Refactor RedundantElseInWhen to use compiler warning (#3214)

detekt-rules-errorprone/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/bugs/RedundantElseInWhen.kt

@@ -7,21 +7,10 @@ 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.builtins.KotlinBuiltIns
-import org.jetbrains.kotlin.cfg.WhenChecker
-import org.jetbrains.kotlin.descriptors.ClassDescriptor
-import org.jetbrains.kotlin.load.kotlin.toSourceElement
+import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.psi.KtWhenExpression
 import org.jetbrains.kotlin.resolve.BindingContext
-import org.jetbrains.kotlin.resolve.BindingContext.DECLARATION_TO_DESCRIPTOR
-import org.jetbrains.kotlin.resolve.calls.callUtil.getType
-import org.jetbrains.kotlin.resolve.descriptorUtil.module
-import org.jetbrains.kotlin.resolve.source.getPsi
 
-/*
- * Based on code from Kotlin compiler:
- * https://github.com/JetBrains/kotlin/blob/v1.3.30/compiler/frontend/src/org/jetbrains/kotlin/cfg/ControlFlowInformationProvider.kt
- */
 /**
  * Turn on this rule to flag `when` expressions that contain a redundant `else` case. This occurs when it can be
  * verified that all cases are already covered when checking cases on an enum or sealed class.
@@ -83,19 +72,10 @@ class RedundantElseInWhen(config: Config = Config.empty) : Rule(config) {
         super.visitWhenExpression(whenExpression)
 
         if (bindingContext == BindingContext.EMPTY) return
-        if (whenExpression.elseExpression == null) return
-        val subjectType = whenExpression.subjectExpression?.getType(bindingContext)
-
-        if (subjectType != null && WhenChecker.getMissingCases(whenExpression, bindingContext).isEmpty()) {
-            val subjectClass = subjectType.constructor.declarationDescriptor as? ClassDescriptor
-            val pseudocodeDescriptor =
-                bindingContext[DECLARATION_TO_DESCRIPTOR, subjectClass?.toSourceElement?.getPsi()]
-            if (subjectClass == null ||
-                KotlinBuiltIns.isBooleanOrNullableBoolean(subjectType) ||
-                subjectClass.module == pseudocodeDescriptor?.module
-            ) {
-                report(CodeSmell(issue, Entity.from(whenExpression), "When expression contains redundant `else` case."))
-            }
+        val elseEntry = whenExpression.entries.lastOrNull { it.isElse } ?: return
+        val compilerReports = bindingContext.diagnostics.forElement(elseEntry)
+        if (compilerReports.any { it.factory == Errors.REDUNDANT_ELSE_IN_WHEN }) {
+            report(CodeSmell(issue, Entity.from(whenExpression), "When expression contains redundant `else` case."))
         }
     }
 }