HADOOP-13852 hadoop build to allow hadoop version property to be explicitly set. Contriibuted by Steve Loughran

BUILDING.txt

@@ -390,7 +390,7 @@ http://www.zlib.net/
 ----------------------------------------------------------------------------------
 Building distributions:
 
- * Build distribution with native code    : mvn package [-Pdist][-Pdocs][-Psrc][-Dtar]
+ * Build distribution with native code    : mvn package [-Pdist][-Pdocs][-Psrc][-Dtar][-Dmaven.javadoc.skip=true]
 
 ----------------------------------------------------------------------------------
 Running compatibility checks with checkcompatibility.py
@@ -402,3 +402,12 @@ managers to compare the compatibility of a previous and current release.
 As an example, this invocation will check the compatibility of interfaces annotated as Public or LimitedPrivate:
 
 ./dev-support/bin/checkcompatibility.py --annotation org.apache.hadoop.classification.InterfaceAudience.Public --annotation org.apache.hadoop.classification.InterfaceAudience.LimitedPrivate --include "hadoop.*" branch-2.7.2 trunk
+
+----------------------------------------------------------------------------------
+Changing the Hadoop version declared returned by VersionInfo
+
+If for compatibility reasons the version of Hadoop has to be declared as a 2.x release in the information returned by
+org.apache.hadoop.util.VersionInfo, set the property declared.hadoop.version to the desired version.
+For example: mvn package -Pdist -Ddeclared.hadoop.version=2.11
+
+If unset, the project version declared in the POM file is used.

hadoop-common-project/hadoop-common/src/main/resources/common-version-info.properties

@@ -16,11 +16,11 @@
 # limitations under the License.
 #
 
-version=${pom.version}
+version=${declared.hadoop.version}
 revision=${version-info.scm.commit}
 branch=${version-info.scm.branch}
 user=${user.name}
 date=${version-info.build.time}
 url=${version-info.scm.uri}
 srcChecksum=${version-info.source.md5}
-protocVersion=${protobuf.version}
+protocVersion=${protobuf.version}

hadoop-project/pom.xml

@@ -126,6 +126,9 @@
     <native-maven-plugin.version>1.0-alpha-8</native-maven-plugin.version>
     <surefire.fork.timeout>900</surefire.fork.timeout>
     <aws-java-sdk.version>1.11.45</aws-java-sdk.version>
+    <!-- the version of Hadoop declared in the version resources; can be overridden
+    so that Hadoop 3.x can declare itself a 2.x artifact. -->
+    <declared.hadoop.version>${pom.version}</declared.hadoop.version>
   </properties>
 
   <dependencyManagement>

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/resources/yarn-version-info.properties

@@ -16,7 +16,7 @@
 # limitations under the License.
 #
 
-version=${pom.version}
+version=${declared.hadoop.version}
 revision=${version-info.scm.commit}
 branch=${version-info.scm.branch}
 user=${user.name}