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

[AbdelHamdyGhanem]

What

Adds a new CLI flag --print-build-order (short form -pbo) that prints the reactor's
topologically-sorted build order and exits, without executing the build lifecycle.

Why

Closes #8733 (MNG-7884). This is useful for analyzing a multi-module build's execution
order without committing to a full build — e.g. in CI diagnostics, scripting, or simply
understanding module interdependencies in large reactors.

How

• Added printBuildOrder() to the MavenOptions API interface (api/maven-api-cli).
• Implemented option parsing in CommonsCliMavenOptions (new PRINT_BUILD_ORDER constant
  and Option registration in the nested CLIManager).
• Added the corresponding merge-layer override in LayeredMavenOptions.
• (In progress) Wiring the parsed value into MavenExecutionRequest via
  MavenInvoker.populateRequest(...).
• (In progress) Adding isPrintBuildOrder()/setPrintBuildOrder(boolean) to
  MavenExecutionRequest/DefaultMavenExecutionRequest.
• (In progress) In DefaultMaven.doExecute(...), after the authoritative buildGraph(session)
  call succeeds, checking the flag and — if set — printing the sorted project list and
  returning a clean success result before lifecycleStarter.execute(session) runs.

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[gnodet]

Review: MNG-7884 — Add --print-build-order option

Verdict: Incomplete — needs more work before merge

The PR adds CLI option parsing for --print-build-order / -pbo across the three expected files in the options layer (MavenOptions.java, CommonsCliMavenOptions.java, LayeredMavenOptions.java). The option name is clear, the short code -pbo doesn't conflict with existing options, and it follows Maven CLI conventions.

However, the feature is not yet functional — the PR description itself notes several pieces are "(In progress)":

Findings

1. Feature not wired up (high)
The option is parsed but never consumed. There is no code in MavenInvoker, MavenExecutionRequest, or DefaultMaven.doExecute() that reads printBuildOrder() and acts on it. Running mvn --print-build-order would accept the flag but silently do nothing.

→ The PR should either be marked as draft until wiring is complete, or include the remaining implementation.

2. Missing @Nonnull annotation (medium)
Every other Optional<...> method in MavenOptions.java has @Nonnull on the return type. The new printBuildOrder() omits it.

3. No tests (medium)
No unit or integration tests are included. At minimum, a parsing test for CommonsCliMavenOptions confirming -pbo / --print-build-order is correctly parsed would be expected.

4. Javadoc @return style (low)
The @return tag deviates from the established pattern. Other methods use:

an {@link Optional} containing true if ..., false if ..., or empty if not specified

The new method uses a different format.

Positive notes

• The JIRA issue MNG-7884 is valid and the feature is genuinely wanted
• Option naming is good and conflict-free
• Placement in the options interface is reasonable

This review was generated by an AI agent and may contain inaccuracies. Please verify all suggestions before applying.

Claude Code on behalf of Guillaume Nodet

[gnodet]

Re-review after new commits

Thanks for addressing the feedback! Two items fixed:

• ✅ @nonnull annotation — added, now consistent with all other Optional<...> methods
• ✅ Javadoc @return style — now matches the established pattern

Still outstanding:

1. Feature not wired up (high) — the option is parsed but still never consumed anywhere in the execution path. mvn --print-build-order would accept the flag but silently do nothing.
2. No tests (medium) — at minimum a parsing test for CommonsCliMavenOptions would be expected.

Consider marking as draft until the wiring (into MavenExecutionRequest / DefaultMaven.doExecute()) is complete, or adding the remaining implementation in follow-up commits.

This review was generated by an AI agent and may contain inaccuracies. Please verify all suggestions before applying.

Claude Code on behalf of Guillaume Nodet