Add module-aware resource handling for modular sources

impl/maven-core/src/test/projects/project-builder/classic-sources-with-explicit-legacy/pom.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>classic-sources-explicit-legacy-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <sources>
+            <!-- Classic (non-modular) source - no module attribute -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <directory>src/main/java</directory>
+            </source>
+            <source>
+                <scope>test</scope>
+                <lang>java</lang>
+                <directory>src/test/java</directory>
+            </source>
+        </sources>
+        <!-- Explicit legacy directories that conflict with <sources> - should trigger ERROR (AC9) -->
+        <sourceDirectory>src/legacy/main/java</sourceDirectory>
+        <testSourceDirectory>src/legacy/test/java</testSourceDirectory>
+    </build>
+</project>

impl/maven-core/src/test/projects/project-builder/duplicate-enabled-sources/pom.xml

@@ -0,0 +1,64 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Tests duplicate handling with the enabled discriminator.
+
+  Expected behavior:
+  - Same (lang, scope, module, directory) with enabled=true appearing twice should trigger a WARNING
+  - Same identity with enabled=false is harmless (explicitly disabled)
+  - First enabled=true entry wins and defines the effective configuration
+-->
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>duplicate-enabled-sources-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <sources>
+            <!-- First enabled source for module (this should win) -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>com.example.dup</module>
+                <enabled>true</enabled>
+            </source>
+            <!-- Duplicate enabled source for same module (implicit directory) - should trigger WARNING -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>com.example.dup</module>
+                <enabled>true</enabled>
+            </source>
+            <!-- Disabled source for same module - this is harmless -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>com.example.dup</module>
+                <enabled>false</enabled>
+            </source>
+            <!-- Different module - should be added normally -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>com.example.other</module>
+            </source>
+            <!-- Test scope duplicate scenario -->
+            <source>
+                <scope>test</scope>
+                <lang>java</lang>
+                <module>com.example.dup</module>
+                <enabled>true</enabled>
+            </source>
+            <source>
+                <scope>test</scope>
+                <lang>java</lang>
+                <module>com.example.dup</module>
+                <enabled>true</enabled>
+            </source>
+        </sources>
+    </build>
+</project>

impl/maven-core/src/test/projects/project-builder/modular-java-with-explicit-source-dir/pom.xml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Tests AC8 scenario 2: Modular project with Java in <sources> for MAIN scope
+  and explicit legacy <sourceDirectory> that differs from default.
+
+  Expected behavior:
+  - ERROR for <sourceDirectory> (modular project, <sources> has Java for MAIN)
+  - Modular Java sources are used, not legacy
+-->
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>modular-java-with-explicit-source-dir-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <!-- Explicit legacy sourceDirectory - triggers ERROR (AC8) -->
+        <sourceDirectory>src/custom/main/java</sourceDirectory>
+
+        <sources>
+            <!-- Modular main Java source -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>org.foo.app</module>
+            </source>
+        </sources>
+    </build>
+</project>

impl/maven-core/src/test/projects/project-builder/modular-no-test-java-with-explicit-test-source-dir/pom.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Tests AC8 scenario 5: Modular project with NO Java in <sources> for TEST scope
+  and explicit legacy <testSourceDirectory> that differs from default.
+
+  Expected behavior:
+  - ERROR for <testSourceDirectory> (modular project, no AC9 fallback)
+  - No test Java sources (legacy rejected, none in <sources>)
+-->
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>modular-no-test-java-with-explicit-test-source-dir-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <!-- Explicit legacy testSourceDirectory - triggers ERROR (AC8, no AC9 fallback for modular) -->
+        <testSourceDirectory>src/custom/test/java</testSourceDirectory>
+
+        <sources>
+            <!-- Modular main Java sources only - no test Java -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>org.foo.app</module>
+            </source>
+            <!-- No test Java sources in <sources> -->
+        </sources>
+    </build>
+</project>

impl/maven-core/src/test/projects/project-builder/modular-resources-only-with-physical-legacy/pom.xml

