diff --git a/core/OWNERS b/core/OWNERS
index 8d612e0..dae34ff 100644
--- a/core/OWNERS
+++ b/core/OWNERS
@@ -1,5 +1,5 @@
-per-file dex_preopt*.mk = ngeoffray@google.com,calin@google.com,mathewi@google.com,skvadrik@google.com
-per-file verify_uses_libraries.sh = ngeoffray@google.com,calin@google.com,skvadrik@google.com
+per-file dex_preopt*.* = ngeoffray@google.com,skvadrik@google.com
+per-file verify_uses_libraries.sh = ngeoffray@google.com,skvadrik@google.com
 
 # For version updates
 per-file version_defaults.mk = aseaton@google.com,lubomir@google.com,pscovanner@google.com,bkhalife@google.com,jainne@google.com
diff --git a/core/base_rules.mk b/core/base_rules.mk
index 7ea9b52..355a22e 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -20,7 +20,11 @@
 # Users can define base-rules-hook in their buildspec.mk to perform
 # arbitrary operations as each module is included.
 ifdef base-rules-hook
-$(if $(base-rules-hook),)
+  ifndef _has_warned_about_base_rules_hook
+    $(warning base-rules-hook is deprecated, please remove usages of it and/or convert to Soong.)
+    _has_warned_about_base_rules_hook := true
+  endif
+  $(if $(base-rules-hook),)
 endif
 
 ###########################################################
diff --git a/core/main.mk b/core/main.mk
index e0efdad..171a761 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -931,7 +931,7 @@
     $(eval my_deps := $(call get-all-shared-libs-deps,$(m)))\
     $(foreach dep,$(my_deps),\
       $(foreach f,$(ALL_MODULES.$(dep).HOST_SHARED_LIBRARY_FILES),\
-        $(if $(filter $(suite),device-tests general-tests),\
+        $(if $(filter $(suite),device-tests general-tests art-host-tests host-unit-tests),\
           $(eval my_testcases := $(HOST_OUT_TESTCASES)),\
           $(eval my_testcases := $$(COMPATIBILITY_TESTCASES_OUT_$(suite))))\
         $(eval target := $(my_testcases)/$(lastword $(subst /, ,$(dir $(f))))/$(notdir $(f)))\
diff --git a/core/product-graph.mk b/core/product-graph.mk
index 379110e..4a44837 100644
--- a/core/product-graph.mk
+++ b/core/product-graph.mk
@@ -25,7 +25,7 @@
 		$(if $(filter $(p),$(_all_products_visited)),, \
 			$(p) \
 			$(eval _all_products_visited += $(p)) \
-			$(call all-products-inner, $(PRODUCTS.$(strip $(p)).INHERITS_FROM))
+			$(call gather-all-makefiles-for-current-product-inner, $(PRODUCTS.$(strip $(p)).INHERITS_FROM))
 		) \
 	)
 endef
diff --git a/core/product_config.rbc b/core/product_config.rbc
index 7ee3dc7..f67ba8e 100644
--- a/core/product_config.rbc
+++ b/core/product_config.rbc
@@ -536,8 +536,11 @@
     """If from file exists, returns [from:to] pair."""
     value = path_pair.split(":", 2)
 
+    if value[0].find('*') != -1:
+        fail("copy_if_exists: input file cannot contain *")
+
     # Check that l[0] exists
-    return [":".join(value)] if rblf_file_exists(value[0]) else []
+    return [":".join(value)] if rblf_wildcard(value[0]) else []
 
 def _enforce_product_packages_exist(handle, pkg_string_or_list=[]):
     """Makes including non-existent modules in PRODUCT_PACKAGES an error."""
@@ -552,10 +555,6 @@
     _setdefault(handle, "PRODUCT_DEX_PREOPT_MODULE_CONFIGS")
     handle.cfg["PRODUCT_DEX_PREOPT_MODULE_CONFIGS"] += [m + "=" + config for m in modules]
 
-def _file_wildcard_exists(file_pattern):
-    """Return True if there are files matching given bash pattern."""
-    return len(rblf_wildcard(file_pattern)) > 0
-
 def _find_and_copy(pattern, from_dir, to_dir):
     """Return a copy list for the files matching the pattern."""
     return sorted([("%s/%s:%s/%s" % (from_dir, f, to_dir, f))
@@ -605,6 +604,21 @@
                 break
     return res
 
+def _first_word(input):
+    """Equivalent to the GNU make function $(firstword)."""
+    input = __words(input)
+    if len(input) == 0:
+        return ""
+    return input[0]
+
+def _last_word(input):
+    """Equivalent to the GNU make function $(lastword)."""
+    input = __words(input)
+    l = len(input)
+    if l == 0:
+        return ""
+    return input[l-1]
+
 def _dir(paths):
     """Equivalent to the GNU make function $(dir).
 
@@ -859,12 +873,12 @@
     dir = _dir,
     enforce_product_packages_exist = _enforce_product_packages_exist,
     expand_wildcard = _expand_wildcard,
-    file_exists = rblf_file_exists,
-    file_wildcard_exists = _file_wildcard_exists,
     filter = _filter,
     filter_out = _filter_out,
     find_and_copy = _find_and_copy,
     findstring = _findstring,
+    first_word = _first_word,
+    last_word = _last_word,
     inherit = _inherit,
     indirect = _indirect,
     mk2rbc_error = _mk2rbc_error,
diff --git a/core/soong_config.mk b/core/soong_config.mk
index d03b687..c84676b 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -170,6 +170,8 @@
 $(call add_json_list, RecoverySnapshotDirsExcluded,      $(RECOVERY_SNAPSHOT_DIRS_EXCLUDED))
 $(call add_json_bool, HostFakeSnapshotEnabled,           $(HOST_FAKE_SNAPSHOT_ENABLE))
 
+$(call add_json_bool, MultitreeUpdateMeta,               $(filter true,$(TARGET_MULTITREE_UPDATE_META)))
+
 $(call add_json_bool, Treble_linker_namespaces,          $(filter true,$(PRODUCT_TREBLE_LINKER_NAMESPACES)))
 $(call add_json_bool, Enforce_vintf_manifest,            $(filter true,$(PRODUCT_ENFORCE_VINTF_MANIFEST)))
 
diff --git a/core/tasks/multitree.mk b/core/tasks/multitree.mk
new file mode 100644
index 0000000..225477e
--- /dev/null
+++ b/core/tasks/multitree.mk
@@ -0,0 +1,16 @@
+# Copyright (C) 2022 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+.PHONY: update-meta
+update-meta: $(SOONG_MULTITREE_METADATA)
diff --git a/core/version_util.mk b/core/version_util.mk
index 3a0d4b5..cbfef96 100644
--- a/core/version_util.mk
+++ b/core/version_util.mk
@@ -56,36 +56,34 @@
 # unreleased API level targetable by this branch, not just those that are valid
 # lunch targets for this branch.
 
