Tolerate the possibility of a swig action depending on headers genera…

…ted by shared actions.

Shared actions produce artifacts with equal exec paths, so we can't use `Maps#uniqueIndex`.

PiperOrigin-RevId: 589123066
Change-Id: Id472319c41ff287218e35173fbecb6a0bd0e089d

src/main/java/com/google/devtools/build/lib/includescanning/IncludeScanningModule.java

@@ -13,11 +13,12 @@
 // limitations under the License.
 package com.google.devtools.build.lib.includescanning;
 
+import static com.google.common.collect.ImmutableMap.toImmutableMap;
+
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.Maps;
 import com.google.common.flogger.GoogleLogger;
 import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.MoreExecutors;
@@ -209,14 +210,22 @@ public void extractSwigIncludes(
               env.getDirectories(),
               env.getSkyframeBuildView().getArtifactFactory(),
               env.getExecRoot());
+      // For Swig include scanning, just point to the output file in the map.
+      ImmutableMap<PathFragment, Artifact> pathToDeclaredHeader =
+          legalOutputPaths.stream()
+              .collect(
+                  toImmutableMap(
+                      Artifact::getExecPath,
+                      artifact -> artifact,
+                      // Headers may be generated by shared actions. If both shared actions' outputs
+                      // are present, just use the first (b/304564144).
+                      (a, b) -> a));
       try {
         scanner.processAsync(
             source,
             ImmutableList.of(source),
-            // For Swig include scanning just point to the output file in the map.
             new IncludeScanningHeaderData.Builder(
-                    Maps.uniqueIndex(legalOutputPaths, Artifact::getExecPath),
-                    /*modularHeaders=*/ ImmutableSet.of())
+                    pathToDeclaredHeader, /* modularHeaders= */ ImmutableSet.of())
                 .build(),
             ImmutableList.of(),
             includes,
@@ -329,8 +338,8 @@ public void executorCreated() {
                   threads,
                   0L,
                   TimeUnit.SECONDS,
-                  new SynchronousQueue<Runnable>(),
-                  new ThreadFactoryBuilder().setNameFormat("Include scanner" + " %d").build(),
+                  new SynchronousQueue<>(),
+                  new ThreadFactoryBuilder().setNameFormat("Include scanner %d").build(),
                   (r, e) -> r.run());
         } else {
           includePool = ExecutorUtil.newSlackPool(threads, "Include scanner");