[MNG-7893] Fix exception loading superpom with invalid modelVersion (#1290)

Even though this should not be supported, Maven 3.x is always using the 4.0.0 superpom.  So if the version is not a supported model version, simply use 4.0.0.  Any invalid value will be later verified by the model validator and eventually throw a meaninful exception.

maven-model-builder/src/main/java/org/apache/maven/model/building/DefaultModelBuilder.java

@@ -87,6 +87,7 @@ import org.apache.maven.model.resolution.ModelResolver;
 import org.apache.maven.model.resolution.UnresolvableModelException;
 import org.apache.maven.model.resolution.WorkspaceModelResolver;
 import org.apache.maven.model.superpom.SuperPomProvider;
+import org.apache.maven.model.validation.DefaultModelValidator;
 import org.apache.maven.model.validation.ModelValidator;
 import org.codehaus.plexus.interpolation.InterpolationException;
 import org.codehaus.plexus.interpolation.MapBasedValueSource;
@@ -747,6 +748,12 @@ public class DefaultModelBuilder implements ModelBuilder {
 
         ModelData resultData = new ModelData(request.getModelSource(), inputModel);
         String superModelVersion = inputModel.getModelVersion() != null ? inputModel.getModelVersion() : "4.0.0";
+        if (!DefaultModelValidator.VALID_MODEL_VERSIONS.contains(superModelVersion)) {
+            // Maven 3.x is always using 4.0.0 version to load the supermodel, so
+            // do the same when loading a dependency.  The model validator will also
+            // check that field later.
+            superModelVersion = "4.0.0";
+        }
         ModelData superData = new ModelData(null, getSuperModel(superModelVersion));
 
         // profile activation

maven-model-builder/src/main/java/org/apache/maven/model/validation/DefaultModelValidator.java

@@ -24,6 +24,7 @@ import javax.inject.Singleton;
 
 import java.io.File;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -67,6 +68,9 @@ import org.apache.maven.model.v4.MavenModelVersion;
 @Singleton
 public class DefaultModelValidator implements ModelValidator {
 
+    public static final List<String> VALID_MODEL_VERSIONS =
+            Collections.unmodifiableList(Arrays.asList("4.0.0", "4.1.0"));
+
     private static final Pattern EXPRESSION_NAME_PATTERN = Pattern.compile("\\$\\{(.+?)}");
     private static final Pattern EXPRESSION_PROJECT_NAME_PATTERN = Pattern.compile("\\$\\{(project.+?)}");
 
@@ -147,7 +151,7 @@ public class DefaultModelValidator implements ModelValidator {
             // The file pom may not contain the modelVersion yet, as it may be set later by the
             // ModelVersionXMLFilter.
             if (m.getModelVersion() != null && !m.getModelVersion().isEmpty()) {
-                validateModelVersion(problems, m.getModelVersion(), m, "4.0.0", "4.1.0");
+                validateModelVersion(problems, m.getModelVersion(), m, VALID_MODEL_VERSIONS);
             }
 
             validateStringNoExpression("groupId", problems, Severity.WARNING, Version.V20, m.getGroupId(), m);
@@ -261,7 +265,7 @@ public class DefaultModelValidator implements ModelValidator {
         // models without a version starting with 3.4.
         validateStringNotEmpty("modelVersion", problems, Severity.ERROR, Version.V20, m.getModelVersion(), m);
 
-        validateModelVersion(problems, m.getModelVersion(), m, "4.0.0", "4.1.0");
+        validateModelVersion(problems, m.getModelVersion(), m, VALID_MODEL_VERSIONS);
 
         String minVersion = new MavenModelVersion().getModelVersion(m);
         if (m.getModelVersion() != null && compareModelVersions(minVersion, m.getModelVersion()) > 0) {
@@ -1478,14 +1482,12 @@ public class DefaultModelValidator implements ModelValidator {
 
     @SuppressWarnings("checkstyle:parameternumber")
     private boolean validateModelVersion(
-            ModelProblemCollector problems, String string, InputLocationTracker tracker, String... validVersions) {
+            ModelProblemCollector problems, String string, InputLocationTracker tracker, List<String> validVersions) {
         if (string == null || string.length() <= 0) {
             return true;
         }
 
-        List<String> values = Arrays.asList(validVersions);
+        if (validVersions.contains(string)) {
-
-        if (values.contains(string)) {
             return true;
         }
 
@@ -1504,8 +1506,8 @@ public class DefaultModelValidator implements ModelValidator {
                     Version.V20,
                     "modelVersion",
                     null,
-                    "of '" + string + "' is newer than the versions supported by this version of Maven: " + values
+                    "of '" + string + "' is newer than the versions supported by this version of Maven: "
-                            + ". Building this project requires a newer version of Maven.",
+                            + validVersions + ". Building this project requires a newer version of Maven.",
                     tracker);
 
         } else if (olderThanAll) {
@@ -1516,8 +1518,8 @@ public class DefaultModelValidator implements ModelValidator {
                     Version.V20,
                     "modelVersion",
                     null,
-                    "of '" + string + "' is older than the versions supported by this version of Maven: " + values
+                    "of '" + string + "' is older than the versions supported by this version of Maven: "
-                            + ". Building this project requires an older version of Maven.",
+                            + validVersions + ". Building this project requires an older version of Maven.",
                     tracker);
 
         } else {
@@ -1527,7 +1529,7 @@ public class DefaultModelValidator implements ModelValidator {
                     Version.V20,
                     "modelVersion",
                     null,
-                    "must be one of " + values + " but is '" + string + "'.",
+                    "must be one of " + validVersions + " but is '" + string + "'.",
                     tracker);
         }