MapGetWithNotNullAssertionOperator.kt

package io.gitlab.arturbosch.detekt.rules.bugs

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.internal.ActiveByDefault
import org.jetbrains.kotlin.lexer.KtTokens
import org.jetbrains.kotlin.name.FqName
import org.jetbrains.kotlin.psi.KtPostfixExpression
import org.jetbrains.kotlin.resolve.calls.util.getResolvedCall
import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameSafe

/**
 * Reports calls of the map access methods `map[]` or `map.get()` with a not-null assertion operator `!!`.
 * This may result in a NullPointerException.
 * Preferred access methods are `map[]` without `!!`, `map.getValue()`, `map.getOrDefault()` or `map.getOrElse()`.
 *
 * Based on an IntelliJ IDEA inspection MapGetWithNotNullAssertionOperatorInspection.
 *
 * <noncompliant>
 *  val map = emptyMap<String, String>()
 *  map["key"]!!
 *
 *  val map = emptyMap<String, String>()
 *  map.get("key")!!
 * </noncompliant>
 *
 * <compliant>
 * val map = emptyMap<String, String>()
 * map["key"]
 *
 * val map = emptyMap<String, String>()
 * map.getValue("key")
 *
 * val map = emptyMap<String, String>()
 * map.getOrDefault("key", "")
 *
 * val map = emptyMap<String, String>()
 * map.getOrElse("key", { "" })
 * </compliant>
 */
@ActiveByDefault(since = "1.21.0")
class MapGetWithNotNullAssertionOperator(config: Config) : Rule(config) {

    override val issue: Issue =
        Issue(
            "MapGetWithNotNullAssertionOperator",
            Severity.CodeSmell,
            "map.get() with not-null assertion operator (!!) can result in a NullPointerException. " +
                "Consider usage of map.getValue(), map.getOrDefault() or map.getOrElse() instead.",
            Debt.FIVE_MINS
        )

    override fun visitPostfixExpression(expression: KtPostfixExpression) {
        if (expression.operationToken == KtTokens.EXCLEXCL && expression.isMapGet()) {
            report(CodeSmell(issue, Entity.from(expression), "map.get() with not-null assertion operator (!!)"))
        }
        super.visitPostfixExpression(expression)
    }

    private fun KtPostfixExpression.isMapGet(): Boolean {
        return this
            .baseExpression
            .getResolvedCall(bindingContext)
            ?.resultingDescriptor
            ?.fqNameSafe == FqName("kotlin.collections.Map.get")
    }
}