Eagerly initialize source to target map

base/src/META-INF/blaze-base.xml

@@ -1,5 +1,5 @@
 <!--
-  ~ Copyright 2016 The Bazel Authors. All rights reserved.
+  ~ Copyright 2025 The Bazel Authors. All rights reserved.
   ~
   ~ Licensed under the Apache License, Version 2.0 (the "License");
   ~ you may not use this file except in compliance with the License.
@@ -625,6 +625,7 @@
 
   <extensions defaultExtensionNs="com.google.idea.blaze">
     <SyncListener implementation="com.google.idea.blaze.base.sync.SyncCache$ClearSyncCache"/>
+    <SyncListener implementation="com.google.idea.blaze.base.sync.SourceToTargetMapInitializer"/>
     <SyncListener implementation="com.google.idea.blaze.base.run.BlazeRunConfigurationSyncListener"/>
     <SyncListener implementation="com.google.idea.blaze.base.sync.status.BlazeSyncStatusListener" order="first"/>
     <SyncListener implementation="com.google.idea.blaze.base.dependencies.ExternalFileProjectManagementHelper$UpdateNotificationsAfterSync"/>

base/src/com/google/idea/blaze/base/sync/SourceToTargetMapInitializer.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2025 The Bazel Authors. All rights reserved.
+ *
+ * Licensed 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 com.google.idea.blaze.base.sync;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.idea.blaze.base.model.BlazeProjectData;
+import com.google.idea.blaze.base.projectview.ProjectViewSet;
+import com.google.idea.blaze.base.scope.BlazeContext;
+import com.google.idea.blaze.base.settings.BlazeImportSettings;
+import com.google.idea.blaze.base.targetmaps.SourceToTargetMap;
+import com.intellij.openapi.project.Project;
+import java.io.File;
+
+public class SourceToTargetMapInitializer implements SyncListener {
+
+  @Override
+  public void onSyncComplete(Project project, BlazeContext context,
+      BlazeImportSettings importSettings, ProjectViewSet projectViewSet,
+      ImmutableSet<Integer> buildIds, BlazeProjectData blazeProjectData, SyncMode syncMode,
+      SyncResult syncResult) {
+    // eagerly instantiate source to target map
+    SourceToTargetMap.getInstance(project).getRulesForSourceFile(new File(""));
+  }
+}

base/src/com/google/idea/blaze/base/targetmaps/AspectSyncSourceToTargetMap.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 The Bazel Authors. All rights reserved.
+ * Copyright 2025 The Bazel Authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@
 import com.google.idea.blaze.base.sync.data.BlazeProjectDataManager;
 import com.google.idea.blaze.base.sync.workspace.ArtifactLocationDecoder;
 import com.intellij.openapi.project.Project;
+import com.intellij.util.concurrency.annotations.RequiresBackgroundThread;
 import java.io.File;
 import java.util.Objects;
 import javax.annotation.Nullable;
@@ -77,6 +78,7 @@ private synchronized ImmutableMultimap<File, TargetKey> getSourceToTargetMap() {
   }
 
   @SuppressWarnings("unused")
+  @RequiresBackgroundThread
   private static ImmutableMultimap<File, TargetKey> computeSourceToTargetMap(
       Project project, BlazeProjectData blazeProjectData) {
     ArtifactLocationDecoder decoder = blazeProjectData.getArtifactLocationDecoder();