Allow build numbers to be arbitrary strings or null

This required changing the `buildNumber` data type from `long` to `String`.

Fixes #75

pom.xml

@@ -6,7 +6,7 @@
 
     <groupId>com.github.danielflower.mavenplugins</groupId>
     <artifactId>multi-module-maven-release-plugin</artifactId>
-    <version>3.2-SNAPSHOT</version> <!-- When changing also update scaffolding.TestProject.PLUGIN_VERSION_FOR_TESTS and add to src/site/markdown/changelog.md -->
+    <version>3.3-SNAPSHOT</version> <!-- When changing also update scaffolding.TestProject.PLUGIN_VERSION_FOR_TESTS and add to src/site/markdown/changelog.md -->
 
     <name>The Multi Module Maven Release Plugin</name>
     <description>A maven release plugin built for multi-maven-module git repositories allowing continuous deployment
@@ -123,6 +123,15 @@
             <artifactId>maven-invoker</artifactId>
             <version>3.0.1</version>
         </dependency>
+        <dependency>
+            <!--
+            The maven-dependency-plugin wants this to be listed explicitly as it comes as a transitive dependency
+            of maven-model.
+            -->
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>3.4</version>
+        </dependency>
         <dependency>
             <groupId>org.eclipse.jgit</groupId>
             <artifactId>org.eclipse.jgit</artifactId>

src/main/java/com/github/danielflower/mavenplugins/release/AnnotatedTag.java

@@ -28,10 +28,10 @@ private AnnotatedTag(Ref ref, String name, JSONObject message) {
         this.message = message;
     }
 
-    public static AnnotatedTag create(String name, String version, long buildNumber) {
+    public static AnnotatedTag create(String name, String version, String buildNumber) {
         JSONObject message = new JSONObject();
         message.put(VERSION, version);
-        message.put(BUILD_NUMBER, String.valueOf(buildNumber));
+        message.put(BUILD_NUMBER, buildNumber);
         return new AnnotatedTag(null, name, message);
     }
 
@@ -67,8 +67,8 @@ public String version() {
         return String.valueOf(message.get(VERSION));
     }
 
-    public long buildNumber() {
-        return Long.parseLong(String.valueOf(message.get(BUILD_NUMBER)));
+    public String buildNumber() {
+        return String.valueOf(message.get(BUILD_NUMBER));
     }
 
     public Ref saveAtHEAD(Git git) throws GitAPIException {

src/main/java/com/github/danielflower/mavenplugins/release/AnnotatedTagFinder.java

@@ -46,18 +46,12 @@ boolean isPotentiallySameVersionIgnoringBuildNumber(String versionWithoutBuildNu
         return buildNumberOf(versionWithoutBuildNumber, refName) != null;
     }
 
-    Long buildNumberOf(String versionWithoutBuildNumber, String refName) {
+    String buildNumberOf(String versionWithoutBuildNumber, String refName) {
         String tagName = AnnotatedTag.stripRefPrefix(refName);
         String prefix = versionWithoutBuildNumber + versionNamer.getDelimiter();
         if (tagName.startsWith(prefix)) {
-            String end = tagName.substring(prefix.length());
-            try {
-                return Long.parseLong(end);
-            } catch (NumberFormatException e) {
-                return null;
-            }
+            return tagName.substring(prefix.length());
         }
         return null;
     }
-
 }

src/main/java/com/github/danielflower/mavenplugins/release/BaseMojo.java

@@ -1,11 +1,13 @@
 package com.github.danielflower.mavenplugins.release;
 
