JVM_IR: generate default constructor

Quoted from https://kotlinlang.org/docs/reference/classes.html

"On the JVM, if all of the parameters of the primary constructor have
 default values, the compiler will generate an additional parameterless
 constructor which will use the default values. This makes it easier to
 use Kotlin with libraries such as Jackson or JPA that create class
 instances through parameterless constructors."

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmLower.kt

@@ -114,6 +114,7 @@ val jvmPhases = namedIrFilePhase<JvmBackendContext>(
             annotationPhase then
             tailrecPhase then
 
+            jvmDefaultConstructorPhase then
             defaultArgumentStubPhase then
 
             interfacePhase then

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmDefaultConstructorLowering.kt

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. 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.backend.jvm.lower
+
+import org.jetbrains.kotlin.backend.common.ClassLoweringPass
+import org.jetbrains.kotlin.backend.common.ir.passTypeArgumentsFrom
+import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
+import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
+import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
+import org.jetbrains.kotlin.ir.builders.declarations.addConstructor
+import org.jetbrains.kotlin.ir.builders.irBlockBody
+import org.jetbrains.kotlin.ir.builders.irDelegatingConstructorCall
+import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.util.constructors
+import org.jetbrains.kotlin.ir.util.hasDefaultValue
+
+internal val jvmDefaultConstructorPhase = makeIrFilePhase(
+    ::JvmDefaultConstructorLowering,
+    name = "JvmDefaultConstructor",
+    description = "Generate default constructors for Java"
+)
+
+// Quoted from https://kotlinlang.org/docs/reference/classes.html
+//
+// "On the JVM, if all of the parameters of the primary constructor have default values, the compiler will generate an additional
+//  parameterless constructor which will use the default values. This makes it easier to use Kotlin with libraries such as Jackson
+//  or JPA that create class instances through parameterless constructors."
+private class JvmDefaultConstructorLowering(val context: JvmBackendContext) : ClassLoweringPass {
+
+    override fun lower(irClass: IrClass) {
+        val primaryConstructor = irClass.constructors.firstOrNull { it.isPrimary } ?: return
+
+        if (!primaryConstructor.valueParameters.all { it.hasDefaultValue() })
+            return
+
+        // Skip if the default constructor is already defined by user.
+        if (irClass.constructors.any { it.valueParameters.isEmpty() })
+            return
+
+        irClass.addConstructor().apply {
+            val irBuilder = context.createIrBuilder(this.symbol, startOffset, endOffset)
+            body = irBuilder.irBlockBody {
+                +irDelegatingConstructorCall(primaryConstructor).apply {
+                    passTypeArgumentsFrom(irClass)
+                    passTypeArgumentsFrom(primaryConstructor, irClass.typeParameters.size)
+                }
+            }
+        }
+    }
+}

compiler/testData/codegen/box/defaultArguments/constructor/checkIfConstructorIsSynthetic.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 // TARGET_BACKEND: JVM
 // WITH_RUNTIME
 

compiler/testData/codegen/box/defaultArguments/constructor/manyArgs.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 // TARGET_BACKEND: JVM
 // WITH_RUNTIME
 

compiler/testData/codegen/box/jvmOverloads/privateClass.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 // TARGET_BACKEND: JVM
 
 // WITH_RUNTIME

compiler/testData/codegen/box/multiplatform/noArgActualConstructor.kt

@@ -1,5 +1,4 @@
 // !LANGUAGE: +MultiPlatformProjects
-// IGNORE_BACKEND: JVM_IR
 // TARGET_BACKEND: JVM
 // WITH_RUNTIME
 // FILE: common.kt

compiler/testData/codegen/box/platformTypes/primitives/equalsNull_withExplicitFlag.kt

@@ -1,5 +1,4 @@
 // KOTLIN_CONFIGURATION_FLAGS: +JVM.NO_EXCEPTION_ON_EXPLICIT_EQUALS_FOR_BOXED_NULL
-// TARGET_BACKEND: JVM
 // WITH_RUNTIME
 // FILE: test.kt
 import kotlin.test.*

compiler/testData/codegen/box/secondaryConstructors/withPrimary.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 // TARGET_BACKEND: JVM
 // FILE: WithPrimary.java
 

compiler/testData/compileJavaAgainstKotlin/class/DefaultConstructor.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 package test
 
 class A(val a: Int = 1)

compiler/testData/compileJavaAgainstKotlin/class/DefaultConstructorWithTwoArgs.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 package test
 
 class A(val a: Int = 1, val b: String = "default")