MNG-7884: Add --print-build-order option to print reactor build order without building

api/maven-api-cli/src/main/java/org/apache/maven/api/cli/mvn/MavenOptions.java

@@ -102,6 +102,15 @@ public interface MavenOptions extends Options {
     @Nonnull
     Optional<Boolean> failFast();
 
+    /**
+     * Requests that Maven print the reactor build order and exit, without executing the build.
+     *
+     * @return an {@link Optional} containing true if the reactor build order should be printed
+     *         and the build skipped, false if not, or empty if not specified.
+     */
+    @Nonnull
+    Optional<Boolean> printBuildOrder();
+
     /**
      * Indicates whether Maven should run all builds but defer error reporting to the end.
      *

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvn/CommonsCliMavenOptions.java

@@ -102,6 +102,14 @@ public Optional<Boolean> failFast() {
         return Optional.empty();
     }
 
+    @Override
+    public Optional<Boolean> printBuildOrder() {
+        if (commandLine.hasOption(CLIManager.PRINT_BUILD_ORDER)) {
+            return Optional.of(Boolean.TRUE);
+        }
+        return Optional.empty();
+    }
+
     @Override
     public Optional<Boolean> failAtEnd() {
         if (commandLine.hasOption(CLIManager.FAIL_AT_END)) {
@@ -238,6 +246,7 @@ protected static class CLIManager extends CommonsCliOptions.CLIManager {
         public static final String CHECKSUM_FAILURE_POLICY = "C";
         public static final String CHECKSUM_WARNING_POLICY = "c";
         public static final String FAIL_FAST = "ff";
+        public static final String PRINT_BUILD_ORDER = "pbo";
         public static final String FAIL_AT_END = "fae";
         public static final String FAIL_NEVER = "fn";
         public static final String RESUME = "r";
@@ -360,6 +369,10 @@ protected void prepareOptions(org.apache.commons.cli.Options options) {
                     .desc(
                             "If set, Maven will load command line options from the specified file and merge with CLI specified ones.")
                     .get());
+            options.addOption(Option.builder(PRINT_BUILD_ORDER)
+                    .longOpt("print-build-order")
+                    .desc("Print the reactor build order and exit without building")
+                    .get());
         }
     }
 }

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvn/LayeredMavenOptions.java

@@ -89,6 +89,11 @@ public Optional<Boolean> failFast() {
         return returnFirstPresentOrEmpty(MavenOptions::failFast);
     }
 
+    @Override
+    public Optional<Boolean> printBuildOrder() {
+        return returnFirstPresentOrEmpty(MavenOptions::printBuildOrder);
+    }
+
     @Override
     public Optional<Boolean> failAtEnd() {
         return returnFirstPresentOrEmpty(MavenOptions::failAtEnd);