Fix issue with root windows drive found in #760

Author: nedtwigg

CHANGES.md

@@ -23,6 +23,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Fixed
 * ktfmt v0.19+ with dropbox-style works again ([#765](https://github.com/diffplug/spotless/pull/765)).
 * prettier no longer throws errors on empty files ([#751](https://github.com/diffplug/spotless/pull/751)).
+* fixed error when running on root of windows mountpoint ([#760](https://github.com/diffplug/spotless/pull/760)).
 
 ## [2.10.2] - 2020-11-16
 ### Fixed

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 DiffPlug
+ * Copyright 2016-2021 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -200,6 +200,9 @@ public static String subpath(String root, String child) {
 		if (child.startsWith(root)) {
 			return child.substring(root.length());
 		} else {
+			if (machineIsWin() && root.endsWith("://") && child.startsWith(root.substring(0, root.length() - 1))) {
+				return child.substring(root.length() - 1);
+			}
 			throw new IllegalArgumentException("Expected '" + child + "' to start with '" + root + "'");
 		}
 	}

plugin-gradle/CHANGES.md

@@ -14,6 +14,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 * `ratchetFrom` now works with git-submodule ([#746](https://github.com/diffplug/spotless/issues/746))
 * ktfmt v0.19+ with dropbox-style works again ([#765](https://github.com/diffplug/spotless/pull/765)).
 * prettier no longer throws errors on empty files ([#751](https://github.com/diffplug/spotless/pull/751)).
+* fixed error when running on root of windows mountpoint ([#760](https://github.com/diffplug/spotless/pull/760)).
 
 ## [5.8.2] - 2020-11-16
 ### Fixed

plugin-maven/CHANGES.md

@@ -16,6 +16,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 * Fix broken test for spotlessFiles parameter on windows ([#737](https://github.com/diffplug/spotless/pull/737))
 * ktfmt v0.19+ with dropbox-style works again ([#765](https://github.com/diffplug/spotless/pull/765)).
 * prettier no longer throws errors on empty files ([#751](https://github.com/diffplug/spotless/pull/751)).
+* fixed error when running on root of windows mountpoint ([#760](https://github.com/diffplug/spotless/pull/760)).
 
 ## [2.6.1] - 2020-11-16
 ### Fixed

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 DiffPlug
+ * Copyright 2016-2021 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@
 import java.util.Collections;
 import java.util.List;
 
+import org.assertj.core.api.Assertions;
 import org.junit.Test;
 
 public class FileSignatureTest extends ResourceHarness {
@@ -79,4 +80,11 @@ private List<File> getTestFiles(final String[] paths) throws IOException {
 	public void testSubpath() {
 		assertThat(FileSignature.subpath("root/", "root/child")).isEqualTo("child");
 	}
+
+	@Test
+	public void windowsRoot() {
+		org.junit.Assume.assumeTrue(FileSignature.machineIsWin());
+		String subpath = FileSignature.subpath("S://", "S:/build.gradle");
+		Assertions.assertThat(subpath).isEqualTo("build.gradle");
+	}
 }