Fix incompatibility with AsciidoctorJ 3.0

AsciidoctorJ 3.0 contains a breaking change to the signature of
Preprocessor#process. This commit avoids this incompatibility
by rewriting the preprocessor extension in Ruby.

Fixes gh-949

spring-restdocs-asciidoctor/build.gradle

@@ -1,6 +1,7 @@
 plugins {
 	id "java-library"
 	id "maven-publish"
+	id "io.spring.compatibility-test" version "0.0.3"
 }
 
 description = "Spring REST Docs Asciidoctor Extension"
@@ -19,3 +20,11 @@ dependencies {
 
 	testRuntimeOnly("org.asciidoctor:asciidoctorj-pdf")
 }
+
+compatibilityTest {
+	dependency("AsciidoctorJ") { asciidoctorj ->
+		asciidoctorj.groupId = "org.asciidoctor"
+		asciidoctorj.artifactId = "asciidoctorj"
+		asciidoctorj.versions = ["3.0.0"]
+	}
+}

spring-restdocs-asciidoctor/src/main/java/org/springframework/restdocs/asciidoctor/RestDocsExtensionRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2023 the original author or authors.
+ * Copyright 2014-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,7 +28,9 @@ public final class RestDocsExtensionRegistry implements ExtensionRegistry {
 
 	@Override
 	public void register(Asciidoctor asciidoctor) {
-		asciidoctor.javaExtensionRegistry().preprocessor(new DefaultAttributesPreprocessor());
+		asciidoctor.rubyExtensionRegistry()
+			.loadClass(RestDocsExtensionRegistry.class.getResourceAsStream("/extensions/default_attributes.rb"))
+			.preprocessor("DefaultAttributes");
 		asciidoctor.rubyExtensionRegistry()
 			.loadClass(RestDocsExtensionRegistry.class.getResourceAsStream("/extensions/operation_block_macro.rb"))
 			.blockMacro("operation", "OperationBlockMacro");

spring-restdocs-asciidoctor/src/main/java/org/springframework/restdocs/asciidoctor/SnippetsDirectoryResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2021 the original author or authors.
+ * Copyright 2014-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,9 +30,14 @@
  *
  * @author Andy Wilkinson
  */
-class SnippetsDirectoryResolver {
+public class SnippetsDirectoryResolver {
 
-	File getSnippetsDirectory(Map<String, Object> attributes) {
+	/**
+	 * Returns the snippets directory derived from the given {@code attributes}.
+	 * @param attributes the attributes
+	 * @return the snippets directory
+	 */
+	public File getSnippetsDirectory(Map<String, Object> attributes) {
 		if (System.getProperty("maven.home") != null) {
 			return getMavenSnippetsDirectory(attributes);
 		}

spring-restdocs-asciidoctor/src/main/resources/extensions/default_attributes.rb

@@ -0,0 +1,14 @@
+require 'asciidoctor/extensions'
+require 'java'
+
+class DefaultAttributes  < Asciidoctor::Extensions::Preprocessor
+
+  def process(document, reader)
+  	resolver = org.springframework.restdocs.asciidoctor.SnippetsDirectoryResolver.new()
+  	attributes = document.attributes
+  	attributes["snippets"] = resolver.getSnippetsDirectory(attributes) unless attributes.has_key?("snippets")
+  	false
+  end
+
+end
+