add a $YEAR as a supported variable in license

This token is replaced by the current year in the following cases:

* the license is missing
* the license in not formatted
* the $YEAR is not like 1990 or 1990-2005

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

@@ -20,6 +20,7 @@
 import java.io.Serializable;
 import java.nio.charset.Charset;
 import java.nio.file.Files;
+import java.time.YearMonth;
 import java.util.Objects;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -35,6 +36,11 @@ public final class LicenseHeaderStep implements Serializable {
 
 	private final String licenseHeader;
 	private final Pattern delimiterPattern;
+	private Pattern yearMatcherPattern;
+	private boolean hasYearToken;
+	private String licenseHeaderBeforeYEARToken;
+	private String licenseHeaderAfterYEARToken;
+	private String licenseHeaderWithYEARTokenReplaced;
 
 	/** Creates a FormatterStep which forces the start of each file to match a license header. */
 	public static FormatterStep createFromHeader(String licenseHeader, String delimiter) {
@@ -74,6 +80,14 @@ private LicenseHeaderStep(String licenseHeader, String delimiter) {
 		}
 		this.licenseHeader = licenseHeader;
 		this.delimiterPattern = Pattern.compile('^' + delimiter, Pattern.UNIX_LINES | Pattern.MULTILINE);
+		hasYearToken = licenseHeader.contains("$YEAR");
+		if (hasYearToken) {
+			int yearTokenIndex = licenseHeader.indexOf("$YEAR");
+			licenseHeaderBeforeYEARToken = licenseHeader.substring(0, yearTokenIndex);
+			licenseHeaderAfterYEARToken = licenseHeader.substring(yearTokenIndex + 5, licenseHeader.length());
+			licenseHeaderWithYEARTokenReplaced = licenseHeader.replace("$YEAR", String.valueOf(YearMonth.now().getYear()));
+			this.yearMatcherPattern = Pattern.compile("[0-9]{4}(-[0-9]{4})?");
+		}
 	}
 
 	/** Reads the license file from the given file. */
@@ -87,7 +101,14 @@ public String format(String raw) {
 		if (!matcher.find()) {
 			throw new IllegalArgumentException("Unable to find delimiter regex " + delimiterPattern);
 		} else {
-			if (matcher.start() == licenseHeader.length() && raw.startsWith(licenseHeader)) {
+			if (hasYearToken) {
+				if (matchesLicenseWithYearToken(raw, matcher)) {
+					//that means we have the license like `licenseHeaderBeforeYEARToken 1990-2015 licenseHeaderAfterYEARToken`
+					return raw;
+				} else {
+					return licenseHeaderWithYEARTokenReplaced + raw.substring(matcher.start());
+				}
+			} else if (matcher.start() == licenseHeader.length() && raw.startsWith(licenseHeader)) {
 				// if no change is required, return the raw string without
 				// creating any other new strings for maximum performance
 				return raw;
@@ -97,4 +118,10 @@ public String format(String raw) {
 			}
 		}
 	}
+
+	private boolean matchesLicenseWithYearToken(String raw, Matcher matcher) {
+		int startOfTheSecondPart = raw.indexOf(licenseHeaderAfterYEARToken);
+		return (raw.startsWith(licenseHeaderBeforeYEARToken) && startOfTheSecondPart + licenseHeaderAfterYEARToken.length() == matcher.start())
+				&& yearMatcherPattern.matcher(raw.substring(licenseHeaderBeforeYEARToken.length(), startOfTheSecondPart)).matches();
+	}
 }

