From 14bb32f4fc3e9a2004c1a6d6d86129b3df8f2f54 Mon Sep 17 00:00:00 2001
From: David Vacca <dvacca@meta.com>
Date: Thu, 20 Feb 2025 17:06:11 -0800
Subject: [PATCH] Create initial version of ReactLegacyArchitectureProcessor
 (#49570)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49570

This diff creates a initial version of the annotation processor to output the list of types that are annotated with LegacyArchitecture

changelog: [internal] internal

Reviewed By: cortinico

Differential Revision: D69929875

fbshipit-source-id: 90a8d299f4667ab8d103c061d287991dbdb291df
---
 .../ReactLegacyArchitectureProcessor.java     | 38 ++++++++++++++++---
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/processing/ReactLegacyArchitectureProcessor.java b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/processing/ReactLegacyArchitectureProcessor.java
index f8c4c3f6c3f..525a2087ba7 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/processing/ReactLegacyArchitectureProcessor.java
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/processing/ReactLegacyArchitectureProcessor.java
@@ -1,26 +1,52 @@
-// (c) Meta Platforms, Inc. and affiliates. Confidential and proprietary.
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
 
 package com.facebook.react.processing;
 
 import com.facebook.annotationprocessors.common.ProcessorBase;
+import com.facebook.react.common.annotations.internal.LegacyArchitecture;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Set;
 import javax.annotation.processing.RoundEnvironment;
 import javax.annotation.processing.SupportedAnnotationTypes;
 import javax.annotation.processing.SupportedSourceVersion;
 import javax.lang.model.SourceVersion;
+import javax.lang.model.element.Element;
 import javax.lang.model.element.TypeElement;
 
 @SupportedAnnotationTypes("com.facebook.react.common.annotations.internal.LegacyArchitecture")
 @SupportedSourceVersion(SourceVersion.RELEASE_11)
 public class ReactLegacyArchitectureProcessor extends ProcessorBase {
 
-  public ReactLegacyArchitectureProcessor() {
-    super();
-  }
-
   @Override
   protected boolean processImpl(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
-    // Do nothing for now
+    String outputFileName = System.getenv().get("RN_LEGACY_ARCH_OUTPUT_FILE_NAME");
+    if (outputFileName == null || outputFileName.trim().isEmpty()) {
+      return true;
+    }
+    Set<? extends Element> elements = roundEnv.getElementsAnnotatedWith(LegacyArchitecture.class);
+    List<String> classes = new ArrayList<>();
+
+    for (Element element : elements) {
+      TypeElement classType = (TypeElement) element;
+      String className = classType.getQualifiedName().toString().replace(".", "/");
+      classes.add("type L" + className + ";");
+    }
+
+    try (FileWriter writer = new FileWriter(outputFileName, true)) {
+      for (String clazz : classes) {
+        writer.write(clazz + "\n");
+      }
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
     return true;
   }
 }