Extract a no-arg constuctor whenever a Kotlin class has default values for all parameters

Author: smowton

java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt

@@ -1049,8 +1049,6 @@ open class KotlinFileExtractor(
     private val jvmOverloadsFqName = FqName("kotlin.jvm.JvmOverloads")
 
     private fun extractGeneratedOverloads(f: IrFunction, parentId: Label<out DbReftype>, maybeSourceParentId: Label<out DbReftype>?, extractBody: Boolean, extractMethodAndParameterTypeAccesses: Boolean, typeSubstitution: TypeSubstitution?, classTypeArgsIncludingOuterClasses: List<IrTypeArgument>?) {
-        if (!f.hasAnnotation(jvmOverloadsFqName))
-            return
 
         fun extractGeneratedOverload(paramList: List<IrValueParameter?>) {
             val overloadParameters = paramList.filterNotNull()
@@ -1096,6 +1094,15 @@ open class KotlinFileExtractor(
             }
         }
 
+        if (!f.hasAnnotation(jvmOverloadsFqName)) {
+            if (f is IrConstructor && f.valueParameters.isNotEmpty() && f.valueParameters.all { it.defaultValue != null }) {
+                // Per https://kotlinlang.org/docs/classes.html#creating-instances-of-classes, a single default overload gets created specifically
+                // when we have all default parameters, regardless of `@JvmOverloads`.
+                extractGeneratedOverload(f.valueParameters.map { _ -> null })
+            }
+            return
+        }
+
         val paramList: MutableList<IrValueParameter?> = f.valueParameters.toMutableList()
         for (n in (f.valueParameters.size - 1) downTo 0) {
             if (f.valueParameters[n].defaultValue != null) {

java/ql/integration-tests/all-platforms/kotlin/jvmoverloads-external-class/User.java

@@ -0,0 +1,5 @@
+public class User {
+
+  public static void test() { new AllDefaultsConstructor(); }
+
+}

java/ql/integration-tests/all-platforms/kotlin/jvmoverloads-external-class/test.kt

@@ -3,3 +3,5 @@ public class Test {
   @JvmOverloads fun f(x: Int = 0, y: Int) { }
 
 }
+
+public class AllDefaultsConstructor(val x: Int = 1, val y: Int = 2) { }

java/ql/integration-tests/all-platforms/kotlin/jvmoverloads-external-class/test.py

@@ -1,4 +1,4 @@
 from create_database_utils import *
 
 os.mkdir('bin')
-run_codeql_database_create(["kotlinc test.kt -d bin", "kotlinc user.kt -cp bin"], lang="java")
+run_codeql_database_create(["kotlinc test.kt -d bin", "kotlinc user.kt -cp bin", "javac User.java -cp bin"], lang="java")