[MCOMPILER-578] Track outputs across compiler executions by wilx · Pull Request #1091 · apache/maven-compiler-plugin

wilx · 2026-07-28T17:46:00Z

Summary

Keep the final class files deterministic when multiple compiler executions use different release levels and share an
output directory.

Root cause

An earlier execution can overwrite an existing class file without changing its filename. IncrementalBuildHelper
compares input and output file names, so a later execution can incorrectly consider its source up to date even though
a different execution produced the shared output.

Changes

Add an Invoker regression test that runs clean compile followed by compile and verifies the Java 8 classes and
Java 11 module descriptor.
Track the last goal@executionId that processed each mapped output in Maven's per-project plugin context.
Recompile when another execution processed an overlapping output, while allowing a repeated invocation of the same
execution to remain up to date.
Avoid filesystem timestamps and their platform-dependent precision.

Validation

mvn -Prun-its verify: 77 passed, 0 failed, 5 environment-specific skips.
Focused MCOMPILER-525 and MCOMPILER-578 Invoker tests: passed.
Unit tests: 32 passed.
Spotless, Checkstyle, and git diff --check: passed.

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Fixes #788

Run clean compile followed by compile and verify that Java 8 classes and the Java 11 module descriptor retain their configured class-file versions. The test exposes the incremental compilation failure before the production fix.

Record the last compiler execution that processed each mapped output in the shared plugin context. Recompile when a different execution overlaps that output while allowing repeated invocations of the same execution to remain up to date. Fixes apache#788

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Pull request overview

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This PR fixes incremental-compilation correctness when multiple compiler executions share an output directory but use different release levels, by tracking which execution last produced each output within the Maven session.

Changes:

Introduces a per-project, per-session output registry keyed by goal@executionId to detect overlapping outputs between executions.
Updates AbstractCompilerMojo incremental rebuild-cause detection to force recompilation when another execution last produced an expected output.
Adds a new Invoker IT (MCOMPILER-578) and unit tests for the output registry behavior.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/main/java/org/apache/maven/plugin/compiler/AbstractCompilerMojo.java	Computes expected outputs and triggers rebuilds when outputs overlap across executions; records processed outputs in plugin context.
src/main/java/org/apache/maven/plugin/compiler/CompilationOutputRegistry.java	New registry to map expected output paths to the last `goal@executionId` that processed them.
src/test/java/org/apache/maven/plugin/compiler/CompilationOutputRegistryTest.java	New unit tests validating registry semantics across executions and disjoint outputs.
src/it/MCOMPILER-578/pom.xml	New integration test project with multiple compile executions using different `--release` values into the same output dir.
src/it/MCOMPILER-578/verify.groovy	Validates resulting classfile major versions for Java 8 class and Java 11 `module-info.class`.
src/it/MCOMPILER-578/invoker.properties	Runs `clean compile` then `compile` to exercise incremental behavior.
src/it/MCOMPILER-578/src/main/java/org/example/Example.java	Minimal class compiled by different executions.
src/it/MCOMPILER-578/src/main/java/org/example/package-info.java	Ensures package presence without generating missing package-info class.
src/it/MCOMPILER-578/src/main/java/module-info.java	Module descriptor compiled with Java 11 settings.

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+    private boolean hasPreviouslyCompiledOutput(String compilerExecution, Set<Path> outputs) {
+        Optional<Path> output = CompilationOutputRegistry.find(getPluginContext(), compilerExecution, outputs);
+        if (output.isPresent() && (getLog().isDebugEnabled() || showCompilationChanges)) {
+            getLog().info("\tOutput from another compiler execution: " + output.get());
+        }
+        return output.isPresent();
+    }


wilx · 2026-07-28T21:00:52Z

+        for (String sourceRoot : sourceRoots) {
+            Path root = Paths.get(sourceRoot).toAbsolutePath().normalize();
+            for (File source : sources) {
+                Path path = source.toPath().toAbsolutePath().normalize();
+                if (path.startsWith(root)) {
+                    for (File output : mapping.getTargetFiles(
+                            outputDirectory, root.relativize(path).toString())) {
+                        outputs.add(output.toPath().toAbsolutePath().normalize());
+                    }
+                }
+            }
+        }


Is this really something people do? SMH

Indeed, don't think that peoples declare both src/main and src/main/java directories in same time.

+def exampleMajorVersion = exampleClass.bytes[7] & 0xFF
+// major_version: 52 = Java 8, from the base-compile execution.
+assert exampleMajorVersion == 52


+def moduleInfoMajorVersion = moduleInfoClass.bytes[7] & 0xFF
+// major_version: 55 = Java 11, from the base-modules-compile execution.
+assert moduleInfoMajorVersion == 55


+    private static final Path OUTPUT = Paths.get("target/classes/Example.class");
+
+    private static final Path OTHER_OUTPUT = Paths.get("target/classes/Other.class");


wilx · 2026-07-28T21:21:31Z

I have pushed a fix for all of the review comments.

desruisseaux · 2026-07-29T10:31:28Z

Flagging as 3.x because 4.x automatically writes the output in a different directory for each Java release when declaring sources in the recommended way (with the new <sources> element).

wilx added 2 commits July 28, 2026 18:41

wilx marked this pull request as ready for review July 28, 2026 17:47

elharo changed the title ~~[MCOMPILER-578] - Track outputs across compiler executions~~ [MCOMPILER-578] Track outputs across compiler executions Jul 28, 2026

elharo requested a review from Copilot July 28, 2026 20:37

Copilot started reviewing on behalf of elharo July 28, 2026 20:53 View session

Copilot AI reviewed Jul 28, 2026

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[MCOMPILER-578] Address review comments

192de3f

desruisseaux added the 3.x label Jul 29, 2026

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[MCOMPILER-578] Track outputs across compiler executions - #1091

[MCOMPILER-578] Track outputs across compiler executions#1091
wilx wants to merge 3 commits into
apache:maven-compiler-plugin-3.xfrom
wilx:issue-788-incremental-multi-execution

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		private static final Path OUTPUT = Paths.get("target/classes/Example.class");

		private static final Path OTHER_OUTPUT = Paths.get("target/classes/Other.class");

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wilx commented Jul 28, 2026

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wilx commented Jul 28, 2026

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