Switch from new File() to a Sentinel reference

Author: blacelle

lib/src/main/java/com/diffplug/spotless/Formatter.java

@@ -39,6 +39,9 @@
 public final class Formatter implements Serializable, AutoCloseable {
 	private static final long serialVersionUID = 1L;
 
+	// This Sentinel reference may be used where Formatter requires a File, while there is no actual File to format
+	public static final File SENTINEL_NO_FILE_ON_DISK = new File("NO_FILE_ON_DISK.sentinel");
+
 	private LineEnding.Policy lineEndingsPolicy;
 	private Charset encoding;
 	private Path rootDir;
@@ -237,8 +240,7 @@ public String compute(String unix, File file) {
 					unix = LineEnding.toUnix(formatted);
 				}
 			} catch (Throwable e) {
-				if (file.getPath().isEmpty()) {
-					// Path.relativize would fail if rootDir is an absolute path
+				if (file == SENTINEL_NO_FILE_ON_DISK) {
 					exceptionPolicy.handleError(e, step, "");
 				} else {
 					// Path may be forged from a different FileSystem than Filesystem.default

lib/src/main/java/com/diffplug/spotless/FormatterStep.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 DiffPlug
+ * Copyright 2016-2023 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,8 +37,8 @@ public interface FormatterStep extends Serializable {
 	 * @param rawUnix
 	 *            the content to format, guaranteed to have unix-style newlines ('\n'); never null
 	 * @param file
-	 *            the file which {@code rawUnix} was obtained from; never null. Pass an empty file using
-	 *            {@code new File("")} if and only if no file is actually associated with {@code rawUnix}
+	 *            the file which {@code rawUnix} was obtained from; never null. Pass the reference
+	 *            {@code Formatter#SENTINEL_NO_FILE_ON_DISK} if and only if no file is actually associated with {@code rawUnix}
 	 * @return the formatted content, guaranteed to only have unix-style newlines; may return null
 	 *         if the formatter step doesn't have any changes to make
 	 * @throws Exception if the formatter step experiences a problem

lib/src/main/java/com/diffplug/spotless/FormatterStepImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 DiffPlug
+ * Copyright 2016-2023 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -109,18 +109,15 @@ protected String format(Integer state, String rawUnix, File file) throws Excepti
 			if (formatter == null) {
 				formatter = formatterSupplier.get();
 				if (formatter instanceof FormatterFunc.Closeable) {
-					throw new AssertionError("NeverUpToDate does not support FormatterFunc.Closeable.  See https://github.com/diffplug/spotless/pull/284");
+					throw new AssertionError("NeverUpToDate does not support FormatterFunc.Closeable. See https://github.com/diffplug/spotless/pull/284");
 				}
 			}
 			return formatter.apply(rawUnix, file);
 		}
 	}
 
-	/** A dummy SENTINEL file. */
-	static final File SENTINEL = new File("");
-
 	static void checkNotSentinel(File file) {
-		if (file == SENTINEL) {
+		if (file == Formatter.SENTINEL_NO_FILE_ON_DISK) {
 			throw new IllegalArgumentException("This step requires the underlying file. If this is a test, use StepHarnessWithFile");
 		}
 	}

testlib/src/test/java/com/diffplug/spotless/FormatterTest.java

@@ -18,6 +18,7 @@
 import java.io.File;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.FileSystem;
 import java.nio.file.FileSystems;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -94,7 +95,7 @@ protected Formatter create() {
 		}.testEquals();
 	}
 
-	// new File("") can be used if there is no File representing this content. It should not conflict with rootDir.relativize(...)
+	// new File("") as filePath is known to fail
 	@Test
 	public void testExceptionWithEmptyPath() throws Exception {
 		LineEnding.Policy lineEndingsPolicy = LineEnding.UNIX.createPolicy();
@@ -116,7 +117,32 @@ public void testExceptionWithEmptyPath() throws Exception {
 				.exceptionPolicy(exceptionPolicy)
 				.build();
 
-		formatter.compute("someFileContent", new File(""));
+		Assertions.assertThrows(IllegalArgumentException.class, () -> formatter.compute("someFileContent", new File("")));
+	}
+
+	// If there is no File actually holding the content, one may rely on Formatter.NO_FILE_ON_DISK
+	@Test
+	public void testExceptionWithSentinelNoFileOnDisk() throws Exception {
+		LineEnding.Policy lineEndingsPolicy = LineEnding.UNIX.createPolicy();
+		Charset encoding = StandardCharsets.UTF_8;
+		FormatExceptionPolicy exceptionPolicy = FormatExceptionPolicy.failOnlyOnError();
+
+		Path rootDir = Paths.get(StandardSystemProperty.USER_DIR.value());
+
+		FormatterStep step = Mockito.mock(FormatterStep.class);
+		Mockito.when(step.getName()).thenReturn("someFailingStep");
+		Mockito.when(step.format(Mockito.anyString(), Mockito.any(File.class))).thenThrow(new IllegalArgumentException("someReason"));
+		List<FormatterStep> steps = Collections.singletonList(step);
+
+		Formatter formatter = Formatter.builder()
+				.lineEndingsPolicy(lineEndingsPolicy)
+				.encoding(encoding)
+				.rootDir(rootDir)
+				.steps(steps)
+				.exceptionPolicy(exceptionPolicy)
+				.build();
+
+		formatter.compute("someFileContent", Formatter.SENTINEL_NO_FILE_ON_DISK);
 	}
 
 	// rootDir may be a path not from the default FileSystem
@@ -127,6 +153,12 @@ public void testExceptionWithRootDirIsNotFileSystem() throws Exception {
 		FormatExceptionPolicy exceptionPolicy = FormatExceptionPolicy.failOnlyOnError();
 
 		Path rootDir = Mockito.mock(Path.class);
+		FileSystem customFileSystem = Mockito.mock(FileSystem.class);
+		Mockito.when(rootDir.getFileSystem()).thenReturn(customFileSystem);
+
+		Path pathFromFile = Mockito.mock(Path.class);
+		Mockito.when(customFileSystem.getPath(Mockito.anyString())).thenReturn(pathFromFile);
+
 		Path relativized = Mockito.mock(Path.class);
 		Mockito.when(rootDir.relativize(Mockito.any(Path.class))).then(invok -> {
 			Path filePath = invok.getArgument(0);
@@ -150,7 +182,7 @@ public void testExceptionWithRootDirIsNotFileSystem() throws Exception {
 				.exceptionPolicy(exceptionPolicy)
 				.build();
 
-		formatter.compute("someFileContent", new File(""));
+		formatter.compute("someFileContent", new File("/some/folder/some.file"));
 	}
 
 }