Add the --experimental_remote_require_cached flag

src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnRunner.java

@@ -236,6 +236,19 @@ public SpawnResult exec(Spawn spawn, SpawnExecutionContext context)
       return execLocallyAndUploadOrFail(action, spawn, context, uploadLocalResults, e);
     }
 
+    if (remoteOptions.remoteRequireCached) {
+      return new SpawnResult.Builder()
+          .setStatus(SpawnResult.Status.EXECUTION_DENIED)
+          .setExitCode(1)
+          .setFailureMessage("Action must be cached due to --experimental_remote_require_cached but it is not")
+          .setFailureDetail(
+              FailureDetail.newBuilder()
+                  .setSpawn(FailureDetails.Spawn.newBuilder().setCode(FailureDetails.Spawn.Code.EXECUTION_DENIED))
+                  .build())
+          .setRunnerName("remote")
+          .build();
+    }
+
     AtomicBoolean useCachedResult = new AtomicBoolean(acceptCachedResult);
     AtomicBoolean forceUploadInput = new AtomicBoolean(false);
     try {

src/main/java/com/google/devtools/build/lib/remote/options/RemoteOptions.java

@@ -229,6 +229,18 @@ public final class RemoteOptions extends CommonRemoteOptions {
       help = "Whether to accept remotely cached action results.")
   public boolean remoteAcceptCached;
 
+  @Option(
+      name = "experimental_remote_require_cached",
+      defaultValue = "false",
+      documentationCategory = OptionDocumentationCategory.REMOTE,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      help =
+          "If set to true, enforce that all actions that can run remotely are cached, or else "
+              + "fail the build. This is useful to troubleshoot non-determinism issues as it "
+              + "allows checking whether actions that should be cached are actually cached "
+              + "without spuriously injecting new results into the cache.")
+  public boolean remoteRequireCached;
+
   @Option(
       name = "remote_local_fallback",
       defaultValue = "false",

src/test/shell/bazel/remote/remote_execution_test.sh

@@ -1263,6 +1263,36 @@ EOF
   expect_not_log "1 local"
 }
 
+function test_require_cached() {
+  mkdir -p a
+  cat > a/BUILD <<'EOF'
+genrule(
+  name = "foo",
+  srcs = ["foo.in"],
+  outs = ["foo.out"],
+  cmd = "cp \"$<\" \"$@\"",
+)
+EOF
+
+  echo "input 1" >a/foo.in
+  bazel build \
+    --remote_executor=grpc://localhost:${worker_port} \
+    //a:foo >& $TEST_log || fail "Failed to build //a:foo"
+
+  expect_log "1 remote"
+
+  echo "input 2" >a/foo.in
+  if bazel build \
+    --remote_executor=grpc://localhost:${worker_port} \
+    --experimental_remote_require_cached \
+    //a:foo >& $TEST_log; then
+    fail "Build of //a:foo succeeded but it should have failed"
+  fi
+
+  expect_log "Action must be cached due to --experimental_remote_require_cached but it is not"
+  expect_not_log "remote cache hit"
+}
+
 function test_nobuild_runfile_links() {
   mkdir data && echo "hello" > data/hello && echo "world" > data/world
     cat > WORKSPACE <<EOF