Refactor cli main function

The logic of setting up beets and running a command was scattered
across the `_raw_main` and `_configure` functions. This is an attempt
to bring more structure to the process and to diminish the dependency
on global state.

beets/ui/__init__.py

@@ -694,6 +694,16 @@ class SubcommandsOptionParser(optparse.OptionParser):
 
         # Super constructor.
         optparse.OptionParser.__init__(self, *args, **kwargs)
+        self.add_option('-l', '--library', dest='library',
+                        help='library database file to use')
+        self.add_option('-d', '--directory', dest='directory',
+                        help="destination music directory")
+        self.add_option('-v', '--verbose', dest='verbose', action='store_true',
+                        help='print debugging information')
+        self.add_option('-c', '--config', dest='config',
+                        help='path to configuration file')
+        self.add_option('-h', '--help', dest='help', action='store_true',
+                        help='how this help message and exit')
 
         # Our root parser needs to stop on the first unrecognized argument.
         self.disable_interspersed_args()
@@ -855,11 +865,18 @@ def _load_plugins():
     plugins.send("pluginload")
 
 
-def _configure(args):
-    """Parse the command line, load configuration files (including
-    loading any indicated plugins), and return the invoked subcomand,
-    the subcommand options, and the subcommand arguments.
+def _setup(options, lib=None):
+    """Prepare and global state and updates it with command line options.
+
+    Returns a list of subcommands, a list of plugins, and a library instance.
     """
+    # Configure the MusicBrainz API.
+    mb.configure()
+
+    _configure(options)
+
+    _load_plugins()
+
     # Temporary: Migrate from 1.0-style configuration.
     from beets.ui import migrate
     migrate.automigrate()
@@ -867,21 +884,20 @@ def _configure(args):
     # Get the default subcommands.
     from beets.ui.commands import default_commands
 
-    # Construct the root parser.
-    parser = SubcommandsOptionParser()
-    parser.add_option('-l', '--library', dest='library',
-                      help='library database file to use')
-    parser.add_option('-d', '--directory', dest='directory',
-                      help="destination music directory")
-    parser.add_option('-v', '--verbose', dest='verbose', action='store_true',
-                      help='print debugging information')
-    parser.add_option('-c', '--config', dest='config',
-                      help='path to configuration file')
-    parser.add_option('-h', '--help', dest='help', action='store_true',
-                      help='how this help message and exit')
+    subcommands = list(default_commands)
+    subcommands.append(migrate.migrate_cmd)
+    subcommands.extend(plugins.commands())
 
-    # Parse the command-line!
-    options, subargs = parser.parse_global_options(args)
+    if lib is None:
+        lib = _open_library(config)
+        plugins.send("library_opened", lib=lib)
+
+    return subcommands, plugins, lib
+
+
+def _configure(options):
+    """Amend the global configuration object with command line options.
+    """
 
     # Add any additional config files specified with --config. This
     # special handling lets specified plugins get loaded before we
@@ -906,54 +922,47 @@ def _configure(args):
         log.debug('no user configuration found at {0}'.format(
             util.displayable_path(config_path)))
 
-    # Add builtin subcommands
-    parser.add_subcommand(*default_commands)
-    parser.add_subcommand(migrate.migrate_cmd)
+    log.debug(u'data directory: {0}'
+              .format(util.displayable_path(config.config_dir())))
 
-    # Now add the plugin commands to the parser.
-    _load_plugins()
-    for cmd in plugins.commands():
-        parser.add_subcommand(cmd)
 
-    # Parse the remainder of the command line with loaded plugins.
-    return parser.parse_subcommand(subargs)
+def _open_library(config):
+    """Create a new library instance from the configuration.
+    """
+    dbpath = config['library'].as_filename()
+    try:
+        lib = library.Library(
+            dbpath,
+            config['directory'].as_filename(),
+            get_path_formats(),
+            get_replacements(),
+        )
+    except sqlite3.OperationalError:
+        raise UserError(u"database file {0} could not be opened".format(
+            util.displayable_path(dbpath)
+        ))
+    log.debug(u'library database: {0}\n'
+              u'library directory: {1}'
+              .format(
+                  util.displayable_path(lib.path),
+                  util.displayable_path(lib.directory),
+              ))
+    return lib
 
 
 def _raw_main(args, lib=None):
     """A helper function for `main` without top-level exception
     handling.
     """
-    subcommand, suboptions, subargs = _configure(args)
 
-    if lib is None:
-        # Open library file.
-        dbpath = config['library'].as_filename()
-        try:
-            lib = library.Library(
-                dbpath,
-                config['directory'].as_filename(),
-                get_path_formats(),
-                get_replacements(),
-            )
-        except sqlite3.OperationalError:
-            raise UserError(u"database file {0} could not be opened".format(
-                util.displayable_path(dbpath)
-            ))
-        plugins.send("library_opened", lib=lib)
+    parser = SubcommandsOptionParser()
+    options, subargs = parser.parse_global_options(args)
 
-    log.debug(u'data directory: {0}\n'
-              u'library database: {1}\n'
-              u'library directory: {2}'
-              .format(
-                  util.displayable_path(config.config_dir()),
-                  util.displayable_path(lib.path),
-                  util.displayable_path(lib.directory),
-              ))
+    subcommands, plugins, lib = _setup(options, lib)
 
-    # Configure the MusicBrainz API.
-    mb.configure()
+    parser.add_subcommand(*subcommands)
+    subcommand, suboptions, subargs = parser.parse_subcommand(subargs)
 
-    # Invoke the subcommand.
     subcommand.func(lib, suboptions, subargs)
     plugins.send('cli_exit', lib=lib)
 

test/test_ui.py

@@ -740,7 +740,7 @@ class ConfigTest(unittest.TestCase, TestHelper):
         beetsdir = os.path.join(self.temp_dir, 'beetsfile')
         open(beetsdir, 'a').close()
         os.environ['BEETSDIR'] = beetsdir
-        self.assertRaises(ConfigError, ui._raw_main, 'test')
+        self.assertRaises(ConfigError, ui._raw_main, ['test'])
 
     def test_beetsdir_config_does_not_load_default_user_config(self):
         os.environ['BEETSDIR'] = self.beetsdir