Add experimental flag to make cpp compile actions shareable

src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfigurationValue.java

@@ -811,6 +811,10 @@ public BuildOptions getOptions() {
     return buildOptions;
   }
 
+  public CoreOptions getCoreOptions() {
+    return options;
+  }
+
   public String getCpu() {
     return options.cpu;
   }

src/main/java/com/google/devtools/build/lib/analysis/config/CoreOptions.java

@@ -894,6 +894,16 @@ public OutputPathsConverter() {
               + " of failing. This is to help use cquery diagnose failures in select.")
   public boolean debugSelectsAlwaysSucceed;
 
+  @Option(
+      name = "experimental_shareable_cpp_compile_actions",
+      defaultValue = "false",
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      effectTags = {OptionEffectTag.BAZEL_INTERNAL_CONFIGURATION},
+      help =
+          "If true, cpp actions will be shareable. This will make Bazel not fail with action"
+            + " conflicts if it finds two identical actions with different configurations.")
+  public boolean experimentalShareableCppCompileActions;
+
   /** Ways configured targets may provide the {@link Fragment}s they require. */
   public enum IncludeConfigFragmentsEnum {
     /**
@@ -936,6 +946,7 @@ public FragmentOptions getHost() {
     host.includeRequiredConfigFragmentsProvider = includeRequiredConfigFragmentsProvider;
     host.debugSelectsAlwaysSucceed = debugSelectsAlwaysSucceed;
     host.checkTestonlyForOutputFiles = checkTestonlyForOutputFiles;
+    host.experimentalShareableCppCompileActions = experimentalShareableCppCompileActions;
 
     // === Runfiles ===
     host.buildRunfilesManifests = buildRunfilesManifests;

src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileActionBuilder.java

@@ -92,7 +92,7 @@ public CppCompileActionBuilder(
       CcToolchainProvider ccToolchain,
       BuildConfigurationValue configuration) {
     this.owner = actionConstructionContext.getActionOwner();
-    this.shareable = false;
+    this.shareable = configuration.getCoreOptions().experimentalShareableCppCompileActions;
     this.configuration = configuration;
     this.cppConfiguration = configuration.getFragment(CppConfiguration.class);
     this.mandatoryInputsBuilder = NestedSetBuilder.stableOrder();