Fail fast when attempting to run PCT against a release with a missing…

… or nondeterministic tag (#499)

src/main/java/org/jenkins/tools/test/hook/TagValidationHook.java

@@ -0,0 +1,27 @@
+package org.jenkins.tools.test.hook;
+
+import edu.umd.cs.findbugs.annotations.NonNull;
+import org.apache.maven.model.Model;
+import org.jenkins.tools.test.exception.PluginSourcesUnavailableException;
+import org.jenkins.tools.test.model.hook.BeforeCheckoutContext;
+import org.jenkins.tools.test.model.hook.PluginCompatTesterHookBeforeCheckout;
+import org.kohsuke.MetaInfServices;
+
+@MetaInfServices(PluginCompatTesterHookBeforeCheckout.class)
+public class TagValidationHook extends PluginCompatTesterHookBeforeCheckout {
+
+    @Override
+    public boolean check(@NonNull BeforeCheckoutContext context) {
+        return context.getConfig().getLocalCheckoutDir() == null;
+    }
+
+    @Override
+    public void action(@NonNull BeforeCheckoutContext context)
+            throws PluginSourcesUnavailableException {
+        Model model = context.getModel();
+        if (model.getScm().getTag() == null || model.getScm().getTag().equals("HEAD")) {
+            throw new PluginSourcesUnavailableException(
+                    "Failed to check out plugin sources for " + model.getVersion());
+        }
+    }
+}