+import org.apache.commons.lang3.StringUtils;
 import org.apache.maven.artifact.factory.ArtifactFactory;
 import org.apache.maven.artifact.repository.ArtifactRepository;
 import org.apache.maven.artifact.resolver.ArtifactResolver;
 import org.apache.maven.model.Scm;
 import org.apache.maven.plugin.AbstractMojo;
 import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugin.MojoFailureException;
 import org.apache.maven.plugin.logging.Log;
 import org.apache.maven.plugins.annotations.Component;
 import org.apache.maven.plugins.annotations.Parameter;
@@ -43,16 +45,37 @@ public abstract class BaseMojo extends AbstractMojo {
 	 * </p>
 	 * <p>
 	 * By default, the plugin will automatically find a suitable build number.
-	 * It will start at version 0 and increment this with each release.
+	 * It will start at 0 and increment this with each release.
 	 * </p>
 	 * <p>
-	 * This can be specified using a command line parameter ("-DbuildNumber=2")
-	 * or in this plugin's configuration.
+	 * This can be specified using a command line parameter (e.g.
+     * <code>-DbuildNumber=2</code>) or in this plugin's configuration.
 	 * </p>
+     * <p>
+     * <strong>null vs. ""</strong>: if you do not define the build number it
+     * is treated as <code>null</code> and the plugin will start at 0. If you
+     * pass an empty string both the build number and the delimiter that
+     * precedes it will be omitted.<br>To define an empty string on the CLI use
+     * <code>-DbuildNumber=''</code>. For the same effect in the POM you can
+     * use <code>&lt;buildNumber&gt;""&lt;/buildNumber&gt;</code> as Maven does
+     * not support empty strings for configuration properties. The plugin will
+     * convert this accordingly.
+     * </p>
 	 */
+	// Maven has historically never supported empty strings in XML plugin configuration (see
+    // http://mail-archives.apache.org/mod_mbox/maven-users/200708.mbox/%[email protected]%3E
+    // from 2007). Hence, if a project defines <buildNumber></buildNumber> the property here will be null. However,
+    // Maven does support -DbuildNumber='' on the CLI.
 	@Parameter(property = "buildNumber")
-	protected Long buildNumber;
+	protected String buildNumber;
 
+    public void setBuildNumber(String buildNumber) {
+        if ("\"\"".equals(buildNumber)) {
+            this.buildNumber = StringUtils.EMPTY;
+        } else {
+            this.buildNumber = buildNumber;
+        }
+    }
 
     /**
      * <p>
@@ -252,5 +275,4 @@ protected static String getRemoteUrlOrNullIfNoneSet(Scm originalScm, Scm actualS
         }
         return GitHelper.scmUrlToRemote(remote);
     }
-
 }

src/main/java/com/github/danielflower/mavenplugins/release/Reactor.java

@@ -1,5 +1,6 @@
 package com.github.danielflower.mavenplugins.release;
 
+import org.apache.commons.lang3.StringUtils;
 import org.apache.maven.model.Dependency;
 import org.apache.maven.plugin.MojoExecutionException;
 import org.apache.maven.plugin.logging.Log;
@@ -28,7 +29,7 @@ public List<ReleasableModule> getModulesInBuildOrder() {
         return modulesInBuildOrder;
     }
 
-    public static Reactor fromProjects(Log log, LocalGitRepo gitRepo, MavenProject rootProject, List<MavenProject> projects, Long buildNumber, List<String> modulesToForceRelease, NoChangesAction actionWhenNoChangesDetected, ResolverWrapper resolverWrapper, VersionNamer versionNamer) throws ValidationException, GitAPIException, MojoExecutionException {
+    public static Reactor fromProjects(Log log, LocalGitRepo gitRepo, MavenProject rootProject, List<MavenProject> projects, String buildNumber, List<String> modulesToForceRelease, NoChangesAction actionWhenNoChangesDetected, ResolverWrapper resolverWrapper, VersionNamer versionNamer) throws ValidationException, GitAPIException, MojoExecutionException {
         DiffDetector detector = new TreeWalkingDiffDetector(gitRepo.git.getRepository());
         List<ReleasableModule> modules = new ArrayList<ReleasableModule>();
 
@@ -42,14 +43,14 @@ public static Reactor fromProjects(Log log, LocalGitRepo gitRepo, MavenProject r
             List<AnnotatedTag> previousTagsForThisModule = annotatedTagFinder.tagsForVersion(gitRepo.git, artifactId, versionWithoutBuildNumber);
 
 
-            Collection<Long> previousBuildNumbers = new ArrayList<Long>();
+            Collection<String> previousBuildNumbers = new ArrayList<>();
             if (previousTagsForThisModule != null) {
                 for (AnnotatedTag previousTag : previousTagsForThisModule) {
                     previousBuildNumbers.add(previousTag.buildNumber());
                 }
             }
 
-            Collection<Long> remoteBuildNumbers = getRemoteBuildNumbers(gitRepo, artifactId, versionWithoutBuildNumber, versionNamer);
+            Collection<String> remoteBuildNumbers = getRemoteBuildNumbers(gitRepo, artifactId, versionWithoutBuildNumber, versionNamer);
             previousBuildNumbers.addAll(remoteBuildNumbers);
 
