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Add ElseCaseInsteadOfExhaustiveWhen rule (#4632)
* Add ElseCaseInEnumOrSealedWhen rule * Adapt to new rule by replacing else cases * Change rule name, support booleans, improve docs * Change variable name of boolean condition * Rename rule to ElseCaseInsteadOfExhaustiveWhen * Improve rule descriptions * Suppress rule for outdated documentation method * Not report sealed class subjects that have an expect modifier * Fix sample code syntax and not compile mulitplatform code
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...src/main/kotlin/io/gitlab/arturbosch/detekt/rules/bugs/ElseCaseInsteadOfExhaustiveWhen.kt
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package io.gitlab.arturbosch.detekt.rules.bugs | ||
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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.RequiresTypeResolution | ||
import org.jetbrains.kotlin.cfg.WhenChecker | ||
import org.jetbrains.kotlin.psi.KtWhenExpression | ||
import org.jetbrains.kotlin.resolve.BindingContext | ||
import org.jetbrains.kotlin.resolve.calls.callUtil.getType | ||
import org.jetbrains.kotlin.types.KotlinType | ||
import org.jetbrains.kotlin.types.typeUtil.isBooleanOrNullableBoolean | ||
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/** | ||
* This rule reports `when` expressions that contain an `else` case even though they have an exhaustive set of cases. | ||
* | ||
* This occurs when the subject of the `when` expression is either an enum class, sealed class or of type boolean. | ||
* Using `else` cases for these expressions can lead to unintended behavior when adding new enum types, sealed subtypes | ||
* or changing the nullability of a boolean, since this will be implicitly handled by the `else` case. | ||
* | ||
* <noncompliant> | ||
* enum class Color { | ||
* RED, | ||
* GREEN, | ||
* BLUE | ||
* } | ||
* | ||
* when(c) { | ||
* Color.RED -> {} | ||
* Color.GREEN -> {} | ||
* else -> {} | ||
* } | ||
* </noncompliant> | ||
* | ||
* <compliant> | ||
* enum class Color { | ||
* RED, | ||
* GREEN, | ||
* BLUE | ||
* } | ||
* | ||
* when(c) { | ||
* Color.RED -> {} | ||
* Color.GREEN -> {} | ||
* Color.BLUE -> {} | ||
* } | ||
* </compliant> | ||
*/ | ||
@RequiresTypeResolution | ||
class ElseCaseInsteadOfExhaustiveWhen(config: Config = Config.empty) : Rule(config) { | ||
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override val issue: Issue = Issue( | ||
"ElseCaseInsteadOfExhaustiveWhen", | ||
Severity.Warning, | ||
"A `when` expression that has an exhaustive set of cases should not contain an `else` case.", | ||
Debt.FIVE_MINS | ||
) | ||
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override fun visitWhenExpression(whenExpression: KtWhenExpression) { | ||
super.visitWhenExpression(whenExpression) | ||
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if (bindingContext == BindingContext.EMPTY) return | ||
checkForElseCaseInsteadOfExhaustiveWhenExpression(whenExpression) | ||
} | ||
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private fun checkForElseCaseInsteadOfExhaustiveWhenExpression(whenExpression: KtWhenExpression) { | ||
val subjectExpression = whenExpression.subjectExpression ?: return | ||
if (whenExpression.elseExpression == null) return | ||
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val subjectType = subjectExpression.getType(bindingContext) | ||
val isEnumSubject = WhenChecker.getClassDescriptorOfTypeIfEnum(subjectType) != null | ||
val isSealedSubject = isNonExpectedSealedClass(subjectType) | ||
val isBooleanSubject = subjectType?.isBooleanOrNullableBoolean() == true | ||
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if (isEnumSubject || isSealedSubject || isBooleanSubject) { | ||
val subjectTypeName = when { | ||
isEnumSubject -> "enum class" | ||
isSealedSubject -> "sealed class" | ||
else -> "boolean" | ||
} | ||
val message = "When expression with $subjectTypeName subject should not contain an `else` case." | ||
report(CodeSmell(issue, Entity.from(whenExpression), message)) | ||
} | ||
} | ||
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/** | ||
* `when` expressions on `expect` sealed classes in the common code of multiplatform projects still require an | ||
* `else` branch. This happens because subclasses of `actual` platform implementations aren't known in the common | ||
* code. | ||
*/ | ||
private fun isNonExpectedSealedClass(type: KotlinType?): Boolean { | ||
val sealedClassDescriptor = WhenChecker.getClassDescriptorOfTypeIfSealed(type) | ||
return sealedClassDescriptor != null && !sealedClassDescriptor.isExpect | ||
} | ||
} |
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