Fail on legacy config in modular projects #11702

ascheman · 2026-02-06T09:45:38Z

Summary

Legacy directories and resources that conflict with modular sources now trigger an ERROR instead of WARNING
Prevents silent loss of user-configured sources/resources
AC8 supersedes AC7 which originally used WARNING

Affected configurations in modular projects:

Explicit <sourceDirectory>/<testSourceDirectory> differing from defaults
Default src/main/java or src/test/java existing on filesystem
Explicit <resources>/<testResources> differing from Super POM defaults

Test plan

ProjectBuilderTest#testModularSourcesWithExplicitResourcesIssuesError passes
ProjectBuilderTest#testMixedSourcesModularMainClassicTest passes

Fixes #11701
See #11701 (comment)

🤖 Generated with Claude Code

In modular projects, legacy directories and resources that would be silently ignored now trigger an ERROR instead of WARNING: - Explicit <sourceDirectory>/<testSourceDirectory> differing from defaults - Default src/main/java or src/test/java existing on filesystem - Explicit <resources>/<testResources> differing from Super POM defaults This prevents silent loss of user-configured sources/resources. AC8 supersedes AC7 which originally used WARNING. Fixes apache#11701 See apache#11701 (comment) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ascheman · 2026-02-06T13:27:44Z

Reviews are welcome, in particular from @elharo and @desruisseaux - thanks!

elharo

not obvious to me how claude code is being used here. Generally I would not expect simply pointing it at this issue without human editing to produce correct results.

elharo · 2026-02-06T18:27:37Z

impl/maven-core/src/main/java/org/apache/maven/project/DefaultProjectBuilder.java

                 *
                 * Additionally, for modular projects, legacy directories are unconditionally
-                 * ignored because it is not clear how to dispatch their content between
+                 * rejected because it is not clear how to dispatch their content between


I don't think this is what we were looking for. The build fails completely, not simply a warning

Proposal: replace "A warning is emitted if …" by "The build fails if …".

elharo · 2026-02-06T18:29:25Z

impl/maven-core/src/main/java/org/apache/maven/project/DefaultProjectBuilder.java

         * </ul>
-         * Legacy directories are unconditionally ignored in modular projects because it is not clear
-         * how to dispatch their content between different modules.
+         * In both cases, the legacy directory conflicts with modular sources and must not be used.


not "and must not be used" but rather the complete build fails.

not "and must not be used" but rather the complete build fails.

Isn't what the next line below is saying?

elharo · 2026-02-06T18:30:36Z

impl/maven-core/src/main/java/org/apache/maven/project/SourceHandlingContext.java

-                            scopeId,
-                            sourcesConfig);
+                    String message = String.format(
+                            "Legacy %s element must not be used because %s resources are configured via %s in <sources>.",


must not be used --> cannot be used in modular projects

elharo · 2026-02-06T18:30:47Z

impl/maven-core/src/main/java/org/apache/maven/project/SourceHandlingContext.java

                if (hasExplicitLegacyResources(resources, scopeId)) {
                    String message = "Legacy " + legacyElement
-                            + " element is ignored because modular sources are configured. "
+                            + " element must not be used because modular sources are configured. "


must not --> cannot

elharo · 2026-02-06T18:31:10Z

impl/maven-core/src/main/java/org/apache/maven/project/SourceHandlingContext.java

-                            scopeId,
-                            sourcesConfig);
+                    String message = String.format(
+                            "Legacy %s element must not be used because %s resources are configured via %s in <sources>.",


elharo · 2026-02-06T18:31:59Z

impl/maven-core/src/test/java/org/apache/maven/project/ProjectBuilderTest.java

-     * Acceptance Criterion: AC2 (unified source tracking for all lang/scope combinations)
+     * Acceptance Criteria:
+     * - AC2 (unified source tracking for all lang/scope combinations)
+     * - AC8 (legacy directories error - supersedes AC7 which originally used WARNING)


not sure how the AC are being used, but shouldn't AC7 be changed rather than superseded?

elharo · 2026-02-06T18:32:48Z

impl/maven-core/src/test/java/org/apache/maven/project/ProjectBuilderTest.java

-     * In modular projects, legacy directories are unconditionally ignored because it is not clear
-     * how to dispatch their content between different modules. A warning is emitted if these
-     * properties are explicitly set (differ from Super POM defaults).
+     * In modular projects, legacy directories must not occur because it is not clear


In modular projects, legacy directories must not occur --> Legacy directories cannot be used in modular projects

- Use "cannot" instead of "must not" in error messages - Update Javadoc: "The build fails" instead of "A warning is emitted"

elharo · 2026-02-10T12:29:20Z

impl/maven-core/src/main/java/org/apache/maven/project/DefaultProjectBuilder.java

                /*
                 * `sourceDirectory`, `testSourceDirectory` and `scriptSourceDirectory`
-                 * are ignored if the POM file contains at least one enabled <source> element
+                 * are not used if the POM file contains at least one enabled <source> element


again here don't we need the build to fail in this case?

