[libcxx][lit] Simplify parsing of trailing executor arguments

Adding a positional argparse.ONE_OR_MORE arguments will correctly remove
the "--" separator after --env and parse only the command. This also has
the advantage that misspelled flags raise an argparse error rather than
silently being added to the command to be executed.

I discovered this while adding a new commandline option to ssh.py to allow
passing additional arguments to the scp/ssh commands since this is required
for our CHERI CI where we need to pass `-F <custom_config_file>` to each
ssh/scp command to set various arguments such as the localhost port, usage
of controlmaster, etc. to speed up connections to our emulated QEMU systems.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D84096

libcxx/utils/run.py

@@ -23,12 +23,9 @@ def main():
     parser.add_argument('--execdir', type=str, required=True)
     parser.add_argument('--codesign_identity', type=str, required=False, default=None)
     parser.add_argument('--env', type=str, nargs='*', required=False, default=dict())
-    (args, remaining) = parser.parse_known_args(sys.argv[1:])
-
-    if len(remaining) < 2:
-        sys.stderr.write('Missing actual commands to run')
-        exit(1)
-    commandLine = remaining[1:] # Skip the '--'
+    parser.add_argument("command", nargs=argparse.ONE_OR_MORE)
+    args = parser.parse_args()
+    commandLine = args.command
 
     # Do any necessary codesigning.
     if args.codesign_identity:

libcxx/utils/ssh.py

@@ -29,13 +29,9 @@ def main():
     parser.add_argument('--execdir', type=str, required=True)
     parser.add_argument('--codesign_identity', type=str, required=False, default=None)
     parser.add_argument('--env', type=str, nargs='*', required=False, default=dict())
-    (args, remaining) = parser.parse_known_args(sys.argv[1:])
-
-    if len(remaining) < 2:
-        sys.stderr.write('Missing actual commands to run')
-        return 1
-
-    commandLine = remaining[1:] # Skip the '--'
+    parser.add_argument("command", nargs=argparse.ONE_OR_MORE)
+    args = parser.parse_args()
+    commandLine = args.command
 
     ssh = lambda command: ['ssh', '-oBatchMode=yes', args.host, command]
     scp = lambda src, dst: ['scp', '-q', '-oBatchMode=yes', src, '{}:{}'.format(args.host, dst)]