             VersionName newVersion = versionNamer.name(project.getVersion(), buildNumber, previousBuildNumbers);
@@ -145,14 +146,14 @@ private static boolean hasSameMavenGAByDependencyLocation(ReleasableModule modul
         return modelId[0].equals(module.getGroupId()) && modelId[1].equals(module.getArtifactId());
     }
 
-    private static Collection<Long> getRemoteBuildNumbers(LocalGitRepo gitRepo, String artifactId, String versionWithoutBuildNumber, VersionNamer versionNamer) throws GitAPIException {
+    private static Collection<String> getRemoteBuildNumbers(LocalGitRepo gitRepo, String artifactId, String versionWithoutBuildNumber, VersionNamer versionNamer) throws GitAPIException {
         Collection<Ref> remoteTagRefs = gitRepo.allTags();
-        Collection<Long> remoteBuildNumbers = new ArrayList<Long>();
+        Collection<String> remoteBuildNumbers = new ArrayList<>();
         String tagWithoutBuildNumber = artifactId + "-" + versionWithoutBuildNumber;
         AnnotatedTagFinder annotatedTagFinder = new AnnotatedTagFinder(versionNamer);
         for (Ref remoteTagRef : remoteTagRefs) {
             String remoteTagName = remoteTagRef.getName();
-            Long buildNumber = annotatedTagFinder.buildNumberOf(tagWithoutBuildNumber, remoteTagName);
+            String buildNumber = annotatedTagFinder.buildNumberOf(tagWithoutBuildNumber, remoteTagName);
             if (buildNumber != null) {
                 remoteBuildNumbers.add(buildNumber);
             }
@@ -190,20 +191,25 @@ static AnnotatedTag hasChangedSinceLastRelease(List<AnnotatedTag> previousTagsFo
         try {
             if (previousTagsForThisModule.size() == 0) return null;
             boolean hasChanged = detector.hasChangedSince(relativePathToModule, project.getModel().getModules(), previousTagsForThisModule);
-            return hasChanged ? null : tagWithHighestBuildNumber(previousTagsForThisModule);
+            return hasChanged ? null : findTagWithHighestBuildNumber(previousTagsForThisModule);
         } catch (Exception e) {
             throw new MojoExecutionException("Error while detecting whether or not " + project.getArtifactId() + " has changed since the last release", e);
         }
     }
 
-    private static AnnotatedTag tagWithHighestBuildNumber(List<AnnotatedTag> tags) {
-        AnnotatedTag cur = null;
+    // Ignores any tags with non-numeric build numbers and finds the one with the largest build number among the others.
+    // The tags are guaranteed to be for the same /business version/ i.e. it's likely a small list.
+    private static AnnotatedTag findTagWithHighestBuildNumber(List<AnnotatedTag> tags) {
+        AnnotatedTag tagWithHighestBuildNumber = null;
         for (AnnotatedTag tag : tags) {
-            if (cur == null || tag.buildNumber() > cur.buildNumber()) {
-                cur = tag;
+            if(StringUtils.isNumeric(tag.buildNumber())) {
+                if (tagWithHighestBuildNumber == null ||
+                    Long.parseLong(tag.buildNumber()) > Long.parseLong(tagWithHighestBuildNumber.buildNumber())) {
+                    tagWithHighestBuildNumber = tag;
+                }
             }
         }
-        return cur;
+        return tagWithHighestBuildNumber;
     }
 
     public ReleasableModule findByLabel(String label) {

src/main/java/com/github/danielflower/mavenplugins/release/ReleasableModule.java

@@ -44,7 +44,7 @@ public String getVersion() {
         return version.businessVersion();
     }
 
-    public long getBuildNumber() {
+    public String getBuildNumber() {
         return version.buildNumber();
     }
 

src/main/java/com/github/danielflower/mavenplugins/release/VersionName.java

@@ -1,33 +1,37 @@
 package com.github.danielflower.mavenplugins.release;
 
+import org.apache.commons.lang3.StringUtils;
+
 public class VersionName {
     private final String version;
-    private final long buildNumber;
+    private final String buildNumber;
     private final String developmentVersion;
     private final String delimiter;
+    private final String releaseVersion;
 
