Seperated argument parser creation from main kas entry point

With Sphinx it is possible to create the command line documentation
automatically if there is a function that returns just the command line
parser.

Currently the creation of the argument parser is rather entangled with
the rest of kas. This patches seperates this.

Signed-off-by: Claudius Heine <ch@denx.de>

kas/build.py

@@ -25,7 +25,7 @@
 
 import os
 from .config import load_config
-from .libkas import find_program, run_cmd
+from .libkas import find_program, run_cmd, kasplugin
 from .libcmds import (Macro, Command, SetupDir, SetupProxy,
                       CleanupSSHAgent, SetupSSHAgent, SetupEnviron,
                       WriteConfig, SetupHome, ReposFetch,
@@ -35,12 +35,17 @@ __license__ = 'MIT'
 __copyright__ = 'Copyright (c) Siemens AG, 2017'
 
 
+@kasplugin
 class Build:
     """
         This class implements the build plugin for kas.
     """
 
-    def __init__(self, parser):
+    @classmethod
+    def get_argparser(cls, parser):
+        """
+            Returns an a parser for the build plugin
+        """
         bld_psr = parser.add_parser('build')
 
         bld_psr.add_argument('config',

kas/kas.py

@@ -42,10 +42,16 @@ try:
 except ImportError:
     HAVE_COLORLOG = False
 
-from .build import Build
-from .shell import Shell
 from . import __version__
 
+# Import kas plugins
+# Since they are added by decorators, they don't need to be called,
+# just imported.
+# pylint: disable=unused-import
+from .libkas import kasplugin
+from . import build
+from . import shell
+
 __license__ = 'MIT'
 __copyright__ = 'Copyright (c) Siemens AG, 2017'
 
@@ -90,12 +96,10 @@ def _atexit_handler(loop):
     os.killpg(os.getpid(), signal.SIGTERM)
 
 
-def kas(argv):
+def kas_get_argparser():
     """
-        The main entry point of kas.
+        Creates a argparser for kas with all plugins.
     """
-    create_logger()
-
     parser = argparse.ArgumentParser(description='Steer ebs-yocto builds')
 
     parser.add_argument('--version', action='version',
@@ -106,12 +110,22 @@ def kas(argv):
                         help='Enable debug logging')
 
     subparser = parser.add_subparsers(help='sub command help', dest='cmd')
-    sub_cmds = [Build(subparser), Shell(subparser)]
+    for ext_plugin in pkg_resources.iter_entry_points('kas.plugins'):
+        ext_plugin.load()
 
-    for plugin in pkg_resources.iter_entry_points('kas.plugins'):
-        cmd = plugin.load()
-        sub_cmds.append(cmd(subparser))
+    for plugin in getattr(kasplugin, 'plugins', []):
+        plugin.get_argparser(subparser)
 
+    return parser
+
+
+def kas(argv):
+    """
+        The main entry point of kas.
+    """
+    create_logger()
+
+    parser = kas_get_argparser()
     args = parser.parse_args(argv)
 
     if args.debug:
@@ -123,8 +137,8 @@ def kas(argv):
         loop.add_signal_handler(sig, interruption)
     atexit.register(_atexit_handler, loop=loop)
 
-    for cmd in sub_cmds:
-        if cmd.run(args):
+    for plugin in getattr(kasplugin, 'plugins', []):
+        if plugin().run(args):
             return
 
     parser.print_help()

kas/libkas.py

@@ -355,3 +355,12 @@ def ssh_no_host_key_check(_):
         os.mkdir(home + '/.ssh')
     with open(home + '/.ssh/config', 'w') as fds:
         fds.write('Host *\n\tStrictHostKeyChecking no\n\n')
+
+
+def kasplugin(plugin_class):
+    """
+        A decorator that registeres kas plugins
+    """
+    if not hasattr(kasplugin, 'plugins'):
+        setattr(kasplugin, 'plugins', [])
+    getattr(kasplugin, 'plugins').append(plugin_class)

kas/shell.py

@@ -25,6 +25,7 @@
 """
 
 import subprocess
+from kas.libkas import kasplugin
 from kas.config import load_config
 from kas.libcmds import (Macro, Command, SetupProxy, SetupEnviron, SetupHome)
 
@@ -32,12 +33,17 @@ __license__ = 'MIT'
 __copyright__ = 'Copyright (c) Siemens AG, 2017'
 
 
+@kasplugin
 class Shell:
     """
         Implements a kas plugin that opens a shell within the kas environment.
     """
 
-    def __init__(self, parser):
+    @classmethod
+    def get_argparser(cls, parser):
+        """
+            Returns a parser for the shell plugin
+        """
         sh_prs = parser.add_parser('shell')
 
         sh_prs.add_argument('config',