UnusedUnaryOperator: fix false positive with var assignment and if expression

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

@@ -17,8 +17,8 @@ import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.KtBinaryExpression
 import org.jetbrains.kotlin.psi.KtExpression
 import org.jetbrains.kotlin.psi.KtPrefixExpression
-import org.jetbrains.kotlin.psi.psiUtil.getTopmostParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.leaves
+import org.jetbrains.kotlin.psi.psiUtil.parents
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.bindingContextUtil.isUsedAsExpression
 import org.jetbrains.kotlin.resolve.calls.util.getResolvedCall
@@ -62,7 +62,7 @@ class UnusedUnaryOperator(config: Config = Config.empty) : Rule(config) {
             .none { it is PsiWhiteSpace && it.textContains('\n') }
         ) return
 
-        val parentOrSelf = (expression.getTopmostParentOfType<KtBinaryExpression>() ?: expression) as KtExpression
+        val parentOrSelf = expression.parentBinaryExpressionOrThis()
         if (parentOrSelf.isUsedAsExpression(bindingContext)) return
 
         val operatorDescriptor = expression.operationReference.getResolvedCall(bindingContext)
@@ -72,4 +72,8 @@ class UnusedUnaryOperator(config: Config = Config.empty) : Rule(config) {
         val message = "This '${parentOrSelf.text}' is not used"
         report(CodeSmell(issue, Entity.from(expression), message))
     }
+
+    private fun KtExpression.parentBinaryExpressionOrThis(): KtExpression {
+        return parents.takeWhile { it is KtBinaryExpression }.lastOrNull() as? KtBinaryExpression ?: this
+    }
 }

detekt-rules-errorprone/src/test/kotlin/io/gitlab/arturbosch/detekt/rules/bugs/UnusedUnaryOperatorSpec.kt

@@ -122,4 +122,20 @@ class UnusedUnaryOperatorSpec(private val env: KotlinCoreEnvironment) {
         val findings = subject.compileAndLintWithContext(env, code)
         assertThat(findings).isEmpty()
     }
+
+    @Test
+    fun `var assignment by if expression`() {
+        val code = """
+            fun test(b: Boolean) {
+                var x = 0
+                x = if (b) {
+                    -1
+                } else {
+                    1
+                }
+            }
+        """
+        val findings = subject.compileAndLintWithContext(env, code)
+        assertThat(findings).isEmpty()
+    }
 }