[MCOMPILER-578] Track outputs across compiler executions

src/it/MCOMPILER-578/invoker.properties

@@ -0,0 +1,20 @@
+# 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 = 17+
+invoker.goals = clean compile
+invoker.goals.2 = compile

src/it/MCOMPILER-578/pom.xml

@@ -0,0 +1,78 @@
+<?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.apache.maven.plugins.compiler.it</groupId>
+  <artifactId>mcompiler-578</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>@project.version@</version>
+        <configuration>
+          <createMissingPackageInfoClass>false</createMissingPackageInfoClass>
+        </configuration>
+        <executions>
+          <execution>
+            <id>default-compile</id>
+            <configuration>
+              <release>${java.vm.specification.version}</release>
+            </configuration>
+          </execution>
+          <execution>
+            <id>base-modules-compile</id>
+            <goals>
+              <goal>compile</goal>
+            </goals>
+            <configuration>
+              <release>11</release>
+              <includes>
+                <include>module-info.java</include>
+              </includes>
+            </configuration>
+          </execution>
+          <execution>
+            <id>base-compile</id>
+            <goals>
+              <goal>compile</goal>
+            </goals>
+            <configuration>
+              <release>8</release>
+              <excludes>
+                <exclude>module-info.java</exclude>
+              </excludes>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/it/MCOMPILER-578/src/main/java/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 org.example {
+    exports org.example;
+}

src/it/MCOMPILER-578/src/main/java/org/example/Example.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.
+ */
+package org.example;
+
+public class Example {}

src/it/MCOMPILER-578/src/main/java/org/example/package-info.java

@@ -0,0 +1,19 @@
+/*
+ * 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.example;

src/it/MCOMPILER-578/verify.groovy

@@ -0,0 +1,35 @@
+/*
+ * 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 majorVersion = { File classFile ->
+    assert classFile.isFile()
+    byte[] bytes = classFile.bytes
+    assert bytes.length >= 8
+    ((bytes[6] & 0xFF) << 8) | (bytes[7] & 0xFF)
+}
+
+def exampleClass = new File( basedir, 'target/classes/org/example/Example.class' )
+def exampleMajorVersion = majorVersion( exampleClass )
+// major_version: 52 = Java 8, from the base-compile execution.
+assert exampleMajorVersion == 52
+
+def moduleInfoClass = new File( basedir, 'target/classes/module-info.class' )
+def moduleInfoMajorVersion = majorVersion( moduleInfoClass )
+// major_version: 55 = Java 11, from the base-modules-compile execution.
+assert moduleInfoMajorVersion == 55

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

@@ -892,7 +892,7 @@
 
         compilerConfiguration.setWorkingDirectory(basedir);
 
         compilerConfiguration.setCompilerVersion(compilerVersion);
 
         compilerConfiguration.setBuildDirectory(buildDirectory);
 
@@ -930,6 +930,9 @@
 
         final Set<File> sources;
 
+        Set<Path> outputs = Collections.emptySet();
+        String compilerExecution = mojoExecution.getGoal() + '@' + mojoExecution.getExecutionId();
+
         IncrementalBuildHelperRequest incrementalBuildHelperRequest = null;
 
         if (useIncrementalCompilation) {
@@ -941,6 +944,9 @@
 
                 preparePaths(sources);
 
+                // Expected output paths let us detect overwrites that IncrementalBuildHelper cannot see.
+                outputs = getOutputPaths(compilerConfiguration, compiler, sources);
+
                 incrementalBuildHelperRequest = new IncrementalBuildHelperRequest().inputFiles(sources);
 
                 // Strategies used to detect modifications.
@@ -954,9 +960,18 @@
                 String inputFileTreeChanged = hasInputFileTreeChanged(incrementalBuildHelper, sources)
                         ? "added or removed source files"
                         : null;
+                // A different execution may have overwritten an otherwise up-to-date output.
+                String outputChanged = hasPreviouslyCompiledOutput(compilerExecution, outputs)
+                        ? "output from another compiler execution"
+                        : null;
 
                 // Get the first cause for the rebuild compilation detection.
-                String cause = Stream.of(immutableOutputFile, dependencyChanged, sourceChanged, inputFileTreeChanged)
+                String cause = Stream.of(
+                                immutableOutputFile,
+                                dependencyChanged,
+                                sourceChanged,
+                                inputFileTreeChanged,
+                                outputChanged)
                         .filter(Objects::nonNull)
                         .findFirst()
                         .orElse(null);
@@ -1267,6 +1282,8 @@
                 getLog().debug(
                                 "skip incrementalBuildHelper#afterRebuildExecution as the output directory doesn't exist");
             }
+            // Make these outputs visible to later compiler executions in this Maven session.
+            recordCompiledOutputs(compilerExecution, outputs);
         }
 
         List<CompilerMessage> warnings = new ArrayList<>();
@@ -1569,6 +1586,56 @@
         return staleSources;
     }
 
+    /**
+     * Maps selected sources to their expected compiler outputs.
+     *
+     * @param compilerConfiguration the compiler configuration
+     * @param compiler the selected compiler
+     * @param sources sources selected by the current execution
+     * @return normalized absolute output paths
+     */
+    private Set<Path> getOutputPaths(CompilerConfiguration compilerConfiguration, Compiler compiler, Set<File> sources)
+            throws CompilerException, MojoExecutionException {
+        SourceMapping mapping = getSourceMapping(compilerConfiguration, compiler);
+
+        File outputDirectory =
+                compiler.getCompilerOutputStyle() == CompilerOutputStyle.ONE_OUTPUT_FILE_FOR_ALL_INPUT_FILES
+                        ? buildDirectory
+                        : getOutputDirectory();
+        try {
+            return CompilationOutputRegistry.mapOutputs(mapping, outputDirectory, getCompileSourceRoots(), sources);
+        } catch (InclusionScanException e) {
+            throw new MojoExecutionException("Error mapping sources to their outputs.", e);
+        }
+    }
+
+    /**
+     * Checks whether a different compiler execution last processed an expected output.
+     *
+     * @param compilerExecution the current execution
+     * @param outputs expected outputs of the current execution
+     * @return whether an output overlaps with another execution
+     */
+    private boolean hasPreviouslyCompiledOutput(String compilerExecution, Set<Path> outputs) {
+        Optional<Path> output = CompilationOutputRegistry.find(getPluginContext(), compilerExecution, outputs);
+        if (output.isPresent() && showCompilationChanges) {
+            getLog().info("\tOutput from another compiler execution: " + output.get());
+        } else if (output.isPresent()) {
+            getLog().debug("\tOutput from another compiler execution: " + output.get());
+        }
+        return output.isPresent();
+    }
+
+    /**
+     * Registers the current execution as the last processor of its expected outputs.
+     *
+     * @param compilerExecution the current execution
+     * @param outputs expected outputs of the current execution
+     */
+    private void recordCompiledOutputs(String compilerExecution, Set<Path> outputs) {
+        CompilationOutputRegistry.register(getPluginContext(), compilerExecution, outputs);
+    }
+
     private SourceMapping getSourceMapping(CompilerConfiguration compilerConfiguration, Compiler compiler)
             throws CompilerException, MojoExecutionException {
         CompilerOutputStyle outputStyle = compiler.getCompilerOutputStyle();