Yes, I think that it is a change that was forgot in the documentation. The actual code raises an error as I read it.

Looking at this more closely, I think we've uncovered an inconsistency:

Current behavior:

Resources (<resources>/<testResources>): ERROR for both modular and classic projects when <sources> conflicts with legacy config (handled in SourceHandlingContext)

Source directories (<sourceDirectory>/<testSourceDirectory>): ERROR only for modular projects, silently skipped for classic projects

AC8 specifically scopes the error behavior to modular projects:

"Legacy directories trigger ERROR in modular projects"

This leaves classic projects with <sources> in an inconsistent state - their legacy resources cause an error, but legacy source directories are silently ignored.

Proposal: If @desruisseaux and @elharo agree, we could add:

AC9: For classic (non-modular) projects, legacy <sourceDirectory> and <testSourceDirectory> also trigger an ERROR when <sources> elements are configured for the same scope/language. This ensures consistency with resource handling and prevents silent configuration loss.

Should I create a follow-up issue for this, or would you prefer to extend the current PR?

Thanks for spotting that. I suggest to extend the current pull request if this is fine for you.

I'm not fully up to speed on all of this. I try to avoid modules. However, the general principle I would follow is that if the client project contains code or resources that the developer likely intended to be included and for some reason we are not including it, then Maven should hard fail the build.

If you agree, we could even simplify AC8 (and won't need a new AC9) as the existence of <sources> would then mean that any existence of legacy configurations should fail the build (independent of the existence of modules):

Revised AC8 Definition

AC8 (Legacy directory validation for projects using <sources>):

For any project using <sources>, the build fails with an ERROR if:

An explicit legacy directory configuration (<sourceDirectory> or <testSourceDirectory>) exists, OR

A <source> element specifies a custom <directory> AND the default legacy directory (e.g., src/main/java) exists physically on the filesystem

Key Point

The presence of <sources> is the trigger, not whether the project is modular or non-modular.

When a project uses <sources>, it opts into the Maven 4.1.0 source model entirely. Legacy directory configurations become invalid regardless of modularity.

Seems very good to me.

Seems very good to me.

OK, I will implement it this way then.

And yet another use case: Assume we have the following structure:

<build> <sources> <source> <scope>main</scope> <lang>resources</lang> <directory>src/main/custom-resources</directory> </source>  </sources> </build>

I would think in a legacy directory structure but 4.1.0-model configuration (but no modules), the legacy directories should still be (implicitly) used, unless explicitly overridden. What do you think, @desruisseaux ?

Said that: the classic values were defined as default by the super POM. Do we expect similar defaults by the super POM for <sources> as well (currently not configured)?

Yes, when the <module> element is not used I think that we can continue to use the legacy directories.

Regarding the default values specified in the super POM, I suggest to not do any change for now (we may revisit in some future version). The default values of <source> elements are implemented in Java code for now, and they are designed in such a way that, when no <module> element is used, they match the default values of the super POM.

ascheman force-pushed the bugfix/11701-fail-on-modular-sources-with-legacy-dirs branch from 70a7358 to c1b431b Compare February 6, 2026 10:05

ascheman marked this pull request as ready for review February 6, 2026 13:27

elharo requested changes Feb 6, 2026

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Address review feedback on wording

a89fc07

- Use "cannot" instead of "must not" in error messages - Update Javadoc: "The build fails" instead of "A warning is emitted"

desruisseaux approved these changes Feb 8, 2026

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elharo requested changes Feb 10, 2026

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ascheman mentioned this pull request Feb 11, 2026

Legacy resources in modular build should fail #11701

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Fail on legacy config in modular projects #11702

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Fail on legacy config in modular projects #11702

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ascheman commented Feb 6, 2026

Summary

Test plan

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ascheman commented Feb 6, 2026

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Revised AC8 Definition

Key Point

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ascheman Feb 12, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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ascheman Feb 12, 2026 •

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