Allow to ignore overloaded methods for the complex interface rule (#5165)

detekt-rules-complexity/src/main/kotlin/io/gitlab/arturbosch/detekt/rules/complexity/ComplexInterface.kt

@@ -18,6 +18,7 @@ import org.jetbrains.kotlin.psi.KtNamedFunction
 import org.jetbrains.kotlin.psi.KtObjectDeclaration
 import org.jetbrains.kotlin.psi.KtProperty
 import org.jetbrains.kotlin.psi.KtTypeParameterListOwner
+import org.jetbrains.kotlin.psi.psiUtil.isExtensionDeclaration
 import org.jetbrains.kotlin.psi.psiUtil.isPrivate
 
 /**
@@ -51,6 +52,9 @@ class ComplexInterface(
     @Configuration("whether private declarations should be included")
     private val includePrivateDeclarations: Boolean by config(defaultValue = false)
 
+    @Configuration("ignore overloaded methods - only count once")
+    private val ignoreOverloaded: Boolean by config(defaultValue = false)
+
     override fun visitClass(klass: KtClass) {
         if (klass.isInterface()) {
             val body = klass.body ?: return
@@ -81,10 +85,26 @@ class ComplexInterface(
         fun PsiElement.considerPrivate() = includePrivateDeclarations ||
             this is KtTypeParameterListOwner && !this.isPrivate()
 
-        fun PsiElement.isMember() = this is KtNamedFunction || this is KtProperty
+        fun countFunctions(psiElements: List<PsiElement>): Int {
+            val functions = psiElements.filterIsInstance<KtNamedFunction>()
+            return if (ignoreOverloaded) {
+                functions.distinctBy { function ->
+                    val receiver = function.receiverTypeReference
+                    if (function.isExtensionDeclaration() && receiver != null) {
+                        "${receiver.text}.${function.name}"
+                    } else {
+                        function.name
+                    }
+                }.size
+            } else {
+                functions.size
+            }
+        }
 
-        return body.children
+        val psiElements = body.children
             .filter(PsiElement::considerPrivate)
-            .count(PsiElement::isMember)
+        val propertyCount = psiElements.count { it is KtProperty }
+        val functionCount = countFunctions(psiElements)
+        return propertyCount + functionCount
     }
 }

detekt-rules-complexity/src/test/kotlin/io/gitlab/arturbosch/detekt/rules/complexity/ComplexInterfaceSpec.kt

@@ -14,6 +14,9 @@ private val staticDeclarationsConfig = TestConfig(
 private val privateDeclarationsConfig = TestConfig(
     defaultConfigMap + ("includePrivateDeclarations" to true)
 )
+private val ignoreOverloadedConfig = TestConfig(
+    defaultConfigMap + ("ignoreOverloaded" to true)
+)
 
 class ComplexInterfaceSpec {
 
@@ -141,6 +144,57 @@ class ComplexInterfaceSpec {
                 assertThat(rule.compileAndLint(code)).hasSize(1)
             }
         }
+
+        @Nested
+        inner class `overloaded methods` {
+            val code = """
+                interface I {
+                    fun f1()
+                    fun f1(i: Int)
+                    val i1: Int
+                    fun fImpl() {}
+                }
+            """
+
+            @Test
+            fun `reports complex interface with overloaded methods`() {
+                assertThat(subject.compileAndLint(code)).hasSize(1)
+            }
+
+            @Test
+            fun `does not report simple interface with ignoreOverloaded`() {
+                val rule = ComplexInterface(ignoreOverloadedConfig)
+                assertThat(rule.compileAndLint(code)).isEmpty()
+            }
+
+            @Test
+            fun `reports complex interface with extension methods with a different receiver`() {
+                val code = """
+                    interface I {
+                        fun f1()
+                        fun String.f1(i: Int)
+                        val i1: Int
+                        fun fImpl() {}
+                    }
+                """
+                val rule = ComplexInterface(ignoreOverloadedConfig)
+                assertThat(rule.compileAndLint(code)).hasSize(1)
+            }
+
+            @Test
+            fun `does not report simple interface with extension methods with the same receiver`() {
+                val code = """
+                    interface I {
+                        fun String.f1()
+                        fun String.f1(i: Int)
+                        val i1: Int
+                        fun fImpl() {}
+                    }
+                """
+                val rule = ComplexInterface(ignoreOverloadedConfig)
+                assertThat(rule.compileAndLint(code)).isEmpty()
+            }
+        }
     }
 
     @Nested