Android: compile shared platform-neutral Java sources in place (step 1 of desktop JVM support)

docs/source/using-executorch-android.md

@@ -20,7 +20,7 @@ All ExecuTorch Android libraries are packaged into an Android library (AAR), exe
 
 The AAR artifact contains the Java library for users to integrate with their Java/Kotlin application code, as well as the corresponding JNI library (.so file), which is loaded by the Java code during initialization.
 
-- [Java library](https://github.com/pytorch/executorch/tree/main/extension/android/executorch_android/src/main/java/org/pytorch/executorch)
+- [Java library](https://github.com/pytorch/executorch/tree/main/extension/java/src/main/java/org/pytorch/executorch) <!-- @lint-ignore (path exists only after this PR lands) -->
 - [Java API Reference (Javadoc)](https://pytorch.org/executorch/main/javadoc/index.html)
 - JNI contains the JNI binding for the corresponding Java code, and ExecuTorch native library, including
   - Core ExecuTorch runtime libraries

extension/android/BUCK

@@ -3,20 +3,35 @@ load("@fbsource//tools/build_defs/android:fb_android_library.bzl", "fb_android_l
 
 oncall("executorch")
 
+# NOTE: the platform-neutral sources live in the shared source directory
+# extension/java/src/main/java and are referenced here in place, so the
+# Android targets keep their historical names, ownership, and attributes
+# (required_for_source_only_abi, pure_kotlin, deps) while compiling the
+# exact same classes as before the move. Log.kt is the Android-backed
+# implementation of the org.pytorch.executorch.Log facade that the shared
+# sources reference.
+#
+# MAINTENANCE: Gradle globs the shared directory (java.srcDirs) while the
+# srcs lists below are explicit per-file. When adding a shared source under
+# extension/java/src/main/java, add it to the matching target here in the
+# same change — otherwise the OSS AAR picks it up while this build silently
+# omits it.
+
 non_fbcode_target(_kind = fb_android_library,
     name = "executorch",
     warnings_as_errors = False,
     required_for_source_only_abi = True,
     srcs = [
-        "executorch_android/src/main/java/org/pytorch/executorch/BackendOptionsMap.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/DType.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/EValue.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/ExecuTorchRuntime.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/ExecutorchRuntimeException.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/MethodMetadata.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/Module.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/Tensor.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/annotations/Experimental.kt",
+        "../java/src/main/java/org/pytorch/executorch/BackendOptionsMap.kt",
+        "../java/src/main/java/org/pytorch/executorch/DType.kt",
+        "../java/src/main/java/org/pytorch/executorch/EValue.kt",
+        "../java/src/main/java/org/pytorch/executorch/ExecuTorchRuntime.kt",
+        "../java/src/main/java/org/pytorch/executorch/ExecutorchRuntimeException.kt",
+        "../java/src/main/java/org/pytorch/executorch/MethodMetadata.kt",
+        "../java/src/main/java/org/pytorch/executorch/Module.kt",
+        "../java/src/main/java/org/pytorch/executorch/Tensor.kt",
+        "../java/src/main/java/org/pytorch/executorch/annotations/Experimental.kt",
+        "executorch_android/src/main/java/org/pytorch/executorch/Log.kt",
     ],
     autoglob = False,
     language = "KOTLIN",
@@ -34,8 +49,8 @@ non_fbcode_target(_kind = fb_android_library,
     name = "executorch_training",
     warnings_as_errors = False,
     srcs = [
-        "executorch_android/src/main/java/org/pytorch/executorch/training/SGD.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/training/TrainingModule.kt",
+        "../java/src/main/java/org/pytorch/executorch/training/SGD.kt",
+        "../java/src/main/java/org/pytorch/executorch/training/TrainingModule.kt",
     ],
     autoglob = False,
     language = "KOTLIN",
@@ -50,10 +65,10 @@ non_fbcode_target(_kind = fb_android_library,
     name = "executorch_llama",
     warnings_as_errors = False,
     srcs = [
-        "executorch_android/src/main/java/org/pytorch/executorch/extension/llm/LlmCallback.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/extension/llm/LlmGenerationConfig.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/extension/llm/LlmModule.kt",
-        "executorch_android/src/main/java/org/pytorch/executorch/extension/llm/LlmModuleConfig.kt",
+        "../java/src/main/java/org/pytorch/executorch/extension/llm/LlmCallback.kt",
+        "../java/src/main/java/org/pytorch/executorch/extension/llm/LlmGenerationConfig.kt",
+        "../java/src/main/java/org/pytorch/executorch/extension/llm/LlmModule.kt",
+        "../java/src/main/java/org/pytorch/executorch/extension/llm/LlmModuleConfig.kt",
     ],
     autoglob = False,
     language = "KOTLIN",