+PLATFORM_VERSION_CODENAME := $(PLATFORM_VERSION_CODENAME.$(TARGET_PLATFORM_VERSION))
 ifndef PLATFORM_VERSION_CODENAME
-  PLATFORM_VERSION_CODENAME := $(PLATFORM_VERSION_CODENAME.$(TARGET_PLATFORM_VERSION))
-  ifndef PLATFORM_VERSION_CODENAME
-    # PLATFORM_VERSION_CODENAME falls back to TARGET_PLATFORM_VERSION
-    PLATFORM_VERSION_CODENAME := $(TARGET_PLATFORM_VERSION)
-  endif
-
-  # This is all of the *active* development codenames.
-  # This confusing name is needed because
-  # all_codenames has been baked into build.prop for ages.
-  #
-  # Should be either the same as PLATFORM_VERSION_CODENAME or a comma-separated
-  # list of additional codenames after PLATFORM_VERSION_CODENAME.
-  PLATFORM_VERSION_ALL_CODENAMES :=
-
-  # Build a list of all active code names. Avoid duplicates, and stop when we
-  # reach a codename that matches PLATFORM_VERSION_CODENAME (anything beyond
-  # that is not included in our build).
-  _versions_in_target := \
-    $(call find_and_earlier,$(ALL_VERSIONS),$(TARGET_PLATFORM_VERSION))
-  $(foreach version,$(_versions_in_target),\
-    $(eval _codename := $(PLATFORM_VERSION_CODENAME.$(version)))\
-    $(if $(filter $(_codename),$(PLATFORM_VERSION_ALL_CODENAMES)),,\
-      $(eval PLATFORM_VERSION_ALL_CODENAMES += $(_codename))))
-
-  # And convert from space separated to comma separated.
-  PLATFORM_VERSION_ALL_CODENAMES := \
-    $(subst $(space),$(comma),$(strip $(PLATFORM_VERSION_ALL_CODENAMES)))
-
+  # PLATFORM_VERSION_CODENAME falls back to TARGET_PLATFORM_VERSION
+  PLATFORM_VERSION_CODENAME := $(TARGET_PLATFORM_VERSION)
 endif
+
+# This is all of the *active* development codenames.
+# This confusing name is needed because
+# all_codenames has been baked into build.prop for ages.
+#
+# Should be either the same as PLATFORM_VERSION_CODENAME or a comma-separated
+# list of additional codenames after PLATFORM_VERSION_CODENAME.
+PLATFORM_VERSION_ALL_CODENAMES :=
+
+# Build a list of all active code names. Avoid duplicates, and stop when we
+# reach a codename that matches PLATFORM_VERSION_CODENAME (anything beyond
+# that is not included in our build).
+_versions_in_target := \
+  $(call find_and_earlier,$(ALL_VERSIONS),$(TARGET_PLATFORM_VERSION))
+$(foreach version,$(_versions_in_target),\
+  $(eval _codename := $(PLATFORM_VERSION_CODENAME.$(version)))\
+  $(if $(filter $(_codename),$(PLATFORM_VERSION_ALL_CODENAMES)),,\
+    $(eval PLATFORM_VERSION_ALL_CODENAMES += $(_codename))))
+
+# And convert from space separated to comma separated.
+PLATFORM_VERSION_ALL_CODENAMES := \
+  $(subst $(space),$(comma),$(strip $(PLATFORM_VERSION_ALL_CODENAMES)))
+
 .KATI_READONLY := \
   PLATFORM_VERSION_CODENAME \
   PLATFORM_VERSION_ALL_CODENAMES
diff --git a/finalize_branch_for_release.sh b/finalize_branch_for_release.sh
index 972ada1..c942eb2 100755
--- a/finalize_branch_for_release.sh
+++ b/finalize_branch_for_release.sh
@@ -21,8 +21,9 @@
 
 m check-vndk-list || update-vndk-list.sh # for new versions of AIDL interfaces
 
-# TODO(b/229413853): test while simulating 'rel' for more requirements AIDL_FROZEN_REL=true
-m # test build
+# for now, we simulate the release state for AIDL, but in the future, we would want
+# to actually turn the branch into the REL state and test with that
+AIDL_FROZEN_REL=true m # test build
 
