[FIR] Unwrap vararg array types for diagnostic rendering

#KT-65770 Fixed

compiler/fir/tree/src/org/jetbrains/kotlin/fir/renderer/FirRenderer.kt

@@ -78,7 +78,7 @@ class FirRenderer(
             propertyAccessorRenderer = null,
             callArgumentsRenderer = FirCallNoArgumentsRenderer(),
             modifierRenderer = FirPartialModifierRenderer(),
-            valueParameterRenderer = FirValueParameterRendererNoDefaultValue(),
+            valueParameterRenderer = FirValueParameterRendererForReadability(),
             declarationRenderer = FirDeclarationRenderer("local ")
         )
     }

compiler/fir/tree/src/org/jetbrains/kotlin/fir/renderer/FirValueParameterRenderer.kt

@@ -15,6 +15,7 @@ open class FirValueParameterRenderer {
     private val annotationRenderer get() = components.annotationRenderer
     protected val declarationRenderer get() = components.declarationRenderer
     private val modifierRenderer get() = components.modifierRenderer
+    protected val typeRenderer get() = components.typeRenderer
 
     fun renderParameters(valueParameters: List<FirValueParameter>) {
         printer.print("(")
@@ -34,10 +35,15 @@ open class FirValueParameterRenderer {
         if (valueParameter.name != SpecialNames.NO_NAME_PROVIDED) {
             printer.print(valueParameter.name.toString() + ": ")
         }
-        valueParameter.returnTypeRef.accept(visitor)
+
+        renderParameterType(valueParameter)
         renderDefaultValue(valueParameter)
     }
 
+    protected open fun renderParameterType(valueParameter: FirValueParameter) {
+        valueParameter.returnTypeRef.accept(visitor)
+    }
+
     protected open fun renderDefaultValue(valueParameter: FirValueParameter) {
         valueParameter.defaultValue?.let {
             printer.print(" = ")

compiler/fir/tree/src/org/jetbrains/kotlin/fir/renderer/FirValueParameterRendererForReadability.kt

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.renderer
+
+import org.jetbrains.kotlin.fir.declarations.FirValueParameter
+import org.jetbrains.kotlin.fir.types.FirResolvedTypeRef
+import org.jetbrains.kotlin.fir.types.arrayElementType
+
+class FirValueParameterRendererForReadability : FirValueParameterRenderer() {
+    override fun renderParameterType(valueParameter: FirValueParameter) {
+        val returnTypeRef = valueParameter.returnTypeRef
+
+        if (valueParameter.isVararg && returnTypeRef is FirResolvedTypeRef) {
+            val arrayElementType = returnTypeRef.type.arrayElementType()
+            if (arrayElementType != null) {
+                typeRenderer.render(arrayElementType)
+                return
+            }
+        }
+
+        super.renderParameterType(valueParameter)
+    }
+
+    override fun renderDefaultValue(valueParameter: FirValueParameter) {
+        valueParameter.defaultValue?.let {
+            printer.print(" = ...")
+        }
+    }
+}

compiler/fir/tree/src/org/jetbrains/kotlin/fir/renderer/FirValueParameterRendererNoDefaultValue.kt

@@ -1,16 +0,0 @@
-/*
- * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.fir.renderer
-
-import org.jetbrains.kotlin.fir.declarations.FirValueParameter
-
-class FirValueParameterRendererNoDefaultValue : FirValueParameterRenderer() {
-    override fun renderDefaultValue(valueParameter: FirValueParameter) {
-        valueParameter.defaultValue?.let {
-            printer.print(" = ...")
-        }
-    }
-}

compiler/fir/tree/src/org/jetbrains/kotlin/fir/types/FirTypeUtils.kt

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.fir.utils.exceptions.withFirEntry
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.StandardClassIds
 import org.jetbrains.kotlin.types.ConstantValueKind
+import org.jetbrains.kotlin.utils.addToStdlib.runIf
 import org.jetbrains.kotlin.utils.exceptions.errorWithAttachment
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
@@ -155,3 +156,27 @@ fun FirTypeProjection.toConeTypeProjection(): ConeTypeProjection = when (this) {
     }
     else -> errorWithAttachment("Unexpected ${this::class.simpleName}") { withFirEntry("projection", this@toConeTypeProjection) }
 }
+
+fun ConeKotlinType.arrayElementType(checkUnsignedArrays: Boolean = true): ConeKotlinType? {
+    return when (val argument = arrayElementTypeArgument(checkUnsignedArrays)) {
+        is ConeKotlinTypeProjection -> argument.type
+        else -> null
+    }
+}
+
+fun ConeKotlinType.arrayElementTypeArgument(checkUnsignedArrays: Boolean = true): ConeTypeProjection? {
+    val type = this.lowerBoundIfFlexible()
+    if (type !is ConeClassLikeType) return null
+    val classId = type.lookupTag.classId
+    if (classId == StandardClassIds.Array) {
+        return type.typeArguments.first()
+    }
+    val elementType = StandardClassIds.elementTypeByPrimitiveArrayType[classId] ?: runIf(checkUnsignedArrays) {
+        StandardClassIds.elementTypeByUnsignedArrayType[classId]
+    }
+    if (elementType != null) {
+        return elementType.constructClassLikeType(emptyArray(), isNullable = false)
+    }
+
+    return null
+}