Fix #2940 - Parse standard git year output in LicenseHeaderStep (#2961)

Author: nedtwigg

CHANGES.md

@@ -15,6 +15,8 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Fixed
 - `FenceStep.preserveWithin` now forwards lints from nested steps while still suppressing lints inside preserved blocks. ([#2962](https://github.com/diffplug/spotless/pull/2962))
 - Support `ktfmt` 0.63 and use its new builder API for formatting options to better avoid future breaking changes.
+- Parse standard git year output in LicenseHeaderStep. ([#2940](https://github.com/diffplug/spotless/issues/2940))
+
 ### Changes
 - Bump default `greclipse` version to latest `4.35` -> `4.39`. ([#2924](https://github.com/diffplug/spotless/pull/2924))
 

lib/src/main/java/com/diffplug/spotless/generic/LicenseHeaderStep.java

@@ -349,7 +349,7 @@ private String replaceYear(String raw) {
 			}
 		}
 
-		private static final Pattern YYYY = Pattern.compile("[0-9]{4}");
+		private static final Pattern YYYY = Pattern.compile("\\d{4}");
 
 		/** Calculates the year to inject. */
 		private String calculateYearExact(String parsedYear) {
@@ -408,6 +408,13 @@ private String calculateYearBySearching(String content) {
 			}
 		}
 
+		// Default git log options to find the commit year.
+		// --follow             - Continue listing the history of a file beyond renames.
+		// --find-renames=40%   - Detect renames with a similarity threshold of 40%.
+		// --format=%cd         - Output the committer date using the format specified by --date.
+		// --date=format:%Y     - Format the date as a 4-digit year only.
+		private static final List<String> GIT_LOG_DEFAULT_OPTIONS = Arrays.asList("--follow", "--find-renames=40%", "--format=%cd", "--date=format:%Y");
+
 		/** Sets copyright years on the given file by finding the oldest and most recent commits throughout git history. */
 		private String setLicenseHeaderYearsFromGitHistory(String raw, File file) throws IOException {
 			if (yearToday == null) {
@@ -420,14 +427,21 @@ private String setLicenseHeaderYearsFromGitHistory(String raw, File file) throws
 
 			String oldYear;
 			try {
-				oldYear = parseYear(Arrays.asList("git", "log", "--follow", "--find-renames=40%", "--diff-filter=A"), file);
+				List<String> cmd = new ArrayList<>(Arrays.asList("git", "log", "--diff-filter=A"));
+				cmd.addAll(GIT_LOG_DEFAULT_OPTIONS);
+				oldYear = parseYear(cmd, file);
 			} catch (IllegalArgumentException e) {
 				// Ideally, git log would always find the commit where it was added.
 				// For some reason, that is sometimes not possible - in that case,
 				// we'll settle for just the most recent, even if it was just a modification.
-				oldYear = parseYear(Arrays.asList("git", "log", "--follow", "--find-renames=40%", "--reverse"), file);
+				List<String> cmd = new ArrayList<>(Arrays.asList("git", "log", "--reverse"));
+				cmd.addAll(GIT_LOG_DEFAULT_OPTIONS);
+				oldYear = parseYear(cmd, file);
 			}
-			String newYear = parseYear(Arrays.asList("git", "log", "--max-count=1"), file);
+
+			List<String> newYearCmd = new ArrayList<>(Arrays.asList("git", "log", "--max-count=1"));
+			newYearCmd.addAll(GIT_LOG_DEFAULT_OPTIONS);
+			String newYear = parseYear(newYearCmd, file);
 			String yearRange;
 			if (oldYear.equals(newYear)) {
 				yearRange = oldYear;
@@ -462,15 +476,15 @@ private static String parseYear(List<String> cmd, File file) throws IOException
 			if (!error.isEmpty()) {
 				throw new IllegalArgumentException("Error for command '" + fullCmd + "':\n" + error);
 			}
-			Matcher matcher = FIND_YEAR.matcher(output);
+			Matcher matcher = FIND_YEAR.matcher(output.trim());
 			if (matcher.find()) {
 				return matcher.group(1);
 			} else {
 				throw new IllegalArgumentException("Unable to parse date from command '" + fullCmd + "':\n" + output);
 			}
 		}
 
-		private static final Pattern FIND_YEAR = Pattern.compile("Date:   .* ([0-9]{4}) ");
+		private static final Pattern FIND_YEAR = Pattern.compile("^(\\d{4})?");
 
 		@SuppressFBWarnings("DM_DEFAULT_ENCODING")
 		private static String drain(InputStream stream) throws IOException {

plugin-gradle/CHANGES.md

@@ -9,6 +9,8 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Fixed
 - `toggleOffOn` no longer disables lint-only steps such as `forbidWildcardImports`. ([#2962](https://github.com/diffplug/spotless/pull/2962))
 - Prevent build caches from interfering when executing under the `-PspotlessIdeHook` mode. ([#2365](https://github.com/diffplug/spotless/issues/2365))
+- Parse standard git year output in LicenseHeaderStep. ([#2940](https://github.com/diffplug/spotless/issues/2940))
+
 ### Changes
 - Bump default `greclipse` version to latest `4.35` -> `4.39`. ([#2924](https://github.com/diffplug/spotless/pull/2924))
 

plugin-maven/CHANGES.md

@@ -4,8 +4,8 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 
 ## [Unreleased]
 ### Fixed
+- Parse standard git year output in LicenseHeaderStep. ([#2940](https://github.com/diffplug/spotless/issues/2940))
 - `<toggleOffOn>` no longer disables lint-only steps such as `<forbidWildcardImports>`. ([#2962](https://github.com/diffplug/spotless/pull/2962))
-
 ### Added
 - Add support for AsciiDoc formatting via `adocfmt`. ([#2960](https://github.com/diffplug/spotless/pull/2960))
 

testlib/src/test/java/com/diffplug/spotless/generic/LicenseHeaderStepTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2025 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,9 +21,11 @@
 import java.time.YearMonth;
 import java.time.ZoneOffset;
 
+import org.eclipse.jgit.api.Git;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
+import com.diffplug.spotless.ClearGitConfig;
 import com.diffplug.spotless.FormatterStep;
 import com.diffplug.spotless.ResourceHarness;
 import com.diffplug.spotless.SerializableEqualityTester;
@@ -309,4 +311,28 @@ void moduleInfo() throws Throwable {
 		StepHarness.forStep(step)
 				.test(ResourceHarness.getTestResource("license/module-info.test"), header + ResourceHarness.getTestResource("license/module-info.test"));
 	}
+
+	@Test
+	@ClearGitConfig
+	void should_setFromGit_year_when_singleCommit() throws Exception {
+		try (Git git = Git.init().setDirectory(rootFolder()).call()) {
+			// Single commit: added once, so old/new year must be equal.
+			setFile("Foo.java").toContent("package foo; // v1\n");
+			git.add()
+					.addFilepattern("Foo.java")
+					.call();
+			git.commit()
+					.setMessage("add")
+					.setAuthor("Test User", "test@example.com")
+					.setCommitter("Test User", "test@example.com")
+					.call();
+		}
+
+		FormatterStep step = LicenseHeaderStep.headerDelimiter(header(HEADER_WITH_$YEAR), PACKAGE_)
+				.withYearMode(YearMode.SET_FROM_GIT)
+				.build();
+
+		StepHarnessWithFile.forStep(this, step)
+				.test("Foo.java", getTestResource(FILE_NO_LICENSE), hasHeaderYear(currentYear()));
+	}
 }