 # Build SDK (TODO)
 # lunch sdk...
diff --git a/orchestrator/demo/buffet_helper.py b/orchestrator/demo/buffet_helper.py
new file mode 100644
index 0000000..fa29aeb
--- /dev/null
+++ b/orchestrator/demo/buffet_helper.py
@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+import os
+import sys
+import yaml
+
+from hierarchy import parse_hierarchy
+
+
+def main():
+  if len(sys.argv) != 2:
+    print('usage: %s target' % sys.argv[0])
+    exit(1)
+
+  args = sys.argv[1].split('-')
+  if len(args) != 2:
+    print('target format: {target}-{variant}')
+    exit(1)
+
+  target, variant = args
+
+  if variant not in ['eng', 'user', 'userdebug']:
+    print('unknown variant "%s": expected "eng", "user" or "userdebug"' %
+          variant)
+    exit(1)
+
+  build_top = os.getenv('BUFFET_BUILD_TOP')
+  if not build_top:
+    print('BUFFET_BUILD_TOP is not set; Did you correctly run envsetup.sh?')
+    exit(1)
+
+  hierarchy_map = parse_hierarchy(build_top)
+
+  if target not in hierarchy_map:
+    raise RuntimeError(
+        "unknown target '%s': couldn't find the target. Supported targets are: %s"
+        % (target, list(hierarchy_map.keys())))
+
+  hierarchy = [target]
+  while hierarchy_map[hierarchy[-1]]:
+    hierarchy.append(hierarchy_map[hierarchy[-1]])
+
+  print('Target hierarchy for %s: %s' % (target, hierarchy))
+
+
+if __name__ == '__main__':
+  main()
diff --git a/orchestrator/demo/build_helper.py b/orchestrator/demo/build_helper.py
new file mode 100644
index 0000000..c481f80
--- /dev/null
+++ b/orchestrator/demo/build_helper.py
@@ -0,0 +1,367 @@
+#!/usr/bin/env python3
+# Copyright (C) 2022 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import collections
+import copy
+import hierarchy
+import json
+import logging
+import filecmp
+import os
+import shutil
+import subprocess
+import sys
+import tempfile
+import collect_metadata
+import utils
+
+BUILD_CMD_TO_ALL = (
+  'clean',
+  'installclean',
+  'update-meta',
+)
+BUILD_ALL_EXEMPTION = (
+  'art',
+)
+
+def get_supported_product(ctx, supported_products):
+  hierarchy_map = hierarchy.parse_hierarchy(ctx.build_top())
+  target = ctx.target_product()
+
+  while target not in supported_products:
+    if target not in hierarchy_map:
+      return None
+    target = hierarchy_map[target]
+  return target
+
+
+def parse_goals(ctx, metadata, goals):
+  """Parse goals and returns a map from each component to goals.
+
+    e.g.
+
+    "m main art timezone:foo timezone:bar" will return the following dict: {
+        "main": {"all"},
+        "art": {"all"},
+        "timezone": {"foo", "bar"},
+    }
+  """
+  # for now, goal should look like:
+  # {component} or {component}:{subgoal}
+
+  ret = collections.defaultdict(set)
+
+  for goal in goals:
+    # check if the command is for all components
+    if goal in BUILD_CMD_TO_ALL:
+      ret['all'].add(goal)
+      continue
+
+    # should be {component} or {component}:{subgoal}
+    try:
+      component, subgoal = goal.split(':') if ':' in goal else (goal, 'all')
+    except ValueError:
+      raise RuntimeError(
+          'unknown goal: %s: should be {component} or {component}:{subgoal}' %
+          goal)
+    if component not in metadata:
+      raise RuntimeError('unknown goal: %s: component %s not found' %
+                         (goal, component))
+    if not get_supported_product(ctx, metadata[component]['lunch_targets']):
+      raise RuntimeError("can't find matching target. Supported targets are: " +
+                         str(metadata[component]['lunch_targets']))
+
+    ret[component].add(subgoal)
+
+  return ret
+
+
+def find_cycle(metadata):
+  """ Finds a cyclic dependency among components.
+
+  This is for debugging.
+  """
+  visited = set()
+  parent_node = dict()
+  in_stack = set()
+
+  # Returns a cycle if one is found
+  def dfs(node):
+    # visit_order[visit_time[node] - 1] == node
+    nonlocal visited, parent_node, in_stack
+
+    visited.add(node)
+    in_stack.add(node)
+    if 'deps' not in metadata[node]:
+      in_stack.remove(node)
+      return None
+    for next in metadata[node]['deps']:
+      # We found a cycle (next ~ node) if next is still in the stack
+      if next in in_stack:
+        cycle = [node]
+        while cycle[-1] != next:
+          cycle.append(parent_node[cycle[-1]])
+        return cycle
+
+      # Else, continue searching
+      if next in visited:
+        continue
+
+      parent_node[next] = node
+      result = dfs(next)
+      if result:
+        return result
+
+    in_stack.remove(node)
+    return None
+
+  for component in metadata:
+    if component in visited:
+      continue
+
+    result = dfs(component)
+    if result:
+      return result
+
+  return None
+
+
+def topological_sort_components(metadata):
+  """ Performs topological sort on components.
+
+  If A depends on B, B appears first.
+  """
+  # If A depends on B, we want B to appear before A. But the graph in metadata
+  # is represented as A -> B (B in metadata[A]['deps']). So we sort in the
+  # reverse order, and then reverse the result again to get the desired order.
+  indegree = collections.defaultdict(int)
+  for component in metadata:
+    if 'deps' not in metadata[component]:
+      continue
+    for dep in metadata[component]['deps']:
+      indegree[dep] += 1
+
+  component_queue = collections.deque()
+  for component in metadata:
+    if indegree[component] == 0:
+      component_queue.append(component)
+
+  result = []
+  while component_queue:
+    component = component_queue.popleft()
+    result.append(component)
+    if 'deps' not in metadata[component]:
+      continue
+    for dep in metadata[component]['deps']:
+      indegree[dep] -= 1
+      if indegree[dep] == 0:
+        component_queue.append(dep)
+
+  # If topological sort fails, there must be a cycle.
+  if len(result) != len(metadata):
+    cycle = find_cycle(metadata)
+    raise RuntimeError('circular dependency found among metadata: %s' % cycle)
+
+  return result[::-1]
+
+
+def add_dependency_goals(ctx, metadata, component, goals):
+  """ Adds goals that given component depends on."""
+  # For now, let's just add "all"
+  # TODO: add detailed goals (e.g. API build rules, library build rules, etc.)
+  if 'deps' not in metadata[component]:
+    return
+
+  for dep in metadata[component]['deps']:
+    goals[dep].add('all')
+
+
+def sorted_goals_with_dependencies(ctx, metadata, parsed_goals):
+  """ Analyzes the dependency graph among components, adds build commands for
+
+  dependencies, and then sorts the goals.
+
+  Returns a list of tuples: (component_name, set of subgoals).
+  Builds should be run in the list's order.
+  """
+  # TODO(inseob@): after topological sort, some components may be built in
+  # parallel.
+
+  topological_order = topological_sort_components(metadata)
+  combined_goals = copy.deepcopy(parsed_goals)
+
+  # Add build rules for each component's dependencies
+  # We do this in reverse order, so it can be transitive.
+  # e.g. if A depends on B and B depends on C, and we build A,
+  # C should also be built, in addition to B.
+  for component in topological_order[::-1]:
+    if component in combined_goals:
+      add_dependency_goals(ctx, metadata, component, combined_goals)
+
+  ret = []
+  for component in ['all'] + topological_order:
+    if component in combined_goals:
+      ret.append((component, combined_goals[component]))
+
+  return ret
+
+
+def run_build(ctx, metadata, component, subgoals):
+  build_cmd = metadata[component]['build_cmd']
+  out_dir = metadata[component]['out_dir']
+  default_goals = ''
+  if 'default_goals' in metadata[component]:
+    default_goals = metadata[component]['default_goals']
+
+  if 'all' in subgoals:
+    goal = default_goals
+  else:
+    goal = ' '.join(subgoals)
+
+  build_vars = ''
+  if 'update-meta' in subgoals:
+    build_vars = 'TARGET_MULTITREE_UPDATE_META=true'
+  # TODO(inseob@): shell escape
+  cmd = [
+      '/bin/bash', '-c',
+      'source build/envsetup.sh && lunch %s-%s && %s %s %s' %
+      (get_supported_product(ctx, metadata[component]['lunch_targets']),
+       ctx.target_build_variant(), build_vars, build_cmd, goal)
+  ]
+  logging.debug('cwd: ' + metadata[component]['path'])
+  logging.debug('running build: ' + str(cmd))
+
+  subprocess.run(cmd, cwd=metadata[component]['path'], check=True)
+
+
+def run_build_all(ctx, metadata, subgoals):
+  for component in metadata:
+    if component in BUILD_ALL_EXEMPTION:
+      continue
+    run_build(ctx, metadata, component, subgoals)
+
+
+def find_components(metadata, predicate):
