Don't rebuild command line parser for each invocation

Makes tests faster

borg/archiver.py

@@ -96,9 +96,10 @@ def with_archive(method):
 
 class Archiver:
 
-    def __init__(self, lock_wait=None):
+    def __init__(self, lock_wait=None, prog=None):
         self.exit_code = EXIT_SUCCESS
         self.lock_wait = lock_wait
+        self.parser = self.build_parser(prog)
 
     def print_error(self, msg, *args):
         msg = args and msg % args or msg
@@ -1118,7 +1119,7 @@ class Archiver:
                     self.print_warning(warning)
         return args
 
-    def build_parser(self, args=None, prog=None):
+    def build_parser(self, prog=None):
         common_parser = argparse.ArgumentParser(add_help=False, prog=prog)
 
         common_group = common_parser.add_argument_group('Common options')
@@ -2062,8 +2063,7 @@ class Archiver:
         # We can't use argparse for "serve" since we don't want it to show up in "Available commands"
         if args:
             args = self.preprocess_args(args)
-        parser = self.build_parser(args)
-        args = parser.parse_args(args or ['-h'])
+        args = self.parser.parse_args(args or ['-h'])
         update_excludes(args)
         return args
 

setup.py

@@ -159,7 +159,7 @@ class build_usage(Command):
         print('generating usage docs')
         # allows us to build docs without the C modules fully loaded during help generation
         from borg.archiver import Archiver
-        parser = Archiver().build_parser(prog='borg')
+        parser = Archiver(prog='borg').parser
         choices = {}
         for action in parser._actions:
             if action.choices is not None: