Make dev tools' home directory configurable

This allows separate projects to keep their own settings where common
settings such as spring.* or server.* don't conflict.

See gh-17924

Author: sfeldstein-vmware

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/env/DevToolsHomePropertiesPostProcessor.java

@@ -93,7 +93,7 @@ private String getPropertySourceName(File file) {
 
 	private void addPropertySource(List<PropertySource<?>> propertySources, String fileName,
 			Function<File, String> propertySourceNamer) {
-		File home = getHomeDirectory();
+		File home = getProjectRootFolder();
 		File file = (home != null) ? new File(home, fileName) : null;
 		FileSystemResource resource = (file != null) ? new FileSystemResource(file) : null;
 		if (resource != null && resource.exists() && resource.isFile()) {
@@ -121,6 +121,17 @@ private boolean canLoadFileExtension(PropertySourceLoader loader, String name) {
 				.anyMatch((fileExtension) -> StringUtils.endsWithIgnoreCase(name, fileExtension));
 	}
 
+	protected File getProjectRootFolder() {
+		String rootFolder = System.getenv("PROJECT_ROOT_FOLDER");
+		if (rootFolder == null) {
+			rootFolder = System.getProperty("PROJECT_ROOT_FOLDER");
+		}
+		if (StringUtils.hasLength(rootFolder)) {
+			return new File(rootFolder);
+		}
+		return getHomeDirectory();
+	}
+
 	protected File getHomeDirectory() {
 		String home = System.getProperty("user.home");
 		if (StringUtils.hasLength(home)) {

spring-boot-project/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/env/DevToolsHomePropertiesPostProcessorTests.java

@@ -47,9 +47,12 @@ class DevToolsHomePropertiesPostProcessorTests {
 
 	private File home;
 
+	private File rootDir;
+
 	@BeforeEach
-	void setup(@TempDir File tempDir) {
+	void setup(@TempDir File tempDir, @TempDir File rootDir) {
 		this.home = tempDir;
+		this.rootDir = rootDir;
 		this.configDir = this.home + "/.config/spring-boot/";
 		new File(this.configDir).mkdirs();
 	}
@@ -63,6 +66,21 @@ void loadsPropertiesFromHomeDirectoryUsingProperties() throws Exception {
 		assertThat(environment.getProperty("abc")).isEqualTo("def");
 	}
 
+	@Test
+	void loadsRootFolderProperties() throws Exception {
+		System.setProperty("PROJECT_ROOT_FOLDER", this.rootDir.getAbsolutePath());
+		Properties properties = new Properties();
+		properties.put("uvw", "xyz");
+		OutputStream out = new FileOutputStream(
+				new File(this.rootDir, ".config/spring-boot/spring-boot-devtools.properties"));
+		properties.store(out, null);
+		out.close();
+		ConfigurableEnvironment environment = new MockEnvironment();
+		MockDevToolHomePropertiesPostProcessor postProcessor = new MockDevToolHomePropertiesPostProcessor();
+		runPostProcessor(() -> postProcessor.postProcessEnvironment(environment, null));
+		assertThat(environment.getProperty("uvw")).isEqualTo("xyz");
+	}
+
 	@Test
 	void loadsPropertiesFromConfigDirectoryUsingProperties() throws Exception {
 		Properties properties = new Properties();