+  for component in metadata:
+    if predicate(component):
+      yield component
+
+
+def import_filegroups(metadata, component, exporting_component, target_file_pairs):
+  imported_filegroup_dir = os.path.join(metadata[component]['path'], 'imported', exporting_component)
+
+  bp_content = ''
+  for name, outpaths in target_file_pairs:
+    bp_content += ('filegroup {{\n'
+                   '    name: "{fname}",\n'
+                   '    srcs: [\n'.format(fname=name))
+    for outpath in outpaths:
+      bp_content += '        "{outfile}",\n'.format(outfile=os.path.basename(outpath))
+    bp_content += ('    ],\n'
+                   '}\n')
+
+    with tempfile.TemporaryDirectory() as tmp_dir:
+      with open(os.path.join(tmp_dir, 'Android.bp'), 'w') as fout:
+        fout.write(bp_content)
+      for _, outpaths in target_file_pairs:
+        for outpath in outpaths:
+          os.symlink(os.path.join(metadata[exporting_component]['path'], outpath),
+                    os.path.join(tmp_dir, os.path.basename(outpath)))
+      cmp_result = filecmp.dircmp(tmp_dir, imported_filegroup_dir)
+      if os.path.exists(imported_filegroup_dir) and len(
+          cmp_result.left_only) + len(cmp_result.right_only) + len(
+              cmp_result.diff_files) == 0:
+        # Files are identical, it doesn't need to be written
+        logging.info(
+            'imported files exists and the contents are identical: {} -> {}'
+            .format(component, exporting_component))
+        continue
+      logging.info('creating symlinks for imported files: {} -> {}'.format(
+          component, exporting_component))
+      os.makedirs(imported_filegroup_dir, exist_ok=True)
+      shutil.rmtree(imported_filegroup_dir, ignore_errors=True)
+      shutil.move(tmp_dir, imported_filegroup_dir)
+
+
+def prepare_build(metadata, component):
+  imported_dir = os.path.join(metadata[component]['path'], 'imported')
+  if utils.META_DEPS not in metadata[component]:
+    if os.path.exists(imported_dir):
+      logging.debug('remove {}'.format(imported_dir))
+      shutil.rmtree(imported_dir)
+    return
+
+  imported_components = set()
+  for exp_comp in metadata[component][utils.META_DEPS]:
+    if utils.META_FILEGROUP in metadata[component][utils.META_DEPS][exp_comp]:
+      filegroups = metadata[component][utils.META_DEPS][exp_comp][utils.META_FILEGROUP]
+      target_file_pairs = []
+      for name in filegroups:
+        target_file_pairs.append((name, filegroups[name]))
+      import_filegroups(metadata, component, exp_comp, target_file_pairs)
+      imported_components.add(exp_comp)
+
+  # Remove directories that are not generated this time.
+  if os.path.exists(imported_dir):
+    if len(imported_components) == 0:
+      shutil.rmtree(imported_dir)
+    else:
+      for remove_target in set(os.listdir(imported_dir)) - imported_components:
+        logging.info('remove unnecessary imported dir: {}'.format(remove_target))
+        shutil.rmtree(os.path.join(imported_dir, remove_target))
+
+
+def main():
+  utils.set_logging_config(logging.DEBUG)
+  ctx = utils.get_build_context()
+
+  logging.info('collecting metadata')
+
+  utils.set_logging_config(True)
+
+  goals = sys.argv[1:]
+  if not goals:
+    logging.debug('empty goals. defaults to main')
+    goals = ['main']
+
+  logging.debug('goals: ' + str(goals))
+
+  # Force update the metadata for the 'update-meta' build
+  metadata_collector = collect_metadata.MetadataCollector(
+      ctx.components_top(), ctx.out_dir(),
+      collect_metadata.COMPONENT_METADATA_DIR,
+      collect_metadata.COMPONENT_METADATA_FILE,
+      force_update='update-meta' in goals)
+  metadata_collector.collect()
+
+  metadata = metadata_collector.get_metadata()
+  logging.debug('metadata: ' + str(metadata))
+
+  parsed_goals = parse_goals(ctx, metadata, goals)
+  logging.debug('parsed goals: ' + str(parsed_goals))
+
+  sorted_goals = sorted_goals_with_dependencies(ctx, metadata, parsed_goals)
+  logging.debug('sorted goals with deps: ' + str(sorted_goals))
+
+  for component, subgoals in sorted_goals:
+    if component == 'all':
+      run_build_all(ctx, metadata, subgoals)
+      continue
+    prepare_build(metadata, component)
+    run_build(ctx, metadata, component, subgoals)
+
+
+if __name__ == '__main__':
+  main()
diff --git a/orchestrator/demo/collect_metadata.py b/orchestrator/demo/collect_metadata.py
new file mode 100755
index 0000000..148167d
--- /dev/null
+++ b/orchestrator/demo/collect_metadata.py
@@ -0,0 +1,428 @@
+#!/usr/bin/env python3
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import argparse
+import copy
+import json
+import logging
+import os
+import sys
+import yaml
+from collections import defaultdict
+from typing import (
+  List,
+  Set,
+)
+
+import utils
+
+# SKIP_COMPONENT_SEARCH = (
+#    'tools',
+# )
+COMPONENT_METADATA_DIR = '.repo'
+COMPONENT_METADATA_FILE = 'treeinfo.yaml'
+GENERATED_METADATA_FILE = 'metadata.json'
+COMBINED_METADATA_FILENAME = 'multitree_meta.json'
+
+
+class Dep(object):
+  def __init__(self, name, component, deps_type):
+    self.name = name
+    self.component = component
+    self.type = deps_type
+    self.out_paths = list()
+
+
+class ExportedDep(Dep):
+  def __init__(self, name, component, deps_type):
+    super().__init__(name, component, deps_type)
+
+  def setOutputPaths(self, output_paths: list):
+    self.out_paths = output_paths
+
+
+class ImportedDep(Dep):
+  required_type_map = {
+    # import type: (required type, get imported module list)
+    utils.META_FILEGROUP: (utils.META_MODULES, True),
+  }
+
+  def __init__(self, name, component, deps_type, import_map):
+    super().__init__(name, component, deps_type)
+    self.exported_deps: Set[ExportedDep] = set()
+    self.imported_modules: List[str] = list()
+    self.required_type = deps_type
+    get_imported_module = False
+    if deps_type in ImportedDep.required_type_map:
+      self.required_type, get_imported_module = ImportedDep.required_type_map[deps_type]
+    if get_imported_module:
+      self.imported_modules = import_map[name]
+    else:
+      self.imported_modules.append(name)
+
+  def verify_and_add(self, exported: ExportedDep):
+    if self.required_type != exported.type:
+      raise RuntimeError(
+          '{comp} components imports {module} for {imp_type} but it is exported as {exp_type}.'
+          .format(comp=self.component, module=exported.name, imp_type=self.required_type, exp_type=exported.type))
+    self.exported_deps.add(exported)
+    self.out_paths.extend(exported.out_paths)
+    # Remove duplicates. We may not use set() which is not JSON serializable
+    self.out_paths = list(dict.fromkeys(self.out_paths))
+
+
+class MetadataCollector(object):
+  """Visit all component directories and collect the metadata from them.
+
+Example of metadata:
+==========
+build_cmd: m    # build command for this component. 'm' if omitted
+out_dir: out    # out dir of this component. 'out' if omitted
+exports:
+  libraries:
+    - name: libopenjdkjvm
+    - name: libopenjdkjvmd
+      build_cmd: mma      # build command for libopenjdkjvmd if specified
+      out_dir: out/soong  # out dir for libopenjdkjvmd if specified
+    - name: libctstiagent
+  APIs:
+    - api1
+    - api2
+imports:
+  libraries:
+    - lib1
+    - lib2
+  APIs:
+    - import_api1
+    - import_api2
+lunch_targets:
+  - arm64
+  - x86_64
+"""
+
+  def __init__(self, component_top, out_dir, meta_dir, meta_file, force_update=False):
+    if not os.path.exists(out_dir):
+      os.makedirs(out_dir)
+
+    self.__component_top = component_top
+    self.__out_dir = out_dir
+    self.__metadata_path = os.path.join(meta_dir, meta_file)
+    self.__combined_metadata_path = os.path.join(self.__out_dir,
+                                                 COMBINED_METADATA_FILENAME)
+    self.__force_update = force_update
+
+    self.__metadata = dict()
+    self.__map_exports = dict()
+    self.__component_set = set()
+
+  def collect(self):
+    """ Read precomputed combined metadata from the json file.
+
+    If any components have updated their metadata, update the metadata
+    information and the json file.
+    """
+    timestamp = self.__restore_metadata()
+    if timestamp and os.path.getmtime(__file__) > timestamp:
+      logging.info('Update the metadata as the orchestrator has been changed')
+      self.__force_update = True
+    self.__collect_from_components(timestamp)
+
+  def get_metadata(self):
+    """ Returns collected metadata from all components"""
+    if not self.__metadata:
+      logging.warning('Metadata is empty')
