Fixing #231 bug/feature: added "allowDowngrade", default "false", fixed range handling wrt downgrading

src/main/java/org/codehaus/mojo/versions/AbstractVersionsUpdaterMojo.java

@@ -289,6 +289,27 @@ public void execute()
      */
     protected ArtifactVersion findLatestVersion( Artifact artifact, VersionRange versionRange,
                                                  Boolean allowingSnapshots, boolean usePluginRepositories )
+            throws ArtifactMetadataRetrievalException, MojoExecutionException
+    {
+        return findLatestVersion( artifact, versionRange, allowingSnapshots, usePluginRepositories, false );
+    }
+
+    /**
+     * Finds the latest version of the specified artifact that matches the version range.
+     *
+     * @param artifact              The artifact.
+     * @param versionRange          The version range.
+     * @param allowingSnapshots     <code>null</code> for no override, otherwise the local override to apply.
+     * @param usePluginRepositories Use plugin repositories
+     * @return The latest version of the specified artifact that matches the specified version range or
+     * <code>null</code> if no matching version could be found.
+     * @throws ArtifactMetadataRetrievalException If the artifact metadata could not be found.
+     * @throws MojoExecutionException             if something goes wrong.
+     * @since 1.0-alpha-1
+     */
+    protected ArtifactVersion findLatestVersion( Artifact artifact, VersionRange versionRange,
+                                                 Boolean allowingSnapshots, boolean usePluginRepositories,
+                                                 boolean allowDowngrade )
         throws ArtifactMetadataRetrievalException, MojoExecutionException
     {
         boolean includeSnapshots = this.allowSnapshots;
@@ -301,7 +322,8 @@ protected ArtifactVersion findLatestVersion( Artifact artifact, VersionRange ver
             includeSnapshots = false;
         }
         final ArtifactVersions artifactVersions = getHelper().lookupArtifactVersions( artifact, usePluginRepositories );
-        return artifactVersions.getNewestVersion( versionRange, includeSnapshots );
+        return artifactVersions.getNewestVersion( versionRange, null, null, includeSnapshots,
+                true, true, allowDowngrade );
     }
 
     /**

src/main/java/org/codehaus/mojo/versions/UpdateParentMojo.java

@@ -65,6 +65,17 @@ public class UpdateParentMojo extends AbstractVersionsUpdaterMojo
     @Parameter( property = "forceUpdate", defaultValue = "false" )
     protected boolean forceUpdate = false;
 
+    /**
+     * <p>Whether to downgrade a snapshot dependency if <code>allowSnapshots</code> is <code>false</code>
+     * and there exists a version within the range fulfilling the criteria.</p>
+     * <p>Default <code>false</code></p>
+     *
+     * @since 2.12.0
+     */
+    @Parameter( property = "allowDowngrade",
+                defaultValue = "false" )
+    protected boolean allowDowngrade;
+
     // -------------------------- OTHER METHODS --------------------------
 
     /**
@@ -98,33 +109,40 @@ protected void update( ModifiedPomXMLEventReader pom )
             version = parentVersion;
         }
 
+        Dependency dependency = new Dependency();
+        dependency.setGroupId( getProject().getParent().getGroupId() );
+        dependency.setArtifactId( getProject().getParent().getArtifactId() );
+        dependency.setVersion( version );
+        dependency.setType( "pom" );
+        Artifact artifact = getHelper().createDependencyArtifact( dependency );
+
         VersionRange versionRange;
         try
         {
             versionRange = VersionRange.createFromVersionSpec( version );
+            if ( versionRange.getRecommendedVersion() != null )
+            {
+                versionRange = versionRange.restrict(
+                        VersionRange.createFromVersionSpec( "[" + versionRange.getRecommendedVersion() + ",)" ) );
+            }
         }
         catch ( InvalidVersionSpecificationException e )
         {
             throw new MojoExecutionException( "Invalid version range specification: " + version, e );
         }
 
-        Dependency dependency = new Dependency();
-        dependency.setGroupId( getProject().getParent().getGroupId() );
-        dependency.setArtifactId( getProject().getParent().getArtifactId() );
-        dependency.setVersion( version );
-        dependency.setType( "pom" );
-        Artifact artifact = getHelper().createDependencyArtifact( dependency );
-
         ArtifactVersion artifactVersion;
         try
         {
-            artifactVersion = findLatestVersion( artifact, versionRange, null, false );
+            artifactVersion = findLatestVersion( artifact, versionRange, false, true,
+                    allowDowngrade );
         }
         catch ( ArtifactMetadataRetrievalException e )
         {
             throw new MojoExecutionException( e.getMessage(), e );
         }
 
