Clear AOT sources only before AOT generation

Prior to this commit, AOT generated sources would be cleared as soon as
the AOT plugin is applied (even if no AOT taks is invoked). This would
lead to AOT-generated sources disappearing at various unexpected time
during the development lifecycle of an application.

This commit ensures that sources are only cleared right before the AOT
generation task is invoked.

Fixes gh-1552

Author: bclozel

spring-aot-gradle-plugin/src/main/java/org/springframework/aot/gradle/SpringAotGradlePlugin.java

@@ -108,7 +108,7 @@ public void apply(final Project project) {
 			// Automatically add the spring-native dependency to the implementation configuration
 			// as it's required for hints
 			addSpringNativeDependency(project);
-			Path generatedFilesPath = createGeneratedSourcesFolder(project);
+			Path generatedFilesPath = resolveGeneratedSourcesFolder(project);
 
 			// deprecation replaced with new API introduced in Gradle 7.1
 			//noinspection deprecation
@@ -117,6 +117,7 @@ public void apply(final Project project) {
 			// Create a detached configuration that holds dependencies for AOT generation
 			SourceSet aotMainSourceSet = createAotMainSourceSet(sourceSets, project.getConfigurations(), generatedFilesPath);
 			GenerateAotSources generateAotSources = createGenerateAotSourcesTask(project, sourceSets);
+			generateAotSources.doFirst(task -> clearGeneratedSourcesFolder(project));
 			project.getTasks().named(aotMainSourceSet.getCompileJavaTaskName(), JavaCompile.class, (aotCompileJava) -> {
 				aotCompileJava.source(generateAotSources.getSourcesOutputDirectory());
 			});
@@ -198,19 +199,23 @@ private void addSpringNativeDependency(Project project) {
 	}
 
 	/**
-	 * Recreate a folder for generated sources and resources, deleting files
-	 * possibly contributed in previous builds.
+	 * Resolve the path to the folder for generated sources and resources.
 	 */
-	private Path createGeneratedSourcesFolder(Project project) {
+	private Path resolveGeneratedSourcesFolder(Project project) {
 		String buildPath = project.getBuildDir().getAbsolutePath();
+		return Paths.get(buildPath, "generated");
+	}
+
+	private void clearGeneratedSourcesFolder(Project project) {
+		Path generatedSourcesFolder = resolveGeneratedSourcesFolder(project);
 		try {
-			Path generatedSourcesFolder = Paths.get(buildPath, "generated");
 			FileSystemUtils.deleteRecursively(generatedSourcesFolder);
-			return Files.createDirectories(generatedSourcesFolder);
+			Files.createDirectories(generatedSourcesFolder);
 		}
 		catch (IOException exc) {
-			throw new GradleException("Failed to recreate folder '" + buildPath + "/generated/'", exc);
+			throw new GradleException("Failed to recreate folder '" + generatedSourcesFolder + "'", exc);
 		}
+
 	}
 
 	private SourceSet createAotMainSourceSet(SourceSetContainer sourceSets, ConfigurationContainer configurations, Path generatedFilesPath) {