Disable consumer POM flattening by default and add an opt-in feature by gnodet · Pull Request #11347 · apache/maven

gnodet · 2025-10-28T12:58:57Z

Summary

This PR introduces a new feature flag maven.consumer.pom.flatten that allows users to control whether consumer POMs are flattened by removing dependency management sections. This addresses dependency management inheritance scenarios and provides better control over consumer POM generation.

The consumer POM are NOT flattened anymore by default.

Changes

Core Implementation

Features.java: Added consumerPomFlatten() method to check the feature flag (defaults to false)
DefaultConsumerPomBuilder: Enhanced to conditionally apply flattening based on the flag
Constants.java: Added comprehensive documentation for the new feature flag and improved existing documentation
Dependency management control: When disabled, consumer POMs preserve dependency management like parent POMs

Integration Tests

Add ability to disable consumer POM flattening to preserve dependency management inheritance #11346-dependency-management-override: New comprehensive test demonstrating dependency management inheritance scenarios
Updated existing tests: Modified several integration tests to explicitly enable flattening where needed for backward compatibility

Feature Behavior

When `maven.consumer.pom.flatten=false` (Default)

Dependency management preserved: Consumer POMs keep dependency management sections like parent POMs
Inheritance enabled: Allows dependency management to be inherited by consumers
Non-POM projects: Processed without flattening dependency management
Backward compatible: Maintains existing dependency resolution behavior

When `maven.consumer.pom.flatten=true` (Opt-in)

Dependency management removed: Consumer POMs are flattened by removing dependency management
Transitive dependencies only: Only direct dependencies with transitive scopes are kept
Traditional behavior: Matches the previous Maven consumer POM behavior

Use Case Example

Consider this dependency scenario:

A 1.0 depends on B 1.0 and manages C to 1.2
B 2.0 depends on C 1.1
D depends on A 1.0 and manages B to 2.0

With maven.consumer.pom.flatten=false (default):

D gets C 1.2 (A's dependency management applies to D's transitive dependencies)
Consumer POMs preserve dependency management for inheritance

With maven.consumer.pom.flatten=true:

Traditional flattened consumer POM behavior
Dependency management sections are removed

Benefits

Better dependency management: Allows dependency management inheritance from consumer POMs
Flexible control: Users can choose between flattened and non-flattened consumer POMs
Improved transitive dependency control: Dependency management can properly control transitive dependency versions
Opt-in safety: Users can choose when to enable the previous flattening behavior

Fixes #11346 and addresses dependency management inheritance scenarios

This commit introduces a new feature flag 'maven.consumer.pom.flatten' that allows users to control whether consumer POMs are flattened or preserve their dependency management sections. Key changes: - Added MAVEN_CONSUMER_POM_FLATTEN constant in Constants.java - Added consumerPomFlatten() method in Features.java - Modified DefaultConsumerPomBuilder to conditionally apply flattening - Added integration test MavenITgh11346DependencyManagementOverrideTest - Renamed test resources to follow GitHub issue naming convention When maven.consumer.pom.flatten=false, consumer POMs preserve dependency management like parent POMs, enabling dependency management inheritance by consumers. This addresses scenarios where transitive dependency management is crucial for maintaining consistent dependency versions. The feature maintains backward compatibility with current default behavior (flattening enabled) while providing opt-in control for projects that need dependency management inheritance. Fixes apache#11346

@SInCE

- Add CONSUMER_POM_FLATTENING feature flag to Constants and Features - Update DefaultConsumerPomBuilder to respect flattening feature flag - Update integration tests to use proper @SInCE annotations and test ordering - Ensure consumer POM functionality works correctly with feature flag control This commit addresses consumer POM flattening control and ensures proper integration test coverage for the new functionality.

gnodet · 2025-10-29T17:11:47Z

@Bukama fwiw, if we go this way, this will require an update to https://maven.apache.org/whatsnewinmaven4.html#Consumer_POM and will require a 4.0.0-rc-5 release imho.

…pache#11347) This PR introduces a new feature flag maven.consumer.pom.flatten that allows users to control whether consumer POMs are flattened by removing dependency management sections. This addresses dependency management inheritance scenarios and provides better control over consumer POM generation. The consumer POM are NOT flattened anymore by default. Fixes apache#11346 (cherry picked from commit d213b58) # Conflicts: # api/maven-api-core/src/main/java/org/apache/maven/api/feature/Features.java # its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng5102MixinsTest.java # its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng8750NewScopesTest.java

gnodet · 2025-10-31T11:40:20Z

💚 All backports created successfully

Status	Branch	Result
✅	maven-4.0.x

Questions ?

