[v3,1/2] bitbake-setup: update: add a --update-bb-conf option

diff --git a/bin/bitbake-setup b/bin/bitbake-setup
index d0a932a6b2..97ca67e155 100755
--- a/bin/bitbake-setup
+++ b/bin/bitbake-setup
@@ -134,7 +134,7 @@  def checkout_layers(layers, layerdir, d):
 
     return layers_fixed_revisions
 
-def setup_bitbake_build(bitbake_config, layerdir, setupdir, thisdir):
+def setup_bitbake_build(bitbake_config, layerdir, setupdir, thisdir, update_bb_conf):
     def _setup_build_conf(layers, filerelative_layers, build_conf_dir):
         os.makedirs(build_conf_dir)
         layers_s = []
@@ -224,9 +224,13 @@  def setup_bitbake_build(bitbake_config, layerdir, setupdir, thisdir):
         raise Exception("Cannot complete setting up a bitbake build directory from OpenEmbedded template '{}' as oe-setup-build was not found in any layers; please use oe-init-build-env manually.".format(template))
 
     bitbake_confdir = os.path.join(bitbake_builddir, 'conf')
-    backup_bitbake_confdir = bitbake_confdir + "-backup.{}".format(time.strftime("%Y%m%d%H%M%S"))
+    timestamp = time.strftime("%Y%m%d%H%M%S")
+    backup_bitbake_confdir = os.path.join(bitbake_builddir, 'conf-backup.{}'.format(timestamp))
+    upstream_bitbake_confdir = os.path.join(bitbake_builddir, 'conf-upstream.{}'.format(timestamp))
+
     if os.path.exists(bitbake_confdir):
         os.rename(bitbake_confdir, backup_bitbake_confdir)
+        print("Existing bitbake configuration directory renamed to {}".format(backup_bitbake_confdir))
 
     if layers:
         filerelative_layers = bitbake_config.get("bb-layers-file-relative") or []
@@ -257,16 +261,32 @@  def setup_bitbake_build(bitbake_config, layerdir, setupdir, thisdir):
         bb.process.run("{} -c '. {} && bitbake-config-build enable-fragment {}'".format(shell, init_script, " ".join(fragments)))
 
     if os.path.exists(backup_bitbake_confdir):
-        bitbake_config_diff = get_diff(backup_bitbake_confdir, bitbake_confdir)
-        if bitbake_config_diff:
-            print("Existing bitbake configuration directory renamed to {}".format(backup_bitbake_confdir))
-            print("The bitbake configuration has changed:")
-            print(bitbake_config_diff)
-        else:
-            shutil.rmtree(backup_bitbake_confdir)
+        conf_diff = get_diff(backup_bitbake_confdir, bitbake_confdir)
+        if not conf_diff:
+            print('New bitbake configuration from upstream is the same as the current one, no need to update it.')
+            shutil.rmtree(bitbake_confdir)
+            os.rename(backup_bitbake_confdir, bitbake_confdir)
+            return
 
-    print("This bitbake configuration provides:\n    {}\n".format(bitbake_config["description"]))
+        print('Upstream bitbake configuration changes were found:')
+        print(conf_diff)
+
+        if update_bb_conf == 'prompt':
+            y_or_n = input('Apply these changes to the current configuration? (y/N): ')
+            if y_or_n != 'y':
+                update_bb_conf = 'no'
 
+        if update_bb_conf == 'no':
+            print('Ignoring upstream bitbake configuration changes')
+            print(f'Leaving the upstream configuration in {upstream_bitbake_confdir}')
+            os.rename(bitbake_confdir, upstream_bitbake_confdir)
+            os.rename(backup_bitbake_confdir, bitbake_confdir)
+            return
+
+        print('Applying upstream bitbake configuration changes')
+        print(f'Leaving the previous configuration in {backup_bitbake_confdir}')
+
+    print("This bitbake configuration provides:\n    {}\n".format(bitbake_config["description"]))
     readme = """{}\n\nAdditional information is in {} and {}\n
 Source the environment using '. {}' to run builds from the command line.
 The bitbake configuration files (local.conf, bblayers.conf and more) can be found in {}/conf
@@ -291,7 +311,7 @@  def get_registry_config(registry_path, id):
                 return os.path.join(root, f)
     raise Exception("Unable to find {} in available configurations; use 'list' sub-command to see what is available".format(id))
 
-def update_build(config, confdir, setupdir, layerdir, d):
+def update_build(config, confdir, setupdir, layerdir, d, update_bb_conf="prompt"):
     layer_config = copy.deepcopy(config["data"]["sources"])
     layer_overrides = config["source-overrides"]["sources"]
     for k,v in layer_overrides.items():
@@ -300,7 +320,7 @@  def update_build(config, confdir, setupdir, layerdir, d):
     sources_fixed_revisions = checkout_layers(layer_config, layerdir, d)
     bitbake_config = config["bitbake-config"]
     thisdir = os.path.dirname(config["path"]) if config["type"] == 'local' else None
-    setup_bitbake_build(bitbake_config, layerdir, setupdir, thisdir)
+    setup_bitbake_build(bitbake_config, layerdir, setupdir, thisdir, update_bb_conf)
     write_sources_fixed_revisions(confdir, sources_fixed_revisions)
 
 def int_input(allowed_values):
@@ -506,7 +526,7 @@  def init_config(top_dir, settings, args):
     bb.event.register("bb.build.TaskProgress", handle_task_progress, data=d)
 
     write_upstream_config(confdir, upstream_config)
-    update_build(upstream_config, confdir, setupdir, layerdir, d)
+    update_build(upstream_config, confdir, setupdir, layerdir, d, update_bb_conf="yes")
     commit_config(confdir)
 
     bb.event.remove("bb.build.TaskProgress", None)
@@ -565,18 +585,25 @@  def build_status(top_dir, settings, args, d, update=False):
     write_upstream_config(confdir, new_upstream_config)
     config_diff = bb.process.run('git -C {} diff'.format(confdir))[0]
 
+    update_bb_conf = 'prompt'
+    try:
+        update_bb_conf = args.update_bb_conf
+    except AttributeError:
+        # this arg is only passed from build_update()
+        pass
+
     if config_diff:
         print('\nConfiguration in {} has changed:\n{}'.format(setupdir, config_diff))
         if update:
             commit_config(confdir)
-            update_build(new_upstream_config, confdir, setupdir, layerdir, d)
+            update_build(new_upstream_config, confdir, setupdir, layerdir, d, update_bb_conf=update_bb_conf)
         else:
             bb.process.run('git -C {} restore config-upstream.json'.format(confdir))
         return
 
     if are_layers_changed(current_upstream_config["data"]["sources"], layerdir, d):
         if update:
-            update_build(current_upstream_config, confdir, setupdir, layerdir, d)
+            update_build(current_upstream_config, confdir, setupdir, layerdir, d, update_bb_conf=update_bb_conf)
         return
 
     print("\nConfiguration in {} has not changed.".format(setupdir))
@@ -836,6 +863,7 @@  def main():
 
     parser_update = subparsers.add_parser('update', help='Update a setup to be in sync with configuration')
     add_setup_dir_arg(parser_update)
+    parser_update.add_argument('--update-bb-conf', choices=['prompt', 'yes', 'no'], default='prompt', help='Update bitbake configuration files (bblayers.conf, local.conf) (default: prompt)')
     parser_update.set_defaults(func=build_update)
 
     parser_install_buildtools = subparsers.add_parser('install-buildtools', help='Install buildtools which can help fulfil missing or incorrect dependencies on the host machine')
diff --git a/doc/bitbake-user-manual/bitbake-user-manual-environment-setup.rst b/doc/bitbake-user-manual/bitbake-user-manual-environment-setup.rst
index 3193952972..dd8d08877f 100644
--- a/doc/bitbake-user-manual/bitbake-user-manual-environment-setup.rst
+++ b/doc/bitbake-user-manual/bitbake-user-manual-environment-setup.rst
@@ -401,6 +401,14 @@  status of the :term:`Setup` before updating it.
 
 In addition, the command can take the following arguments:
 
+-  ``--update-bb-conf``: whether to update the :term:`BitBake Build`
+   configuration (``local.conf``, ``bblayers.conf``, etc.). This argument can
+   take up to three values:
+
+   -  ``prompt`` (default): ask the user whether to update.
+   -  ``yes``: update the configuration files.
+   -  ``no``: don't update the configuration files.
+
 -  ``--setup-dir``: path to the :term:`Setup` to update. Not required if the
    command is invoked from an initialized BitBake environment that contains
    :term:`BBPATH`.
diff --git a/lib/bb/tests/setup.py b/lib/bb/tests/setup.py
index 73ba3b2bc8..18b560b93d 100644
--- a/lib/bb/tests/setup.py
+++ b/lib/bb/tests/setup.py
@@ -311,7 +311,7 @@  print("BBPATH is {{}}".format(os.environ["BBPATH"]))
                 os.environ['BBPATH'] = os.path.join(setuppath, 'build')
                 out = self.runbbsetup("status")
                 self.assertIn("Configuration in {} has not changed".format(setuppath), out[0])
-                out = self.runbbsetup("update")
+                out = self.runbbsetup("update --update-bb-conf='yes'")
                 self.assertIn("Configuration in {} has not changed".format(setuppath), out[0])
 
         # install buildtools
@@ -332,7 +332,7 @@  print("BBPATH is {{}}".format(os.environ["BBPATH"]))
             os.environ['BBPATH'] = os.path.join(setuppath, 'build')
             out = self.runbbsetup("status")
             self.assertIn("Layer repository file://{} checked out into {}/layers/test-repo updated revision master from".format(self.testrepopath, setuppath), out[0])
-            out = self.runbbsetup("update")
+            out = self.runbbsetup("update --update-bb-conf='yes'")
             if c in ('gadget', 'gizmo'):
                 self.assertIn("Existing bitbake configuration directory renamed to {}/build/conf-backup.".format(setuppath), out[0])
                 self.assertIn('-{}+{}'.format(prev_test_file_content, test_file_content), out[0])
@@ -356,7 +356,7 @@  print("BBPATH is {{}}".format(os.environ["BBPATH"]))
             out = self.runbbsetup("status")
             self.assertIn("Configuration in {} has changed:".format(setuppath), out[0])
             self.assertIn('-                    "rev": "master"\n+                    "rev": "another-branch"', out[0])
-            out = self.runbbsetup("update")
+            out = self.runbbsetup("update --update-bb-conf='yes'")
             if c in ('gadget', 'gizmo'):
                 self.assertIn("Existing bitbake configuration directory renamed to {}/build/conf-backup.".format(setuppath), out[0])
                 self.assertIn('-{}+{}'.format(prev_test_file_content, test_file_content), out[0])