Bypass execroot symlink forest creation when using virtual roots.

To support Skymeld, there is somewhat duplicated logic in `SkyframeExecutor` (non-Skymeld) and `ExecutionTool` (Skymeld).

PiperOrigin-RevId: 642334521
Change-Id: I2d81e81cb214e6605bbf716874f7ce6f1a138995

src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java

@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.buildtool;
 
+import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.collect.ImmutableSet.toImmutableSet;
 
 import com.google.common.annotations.VisibleForTesting;
@@ -256,33 +257,34 @@ TestActionContext getTestActionContext() {
    *
    * <p>TODO(b/213040766): Write tests for these setup steps.
    */
-  public void prepareForExecution(Stopwatch executionTimer)
+  void prepareForExecution(Stopwatch executionTimer)
       throws AbruptExitException,
           BuildFailedException,
           InterruptedException,
           InvalidConfigurationException {
     init();
     BuildRequestOptions buildRequestOptions = request.getBuildOptions();
-
     SkyframeExecutor skyframeExecutor = env.getSkyframeExecutor();
+    boolean localActionsSupported =
+        env.getOutputService().actionFileSystemType().supportsLocalActions();
+
+    // TODO: b/290617036 - Reconsider this for local action support with virtual roots.
+    checkState(
+        !localActionsSupported || env.getDirectories().getVirtualSourceRoot() == null,
+        "Local actions are incompatible with virtual roots");
 
     try (SilentCloseable c = Profiler.instance().profile("preparingExecroot")) {
-      boolean shouldSymlinksBePlanted =
-          skyframeExecutor.getForcedSingleSourceRootIfNoExecrootSymlinkCreation() == null;
-      Root singleSourceRoot =
-          shouldSymlinksBePlanted
-              ? Iterables.getOnlyElement(env.getPackageLocator().getPathEntries())
-              : skyframeExecutor.getForcedSingleSourceRootIfNoExecrootSymlinkCreation();
       IncrementalPackageRoots incrementalPackageRoots =
           IncrementalPackageRoots.createAndRegisterToEventBus(
               getExecRoot(),
-              singleSourceRoot,
+              // Single package path is a Skymeld prerequisite.
+              Iterables.getOnlyElement(env.getPackageLocator().getPathEntries()),
               env.getEventBus(),
               env.getDirectories().getProductName() + "-",
               skyframeExecutor.getIgnoredPaths(),
               request.getOptions(BuildLanguageOptions.class).experimentalSiblingRepositoryLayout,
               runtime.getWorkspace().doesAllowExternalRepositories());
-      if (shouldSymlinksBePlanted) {
+      if (localActionsSupported) {
         incrementalPackageRoots.eagerlyPlantSymlinksToSingleSourceRoot();
       }
 
@@ -294,7 +296,7 @@ public void prepareForExecution(Stopwatch executionTimer)
     OutputService outputService = env.getOutputService();
     ModifiedFileSet modifiedOutputFiles =
         startBuildAndDetermineModifiedOutputFiles(request.getId(), outputService);
-    if (outputService.actionFileSystemType().supportsLocalActions()) {
+    if (localActionsSupported) {
       // Must be created after the output path is created above.
       try (SilentCloseable c = Profiler.instance().profile("createActionLogDirectory")) {
         createActionLogDirectory();
@@ -374,8 +376,7 @@ public void prepareForExecution(Stopwatch executionTimer)
    * @param analysisResult the analysis phase output
    * @param buildResult the mutable build result
    * @param packageRoots package roots collected from loading phase and {@link
-   *     BuildConfigurationValue} creation. May be empty if {@link
-   *     SkyframeExecutor#getForcedSingleSourceRootIfNoExecrootSymlinkCreation} is false.
+   *     BuildConfigurationValue} creation. May be empty if using virtual roots.
    */
   void executeBuild(
       UUID buildId,
@@ -738,7 +739,7 @@ private static BuildConfigurationValue getConfiguration(
    *
    * @return map of convenience symlink name to target
    */
-  public ImmutableMap<PathFragment, PathFragment> handleConvenienceSymlinks(
+  ImmutableMap<PathFragment, PathFragment> handleConvenienceSymlinks(
       ImmutableSet<ConfiguredTarget> targetsToBuild, BuildConfigurationValue configuration) {
     try (SilentCloseable c =
         Profiler.instance().profile("ExecutionTool.handleConvenienceSymlinks")) {
@@ -902,7 +903,7 @@ public void handle(Event event) {
    *
    * @param configuredTargets The configured targets whose artifacts are to be built.
    */
-  static ImmutableSet<ConfiguredTarget> determineSuccessfulTargets(
+  private static ImmutableSet<ConfiguredTarget> determineSuccessfulTargets(
       Collection<ConfiguredTarget> configuredTargets, Set<ConfiguredTargetKey> builtTargets) {
     // Maintain the ordering by copying builtTargets into an ImmutableSet.Builder in the same
     // iteration order as configuredTargets.
@@ -915,14 +916,14 @@ static ImmutableSet<ConfiguredTarget> determineSuccessfulTargets(
     return successfulTargets.build();
   }
 
