Generate astubx from JSON output of jdk-javac-plugin (#1243)

This support will be used to generate an astubx JDK model from the
JSpecify annotated JDK. Includes extensive unit testing and integration
testing of the support. We will likely need to add more features as we
try to support all the annotations present in the JDK (on wildcards,
etc.).

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Added an ASTUBX generator and CLI to produce .astubx bundles capturing
method return-type and nullability metadata; added annotated and
unannotated test libraries and a service provider to supply generated
stubx files.

- **Chores**
- Integrated .astubx generation into the build lifecycle, added new
modules, migrated projects to Java 21 toolchains, and updated formatting
guard to exclude the jdk-annotations module.

- **Tests**
- Added unit and integration tests validating JDK/JSPECIFY nullability
scenarios and end-to-end .astubx generation.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Manu Sridharan <[email protected]>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: 3 people

build.gradle

@@ -114,7 +114,7 @@ subprojects { project ->
 
     // Spotless complains when applied to the folders containing projects
     // when they do not have a build.gradle file
-    if (project.name != "jar-infer" && project.name != "library-model") {
+    if (project.name != "jar-infer" && project.name != "library-model" && project.name != "jdk-annotations") {
         project.apply plugin: "com.diffplug.spotless"
         spotless {
             java {

code-coverage-report/build.gradle

@@ -83,4 +83,6 @@ dependencies {
     implementation project(':library-model:library-model-generator')
     implementation project(':library-model:library-model-generator-integration-test')
     implementation project(':jdk-javac-plugin')
+    implementation project(':jdk-annotations:astubx-generator')
+    implementation project(':jdk-annotations:jdk-integration-test')
 }

jdk-annotations/astubx-generator-cli/build.gradle

@@ -0,0 +1,41 @@
+plugins {
+    id "java-library"
+    id "com.gradleup.shadow"
+}
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+// Allow Java 21 features for this module
+tasks.withType(JavaCompile).configureEach {
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
+}
+
+
+jar{
+    manifest {
+        attributes('Main-Class':'com.uber.nullaway.jdkannotations.AstubxGeneratorCLI')
+    }
+    // add this classifier so that the output file for the jar task differs from
+    // the output file for the shadowJar task (otherwise they overwrite each other's
+    // outputs, forcing the tasks to always re-run)
+    archiveClassifier = "nonshadow"
+}
+
+shadowJar {
+    mergeServiceFiles()
+    configurations = [
+        project.configurations.runtimeClasspath
+    ]
+    archiveClassifier = ""
+}
+shadowJar.dependsOn jar
+assemble.dependsOn shadowJar
+
+dependencies {
+    implementation project(":jdk-annotations:astubx-generator")
+}

jdk-annotations/astubx-generator-cli/src/main/java/com/uber/nullaway/jdkannotations/AstubxGeneratorCLI.java

@@ -0,0 +1,11 @@
+package com.uber.nullaway.jdkannotations;
+
+public class AstubxGeneratorCLI {
+  public static void main(String[] args) {
+    if (args.length != 2) {
+      System.err.println("Invalid number of arguments. Required: <inputPath> <outputPath>");
+      System.exit(2);
+    }
+    AstubxGenerator.generateAstubx(args[0], args[1]);
+  }
+}

jdk-annotations/astubx-generator/build.gradle

@@ -0,0 +1,40 @@
+plugins {
+    id "java-library"
+    id 'nullaway.java-test-conventions'
+}
+
+// Require JDK 21, since the jdk-javac-plugin requires it
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+// Allow Java 21 features for this module
+tasks.withType(JavaCompile).configureEach {
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
+}
+
+// Don't test on JDK 17; we require JDK 21
+tasks.named("testJdk17").configure {
+    onlyIf { false }
+}
+
+tasks.withType(Test).configureEach { test ->
+    // Ensure the plugin JAR exists
+    dependsOn(":jdk-javac-plugin:shadowJar")
+}
+
+dependencies {
+    implementation project(":library-model:library-model-generator")
+    implementation project(":jdk-javac-plugin")
+    implementation deps.build.gson
+    implementation deps.build.guava
+
+    testImplementation deps.test.junit4
+    testImplementation deps.build.jspecify
+    testImplementation(deps.build.errorProneTestHelpers) {
+        exclude group: "junit", module: "junit"
+    }
+}