Save attached outputs for compile-only cache entries

src/main/java/org/apache/maven/buildcache/BuildCacheMojosExecutionStrategy.java

@@ -23,6 +23,7 @@
 import javax.inject.Named;
 
 import java.io.File;
+import java.io.IOException;
 import java.nio.file.Path;
 import java.util.HashSet;
 import java.util.List;
@@ -138,33 +139,58 @@ public void execute(
 
  boolean restorable = result.isSuccess() || result.isPartialSuccess();
  boolean restored = false; // if partially restored need to save increment
+
  if (restorable) {
  CacheRestorationStatus cacheRestorationStatus =
  restoreProject(result, mojoExecutions, mojoExecutionRunner, cacheConfig);
  restored = CacheRestorationStatus.SUCCESS == cacheRestorationStatus;
  executeExtraCleanPhaseIfNeeded(cacheRestorationStatus, cleanPhase, mojoExecutionRunner);
  }
- if (!restored) {
- for (MojoExecution mojoExecution : mojoExecutions) {
- if (source == Source.CLI
- || mojoExecution.getLifecyclePhase() == null
- || lifecyclePhasesHelper.isLaterPhaseThanClean(mojoExecution.getLifecyclePhase())) {
- mojoExecutionRunner.run(mojoExecution);
+
+ try {
+ if (!restored && !forkedExecution) {
+ // Move pre-existing artifacts to staging directory to prevent caching stale files
+ // from previous builds (e.g., after git branch switch, or from cache restored
+ // with clock skew). This ensures save() only sees fresh files built during this session.
+ // Skip for forked executions since they don't cache and shouldn't modify artifacts.
+ try {
+ cacheController.stagePreExistingArtifacts(session, project);
+ } catch (IOException e) {
+ LOGGER.debug("Failed to stage pre-existing artifacts: {}", e.getMessage());
+ // Continue build - if staging fails, we'll just cache what exists
  }
  }
- }
 
- if (cacheState == INITIALIZED && (!result.isSuccess() || !restored)) {
- if (cacheConfig.isSkipSave()) {
- LOGGER.info("Cache saving is disabled.");
- } else if (cacheConfig.isMandatoryClean()
- && lifecyclePhasesHelper
- .getCleanSegment(project, mojoExecutions)
- .isEmpty()) {
- LOGGER.info("Cache storing is skipped since there was no \"clean\" phase.");
- } else {
- final Map<String, MojoExecutionEvent> executionEvents = mojoListener.getProjectExecutions(project);
- cacheController.save(result, mojoExecutions, executionEvents);
+ if (!restored) {
+ for (MojoExecution mojoExecution : mojoExecutions) {
+ if (source == Source.CLI
+ || mojoExecution.getLifecyclePhase() == null
+ || lifecyclePhasesHelper.isLaterPhaseThanClean(mojoExecution.getLifecyclePhase())) {
+ mojoExecutionRunner.run(mojoExecution);
+ }
+ }
+ }
+
+ if (cacheState == INITIALIZED && (!result.isSuccess() || !restored)) {
+ if (cacheConfig.isSkipSave()) {
+ LOGGER.debug("Cache saving is disabled.");
+ } else if (cacheConfig.isMandatoryClean()
+ && lifecyclePhasesHelper
+ .getCleanSegment(project, mojoExecutions)
+ .isEmpty()) {
+ LOGGER.debug("Cache storing is skipped since there was no \"clean\" phase.");
+ } else {
+ final Map<String, MojoExecutionEvent> executionEvents =
+ mojoListener.getProjectExecutions(project);
+ cacheController.save(result, mojoExecutions, executionEvents);
+ }
+ }
+ } finally {
+ // Always restore staged files after build completes (whether save ran or not).
+ // Files that were rebuilt are discarded; files that weren't rebuilt are restored.
+ // Skip for forked executions since they don't stage artifacts.
+ if (!restored && !forkedExecution) {
+ cacheController.restoreStagedArtifacts(session, project);
  }
  }
 

src/main/java/org/apache/maven/buildcache/CacheController.java

@@ -18,6 +18,7 @@
  */
 package org.apache.maven.buildcache;
 
+import java.io.IOException;
 import java.util.List;
 import java.util.Map;
 
@@ -45,4 +46,23 @@ void save(
  boolean isForcedExecution(MavenProject project, MojoExecution execution);
 
  void saveCacheReport(MavenSession session);
+
+ /**
+ * Move pre-existing artifacts to staging directory to prevent caching stale files.
+ * Called before mojos run to ensure save() only sees fresh files.
+ *
+ * @param session the Maven session
+ * @param project the Maven project
+ * @throws IOException if file operations fail
+ */
+ void stagePreExistingArtifacts(MavenSession session, MavenProject project) throws IOException;
+
+ /**
+ * Restore staged artifacts after save() completes.
+ * Files that were rebuilt are discarded; files that weren't rebuilt are restored.
+ *
+ * @param session the Maven session
+ * @param project the Maven project
+ */
+ void restoreStagedArtifacts(MavenSession session, MavenProject project);
 }