+    return copy.deepcopy(self.__metadata)
+
+  def __collect_from_components(self, timestamp):
+    """ Read metadata from all components
+
+    If any components have newer metadata files or are removed, update the
+    combined metadata.
+    """
+    metadata_updated = False
+    for component in os.listdir(self.__component_top):
+      # if component in SKIP_COMPONENT_SEARCH:
+      #     continue
+      if self.__read_component_metadata(timestamp, component):
+        metadata_updated = True
+      if self.__read_generated_metadata(timestamp, component):
+        metadata_updated = True
+
+    deleted_components = set()
+    for meta in self.__metadata:
+      if meta not in self.__component_set:
+        logging.info('Component {} is removed'.format(meta))
+        deleted_components.add(meta)
+        metadata_updated = True
+    for meta in deleted_components:
+      del self.__metadata[meta]
+
+    if metadata_updated:
+      self.__update_dependencies()
+      self.__store_metadata()
+      logging.info('Metadata updated')
+
+  def __read_component_metadata(self, timestamp, component):
+    """ Search for the metadata file from a component.
+
+    If the metadata is modified, read the file and update the metadata.
+    """
+    component_path = os.path.join(self.__component_top, component)
+    metadata_file = os.path.join(component_path, self.__metadata_path)
+    logging.info(
+        'Reading a metadata file from {} component ...'.format(component))
+    if not os.path.isfile(metadata_file):
+      logging.warning('Metadata file {} not found!'.format(metadata_file))
+      return False
+
+    self.__component_set.add(component)
+    if not self.__force_update and timestamp and timestamp > os.path.getmtime(metadata_file):
+      logging.info('... yaml not changed. Skip')
+      return False
+
+    with open(metadata_file) as f:
+      meta = yaml.load(f, Loader=yaml.SafeLoader)
+
+    meta['path'] = component_path
+    if utils.META_BUILDCMD not in meta:
+      meta[utils.META_BUILDCMD] = utils.DEFAULT_BUILDCMD
+    if utils.META_OUTDIR not in meta:
+      meta[utils.META_OUTDIR] = utils.DEFAULT_OUTDIR
+
+    if utils.META_IMPORTS not in meta:
+      meta[utils.META_IMPORTS] = defaultdict(dict)
+    if utils.META_EXPORTS not in meta:
+      meta[utils.META_EXPORTS] = defaultdict(dict)
+
+    self.__metadata[component] = meta
+    return True
+
+  def __read_generated_metadata(self, timestamp, component):
+    """ Read a metadata gerated by 'update-meta' build command from the soong build system
+
+    Soong generate the metadata that has the information of import/export module/files.
+    Build orchestrator read the generated metadata to collect the dependency information.
+
+    Generated metadata has the following format:
+    {
+      "Imported": {
+        "FileGroups": {
+          "<name_of_filegroup>": [
+            "<exported_module_name>",
+            ...
+          ],
+          ...
+        }
+      }
+      "Exported": {
+        "<exported_module_name>": [
+          "<output_file_path>",
+          ...
+        ],
+        ...
+      }
+    }
+    """
+    if component not in self.__component_set:
+      # skip reading generated metadata if the component metadata file was missing
+      return False
+    component_out = os.path.join(self.__component_top, component, self.__metadata[component][utils.META_OUTDIR])
+    generated_metadata_file = os.path.join(component_out, 'soong', 'multitree', GENERATED_METADATA_FILE)
+    if not os.path.isfile(generated_metadata_file):
+      logging.info('... Soong did not generated the metadata file. Skip')
+      return False
+    if not self.__force_update and timestamp and timestamp > os.path.getmtime(generated_metadata_file):
+      logging.info('... Soong generated metadata not changed. Skip')
+      return False
+
+    with open(generated_metadata_file, 'r') as gen_meta_json:
+      try:
+        gen_metadata = json.load(gen_meta_json)
+      except json.decoder.JSONDecodeError:
+        logging.warning('JSONDecodeError!!!: skip reading the {} file'.format(
+            generated_metadata_file))
+        return False
+
+    if utils.SOONG_IMPORTED in gen_metadata:
+      imported = gen_metadata[utils.SOONG_IMPORTED]
+      if utils.SOONG_IMPORTED_FILEGROUPS in imported:
+        self.__metadata[component][utils.META_IMPORTS][utils.META_FILEGROUP] = imported[utils.SOONG_IMPORTED_FILEGROUPS]
+    if utils.SOONG_EXPORTED in gen_metadata:
+      self.__metadata[component][utils.META_EXPORTS][utils.META_MODULES] = gen_metadata[utils.SOONG_EXPORTED]
+
+    return True
+
+  def __update_export_map(self):
+    """ Read metadata of all components and update the export map
+
+    'libraries' and 'APIs' are special exproted types that are provided manually
+    from the .yaml metadata files. These need to be replaced with the implementation
+    in soong gerated metadata.
+    The export type 'module' is generated from the soong build system from the modules
+    with 'export: true' property. This export type includes a dictionary with module
+    names as keys and their output files as values. These output files will be used as
+    prebuilt sources when generating the imported modules.
+    """
+    self.__map_exports = dict()
+    for comp in self.__metadata:
+      if utils.META_EXPORTS not in self.__metadata[comp]:
+        continue
+      exports = self.__metadata[comp][utils.META_EXPORTS]
+
+      for export_type in exports:
+        for module in exports[export_type]:
+          if export_type == utils.META_LIBS:
+            name = module[utils.META_LIB_NAME]
+          else:
+            name = module
+
+          if name in self.__map_exports:
+            raise RuntimeError(
+                'Exported libs conflict!!!: "{name}" in the {comp} component is already exported by the {prev} component.'
+                .format(name=name, comp=comp, prev=self.__map_exports[name][utils.EXP_COMPONENT]))
+          exported_deps = ExportedDep(name, comp, export_type)
+          if export_type == utils.META_MODULES:
+            exported_deps.setOutputPaths(exports[export_type][module])
+          self.__map_exports[name] = exported_deps
+
+  def __verify_and_add_dependencies(self, component):
+    """ Search all imported items from the export_map.
+
+    If any imported items are not provided by the other components, report
+    an error.
+    Otherwise, add the component dependency and update the exported information to the
+    import maps.
+    """
+    def verify_and_add_dependencies(imported_dep: ImportedDep):
+      for module in imported_dep.imported_modules:
+        if module not in self.__map_exports:
+          raise RuntimeError(
+              'Imported item not found!!!: Imported module "{module}" in the {comp} component is not exported from any other components.'
+              .format(module=module, comp=imported_dep.component))
+        imported_dep.verify_and_add(self.__map_exports[module])
+
+        deps = self.__metadata[component][utils.META_DEPS]
+        exp_comp = self.__map_exports[module].component
+        if exp_comp not in deps:
+          deps[exp_comp] = defaultdict(defaultdict)
+        deps[exp_comp][imported_dep.type][imported_dep.name] = imported_dep.out_paths
+
+    self.__metadata[component][utils.META_DEPS] = defaultdict()
+    imports = self.__metadata[component][utils.META_IMPORTS]
+    for import_type in imports:
+      for module in imports[import_type]:
+        verify_and_add_dependencies(ImportedDep(module, component, import_type, imports[import_type]))
+
+  def __check_imports(self):
+    """ Search the export map to find the component to import libraries or APIs.
+
+    Update the 'deps' field that includes the dependent components.
+    """
+    for component in self.__metadata:
+      self.__verify_and_add_dependencies(component)
+      if utils.META_DEPS in self.__metadata[component]:
+        logging.debug('{comp} depends on {list} components'.format(
+            comp=component, list=self.__metadata[component][utils.META_DEPS]))
+
+  def __update_dependencies(self):
+    """ Generate a dependency graph for the components
+
+    Update __map_exports and the dependency graph with the maps.
+    """
+    self.__update_export_map()
+    self.__check_imports()
+
+  def __store_metadata(self):
+    """ Store the __metadata dictionary as json format"""
+    with open(self.__combined_metadata_path, 'w') as json_file:
+      json.dump(self.__metadata, json_file, indent=2)
+
+  def __restore_metadata(self):
