Remote caching: don't crash for actions with no inputs

Fixes #3004.

Change-Id: I6dcef92e9f23df574e0874a81b2901754042cf9a

Closes #3085.

Change-Id: I6dcef92e9f23df574e0874a81b2901754042cf9a
PiperOrigin-RevId: 157612661

3 files changed, 46 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/remote/TreeNodeRepository.java b/src/main/java/com/google/devtools/build/lib/remote/TreeNodeRepository.java
index fa9eb7d6ee..8272295a84 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/TreeNodeRepository.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/TreeNodeRepository.java
@@ -68,6 +68,7 @@ public final class TreeNodeRepository extends TreeTraverser<TreeNodeRepository.T
     /** A pair of path segment, TreeNode. */
     @Immutable
     public static final class ChildEntry {
+
       private final String segment;
       private final TreeNode child;
 
@@ -176,6 +177,8 @@ public final class TreeNodeRepository extends TreeTraverser<TreeNodeRepository.T
     }
   }
 
+  private static final TreeNode EMPTY_NODE = new TreeNode(ImmutableList.<TreeNode.ChildEntry>of());
+
   // Keep only one canonical instance of every TreeNode in the repository.
   private final Interner<TreeNode> interner = BlazeInterners.newWeakInterner();
   // Merkle hashes are computed and cached by the repository, therefore execRoot must
@@ -264,6 +267,12 @@ public final class TreeNodeRepository extends TreeTraverser<TreeNodeRepository.T
       int inputsStart,
       int inputsEnd,
       int segmentIndex) {
+    if (segments.isEmpty()) {
+      // We sometimes have actions with no inputs (e.g., echo "xyz" > $@), so we need to handle that
+      // case here.
+      Preconditions.checkState(inputs.isEmpty());
+      return EMPTY_NODE;
+    }
     if (segmentIndex == segments.get(inputsStart).size()) {
       // Leaf node reached. Must be unique.
       Preconditions.checkArgument(
diff --git a/src/test/java/com/google/devtools/build/lib/remote/TreeNodeRepositoryTest.java b/src/test/java/com/google/devtools/build/lib/remote/TreeNodeRepositoryTest.java
index 4bb8883269..f9ef9111a6 100644
--- a/src/test/java/com/google/devtools/build/lib/remote/TreeNodeRepositoryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/remote/TreeNodeRepositoryTest.java
@@ -152,4 +152,14 @@ public class TreeNodeRepositoryTest {
         .containsExactly(
             rootDigest, aDigest, barDigest, barContentsDigest, fooDigest, fooContentsDigest);
   }
+
+  @Test
+  public void testEmptyTree() throws Exception {
+    SortedMap<PathFragment, ActionInput> inputs = new TreeMap<>();
+    TreeNodeRepository repo = createTestTreeNodeRepository();
+    TreeNode root = repo.buildFromActionInputs(inputs);
+    repo.computeMerkleDigests(root);
+
+    assertThat(root.getChildEntries()).isEmpty();
+  }
 }
diff --git a/src/test/shell/bazel/remote_execution_test.sh b/src/test/shell/bazel/remote_execution_test.sh
index 1a8748da02..e460bff30e 100755
--- a/src/test/shell/bazel/remote_execution_test.sh
+++ b/src/test/shell/bazel/remote_execution_test.sh
@@ -224,6 +224,33 @@ EOF
       || fail "Failed to run //a:test with remote execution"
 }
 
+function test_noinput_action() {
+  mkdir -p a
+  cat > a/rule.bzl <<'EOF'
+def _impl(ctx):
+  output = ctx.outputs.out
+  ctx.action(
+      outputs=[output],
+      command="echo 'Hello World' > %s" % (output.path))
+
+empty = rule(
+    implementation=_impl,
+    outputs={"out": "%{name}.txt"},
+)
+EOF
+  cat > a/BUILD <<'EOF'
+load("//a:rule.bzl", "empty")
+package(default_visibility = ["//visibility:public"])
+empty(name = 'test')
+EOF
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+      --spawn_strategy=remote \
+      --remote_cache=localhost:${worker_port} \
+      --test_output=errors \
+      //a:test >& $TEST_log \
+      || fail "Failed to run //a:test with remote execution"
+}
+
 # TODO(alpha): Add a test that fails remote execution when remote worker
 # supports sandbox.