Mount TreeArtifact directories as inputs to Spawns.

Fixes bazelbuild#1928.

--
PiperOrigin-RevId: 141077737
MOS_MIGRATED_REVID=141077737

src/main/java/com/google/devtools/build/lib/sandbox/SpawnHelpers.java

@@ -187,6 +187,17 @@ void mountInputs(
       }
     }
 
+    // ActionInputHelper#expandArtifacts above expands empty TreeArtifacts into an empty list.
+    // However, actions that accept TreeArtifacts as inputs generally expect that the empty
+    // directory is created. So here we explicitly mount the directories of the TreeArtifacts as
+    // inputs.
+    for (ActionInput input : spawn.getInputFiles()) {
+      if (input instanceof Artifact && ((Artifact) input).isTreeArtifact()) {
+        PathFragment mount = new PathFragment(input.getExecPathString());
+        mounts.put(mount, execRoot.getRelative(mount));
+      }
+    }
+
     for (ActionInput input : inputs) {
       if (input.getExecPathString().contains("internal/_middlemen/")) {
         continue;

src/test/shell/bazel/android/android_integration_test.sh

@@ -234,6 +234,29 @@ function test_android_binary_clang() {
   check_soname
 }
 
+# Regression test for https://github.com/bazelbuild/bazel/issues/1928.
+function test_empty_tree_artifact_action_inputs_mount_empty_directories() {
+  create_new_workspace
+  setup_android_support
+  cat > AndroidManifest.xml <<EOF
+<manifest package="com.test"/>
+EOF
+  mkdir res
+  zip test.aar AndroidManifest.xml res/
+  cat > BUILD <<EOF
+aar_import(
+  name = "test",
+  aar = "test.aar",
+)
+EOF
+  # Building aar_import invokes the AndroidResourceProcessingAction with a
+  # TreeArtifact of the AAR resources as the input. Since there are no
+  # resources, the Bazel sandbox should create an empty directory. If the
+  # directory is not created, the action thinks that its inputs do not exist and
+  # crashes.
+  bazel build :test
+}
+
 # ndk r10 and earlier
 if [[ ! -r "${TEST_SRCDIR}/androidndk/ndk/RELEASE.TXT" ]]; then
   # ndk r11 and later