plugin-gradle/README.md

@@ -273,6 +273,32 @@ spotless {
 }
 ```
 
+<a name="license-header"></a>
+
+## License header options
+
+The license header can contains a `$YEAR` variable that will be replaced by the current year.
+
+For example:
+```
+/* Licensed under Apache-2.0 $YEAR. */
+``` 
+will produce
+```
+/* Licensed under Apache-2.0 2017. */
+``` 
+if build is launched in 2017 
+
+
+The step will change the license according to the following rules
+* It replace the license using the current year when
+    * The license is missing
+    * The license is not formatted correctly
+* It will *not* replace the license when
+    * The year variable is already present and is a single year, e.g. `/* Licensed under Apache-2.0 1990. */`
+    * The year variable is already present and is a year span, e.g. `/* Licensed under Apache-2.0 1990-2003. */`
+
+
 <a name="custom"></a>
 
 ## Custom rules

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

@@ -16,8 +16,11 @@
 package com.diffplug.spotless.generic;
 
 import java.io.File;
+import java.io.IOException;
 import java.nio.charset.StandardCharsets;
+import java.time.YearMonth;
 
+import com.diffplug.spotless.StepHarness;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -29,6 +32,11 @@ public class LicenseHeaderStepTest extends ResourceHarness {
 	private static final String KEY_LICENSE = "license/TestLicense";
 	private static final String KEY_FILE_NOTAPPLIED = "license/MissingLicense.test";
 	private static final String KEY_FILE_APPLIED = "license/HasLicense.test";
+	private static final String KEY_LICENSE_WITH_YEAR = "license/TestLicencseWithYear";
+	private static final String KEY_FILE_WITHOUT_LICENSE = "license/MissLicenseWithYear.test";
+	private static final String KEY_FILE_WITH_PREVIOUS_YEAR = "license/LicenseWithPreviousYear.test";
+	private static final String KEY_FILE_WITH_PREVIOUS_YEARS = "license/LicenseWithPreviousYears.test";
+	private static final String KEY_FILE_WITH_CURRENT_YEAR = "license/LicenseWithYear.test";
 
 	// If this constant changes, don't forget to change the similarly-named one in
 	// plugin-gradle/src/main/java/com/diffplug/gradle/spotless/JavaExtension.java as well
@@ -46,6 +54,27 @@ public void fromFile() throws Throwable {
 		assertOnResources(step, KEY_FILE_NOTAPPLIED, KEY_FILE_APPLIED);
 	}
 
+	@Test
+	public void should_apply_license_containing_YEAR_variable() throws Throwable {
+		FormatterStep step = LicenseHeaderStep.createFromFile(createTestFile(KEY_LICENSE_WITH_YEAR), StandardCharsets.UTF_8, LICENSE_HEADER_DELIMITER);
+
+
+		StepHarness.forStep(step)
+				.test(getTestResource(KEY_FILE_WITHOUT_LICENSE), getFileContentWithYEAR(currentYear()))
+				.testUnaffected(getFileContentWithYEAR(currentYear()))
+				.testUnaffected(getFileContentWithYEAR("2003"))
+				.testUnaffected(getFileContentWithYEAR("1990-2015"))
+				.test(getFileContentWithYEAR("not a year"), getFileContentWithYEAR(currentYear()));
+	}
+
+	private String getFileContentWithYEAR(String year) throws IOException {
+		return getTestResource(KEY_FILE_WITH_CURRENT_YEAR).replace("__YEAR_to_replace_in_tests__", year);
+	}
+
+	private String currentYear() {
+		return String.valueOf(YearMonth.now().getYear());
+	}
+
 	@Test
 	public void efficient() throws Throwable {
 		FormatterStep step = LicenseHeaderStep.createFromHeader("LicenseHeader\n", "contentstart");

testlib/src/test/resources/license/LicenseWithYear.test

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) __YEAR_to_replace_in_tests__. ACME corp.
+ * This library is free software; you can redistribute it and/or modify it under the terms
+ * of the GNU Lesser General Public License as published by the Free Software Foundation
+ * version 2.1 of the License.
+ * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU Lesser General Public License for more details.
+ * You should have received a copy of the GNU Lesser General Public License along with this
+ * program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
+ * Floor, Boston, MA 02110-1301, USA.
+ **/
+package com.acme;
+
+import java.util.function.Function;
+
+
+public class Java8Test {
+    public void doStuff() throws Exception {
+        Function<String, Integer> example = Integer::parseInt;
+        example.andThen(val -> {
+            return val + 2;
+        } );
+        SimpleEnum val = SimpleEnum.A;
+        switch (val) {
+            case A:
+                break;
+            case B:
+                break;
+            case C:
+                break;
+            default:
+                throw new Exception();
+        }
+    }
+
+    public enum SimpleEnum {
+        A, B, C;
+    }
+}

testlib/src/test/resources/license/MissLicenseWithYear.test

@@ -0,0 +1,28 @@
+package com.acme;
+
+import java.util.function.Function;
+
+
+public class Java8Test {
+    public void doStuff() throws Exception {
+        Function<String, Integer> example = Integer::parseInt;
+        example.andThen(val -> {
+            return val + 2;
+        } );
+        SimpleEnum val = SimpleEnum.A;
+        switch (val) {
+            case A:
+                break;
+            case B:
+                break;
+            case C:
+                break;
+            default:
+                throw new Exception();
+        }
+    }
+
+    public enum SimpleEnum {
+        A, B, C;
+    }
+}

testlib/src/test/resources/license/TestLicencseWithYear

@@ -0,0 +1,12 @@
+/*
+ * Copyright (C) $YEAR. ACME corp.
+ * This library is free software; you can redistribute it and/or modify it under the terms
+ * of the GNU Lesser General Public License as published by the Free Software Foundation
+ * version 2.1 of the License.
+ * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU Lesser General Public License for more details.
+ * You should have received a copy of the GNU Lesser General Public License along with this
+ * program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
+ * Floor, Boston, MA 02110-1301, USA.
+ **/