visitIfExpression(expression: KtIfExpression) {
        super.visitIfExpression(expression)
        val condition = expression.condition as? KtBinaryExpression ?: return

        if (condition.isNullCheck() && isExpressionNull(expression.then)) {
            report(CodeSmell(issue, Entity.from(expression), issue.description))
        } else if (condition.isNonNullCheck() && isExpressionNull(expression.`else`)) {
            report(CodeSmell(issue, Entity.from(expression), issue.description))
        }
    }
}