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Tests AC8: Modular project with only resources in <sources> and physical default legacy directory.
+
+  Expected behavior:
+  - Modular resources from <sources> are processed
+  - Physical src/main/java and src/test/java directories exist but would be ignored
+  - ERROR is raised because physical default directories exist (AC8 physical presence check)
+  - Unlike non-modular projects (AC9), modular projects cannot use legacy directories as fallback
+
+  Note: The src/main/java and src/test/java directories are created empty to trigger
+  the physical presence check.
+-->
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>modular-resources-only-with-physical-legacy-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <!-- No explicit sourceDirectory/testSourceDirectory - uses Super POM defaults -->
+        <!-- But physical src/main/java and src/test/java directories exist -->
+
+        <sources>
+            <!-- Only modular resources - no Java sources -->
+            <source>
+                <scope>main</scope>
+                <lang>resources</lang>
+                <module>org.example.app</module>
+            </source>
+            <source>
+                <scope>test</scope>
+                <lang>resources</lang>
+                <module>org.example.app</module>
+            </source>
+        </sources>
+    </build>
+</project>

impl/maven-core/src/test/projects/project-builder/modular-sources-with-explicit-resources/pom.xml

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>modular-sources-explicit-resources-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <sources>
+            <!-- Module A - main java -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>org.foo.moduleA</module>
+            </source>
+            <!-- Module B - main java -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>org.foo.moduleB</module>
+            </source>
+        </sources>
+        <!-- Legacy resources are IGNORED when modular sources are configured - a warning should be issued -->
+        <resources>
+            <resource>
+                <directory>src/custom/resources</directory>
+            </resource>
+        </resources>
+        <testResources>
+            <testResource>
+                <directory>src/custom/test-resources</directory>
+            </testResource>
+        </testResources>
+    </build>
+</project>

impl/maven-core/src/test/projects/project-builder/modular-sources/pom.xml

@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>modular-sources-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <sources>
+            <!-- Module A - main java -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>org.foo.moduleA</module>
+            </source>
+            <!-- Module A - test java -->
+            <source>
+                <scope>test</scope>
+                <lang>java</lang>
+                <module>org.foo.moduleA</module>
+            </source>
+            <!-- Module B - main java -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>org.foo.moduleB</module>
+            </source>
+            <!-- Module B - test java -->
+            <source>
+                <scope>test</scope>
+                <lang>java</lang>
+                <module>org.foo.moduleB</module>
+            </source>
+        </sources>
+    </build>
+</project>

impl/maven-core/src/test/projects/project-builder/modular-with-physical-legacy/pom.xml

@@ -0,0 +1,41 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Tests AC8: Modular project with physical default legacy directory.
+
+  Expected behavior:
+  - Modular Java sources from <sources> are processed
+  - Physical src/main/java and src/test/java directories exist but would be ignored
+  - ERROR is raised because physical default directories exist (AC8 physical presence check)
+
+  Note: The src/main/java and src/test/java directories are created empty to trigger
+  the physical presence check.
+-->
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>modular-with-physical-legacy-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <!-- No explicit sourceDirectory/testSourceDirectory - uses Super POM defaults -->
+        <!-- But physical src/main/java and src/test/java directories exist -->
+
+        <sources>
+            <!-- Modular Java sources -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>org.example.app</module>
+            </source>
+            <source>
+                <scope>test</scope>
+                <lang>java</lang>
+                <module>org.example.app</module>
+            </source>
+        </sources>
+    </build>
+</project>

impl/maven-core/src/test/projects/project-builder/multiple-directories-same-module/pom.xml

@@ -0,0 +1,51 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Tests multiple source directories for the same (lang, scope, module) combination.
+  This is a valid use case: users may have generated sources alongside regular sources.
+
+  Expected behavior:
+  - Both directories should be added as source roots
+  - Both should have the same module attribute
+  - The compiler will merge sources from both directories into the same output
+-->
+<project xmlns="http://maven.apache.org/POM/4.1.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+    <modelVersion>4.1.0</modelVersion>
+
+    <groupId>org.apache.maven.tests</groupId>
+    <artifactId>multiple-directories-same-module-test</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <build>
+        <sources>
+            <!-- Primary Java source for module (uses implicit directory) -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>com.example.app</module>
+            </source>
+            <!-- Generated sources for the same module (explicit directory) -->
+            <source>
+                <scope>main</scope>
+                <lang>java</lang>
+                <module>com.example.app</module>
+                <directory>target/generated-sources/com.example.app/java</directory>
+            </source>
+            <!-- Test sources for module -->
+            <source>
+                <scope>test</scope>
+                <lang>java</lang>
+                <module>com.example.app</module>
+            </source>
+            <!-- Generated test sources -->
+            <source>
+                <scope>test</scope>
+                <lang>java</lang>
+                <module>com.example.app</module>
+                <directory>target/generated-test-sources/com.example.app/java</directory>
+            </source>
+        </sources>
+    </build>
+</project>