[MCOMPILER-561] - Add new rebuild detection for bytecode changes

src/it/MCOMPILER-561/invoker.properties

@@ -0,0 +1,22 @@
+# 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.debug = false
+invoker.java.version = 11+
+invoker.goals = compile -Dmaven.compiler.release=8 -Dmaven.compiler.showCompilationChanges=true -ntp
+invoker.goals.2 = compile -Dmaven.compiler.release=11 -Dmaven.compiler.showCompilationChanges=true -ntp
+invoker.goals.3 = compile -Dmaven.compiler.release=9 -Dmaven.compiler.showCompilationChanges=true -ntp

src/it/MCOMPILER-561/pom.xml

@@ -0,0 +1,42 @@
+<?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/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>org.apache.maven.plugins</groupId>
+  <artifactId>MCOMPILER-561</artifactId>
+  <name>MCOMPILER-561</name>
+  <packaging>jar</packaging>
+  <version>1.0-SNAPSHOT</version>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>@project.version@</version>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/MCOMPILER-561/src/main/java/myproject/HelloWorld.java

@@ -0,0 +1,34 @@
+/*
+ * 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 myproject;
+
+/**
+ * The classic Hello World App.
+ */
+public class HelloWorld {
+
+    /**
+     * Main method.
+     *
+     * @param args Not used
+     */
+    public static void main(String[] args) {
+        System.out.println("Hi!");
+    }
+}

src/it/MCOMPILER-561/verify.groovy

@@ -0,0 +1,27 @@
+
+/*
+ * 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.
+ */
+
+def log = new File(basedir, 'build.log').text
+
+assert log.count('[INFO] Recompiling the module because of changed source code.') == 1
+assert log.count('[INFO] Recompiling the module because of bytecode version changed.') == 2
+
+assert log.count('from 8 to 11') == 1
+assert log.count('from 11 to 9') == 1

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

@@ -21,6 +21,7 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.UncheckedIOException;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.nio.charset.Charset;
@@ -43,6 +44,8 @@
 import java.util.Optional;
 import java.util.Properties;
 import java.util.Set;
+import java.util.function.Function;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -80,6 +83,7 @@
 import org.codehaus.plexus.compiler.util.scan.mapping.SourceMapping;
 import org.codehaus.plexus.compiler.util.scan.mapping.SuffixMapping;
 import org.codehaus.plexus.languages.java.jpms.JavaModuleDescriptor;
+import org.codehaus.plexus.languages.java.version.JavaClassfileVersion;
 import org.codehaus.plexus.languages.java.version.JavaVersion;
 import org.codehaus.plexus.util.FileUtils;
 import org.eclipse.aether.RepositorySystem;
@@ -906,12 +910,17 @@ public void execute() throws MojoExecutionException, CompilationFailureException
                 String inputFileTreeChanged = hasInputFileTreeChanged(incrementalBuildHelper, sources)
                         ? "added or removed source files"
                         : null;
+                Supplier<String> bytecodeChanged = () -> hasBytecodeChanged() ? "bytecode version changed" : null;
 
                 // Get the first cause for the rebuild compilation detection.
                 String cause = Stream.of(immutableOutputFile, dependencyChanged, sourceChanged, inputFileTreeChanged)
                         .filter(Objects::nonNull)
                         .findFirst()
-                        .orElse(null);
+                        .orElseGet(() -> Stream.of(bytecodeChanged)
+                                .map(Supplier::get)
+                                .filter(Objects::nonNull)
+                                .findFirst()
+                                .orElse(null));
 
                 if (cause != null) {
                     getLog().info("Recompiling the module because of "
@@ -1842,6 +1851,48 @@ private boolean hasInputFileTreeChanged(IncrementalBuildHelper ibh, Set<File> in
         return inputTreeChanges.hasChanged();
     }
 
+    private static final int MAX_FILE_WALK_LIMIT = 20;
+
+    /**
+     * Performs a check on compiled class files to ensure that the bytecode version
+     * hasn't changed between runs.
+     *
+     * <p>This is limited to check a maximum of {@link #MAX_FILE_WALK_LIMIT}.
+     *
+     * @return true if a bytecode version differs from the actual release version.
+     */
+    private boolean hasBytecodeChanged() {
+        String currentVersion = getVersionRelease();
+        JavaVersion javaVersion = JavaVersion.parse(currentVersion).asMajor();
+
+        try (Stream<Path> walk = Files.walk(getOutputDirectory().toPath())) {
+            Map<Path, JavaClassfileVersion> pathVersionMap = walk.filter(file -> "class"
+                            .equals(FileUtils.extension(file.getFileName().toString())))
+                    .limit(MAX_FILE_WALK_LIMIT)
+                    .collect(Collectors.toMap(Function.identity(), JavaClassfileVersion::of));
+            for (Map.Entry<Path, JavaClassfileVersion> entry : pathVersionMap.entrySet()) {
+                Path path = entry.getKey();
+                JavaClassfileVersion classFileVersion = entry.getValue();
+                JavaVersion javaFileVersion = classFileVersion.javaVersion().asMajor();
+                if (enablePreview != classFileVersion.isPreview() || javaFileVersion.compareTo(javaVersion) != 0) {
+                    if (getLog().isDebugEnabled() || showCompilationChanges) {
+                        getLog().info(String.format(
+                                "\tBytecode file change: %s from %s to %s", path, javaFileVersion, javaVersion));
+                    }
+                    return true;
+                }
+            }
+            return false;
+        } catch (UncheckedIOException | IOException e) {
+            getLog().warn("Error reading bytecode version", e);
+            return false;
+        }
+    }
+
+    private String getVersionRelease() {
+        return getRelease() != null ? getRelease() : getTarget() != null ? getTarget() : DEFAULT_TARGET;
+    }
+
     public void setTarget(String target) {
         this.target = target;
         targetOrReleaseSet = true;