Resolve correct version when application version is unset

extensions/container-image/deployment/src/main/java/io/quarkus/container/image/deployment/ContainerImageProcessor.java

@@ -1,6 +1,8 @@
 package io.quarkus.container.image.deployment;
 
 import static io.quarkus.container.image.deployment.util.EnablementUtil.*;
+import static io.quarkus.container.spi.ImageReference.DEFAULT_TAG;
+import static io.quarkus.deployment.builditem.ApplicationInfoBuildItem.UNSET_VALUE;
 
 import java.util.Collections;
 import java.util.Optional;
@@ -91,7 +93,11 @@ public void publishImageInfo(ApplicationInfoBuildItem app,
                     + effectiveGroup + "' and name '" + effectiveName + "' is invalid");
         }
 
-        final String effectiveTag = containerImageConfig.tag.orElse(app.getVersion());
+        String effectiveTag = containerImageConfig.tag.orElse(app.getVersion());
+        if (effectiveTag.equals(UNSET_VALUE)) {
+            effectiveTag = DEFAULT_TAG;
+        }
+
         if (!ImageReference.isValidTag(effectiveTag)) {
             throw new IllegalArgumentException("The supplied container-image tag '" + effectiveTag + "' is invalid");
         }

extensions/container-image/spi/src/main/java/io/quarkus/container/spi/ImageReference.java

@@ -26,8 +26,8 @@
  */
 public class ImageReference {
 
+    public static final String DEFAULT_TAG = "latest";
     private static final String DOCKER_HUB_REGISTRY = "registry-1.docker.io";
-    private static final String DEFAULT_TAG = "latest";
     private static final String LIBRARY_REPOSITORY_PREFIX = "library/";
 
     /**

extensions/kubernetes/vanilla/deployment/src/main/java/io/quarkus/kubernetes/deployment/KubernetesConfigUtil.java

@@ -1,5 +1,7 @@
 package io.quarkus.kubernetes.deployment;
 
+import static io.quarkus.container.spi.ImageReference.DEFAULT_TAG;
+import static io.quarkus.deployment.builditem.ApplicationInfoBuildItem.UNSET_VALUE;
 import static io.quarkus.kubernetes.deployment.Constants.DEPLOY;
 import static io.quarkus.kubernetes.deployment.Constants.DEPLOYMENT_TARGET;
 import static io.quarkus.kubernetes.deployment.Constants.DOCKER;
@@ -142,7 +144,9 @@ public static Map<String, Object> toMap(PlatformConfiguration... platformConfigu
         Arrays.stream(platformConfigurations).forEach(p -> {
             p.getPartOf().ifPresent(g -> quarkusPrefixed.put(DEKORATE_PREFIX + p.getConfigName() + ".part-of", g));
             p.getName().ifPresent(n -> quarkusPrefixed.put(DEKORATE_PREFIX + p.getConfigName() + ".name", n));
-            p.getVersion().ifPresent(v -> quarkusPrefixed.put(DEKORATE_PREFIX + p.getConfigName() + ".version", v));
+            p.getVersion()
+                    .map(v -> v.equals(UNSET_VALUE) ? DEFAULT_TAG : v)
+                    .ifPresent(v -> quarkusPrefixed.put(DEKORATE_PREFIX + p.getConfigName() + ".version", v));
         });
 
         Map<String, Object> unPrefixed = StreamSupport.stream(config.getPropertyNames().spliterator(), false)

integration-tests/kubernetes/quarkus-standard-way/src/test/java/io/quarkus/it/kubernetes/KubernetesWithDefaultApplicationVersionTest.java

@@ -0,0 +1,64 @@
+package io.quarkus.it.kubernetes;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.entry;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.fabric8.kubernetes.api.model.HasMetadata;
+import io.fabric8.kubernetes.api.model.apps.Deployment;
+import io.quarkus.deployment.builditem.ApplicationInfoBuildItem;
+import io.quarkus.test.ProdBuildResults;
+import io.quarkus.test.ProdModeTestResults;
+import io.quarkus.test.QuarkusProdModeTest;
+
+public class KubernetesWithDefaultApplicationVersionTest {
+
+    private static final String APP_NAME = "kubernetes-with-default-application-version";
+    private static final String EXPECTED_VERSION = "latest";
+
+    @RegisterExtension
+    static final QuarkusProdModeTest config = new QuarkusProdModeTest()
+            .withApplicationRoot((jar) -> jar.addClasses(GreetingResource.class))
+            .setApplicationName(APP_NAME)
+            // Simulates when there is no application version
+            .setApplicationVersion(ApplicationInfoBuildItem.UNSET_VALUE);
+
+    @ProdBuildResults
+    private ProdModeTestResults prodModeTestResults;
+
+    @Test
+    public void assertGeneratedResources() throws IOException {
+        final Path kubernetesDir = prodModeTestResults.getBuildDir().resolve("kubernetes");
+        assertThat(kubernetesDir)
+                .isDirectoryContaining(p -> p.getFileName().endsWith("kubernetes.json"))
+                .isDirectoryContaining(p -> p.getFileName().endsWith("kubernetes.yml"))
+                .satisfies(p -> assertThat(p.toFile().listFiles()).hasSize(2));
+        List<HasMetadata> kubernetesList = DeserializationUtil
+                .deserializeAsList(kubernetesDir.resolve("kubernetes.yml"));
+
+        assertThat(kubernetesList.get(0)).isInstanceOfSatisfying(Deployment.class, d -> {
+            assertThat(d.getMetadata()).satisfies(m -> {
+                assertThat(m.getName()).isEqualTo(APP_NAME);
+                assertThat(m.getLabels()).contains(entry("app.kubernetes.io/name", APP_NAME),
+                        entry("app.kubernetes.io/version", EXPECTED_VERSION));
+            });
+
+            assertThat(d.getSpec()).satisfies(deploymentSpec -> {
+                assertThat(deploymentSpec.getTemplate()).satisfies(t -> {
+                    assertThat(t.getSpec()).satisfies(podSpec -> {
+                        assertThat(podSpec.getContainers()).singleElement().satisfies(container -> {
+                            // then, we should use `latest` and not `<< unset >>` which gives an exception.
+                            assertThat(container.getImage()).endsWith(APP_NAME + ":" + EXPECTED_VERSION);
+                        });
+                    });
+                });
+            });
+        });
+    }
+}