+    """ Read the stored json file and return the time stamps of the
+
+        metadata file.
+        """
+    if not os.path.exists(self.__combined_metadata_path):
+      return None
+
+    with open(self.__combined_metadata_path, 'r') as json_file:
+      try:
+        self.__metadata = json.load(json_file)
+      except json.decoder.JSONDecodeError:
+        logging.warning('JSONDecodeError!!!: skip reading the {} file'.format(
+            self.__combined_metadata_path))
+        return None
+
+    logging.info('Metadata restored from {}'.format(
+        self.__combined_metadata_path))
+    self.__update_export_map()
+    return os.path.getmtime(self.__combined_metadata_path)
+
+
+def get_args():
+
+  def check_dir(path):
+    if os.path.exists(path) and os.path.isdir(path):
+      return os.path.normpath(path)
+    else:
+      raise argparse.ArgumentTypeError('\"{}\" is not a directory'.format(path))
+
+  parser = argparse.ArgumentParser()
+  parser.add_argument(
+      '--component-top',
+      help='Scan all components under this directory.',
+      default=os.path.join(os.path.dirname(__file__), '../../../components'),
+      type=check_dir)
+  parser.add_argument(
+      '--meta-file',
+      help='Name of the metadata file.',
+      default=COMPONENT_METADATA_FILE,
+      type=str)
+  parser.add_argument(
+      '--meta-dir',
+      help='Each component has the metadata in this directory.',
+      default=COMPONENT_METADATA_DIR,
+      type=str)
+  parser.add_argument(
+      '--out-dir',
+      help='Out dir for the outer tree. The orchestrator stores the collected metadata in this directory.',
+      default=os.path.join(os.path.dirname(__file__), '../../../out'),
+      type=os.path.normpath)
+  parser.add_argument(
+      '--force',
+      '-f',
+      action='store_true',
+      help='Force to collect metadata',
+  )
+  parser.add_argument(
+      '--verbose',
+      '-v',
+      help='Increase output verbosity, e.g. "-v", "-vv".',
+      action='count',
+      default=0)
+  return parser.parse_args()
+
+
+def main():
+  args = get_args()
+  utils.set_logging_config(args.verbose)
+
+  metadata_collector = MetadataCollector(args.component_top, args.out_dir,
+                                         args.meta_dir, args.meta_file, args.force)
+  metadata_collector.collect()
+
+
+if __name__ == '__main__':
+  main()
diff --git a/orchestrator/demo/envsetup.sh b/orchestrator/demo/envsetup.sh
new file mode 100644
index 0000000..902a37c
--- /dev/null
+++ b/orchestrator/demo/envsetup.sh
@@ -0,0 +1,48 @@
+#!/bin/bash
+
+function buffet()
+{
+    local product variant selection
+    if [[ $# -ne 1 ]]; then
+        echo "usage: buffet [target]" >&2
+        return 1
+    fi
+
+    selection=$1
+    product=${selection%%-*} # Trim everything after first dash
+    variant=${selection#*-} # Trim everything up to first dash
+
+    if [ -z "$product" ]
+    then
+        echo
+        echo "Invalid lunch combo: $selection"
+        return 1
+    fi
+
+    if [ -z "$variant" ]
+    then
+        if [[ "$product" =~ .*_(eng|user|userdebug) ]]
+        then
+            echo "Did you mean -${product/*_/}? (dash instead of underscore)"
+        fi
+        return 1
+    fi
+
+    BUFFET_BUILD_TOP=$(pwd) python3 tools/build/orchestrator/buffet_helper.py $1 || return 1
+
+    export BUFFET_BUILD_TOP=$(pwd)
+    export BUFFET_COMPONENTS_TOP=$BUFFET_BUILD_TOP/components
+    export BUFFET_TARGET_PRODUCT=$product
+    export BUFFET_TARGET_BUILD_VARIANT=$variant
+    export BUFFET_TARGET_BUILD_TYPE=release
+}
+
+function m()
+{
+    if [ -z "$BUFFET_BUILD_TOP" ]
+    then
+        echo "Run \"buffet [target]\" first"
+        return 1
+    fi
+    python3 $BUFFET_BUILD_TOP/tools/build/orchestrator/build_helper.py "$@"
+}
diff --git a/orchestrator/demo/hierarchy.py b/orchestrator/demo/hierarchy.py
new file mode 100644
index 0000000..ae1825c
--- /dev/null
+++ b/orchestrator/demo/hierarchy.py
@@ -0,0 +1,79 @@
+# Copyright (C) 2022 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import os
+import yaml
+
+
+def parse_hierarchy(build_top):
+  """Parse build hierarchy file from given build top directory, and returns a dict from child targets to parent targets.
+
+  Example of hierarchy file:
+  ==========
+  aosp_arm64:
+  - armv8
+  - aosp_cf_arm64_phone
+
+  armv8:
+  - aosp_oriole
+  - aosp_sunfish
+
+  aosp_oriole:
+  - oriole
+
+  aosp_sunfish:
+  - sunfish
+
+  oriole:
+  # leaf
+
+  sunfish:
+  # leaf
+  ==========
+
+  If we parse this yaml, we get a dict looking like:
+
+  {
+      "sunfish": "aosp_sunfish",
+      "oriole": "aosp_oriole",
+      "aosp_oriole": "armv8",
+      "aosp_sunfish": "armv8",
+      "armv8": "aosp_arm64",
+      "aosp_cf_arm64_phone": "aosp_arm64",
+      "aosp_arm64": None, # no parent
+  }
+  """
+  metadata_path = os.path.join(build_top, 'tools', 'build', 'hierarchy.yaml')
+  if not os.path.isfile(metadata_path):
+    raise RuntimeError("target metadata file %s doesn't exist" % metadata_path)
+
+  with open(metadata_path, 'r') as f:
+    hierarchy_yaml = yaml.load(f, Loader=yaml.SafeLoader)
+
+  hierarchy_map = dict()
+
+  for parent_target, child_targets in hierarchy_yaml.items():
+    if not child_targets:
+      # leaf
+      continue
+    for child_target in child_targets:
+      hierarchy_map[child_target] = parent_target
+
+  for parent_target in hierarchy_yaml:
+    # targets with no parent
+    if parent_target not in hierarchy_map:
+      hierarchy_map[parent_target] = None
+
+  return hierarchy_map
diff --git a/orchestrator/demo/hierarchy.yaml b/orchestrator/demo/hierarchy.yaml
new file mode 100644
index 0000000..cc6de4d
--- /dev/null
+++ b/orchestrator/demo/hierarchy.yaml
@@ -0,0 +1,37 @@
+# hierarchy of targets
+
+aosp_arm64:
+- armv8
+- aosp_cf_arm64_phone
+
+armv8:
+- mainline_modules_arm64
+
+mainline_modules_arm64:
+- aosp_oriole
+- aosp_sunfish
+- aosp_raven
+
+aosp_oriole:
+- oriole
+
+aosp_sunfish:
+- sunfish
+
+aosp_raven:
+- raven
+
+oriole:
+# leaf
+
+sunfish:
+# leaf
+
+raven:
+# leaf
+
+aosp_cf_arm64_phone:
+- cf_arm64_phone
+
+cf_arm64_phone:
+# leaf
diff --git a/orchestrator/demo/utils.py b/orchestrator/demo/utils.py
new file mode 100644
index 0000000..5dbbe4a
--- /dev/null
+++ b/orchestrator/demo/utils.py
@@ -0,0 +1,89 @@
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import logging
+import os
+
+# default build configuration for each component
+DEFAULT_BUILDCMD = 'm'
+DEFAULT_OUTDIR = 'out'
+
+# yaml fields
+META_BUILDCMD = 'build_cmd'
+META_OUTDIR = 'out_dir'
+META_EXPORTS = 'exports'
+META_IMPORTS = 'imports'
+META_TARGETS = 'lunch_targets'
+META_DEPS = 'deps'
+# fields under 'exports' and 'imports'
+META_LIBS = 'libraries'
+META_APIS = 'APIs'
+META_FILEGROUP = 'filegroup'
+META_MODULES = 'modules'
+# fields under 'libraries'
+META_LIB_NAME = 'name'
+
+# fields for generated metadata file
+SOONG_IMPORTED = 'Imported'
+SOONG_IMPORTED_FILEGROUPS = 'FileGroups'
+SOONG_EXPORTED = 'Exported'
+
+# export map items
+EXP_COMPONENT = 'component'
+EXP_TYPE = 'type'
+EXP_OUTPATHS = 'outpaths'
+
+class BuildContext:
+
+  def __init__(self):
+    self._build_top = os.getenv('BUFFET_BUILD_TOP')
+    self._components_top = os.getenv('BUFFET_COMPONENTS_TOP')
+    self._target_product = os.getenv('BUFFET_TARGET_PRODUCT')
+    self._target_build_variant = os.getenv('BUFFET_TARGET_BUILD_VARIANT')
+    self._target_build_type = os.getenv('BUFFET_TARGET_BUILD_TYPE')
+    self._out_dir = os.path.join(self._build_top, 'out')
+
+    if not self._build_top:
+      raise RuntimeError("Can't find root. Did you run buffet?")
+
+  def build_top(self):
+    return self._build_top
+
+  def components_top(self):
+    return self._components_top
+
+  def target_product(self):
+    return self._target_product
+
+  def target_build_variant(self):
+    return self._target_build_variant
+
+  def target_build_type(self):
+    return self._target_build_type
+
+  def out_dir(self):
+    return self._out_dir
+
+
+def get_build_context():
+  return BuildContext()
+
+
+def set_logging_config(verbose_level):
+  verbose_map = (logging.WARNING, logging.INFO, logging.DEBUG)
+  verbosity = min(verbose_level, 2)
+  logging.basicConfig(
+      format='%(levelname)-8s [%(filename)s:%(lineno)d] %(message)s',
+      level=verbose_map[verbosity])
diff --git a/tests/run.rbc b/tests/run.rbc
index 2d35e85..107be09 100644
--- a/tests/run.rbc
+++ b/tests/run.rbc
@@ -81,6 +81,15 @@
 assert_eq(cwd+"/foo/bar "+cwd+"/foo/baz", rblf.abspath("foo/bar foo/baz"))
 assert_eq("/baz", rblf.abspath("/../../../../../../../../../../../../../../../../baz"))
 