+
         if ( !shouldApplyUpdate( artifact, currentVersion, artifactVersion, forceUpdate ) )
         {
             return;

src/main/java/org/codehaus/mojo/versions/api/AbstractVersionDetails.java

@@ -19,8 +19,11 @@
  * under the License.
  */
 
+import java.util.Arrays;
+import java.util.Collections;
 import java.util.Set;
 import java.util.TreeSet;
+import java.util.stream.Collectors;
 
 import org.apache.maven.artifact.ArtifactUtils;
 import org.apache.maven.artifact.versioning.ArtifactVersion;
@@ -156,11 +159,26 @@ public final ArtifactVersion getNewestVersion( VersionRange versionRange, Artifa
                                                    ArtifactVersion upperBound, boolean includeSnapshots,
                                                    boolean includeLower, boolean includeUpper )
     {
-        ArtifactVersion latest = null;
+        return getNewestVersion( versionRange, lowerBound, upperBound, includeSnapshots, includeLower,
+                includeUpper, false );
+    }
+
+    private static <T> Iterable<T> reverse( T[] array )
+    {
+        return Arrays.stream( array ).sorted( Collections.reverseOrder() ).collect( Collectors.toList() );
+    }
+
+    public final ArtifactVersion getNewestVersion( VersionRange versionRange, ArtifactVersion lowerBound,
+                                                   ArtifactVersion upperBound, boolean includeSnapshots,
+                                                   boolean includeLower, boolean includeUpper, boolean allowDowngrade )
+    {
         final VersionComparator versionComparator = getVersionComparator();
-        for ( ArtifactVersion candidate : getVersions( includeSnapshots ) )
+        // reverse( getVersions( ... ) ) will contain versions sorted from latest to oldest,
+        // so we only need to find the first candidate fulfilling the criteria
+        for ( ArtifactVersion candidate : reverse( getVersions( includeSnapshots ) ) )
         {
-            if ( versionRange != null && !ArtifactVersions.isVersionInRange( candidate, versionRange ) )
+            if ( !allowDowngrade && versionRange != null
+                    && !ArtifactVersions.isVersionInRange( candidate, versionRange ) )
             {
                 continue;
             }
@@ -178,17 +196,9 @@ public final ArtifactVersion getNewestVersion( VersionRange versionRange, Artifa
             {
                 continue;
             }
-            if ( latest == null )
-            {
-                latest = candidate;
-            }
-            else if ( versionComparator.compare( latest, candidate ) < 0 )
-            {
-                latest = candidate;
-            }
-
+            return candidate;
         }
-        return latest;
+        return null;
     }
 
     public final ArtifactVersion getNewestVersion( ArtifactVersion lowerBound, ArtifactVersion upperBound,

src/main/java/org/codehaus/mojo/versions/api/ArtifactVersions.java

@@ -20,7 +20,6 @@
  */
 
 import java.util.List;
-import java.util.Set;
 import java.util.SortedSet;
 import java.util.TreeSet;
 
@@ -96,7 +95,8 @@ public static boolean isVersionInRange( ArtifactVersion version, VersionRange ra
         {
             return false;
         }
-        for ( Restriction r : ( (List<Restriction>) range.getRestrictions() ) )
+
+        for ( Restriction r : range.getRestrictions() )
         {
             if ( r.containsVersion( version ) )
             {
@@ -157,24 +157,10 @@ public String getArtifactId()
 
     public ArtifactVersion[] getVersions( boolean includeSnapshots )
     {
-        Set<ArtifactVersion> result;
-        if ( includeSnapshots )
-        {
-            result = versions;
-        }
-        else
-        {
-            result = new TreeSet<>( versionComparator );
-            for ( ArtifactVersion candidate : versions )
-            {
-                if ( ArtifactUtils.isSnapshot( candidate.toString() ) )
-                {
-                    continue;
-                }
-                result.add( candidate );
-            }
-        }
-        return result.toArray( new ArtifactVersion[0] );
+        return includeSnapshots
+                ? versions.toArray( new ArtifactVersion[0] )
+                : versions.stream().filter( v -> !ArtifactUtils.isSnapshot( v.toString() ) )
+                .toArray( ArtifactVersion[]::new );
     }
 
     public VersionComparator getVersionComparator()