[MCOMPILER-374] Unable to compile MR-JAR code against older directories when module-info.java is present

src/it/MCOMPILER-374_mrjar/invoker.properties

@@ -0,0 +1,18 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+invoker.java.version = 11+

src/it/MCOMPILER-374_mrjar/pom.xml

@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.maven.bug</groupId>
+  <artifactId>mcompiler374</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>@project.version@</version>
+        <configuration>
+          <release>8</release>
+          <testRelease>11</testRelease>
+        </configuration>
+        <executions>
+          <execution>
+            <id>java9</id>
+            <phase>compile</phase>
+            <goals>
+              <goal>compile</goal>
+            </goals>
+            <configuration>
+              <release>9</release>
+              <compileSourceRoots>
+                <compileSourceRoot>${project.basedir}/src/main/java9</compileSourceRoot>
+              </compileSourceRoots>
+              <multiReleaseOutput>true</multiReleaseOutput>
+            </configuration>
+          </execution>
+          <execution>
+            <id>java11</id>
+            <phase>compile</phase>
+            <goals>
+              <goal>compile</goal>
+            </goals>
+            <configuration>
+              <release>11</release>
+              <compileSourceRoots>
+                <compileSourceRoot>${project.basedir}/src/main/java11</compileSourceRoot>
+              </compileSourceRoots>
+              <multiReleaseOutput>true</multiReleaseOutput>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/MCOMPILER-374_mrjar/src/main/java/org/maven/bug/A.java

@@ -0,0 +1,25 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.maven.bug;
+
+public class A {
+    static int getCount() {
+        return 1;
+    }
+}

src/it/MCOMPILER-374_mrjar/src/main/java/org/maven/bug/B.java

@@ -0,0 +1,25 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.maven.bug;
+
+public class B {
+    static int getCount() {
+        return A.getCount() + 1;
+    }
+}

src/it/MCOMPILER-374_mrjar/src/main/java11/module-info.java

@@ -0,0 +1,21 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+module mrjar {
+    exports org.maven.bug;
+}

src/it/MCOMPILER-374_mrjar/src/main/java11/org/maven/bug/B.java

@@ -0,0 +1,29 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.maven.bug;
+
+public class B {
+    static int getCount() {
+        return A9.getCount() + 2;
+    }
+
+    static int getVersion() {
+        return 11;
+    }
+}

src/it/MCOMPILER-374_mrjar/src/main/java9/org/maven/bug/A9.java

@@ -0,0 +1,25 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.maven.bug;
+
+public class A9 {
+    static int getCount() {
+        return A.getCount() + 1;
+    }
+}

src/it/MCOMPILER-374_mrjar/src/main/java9/org/maven/bug/B.java

@@ -0,0 +1,25 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.maven.bug;
+
+public class B {
+    static int getCount() {
+        return A9.getCount() + 1;
+    }
+}

src/it/MCOMPILER-374_mrjar/src/test/java/org/maven/bug/MrJarTest.java

@@ -0,0 +1,25 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.maven.bug;
+
+class MrJarTest {
+    static int getCount() {
+        return A.getCount() + A9.getCount() + B.getVersion();
+    }
+}

src/it/MCOMPILER-374_mrjar/verify.groovy

@@ -0,0 +1,26 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+assert new File(basedir, 'target/classes/org/maven/bug/A.class').exists()
+assert new File(basedir, 'target/classes/org/maven/bug/B.class').exists()
+assert new File(basedir, 'target/classes/META-INF/versions/9/org/maven/bug/A9.class').exists()
+assert new File(basedir, 'target/classes/META-INF/versions/9/org/maven/bug/B.class').exists()
+assert new File(basedir, 'target/classes/META-INF/versions/11/module-info.class').exists()
+assert new File(basedir, 'target/classes/META-INF/versions/11/org/maven/bug/B.class').exists()
+assert new File(basedir, 'target/test-classes/org/maven/bug/MrJarTest.class').exists()

src/main/java/org/apache/maven/plugin/compiler/AbstractCompilerMojo.java

@@ -701,6 +701,32 @@ protected final Optional<Path> getModuleDeclaration(final Set<File> sourceFiles)
         return Optional.empty();
     }
 
+    /**
+     * Returns existing multirelease JAR output directories through the given release in descending order.
+     * The base output directory is returned last.
+     */
+    protected static List<File> getProjectOutputDirectories(File outputDirectory, int release) {
+        List<File> directories = new ArrayList<>();
+        File versionsFolder = new File(outputDirectory, "META-INF/versions");
+
+        for (int version = release; version >= 9; version--) {
+            File versionSubFolder = new File(versionsFolder, String.valueOf(version));
+            if (versionSubFolder.isDirectory()) {
+                directories.add(versionSubFolder);
+            }
+        }
+
+        directories.add(outputDirectory);
+        return directories;
+    }
+
+    /**
+     * Returns the major Java version from its legacy or current string representation.
+     */
+    protected static int getJavaMajorVersion(String version) {
+        return Integer.parseInt(version.startsWith("1.") ? version.substring(2) : version);
+    }
+
     private boolean targetOrReleaseSet;
 
     @Override