+assert_eq("foo", rblf.first_word("foo bar"))
+assert_eq("foo", rblf.first_word(["foo", "bar"]))
+assert_eq("", rblf.first_word(""))
+assert_eq("", rblf.first_word([]))
+assert_eq("bar", rblf.last_word("foo bar"))
+assert_eq("bar", rblf.last_word(["foo", "bar"]))
+assert_eq("", rblf.last_word(""))
+assert_eq("", rblf.last_word([]))
+
 assert_eq(
     ["build/make/tests/board.rbc", "build/make/tests/board_input_vars.rbc"],
     rblf.expand_wildcard("build/make/tests/board*.rbc")
diff --git a/tools/rbcrun/host.go b/tools/rbcrun/host.go
index c6e89f0..32afa45 100644
--- a/tools/rbcrun/host.go
+++ b/tools/rbcrun/host.go
@@ -20,6 +20,7 @@
 	"os"
 	"os/exec"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	"go.starlark.net/starlark"
@@ -111,19 +112,6 @@
 	return e.globals, e.err
 }
 
-// fileExists returns True if file with given name exists.
-func fileExists(_ *starlark.Thread, b *starlark.Builtin, args starlark.Tuple,
-	kwargs []starlark.Tuple) (starlark.Value, error) {
-	var path string
-	if err := starlark.UnpackPositionalArgs(b.Name(), args, kwargs, 1, &path); err != nil {
-		return starlark.None, err
-	}
-	if _, err := os.Stat(path); err != nil {
-		return starlark.False, nil
-	}
-	return starlark.True, nil
-}
-
 // wildcard(pattern, top=None) expands shell's glob pattern. If 'top' is present,
 // the 'top/pattern' is globbed and then 'top/' prefix is removed.
 func wildcard(_ *starlark.Thread, b *starlark.Builtin, args starlark.Tuple,
@@ -150,6 +138,10 @@
 			files[i] = strings.TrimPrefix(files[i], prefix)
 		}
 	}
+	// Kati uses glob(3) with no flags, which means it's sorted
+	// because GLOB_NOSORT is not passed. Go's glob is not
+	// guaranteed to sort the results.
+	sort.Strings(files)
 	return makeStringList(files), nil
 }
 