-  static ImmutableSet<AspectKey> determineSuccessfulAspects(
+  private static ImmutableSet<AspectKey> determineSuccessfulAspects(
       ImmutableSet<AspectKey> aspects, Set<AspectKey> builtAspects) {
     // Maintain the ordering.
     return aspects.stream().filter(builtAspects::contains).collect(ImmutableSet.toImmutableSet());
   }
 
   /** Get action cache if present or reload it from the on-disk cache. */
-  ActionCache getOrLoadActionCache() throws AbruptExitException {
+  private ActionCache getOrLoadActionCache() throws AbruptExitException {
     try {
       return env.getBlazeWorkspace().getOrLoadPersistentActionCache(getReporter());
     } catch (IOException e) {

src/main/java/com/google/devtools/build/lib/skyframe/BUILD

@@ -156,6 +156,7 @@ java_library(
         ":package_lookup_function",
         ":package_lookup_value",
         ":package_progress_receiver",
+        ":package_roots_no_symlink_creation",
         ":package_value",
         ":pattern_expanding_error",
         ":precomputed_function",

src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java

@@ -1077,20 +1077,6 @@ protected GlobbingStrategy getGlobbingStrategy() {
     return GlobbingStrategy.NON_SKYFRAME;
   }
 
-  /**
-   * If not null, this is the only source root in the build, corresponding to the single element in
-   * a single-element package path. Such a single-source-root build need not plant the execroot
-   * symlink forest, and can trivially resolve source artifacts from exec paths. As a consequence,
-   * builds where this is not null do not need to track a package -> source root map. In addition,
-   * such builds can only occur in a monorepo, and thus do not need to produce repo mapping
-   * manifests for runfiles.
-   */
-  // TODO(wyv): To be safe, fail early if we're in a multi-repo setup but this is not being tracked.
-  @Nullable
-  public Root getForcedSingleSourceRootIfNoExecrootSymlinkCreation() {
-    return null;
-  }
-
   private boolean shouldStoreTransitivePackagesInLoadingAndAnalysis() {
     // Transitive packages may be needed for either RepoMappingManifestAction or Skymeld with
     // external repository support. They are never needed if external repositories are disabled. To
@@ -2117,9 +2103,18 @@ protected ConfigureTargetsResult configureTargets(
         getPackageRoots());
   }
 
-  @ForOverride
-  protected PackageRoots getPackageRoots() {
-    return new MapAsPackageRoots(collectPackageRoots());
+  private PackageRoots getPackageRoots() {
+    Root virtualSourceRoot = directories.getVirtualSourceRoot();
+    if (virtualSourceRoot == null) {
+      return new MapAsPackageRoots(collectPackageRoots());
+    }
+
+    // No need to plant symlinks when using virtual roots.
+    // TODO: b/290617036 - Reconsider this for local action support with virtual roots.
+    checkState(
+        !outputService.actionFileSystemType().supportsLocalActions(),
+        "Local actions are incompatible with virtual roots");
+    return new PackageRootsNoSymlinkCreation(virtualSourceRoot);
   }
 
   @Nullable