Provide more control over registration of GeneratedFiles

This commit provides an advanced handling of generated files that
provides more control over files registration. The callback provides
a FileHandler that can determine if the file already exists and its
content. The caller can then chose to override the content or leave it
as it is.

Closes gh-31331

spring-core/src/test/java/org/springframework/aot/generate/FileSystemGeneratedFilesTests.java

@@ -23,16 +23,20 @@ import java.util.function.Function;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
+import org.springframework.aot.generate.GeneratedFiles.FileHandler;
 import org.springframework.aot.generate.GeneratedFiles.Kind;
 import org.springframework.core.io.ByteArrayResource;
+import org.springframework.util.function.ThrowingConsumer;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 
 /**
  * Tests for {@link FileSystemGeneratedFiles}.
  *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  */
 class FileSystemGeneratedFilesTests {
 
@@ -82,7 +86,7 @@ class FileSystemGeneratedFilesTests {
 	void createWhenRootsResultsInNullThrowsException() {
 		assertThatIllegalArgumentException()
 				.isThrownBy(() -> new FileSystemGeneratedFiles(kind -> (kind != Kind.CLASS) ?
-								this.root.resolve(kind.toString()) : null))
+						this.root.resolve(kind.toString()) : null))
 				.withMessage("'roots' must return a value for all file kinds");
 	}
 
@@ -94,6 +98,46 @@ class FileSystemGeneratedFilesTests {
 		assertPathMustBeRelative(generatedFiles, "test/../../test");
 	}
 
+	@Test
+	void addFileWhenFileAlreadyAddedThrowsException() {
+		FileSystemGeneratedFiles generatedFiles = new FileSystemGeneratedFiles(this.root);
+		generatedFiles.addResourceFile("META-INF/test", "test");
+		assertThatIllegalStateException().isThrownBy(
+						() -> generatedFiles.addResourceFile("META-INF/test", "test"))
+				.withMessageContaining("META-INF/test", "already exists");
+	}
+
+	@Test
+	void handleFileWhenFileExistsProvidesFileHandler() {
+		FileSystemGeneratedFiles generatedFiles = new FileSystemGeneratedFiles(this.root);
+		generatedFiles.addResourceFile("META-INF/test", "test");
+		generatedFiles.handleFile(Kind.RESOURCE, "META-INF/test", handler -> {
+			assertThat(handler.exists()).isTrue();
+			assertThat(handler.getContent()).isNotNull();
+			assertThat(handler.getContent().getInputStream()).hasContent("test");
+		});
+		assertThat(this.root.resolve("resources/META-INF/test")).content().isEqualTo("test");
+	}
+
+	@Test
+	void handleFileWhenFileExistsFailsToCreate() {
+		FileSystemGeneratedFiles generatedFiles = new FileSystemGeneratedFiles(this.root);
+		generatedFiles.addResourceFile("META-INF/test", "test");
+		ThrowingConsumer<FileHandler> consumer = handler -> handler.create(new ByteArrayResource("should fail".getBytes(StandardCharsets.UTF_8)));
+		assertThatIllegalStateException()
+				.isThrownBy(() -> generatedFiles.handleFile(Kind.RESOURCE, "META-INF/test", consumer))
+				.withMessageContaining("META-INF/test", "already exists");
+	}
+
+	@Test
+	void handleFileWhenFileExistsCanOverrideContent() {
+		FileSystemGeneratedFiles generatedFiles = new FileSystemGeneratedFiles(this.root);
+		generatedFiles.addResourceFile("META-INF/test", "test");
+		generatedFiles.handleFile(Kind.RESOURCE, "META-INF/test", handler ->
+				handler.override(new ByteArrayResource("overridden".getBytes(StandardCharsets.UTF_8))));
+		assertThat(this.root.resolve("resources/META-INF/test")).content().isEqualTo("overridden");
+	}
+
 	private void assertPathMustBeRelative(FileSystemGeneratedFiles generatedFiles, String path) {
 		assertThatIllegalArgumentException()
 				.isThrownBy(() -> generatedFiles.addResourceFile(path, "test"))

spring-core/src/test/java/org/springframework/aot/generate/GeneratedFilesTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -32,6 +32,8 @@ import org.springframework.core.io.Resource;
 import org.springframework.javapoet.JavaFile;
 import org.springframework.javapoet.MethodSpec;
 import org.springframework.javapoet.TypeSpec;
+import org.springframework.lang.Nullable;
+import org.springframework.util.function.ThrowingConsumer;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
@@ -40,6 +42,7 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
  * Tests for {@link GeneratedFiles}.
  *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  */
 class GeneratedFilesTests {
 
@@ -159,30 +162,45 @@ class GeneratedFilesTests {
 		return this.generatedFiles.assertThatFileAdded(kind, path);
 	}
 
-	static class TestGeneratedFiles implements GeneratedFiles {
+	static class TestGeneratedFiles extends GeneratedFiles {
 
 		private Kind kind;
 
 		private String path;
 
-		private InputStreamSource content;
+		private final TestFileHandler fileHandler = new TestFileHandler();
 
 		@Override
-		public void addFile(Kind kind, String path, InputStreamSource content) {
+		public void handleFile(Kind kind, String path, ThrowingConsumer<FileHandler> handler) {
 			this.kind = kind;
 			this.path = path;
-			this.content = content;
+			handler.accept(this.fileHandler);
 		}
 
 		AbstractStringAssert<?> assertThatFileAdded(Kind kind, String path)
 				throws IOException {
 			assertThat(this.kind).as("kind").isEqualTo(kind);
 			assertThat(this.path).as("path").isEqualTo(path);
+			assertThat(this.fileHandler.content).as("content").isNotNull();
 			ByteArrayOutputStream out = new ByteArrayOutputStream();
-			this.content.getInputStream().transferTo(out);
+			this.fileHandler.content.getInputStream().transferTo(out);
 			return assertThat(out.toString(StandardCharsets.UTF_8));
 		}
 
+		private static class TestFileHandler extends FileHandler {
+
+			@Nullable
+			private InputStreamSource content;
+
+			TestFileHandler() {
+				super(false, () -> null);
+			}
+
+			@Override
+			protected void copy(InputStreamSource content, boolean override) {
+				this.content = content;
+			}
+		}
 	}
 
 }

spring-core/src/test/java/org/springframework/aot/generate/InMemoryGeneratedFilesTests.java

@@ -44,7 +44,7 @@ class InMemoryGeneratedFilesTests {
 		this.generatedFiles.addResourceFile("META-INF/test", "test");
 		assertThatIllegalStateException().isThrownBy(
 				() -> this.generatedFiles.addResourceFile("META-INF/test", "test"))
-				.withMessage("Path 'META-INF/test' already in use");
+				.withMessage("META-INF/test already exists");
 	}
 
 	@Test