@@ -269,8 +261,6 @@
 		"struct":   starlark.NewBuiltin("struct", starlarkstruct.Make),
 		"rblf_cli": structFromEnv(env),
 		"rblf_env": structFromEnv(os.Environ()),
-		// To convert makefile's $(wildcard foo)
-		"rblf_file_exists": starlark.NewBuiltin("rblf_file_exists", fileExists),
 		// To convert find-copy-subdir and product-copy-files-by pattern
 		"rblf_find_files": starlark.NewBuiltin("rblf_find_files", find),
 		// To convert makefile's $(shell cmd)
diff --git a/tools/rbcrun/testdata/file_ops.star b/tools/rbcrun/testdata/file_ops.star
index 50e39bf..2ee78fc 100644
--- a/tools/rbcrun/testdata/file_ops.star
+++ b/tools/rbcrun/testdata/file_ops.star
@@ -4,9 +4,6 @@
 
 def test():
     myname = "file_ops.star"
-    assert.true(rblf_file_exists("."), "./ exists ")
-    assert.true(rblf_file_exists(myname), "the file %s does exist" % myname)
-    assert.true(not rblf_file_exists("no_such_file"), "the file no_such_file does not exist")
     files = rblf_wildcard("*.star")
     assert.true(myname in files, "expected %s in  %s" % (myname, files))
     files = rblf_wildcard("*.star", rblf_env.TEST_DATA_DIR)
diff --git a/tools/rbcrun/testdata/module1.star b/tools/rbcrun/testdata/module1.star
index 913fb7d..be04f75 100644
--- a/tools/rbcrun/testdata/module1.star
+++ b/tools/rbcrun/testdata/module1.star
@@ -2,6 +2,6 @@
 load("assert.star", "assert")
 
 # Make sure that builtins are defined for the loaded module, too
-assert.true(rblf_file_exists("module1.star"))
-assert.true(not rblf_file_exists("no_such file"))
+assert.true(rblf_wildcard("module1.star"))
+assert.true(not rblf_wildcard("no_such file"))
 test = "module1"