Add --setup-no-install command

Acts the same as --setup, but does not install any packages. Will
raise an error if any required package is not already installed.

INSTALL

@@ -20,6 +20,7 @@
     ppp \
     pppoe \
     python3 \
+    python3-apt \
     python3-augeas \
     python3-bootstrapform \
     python3-cherrypy3 \

plinth/__main__.py

@@ -21,7 +21,6 @@ import django.conf
 from django.contrib.messages import constants as message_constants
 import django.core.management
 import django.core.wsgi
-from django.utils import translation
 import importlib
 import logging
 import os
@@ -55,6 +54,9 @@ def parse_arguments():
     parser.add_argument(
         '--setup', default=False, nargs='*',
         help='run setup tasks on all essential modules and exit')
+    parser.add_argument(
+        '--setup-no-install', default=False, nargs='*',
+        help='run setup tasks without installing packages and exit')
     parser.add_argument(
         '--diagnose', action='store_true', default=False,
         help='run diagnostic tests and exit')
@@ -249,14 +251,14 @@ def configure_django():
     os.chmod(cfg.store_file, stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP)
 
 
-def run_setup_and_exit(module_list):
+def run_setup_and_exit(module_list, allow_install=True):
     """Run setup on all essential modules and exit."""
     error_code = 0
     try:
         if not module_list:
-            setup.setup_modules(essential=True)
+            setup.setup_modules(essential=True, allow_install=allow_install)
         else:
-            setup.setup_modules(module_list)
+            setup.setup_modules(module_list, allow_install=allow_install)
     except Exception as exception:
         logger.error('Error running setup - %s', exception)
         error_code = 1
@@ -302,6 +304,8 @@ def main():
     module_loader.load_modules()
     if arguments.setup is not False:
         run_setup_and_exit(arguments.setup)
+    if arguments.setup_no_install is not False:
+        run_setup_and_exit(arguments.setup, allow_install=False)
 
     if arguments.diagnose:
         run_diagnostics_and_exit()

plinth/errors.py

@@ -33,3 +33,8 @@ class ActionError(PlinthError):
 class DomainRegistrationError(PlinthError):
     """Domain registration failed"""
     pass
+
+
+class PackageNotInstalledError(PlinthError):
+    """Could not complete module setup due to missing package."""
+    pass

plinth/setup.py

@@ -19,10 +19,12 @@
 Plinth module with utilites for performing application setup operations.
 """
 
+import apt
 import logging
 import threading
 
 from . import package
+from .errors import PackageNotInstalledError
 import plinth
 
 logger = logging.getLogger(__name__)
@@ -58,7 +60,7 @@ class Helper(object):
         self.is_finished = None
         return exception
 
-    def run(self):
+    def run(self, allow_install=True):
         """Execute the setup process."""
         # Setup for the module is already running
         if self.current_operation:
@@ -68,6 +70,7 @@ class Helper(object):
         if current_version >= self.module.version:
             return
 
+        self.allow_install = allow_install
         self.exception = None
         self.current_operation = None
         self.is_finished = False
@@ -89,6 +92,14 @@ class Helper(object):
 
     def install(self, package_names):
         """Install a set of packages marking progress."""
+        if self.allow_install is False:
+            # Raise error if packages are not already installed.
+            cache = apt.Cache()
+            for package_name in package_names:
+                if not cache[package_name].is_installed:
+                    raise PackageNotInstalledError(package_name)
+            return
+
         logger.info('Running install for module - %s, packages - %s',
                     self.module_name, package_names)
 
@@ -150,7 +161,7 @@ def init(module_name, module):
         module.setup_helper = Helper(module_name, module)
 
 
-def setup_modules(module_list=None, essential=False):
+def setup_modules(module_list=None, essential=False, allow_install=True):
     """Run setup on selected or essential modules."""
     logger.info('Running setup for modules, essential - %s, '
                 'selected modules - %s', essential, module_list)
@@ -161,4 +172,4 @@ def setup_modules(module_list=None, essential=False):
         if module_list and module_name not in module_list:
             continue
 
-        module.setup_helper.run()
+        module.setup_helper.run(allow_install=allow_install)

requirements.txt

@@ -3,5 +3,6 @@ coverage >= 3.7
 django >= 1.10.0
 django-stronghold
 psutil
+python-apt
 python-augeas
 ruamel.yaml

setup.py

@@ -184,6 +184,7 @@ setuptools.setup(
         'django-bootstrap-form',
         'django-stronghold',
         'psutil',
+        'python-apt',
         'python-augeas',
         'requests',
         'ruamel.yaml',