Lower kotlin.emptyArray() calls to arrayOf() calls.

The file where `emptyArray()` is defined is considered being part of the builtins of the standard library and K2 loads the definition of the function from the builtins instead of the binary source. This breaks the inlining of the function when we will switch to K2.

PiperOrigin-RevId: 688888434

transpiler/java/com/google/j2cl/transpiler/frontend/kotlin/lower/EmptyArrayLowering.kt

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2024 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.j2cl.transpiler.frontend.kotlin.lower
+
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.common.IrElementTransformerVoidWithContext
+import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
+import org.jetbrains.kotlin.backend.jvm.ir.createJvmIrBuilder
+import org.jetbrains.kotlin.backend.jvm.ir.irArrayOf
+import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.declarations.IrPackageFragment
+import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.IrFunctionAccessExpression
+import org.jetbrains.kotlin.ir.types.makeNotNull
+import org.jetbrains.kotlin.ir.types.toArrayOrPrimitiveArrayType
+
+/**
+ * Lower `kotlin.emptyArray()` calls to `arrayOf()` calls.
+ *
+ * The file where `emptyArray()` is defined is part of the builtins of the standard library and K2
+ * loads the definition of the function from the builtins instead of the binaray source. This breaks
+ * the inlining of the function.
+ *
+ * TODO(b/374966022): Check if this pass is still needed once the klib based inliner is implemented.
+ */
+class EmptyArrayLowering(val context: JvmBackendContext) :
+  FileLoweringPass, IrElementTransformerVoidWithContext() {
+
+  override fun lower(irFile: IrFile) {
+    irFile.transformChildrenVoid()
+  }
+
+  @OptIn(org.jetbrains.kotlin.ir.symbols.UnsafeDuringIrConstructionAPI::class)
+  override fun visitFunctionAccess(expression: IrFunctionAccessExpression): IrExpression {
+    expression.transformChildrenVoid()
+
+    val callee = expression.symbol.owner
+    val parent = callee.parent
+
+    if (
+      callee.name.asString() == "emptyArray" &&
+        parent is IrPackageFragment &&
+        parent.packageFqName.asString() == "kotlin"
+    ) {
+      val arrayType = expression.getTypeArgument(0)!!.makeNotNull()
+      return context
+        .createJvmIrBuilder(currentScope!!)
+        .irArrayOf(arrayType.toArrayOrPrimitiveArrayType(context.irBuiltIns))
+    }
+    return expression
+  }
+}

transpiler/java/com/google/j2cl/transpiler/frontend/kotlin/lower/LoweringPasses.kt

@@ -107,6 +107,8 @@ private val loweringPassFactories: List<J2clLoweringPassFactory> = buildList {
   // Remove inline functions with reified type parameters as these functions cannot be called from
   // Java
   add(::RemoveInlineDeclarationsWithReifiedTypeParametersLowering)
+  // Replace `emptyArray()` calls with `arrayOf()` calls.
+  add(::EmptyArrayLowering)
   // Remove functions that contain unsigned varargs in the signature as a temporary workaround for
   // b/242573966.
   // TODO(b/242573966): Remove this when we can handle unsigned vararg types.