Please refer to the Backport tool documentation

…pache#11347) This PR introduces a new feature flag maven.consumer.pom.flatten that allows users to control whether consumer POMs are flattened by removing dependency management sections. This addresses dependency management inheritance scenarios and provides better control over consumer POM generation. The consumer POM are NOT flattened anymore by default. Fixes apache#11346 (cherry picked from commit d213b58) # Conflicts: # api/maven-api-core/src/main/java/org/apache/maven/api/feature/Features.java # its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng5102MixinsTest.java # its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng8750NewScopesTest.java

…pache#11347) This PR introduces a new feature flag maven.consumer.pom.flatten that allows users to control whether consumer POMs are flattened by removing dependency management sections. This addresses dependency management inheritance scenarios and provides better control over consumer POM generation. The consumer POM are NOT flattened anymore by default. Fixes apache#11346 (cherry picked from commit d213b58) # Conflicts: # api/maven-api-core/src/main/java/org/apache/maven/api/feature/Features.java # its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng5102MixinsTest.java # its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng8750NewScopesTest.java # Conflicts: # its/core-it-suite/src/test/java/org/apache/maven/it/TestSuiteOrdering.java

…11347) (#11370) This PR introduces a new feature flag maven.consumer.pom.flatten that allows users to control whether consumer POMs are flattened by removing dependency management sections. This addresses dependency management inheritance scenarios and provides better control over consumer POM generation. The consumer POM are NOT flattened anymore by default. Fixes #11346 (cherry picked from commit d213b58) # Conflicts: # api/maven-api-core/src/main/java/org/apache/maven/api/feature/Features.java # its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng5102MixinsTest.java # its/core-it-suite/src/test/java/org/apache/maven/it/MavenITmng8750NewScopesTest.java # Conflicts: # its/core-it-suite/src/test/java/org/apache/maven/it/TestSuiteOrdering.java

jglick · 2025-11-20T13:42:00Z

api/maven-api-core/src/main/java/org/apache/maven/api/Constants.java

+     * When set to <code>true</code> (default), consumer POMs are flattened by removing
+     * dependency management and keeping only direct dependencies with transitive scopes.
+     * When set to <code>false</code>, consumer POMs preserve dependency management


This says true is the default, but the code and the PR description says false is the default…?

jglick · 2025-11-20T13:45:34Z

api/maven-api-core/src/main/java/org/apache/maven/api/Constants.java

    public static final String MAVEN_CONSUMER_POM = "maven.consumer.pom";

+    /**
+     * User property for controlling consumer POM flattening behavior.


Do I understand correctly that this can only be controlled by a -D flag? So you cannot easily enable flattening on specific modules. I guess you could add -D to .mvn/maven.config if you wished to enable flattening on all modules in a given reactor (such as one Git repository). Has any thought been given to controlling this mode based on a flag set in the POM itself (if that is even possible)? Or as a configuration option to the install mojo, etc.?

gnodet added enhancement New feature or request backport-to-4.0.x labels Oct 28, 2025

gnodet force-pushed the gh-11346-consumer-pom-flatten-control branch from ec3c886 to 67f11aa Compare October 28, 2025 22:16

gnodet added 7 commits October 29, 2025 10:12

Do not change the pom description

8f4587a

Fix ITs requiring flattening

5ee477e

Fix MavenITmng6957BuildConsumer

381776a

More fixes

42674fa

Remove unrelated javadoc change

fac3c7d

Remove unrelated javadoc change

2a98a59

gnodet added the breaking Pull requests that break existing features label Oct 29, 2025

gnodet requested a review from cstamas October 29, 2025 16:06

gnodet changed the title ~~Add consumer POM flattening control feature~~ Disable consumer POM flattening by default and add an opt-in feature Oct 29, 2025

cstamas approved these changes Oct 29, 2025

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gnodet merged commit d213b58 into apache:master Oct 31, 2025
37 of 38 checks passed

github-actions bot assigned gnodet Oct 31, 2025

github-actions bot added this to the 4.1.0 milestone Oct 31, 2025

gnodet mentioned this pull request Oct 31, 2025

[maven-4.0.x] Disable consumer POM flattening by default and add an opt-in feature (#11347) #11370

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jglick reviewed Nov 20, 2025

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Disable consumer POM flattening by default and add an opt-in feature#11347

Disable consumer POM flattening by default and add an opt-in feature#11347
gnodet merged 8 commits intoapache:masterfrom
gnodet:gh-11346-consumer-pom-flatten-control

gnodet commented Oct 28, 2025 •

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jglick Nov 20, 2025

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gnodet commented Oct 28, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

Changes

Core Implementation

Integration Tests

Feature Behavior

When maven.consumer.pom.flatten=false (Default)

When maven.consumer.pom.flatten=true (Opt-in)

Use Case Example

Benefits

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gnodet commented Oct 31, 2025

💚 All backports created successfully

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gnodet commented Oct 28, 2025 •

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When `maven.consumer.pom.flatten=false` (Default)

When `maven.consumer.pom.flatten=true` (Opt-in)

gnodet commented Oct 29, 2025 •

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