[MNG-8586] Expose Maven version segments as properties (#2116)

Expose version segments. Also add the properties to generated doco.

---

https://issues.apache.org/jira/browse/MNG-8586

Author: cstamas

api/maven-api-annotations/src/main/java/org/apache/maven/api/annotations/Config.java

@@ -38,8 +38,21 @@
 
     boolean readOnly() default false;
 
+    /**
+     * Property source.
+     */
     enum Source {
+        /**
+         * Maven system properties.
+         */
+        SYSTEM_PROPERTIES,
+        /**
+         * Maven user properties.
+         */
         USER_PROPERTIES,
+        /**
+         * Project properties.
+         */
         MODEL
     }
 }

api/maven-api-core/src/main/java/org/apache/maven/api/Constants.java

@@ -30,9 +30,57 @@ public final class Constants {
      *
      * @since 3.0.0
      */
-    @Config(readOnly = true)
+    @Config(readOnly = true, source = Config.Source.SYSTEM_PROPERTIES)
     public static final String MAVEN_HOME = "maven.home";
 
+    /**
+     * Maven version.
+     *
+     * @since 3.0.0
+     */
+    @Config(readOnly = true, source = Config.Source.SYSTEM_PROPERTIES)
+    public static final String MAVEN_VERSION = "maven.version";
+
+    /**
+     * Maven major version: contains the major segment of this Maven version.
+     *
+     * @since 4.0.0
+     */
+    @Config(readOnly = true, source = Config.Source.SYSTEM_PROPERTIES)
+    public static final String MAVEN_VERSION_MAJOR = "maven.version.major";
+
+    /**
+     * Maven minor version: contains the minor segment of this Maven version.
+     *
+     * @since 4.0.0
+     */
+    @Config(readOnly = true, source = Config.Source.SYSTEM_PROPERTIES)
+    public static final String MAVEN_VERSION_MINOR = "maven.version.minor";
+
+    /**
+     * Maven patch version: contains the patch segment of this Maven version.
+     *
+     * @since 4.0.0
+     */
+    @Config(readOnly = true, source = Config.Source.SYSTEM_PROPERTIES)
+    public static final String MAVEN_VERSION_PATCH = "maven.version.patch";
+
+    /**
+     * Maven snapshot: contains "true" if this Maven is a snapshot version.
+     *
+     * @since 4.0.0
+     */
+    @Config(readOnly = true, source = Config.Source.SYSTEM_PROPERTIES)
+    public static final String MAVEN_VERSION_SNAPSHOT = "maven.version.snapshot";
+
+    /**
+     * Maven build version: a human-readable string containing this Maven version, buildnumber, and time of its build.
+     *
+     * @since 3.0.0
+     */
+    @Config(readOnly = true, source = Config.Source.SYSTEM_PROPERTIES)
+    public static final String MAVEN_BUILD_VERSION = "maven.build.version";
+
     /**
      * Maven installation configuration directory.
      *

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/BaseParser.java

@@ -350,10 +350,26 @@ protected Map<String, String> populateSystemProperties(LocalContext context) {
         Properties buildProperties = CLIReportingUtils.getBuildProperties();
 
         String mavenVersion = buildProperties.getProperty(CLIReportingUtils.BUILD_VERSION_PROPERTY);
-        systemProperties.setProperty("maven.version", mavenVersion);
+        systemProperties.setProperty(Constants.MAVEN_VERSION, mavenVersion);
+
+        boolean snapshot = mavenVersion.endsWith("SNAPSHOT");
+        if (snapshot) {
+            mavenVersion = mavenVersion.substring(0, mavenVersion.length() - "SNAPSHOT".length());
+            if (mavenVersion.endsWith("-")) {
+                mavenVersion = mavenVersion.substring(0, mavenVersion.length() - 1);
+            }
+        }
+        String[] versionElements = mavenVersion.split("\\.");
+        if (versionElements.length != 3) {
+            throw new IllegalStateException("Maven version is expected to have 3 segments: '" + mavenVersion + "'");
+        }
+        systemProperties.setProperty(Constants.MAVEN_VERSION_MAJOR, versionElements[0]);
+        systemProperties.setProperty(Constants.MAVEN_VERSION_MINOR, versionElements[1]);
+        systemProperties.setProperty(Constants.MAVEN_VERSION_PATCH, versionElements[2]);
+        systemProperties.setProperty(Constants.MAVEN_VERSION_SNAPSHOT, Boolean.toString(snapshot));
 
         String mavenBuildVersion = CLIReportingUtils.createMavenVersionString(buildProperties);
-        systemProperties.setProperty("maven.build.version", mavenBuildVersion);
+        systemProperties.setProperty(Constants.MAVEN_BUILD_VERSION, mavenBuildVersion);
 
         Map<String, String> result = toMap(systemProperties);
         result.putAll(context.systemPropertiesOverrides);