Fix Signatures.kt:buildFunctionSignature

detekt-api/src/main/kotlin/io/gitlab/arturbosch/detekt/api/internal/Signatures.kt

@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.psi.psiUtil.endOffset
 import org.jetbrains.kotlin.psi.psiUtil.getNonStrictParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.parents
 import org.jetbrains.kotlin.psi.psiUtil.startOffset
+import org.jetbrains.kotlin.psi.psiUtil.startOffsetSkippingComments
 import java.io.File
 
 private val multipleWhitespaces = Regex("\\s{2,}")
@@ -92,21 +93,15 @@ private fun buildClassSignature(classOrObject: KtClassOrObject): String {
 }
 
 private fun buildFunctionSignature(element: KtNamedFunction): String {
-    var methodStart = 0
-    element.docComment?.let {
-        methodStart = it.endOffset - it.startOffset
-    }
-    var methodEnd = element.endOffset - element.startOffset
-    val typeReference = element.typeReference
-    if (typeReference != null) {
-        methodEnd = typeReference.endOffset - element.startOffset
+    val startOffset = element.startOffsetSkippingComments - element.startOffset
+    val endOffset = if (element.typeReference != null) {
+        element.typeReference?.endOffset ?: 0
     } else {
-        element.valueParameterList?.let {
-            methodEnd = it.endOffset - element.startOffset
-        }
-    }
-    require(methodStart < methodEnd) {
-        "Error building function signature with range $methodStart - $methodEnd for element: ${element.text}"
+        element.valueParameterList?.endOffset ?: 0
+    } - element.startOffset
+
+    require(startOffset < endOffset) {
+        "Error building function signature with range $startOffset - $endOffset for element: ${element.text}"
     }
-    return element.text.substring(methodStart, methodEnd)
+    return element.text.substring(startOffset, endOffset)
 }

detekt-api/src/test/kotlin/io/gitlab/arturbosch/detekt/api/internal/SignaturesSpec.kt

@@ -0,0 +1,47 @@
+package io.gitlab.arturbosch.detekt.api.internal
+
+import io.github.detekt.test.utils.compileContentForTest
+import org.assertj.core.api.Assertions.assertThat
+import org.assertj.core.api.Assertions.assertThatThrownBy
+import org.jetbrains.kotlin.psi.KtNamedFunction
+import org.junit.jupiter.api.Test
+
+class SignaturesSpec {
+    @Test
+    fun `function with type reference`() {
+        val result = compileContentForTest("fun data(): Int = 0")
+            .findChildByClass(KtNamedFunction::class.java)!!
+            .buildFullSignature()
+
+        assertThat(result).isEqualTo("Test.kt\$fun data(): Int")
+    }
+
+    @Test
+    fun `function without type reference`() {
+        val result = compileContentForTest("fun data() = 0")
+            .findChildByClass(KtNamedFunction::class.java)!!
+            .buildFullSignature()
+
+        assertThat(result).isEqualTo("Test.kt\$fun data()")
+    }
+
+    @Test
+    fun `function with comments`() {
+        val result = compileContentForTest("/* comments */ fun data() = 0")
+            .findChildByClass(KtNamedFunction::class.java)!!
+            .buildFullSignature()
+
+        assertThat(result).isEqualTo("Test.kt\$fun data()")
+    }
+
+    @Test
+    fun `function throws exception`() {
+        assertThatThrownBy {
+            compileContentForTest("{ fun data() = 0 }")
+                .findChildByClass(KtNamedFunction::class.java)!!
+                .buildFullSignature()
+        }
+            .isInstanceOf(IllegalArgumentException::class.java)
+            .hasMessageContaining("Error building function signature")
+    }
+}