change buildAndLoadNativePlatform to buildAndLoadSinglePlatform

Signed-off-by: Marsette Vona <martyvona@gmail.com>

Author: martyvona

Diff for: src/main/asciidoc/inc/build/_buildx.adoc

@@ -1,15 +1,21 @@
 
 [[build-buildx]]
 
-Buildx is enabled when there is a non-empty `<platform>` element inside the  `<buildx>` configuration.  Only the native platform
-is built and saved in the local image cache by the `build` goal.  All specified platforms are built and pushed into the remote
-repository by the `push` goal. This behavior is to prevent non-native images from tainting the local image cache.
+Buildx is enabled when there is a non-empty `<platform>` element inside the  `<buildx>` configuration.
 
-The local image cache cannot hold multi-architecture images nor can it have two platform specific images of the same name. The
-recommended `<buildx>` configuration is to specify all supported platforms, including the native platform, in the `<platforms>`
-element.  This allows local integration testing of the build image from the local cache. During install or deploy phase, the
-build machine will build and push all images to the registry.  Any downstream consumers, regardless of native architecture, will
-be able to use the multi-architecture image.
+The local image cache cannot hold multi-architecture images nor can it have two platform specific images of the same name.
+Thus the `build` goal will build and save a single-architecture image to the local image cache if possible:
+
+* If the `<platform>` element contains a single platform, that image will be built.
+* If the `<platform>` element contains more than one platform including the native platform, the native platform be used.
+* If the `<platform>` element contains more than one platform not including the native platform, no image will be built.
+
+These rules only apply to the image built and loaded into the local image cache with the `build` goal.  They do not apply to the `push` goal which will always build and push either a single-architecture or multi-architecture image with whatever platforms are specified in the `<platform>` element.
+
+The recommended `<buildx>` configuration is to specify all supported platforms, including the native platform, in the
+`<platform>` element.  This allows local integration testing of the build image from the local cache. During install or deploy
+phase, the build machine will build and push a multi-architecture image containing all specified platforms to the registry.
+Any downstream consumers, regardless of native architecture, will be able to use the multi-architecture image.
 
 The `<buildx>` element within `<build>` defines how to build multi-architecture images.
 
@@ -75,4 +81,4 @@ You can now override the built platforms using a command line define:
 [source,bash]
 ----
 mvn clean deploy -Ddocker.platforms=linux/amd64,linux/arm64
-----
+----

Diff for: src/main/java/io/fabric8/maven/docker/service/BuildXService.java

@@ -49,7 +49,7 @@ public BuildXService(DockerAccess dockerAccess, DockerAssemblyManager dockerAsse
     }
 
     public void build(ProjectPaths projectPaths, ImageConfiguration imageConfig, String  configuredRegistry, AuthConfig authConfig, File buildArchive) throws MojoExecutionException {
-        useBuilder(projectPaths, imageConfig,  configuredRegistry, authConfig, buildArchive, this::buildAndLoadNativePlatform);
+        useBuilder(projectPaths, imageConfig,  configuredRegistry, authConfig, buildArchive, this::buildAndLoadSinglePlatform);
     }
 
     public void push(ProjectPaths projectPaths, ImageConfiguration imageConfig, String configuredRegistry, AuthConfig authConfig) throws MojoExecutionException {
@@ -92,14 +92,16 @@ private void removeConfigJson(Path configJson) {
         }
     }
 
-    private void buildAndLoadNativePlatform(List<String> buildX, String builderName, BuildDirs buildDirs, ImageConfiguration imageConfig, String configuredRegistry, File buildArchive) throws MojoExecutionException {
+    private void buildAndLoadSinglePlatform(List<String> buildX, String builderName, BuildDirs buildDirs, ImageConfiguration imageConfig, String configuredRegistry, File buildArchive) throws MojoExecutionException {
         List<String> platforms = imageConfig.getBuildConfiguration().getBuildX().getPlatforms();
-        // build and load the native image by re-building, image should be cached and build should be quick
+        // build and load the single-platform image by re-building, image should be cached and build should be quick
         String nativePlatform = dockerAccess.getNativePlatform();
-        if (platforms.contains(nativePlatform)) {
+        if (platforms.size() == 1) {
+            buildX(buildX, builderName, buildDirs, imageConfig,  configuredRegistry, platforms, buildArchive, "--load");
+        } else if (platforms.contains(nativePlatform)) {
             buildX(buildX, builderName, buildDirs, imageConfig,  configuredRegistry, Collections.singletonList(nativePlatform), buildArchive, "--load");
         } else  {
-            logger.info("Native platform not specified, no image built");
+            logger.info("More than one platform specified not including native %s, no image built", nativePlatform);
         }
     }