-    public VersionName(String developmentVersion, String version, long buildNumber, String delimiter) {
+    public VersionName(String developmentVersion, String version, String buildNumber, String delimiter) {
         Guard.notBlank("developmentVersion", developmentVersion);
         Guard.notBlank("version", version);
         Guard.notNull("buildNumber", buildNumber);
         this.version = version;
         this.buildNumber = buildNumber;
         this.developmentVersion = developmentVersion;
         this.delimiter = delimiter;
+        this.releaseVersion = buildNumber.length() > 0 ? version + delimiter + buildNumber : version;
     }
 
-    public VersionName(String developmentVersion, String version, long buildNumber) {
+    public VersionName(String developmentVersion, String version, String buildNumber) {
         this(developmentVersion, version, buildNumber, ".");
     }
 
     /**
-     * For example, "1.0" if the development version is "1.0-SNAPSHOT"
+     * For example, "1.0" if the development version is "1.0-SNAPSHOT".
      */
     public String businessVersion() {
         return version;
     }
 
-    public long buildNumber() {
+    public String buildNumber() {
         return buildNumber;
     }
 
@@ -42,6 +46,6 @@ public String developmentVersion() {
      * The business version with the build number appended, e.g. "1.0.1"
      */
     public String releaseVersion() {
-        return version + delimiter + buildNumber;
+        return releaseVersion;
     }
 }

src/main/java/com/github/danielflower/mavenplugins/release/VersionNamer.java

@@ -1,5 +1,6 @@
 package com.github.danielflower.mavenplugins.release;
 
+import org.apache.commons.lang3.StringUtils;
 import org.apache.maven.plugins.annotations.Parameter;
 import org.eclipse.jgit.lib.Repository;
 
@@ -33,35 +34,38 @@ public VersionNamer() {
         this(".");
     }
 
-    public VersionName name(String pomVersion, Long buildNumber, Collection<Long> previousBuildNumbers) throws ValidationException {
-
+    public VersionName name(String pomVersion, String buildNumber, Collection<String> previousBuildNumbers) throws ValidationException {
+        String effectiveBuildNumber = buildNumber;
         if (buildNumber == null) {
-            if (previousBuildNumbers.size() == 0) {
-                buildNumber = 0L;
+            if (previousBuildNumbers == null || previousBuildNumbers.isEmpty()) {
+                effectiveBuildNumber = "0";
             } else {
-                buildNumber = nextBuildNumber(previousBuildNumbers);
+                effectiveBuildNumber = nextBuildNumber(previousBuildNumbers);
             }
         }
 
-        VersionName versionName = new VersionName(pomVersion, pomVersion.replace("-SNAPSHOT", ""), buildNumber, this.delimiter);
+        VersionName versionName = new VersionName(pomVersion, pomVersion.replace("-SNAPSHOT", ""), effectiveBuildNumber, this.delimiter);
 
         if (!Repository.isValidRefName("refs/tags/" + versionName.releaseVersion())) {
             String summary = "Sorry, '" + versionName.releaseVersion() + "' is not a valid version.";
             throw new ValidationException(summary, asList(
                 summary,
-                "Version numbers are used in the Git tag, and so can only contain characters that are valid in git tags.",
+                "Version numbers are used in the Git tag, and so can only contain characters that are valid in Git tags.",
                 "Please see https://www.kernel.org/pub/software/scm/git/docs/git-check-ref-format.html for tag naming rules."
             ));
         }
         return versionName;
     }
 
-    private static long nextBuildNumber(Collection<Long> previousBuildNumbers) {
+    // Increments the largest previous build number. Skips over any non-numeric previous build numbers.
+    private static String nextBuildNumber(Collection<String> previousBuildNumbers) {
         long max = 0;
-        for (Long buildNumber : previousBuildNumbers) {
-            max = Math.max(max, buildNumber);
+        for (String buildNumber : previousBuildNumbers) {
+            if (StringUtils.isNumeric(buildNumber)) {
+                max = Math.max(max, Long.parseLong(buildNumber));
+            }
         }
-        return max + 1;
+        return String.valueOf(max + 1);
     }
 
     String getDelimiter() {

src/site/markdown/changelog.md

@@ -1,6 +1,10 @@
 Changelog
 ---------
 
+### 3.3.0
+
+* Allow build numbers to be arbitrary strings or null, #75
+
 ### 3.2.0
 
 * Added support for processing version properties e.g. `<version>${foo.version}</version>`