extension/android/executorch_android/build.gradle

@@ -16,7 +16,7 @@ plugins {
 
 spotless {
     kotlin {
-        target '**/*.kt'
+        target '**/*.kt', '../../java/src/main/java/**/*.kt'
         ktfmt()
     }
 }
@@ -44,6 +44,9 @@ android {
     sourceSets {
         main {
             jniLibs.srcDirs = ['../../../cmake-out-android-so/']
+            // Platform-neutral API sources shared with the desktop JVM artifact.
+            // They are compiled directly into this AAR, keeping it self-contained.
+            java.srcDirs += ['../../java/src/main/java']
         }
         androidTest {
             resources.srcDirs += ['src/androidTest/resources']

extension/android/executorch_android/src/main/java/org/pytorch/executorch/Log.kt

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package org.pytorch.executorch
+
+/**
+ * Platform logging facade used by the shared sources under extension/java.
+ *
+ * <p>The shared sources reference [Log] by simple name (same package, no import), and each platform
+ * artifact compiles its own implementation:
+ * <ul>
+ * <li>Android (this file): delegates to [android.util.Log], so logcat output — tags, priorities,
+ *   and messages — is byte-for-byte identical to logging directly from the caller.
+ * <li>Desktop JVM (extension/jvm, added separately): a console-backed implementation.
+ * </ul>
+ *
+ * The shared source set itself contains no [Log] definition, so there is exactly one implementation
+ * per artifact and no duplicate-class collision.
+ */
+internal object Log {
+  @JvmStatic fun v(tag: String, msg: String): Int = android.util.Log.v(tag, msg)
+
+  @JvmStatic fun d(tag: String, msg: String): Int = android.util.Log.d(tag, msg)
+
+  @JvmStatic fun i(tag: String, msg: String): Int = android.util.Log.i(tag, msg)
+
+  @JvmStatic fun w(tag: String, msg: String): Int = android.util.Log.w(tag, msg)
+
+  @JvmStatic fun w(tag: String, msg: String, tr: Throwable): Int = android.util.Log.w(tag, msg, tr)
+
+  @JvmStatic fun e(tag: String, msg: String): Int = android.util.Log.e(tag, msg)
+
+  @JvmStatic fun e(tag: String, msg: String, tr: Throwable): Int = android.util.Log.e(tag, msg, tr)
+}

extension/java/README.md

@@ -0,0 +1,42 @@
+# ExecuTorch shared Java sources
+
+This directory holds the **platform-neutral** Java/Kotlin API sources
+(`Module`, `Tensor`, `EValue`, `DType`, `LlmModule`, `AsrModule`, training,
+…) that are shared by every Java-platform artifact.
+
+## How the sources are consumed
+
+These sources are **not** published as their own artifact. Each platform
+build compiles them directly into its own, self-contained artifact by
+referencing this directory as an additional source root:
+
+- **Android** (`extension/android/executorch_android`) adds
+  `../../java/src/main/java` via `java.srcDirs`, so the shipping AAR embeds
+  the same classes it always has — no new transitive dependency, unchanged
+  bytecode target (Java 11), unchanged manifest.
+- **Desktop JVM** (`extension/jvm`, added separately) compiles the same
+  sources into its own jar.
+
+## Contract for sources in this directory
+
+1. **No platform APIs.** Sources here must not import `android.*`,
+   `java.awt.*`, or any other platform-specific API. The only permitted
+   dependencies are the JDK, fbjni, and soloader.
+2. **Logging goes through the `org.pytorch.executorch.Log` facade.** The
+   facade is referenced by simple name (same package, no import) and is
+   *not* defined in this directory. Each platform artifact compiles exactly
+   one implementation (Android: backed by `android.util.Log`; desktop:
+   console-backed), so there is never a duplicate-class collision and each
+   platform keeps its native logging behavior.
+3. **Native library loading stays per-platform.** Shared sources load the
+   native library through soloader's `NativeLoader`, whose delegate is
+   configured by the platform runtime, not by a cross-platform mutable
+   global.
+
+## Adding a source here
+
+Gradle (`extension/android/executorch_android/build.gradle`) globs this whole
+directory, but `extension/android/BUCK` lists each shared file explicitly.
+**Update the matching BUCK target's `srcs` in the same change** whenever you
+add or remove a file here — otherwise the OSS AAR picks it up while the Buck
+build silently omits it.

extension/android/executorch_android/src/main/java/org/pytorch/executorch/Tensor.kt → extension/java/src/main/java/org/pytorch/executorch/Tensor.kt

@@ -8,7 +8,6 @@
 
 package org.pytorch.executorch
 
-import android.util.Log
 import com.facebook.jni.HybridData
 import com.facebook.jni.annotations.DoNotStrip
 import java.nio.Buffer