The `--` mechanism for splitting arguments doesn't get forwarded correctly

[simonw]

Spotted this for my llm command, which uses click-default-group to set the default command to llm prompt.

If you run this:

llm -- '--help means what?'

You get this error:

Usage: llm prompt [OPTIONS] [PROMPT]
Try 'llm prompt --help' for help.

Error: No such option: --help means what?

But if you run the full command instead:

llm prompt -- '--help means what?'

You get the expected answer:

"--help" is a command that can be used in various computer programs and ...

Bug reported here:

• llm -- "--find me" doesn't work but llm prompt -- "--find me" does simonw/llm#245

[simonw]

Related code search in the Click source code: https://github.com/search?q=repo%3Apallets%2Fclick+%2F%5B%5E-%5D--%5B%5E-%5D%2F&type=code - had to search for repo:pallets/click /[^-]--[^-]/.

[simonw]

Here's a test that illustrates the bug:

@click.group(cls=DefaultGroup, default="baz", invoke_without_command=True)
def cli_with_argument_and_option():
    pass


@cli_with_argument_and_option.command()
@click.argument("argument")
@click.option("--option")
def baz(argument, option):
    click.echo(f"baz: argument: {argument}, option: {option}")


def test_cli_with_argument_and_option():
    result = r.invoke(
        cli_with_argument_and_option, ["argument", "--option", "option"]
    )
    assert result.output == "baz: argument: argument, option: option\n"
    # Now try with a -- prefixed argument
    result2 = r.invoke(
        cli_with_argument_and_option, ["--", "--starts-with-hyphens"]
    )
    assert result2.output == "baz: argument: --starts-with-hyphens, option: None\n"

Currently fails like this:

>       assert result2.output == "baz: argument: --starts-with-hyphens, option: None\n"
E       AssertionError: assert 'Usage: cli-w...ith-hyphens\n' == 'baz: argumen...ption: None\n'
E         - baz: argument: --starts-with-hyphens, option: None
E         + Usage: cli-with-argument-and-option baz [OPTIONS] ARGUMENT
E         + Try 'cli-with-argument-and-option baz --help' for help.
E         + 
E         + Error: No such option: --starts-with-hyphens

[simonw]

Stepping through with the debugger it gets to here:

> /Users/simon/.local/share/virtualenvs/click-default-group-mhmnP7bF/lib/python3.10/site-packages/click/core.py(1644)parse_args()
-> rest = super().parse_args(ctx, args)
(Pdb) list
1639 	    def parse_args(self, ctx: Context, args: t.List[str]) -> t.List[str]:
1640 	        if not args and self.no_args_is_help and not ctx.resilient_parsing:
1641 	            echo(ctx.get_help(), color=ctx.color)
1642 	            ctx.exit()
1643 	
1644 ->	        rest = super().parse_args(ctx, args)
1645 	
1646 	        if self.chain:
1647 	            ctx.protected_args = rest
1648 	            ctx.args = []
1649 	        elif rest:
(Pdb) args
self = <DefaultGroup cli-with-argument-and-option>
ctx = <click.core.Context object at 0x105a9f280>
args = ['--', '--starts-with-hyphens']

Before that rest = super().parse_args(ctx, args) line args is ['--', '--starts-with-hyphens']

But after that line it is ['--starts-with-hyphens'].

[simonw]

More debugger:

> /Users/simon/.local/share/virtualenvs/click-default-group-mhmnP7bF/lib/python3.10/site-packages/click/parser.py(335)parse_args()
-> state = ParsingState(args)
(Pdb) list
330  	        for the parsed options and arguments as well as the leftover
331  	        arguments if there are any.  The order is a list of objects as they
332  	        appear on the command line.  If arguments appear multiple times they
333  	        will be memorized multiple times as well.
334  	        """
335  ->	        state = ParsingState(args)
336  	        try:
337  	            self._process_args_for_options(state)
338  	            self._process_args_for_args(state)
339  	        except UsageError:
340  	            if self.ctx is None or not self.ctx.resilient_parsing:
(Pdb) n
> /Users/simon/.local/share/virtualenvs/click-default-group-mhmnP7bF/lib/python3.10/site-packages/click/parser.py(336)parse_args()
-> try:
(Pdb) state
<click.parser.ParsingState object at 0x107cdb130>
(Pdb) args
self = <click.parser.OptionParser object at 0x107cdb190>
args = ['--', '--starts-with-hyphens']
(Pdb) n
> /Users/simon/.local/share/virtualenvs/click-default-group-mhmnP7bF/lib/python3.10/site-packages/click/parser.py(337)parse_args()
-> self._process_args_for_options(state)
(Pdb) args
self = <click.parser.OptionParser object at 0x107cdb190>
args = ['--', '--starts-with-hyphens']
(Pdb) n
> /Users/simon/.local/share/virtualenvs/click-default-group-mhmnP7bF/lib/python3.10/site-packages/click/parser.py(338)parse_args()
-> self._process_args_for_args(state)
(Pdb) args
self = <click.parser.OptionParser object at 0x107cdb190>
args = ['--starts-with-hyphens']

So the call to self._process_args_for_options(state) left that -- in place... but that call to self._process_args_for_args(state) was the thing that removed -- from the args list.

Here's that code in Click: https://github.com/pallets/click/blob/874ca2bc1c30d93a4ac6e36a15ed685eafe89097/src/click/parser.py#L326-L342

[simonw]

I think I found it:

> /Users/simon/.local/share/virtualenvs/click-default-group-mhmnP7bF/lib/python3.10/site-packages/click/parser.py(358)_process_args_for_options()
-> arglen = len(arg)
(Pdb) list
353  	        state.rargs = []
354  	
355  	    def _process_args_for_options(self, state: ParsingState) -> None:
356  	        while state.rargs:
357  	            arg = state.rargs.pop(0)
358  ->	            arglen = len(arg)
359  	            # Double dashes always handled explicitly regardless of what
360  	            # prefixes are valid.
361  	            if arg == "--":
362  	                return

It looks like that bit of code there is popping off that -- (removing it from the args) list, then noticing that it is a double hyphen and shortcutting itself with that return.

[simonw]

... and that's as far as I got. I'm lost in Click internals now and I'm not sure how to fix this.

Here's my diff from where I was investigating with that test and a breakpoint:

diff --git a/click_default_group.py b/click_default_group.py
index 735c54b..f743ce7 100644
--- a/click_default_group.py
+++ b/click_default_group.py
@@ -77,9 +77,17 @@ class DefaultGroup(click.Group):
         self.default_cmd_name = cmd_name
 
     def parse_args(self, ctx, args):
+        separator_index = None
+        original_args = args[:]
+        if "--" in args:
+            # Remember where it was so we can put it back later
+            separator_index = args.index("--")
         if not args and self.default_if_no_args:
             args.insert(0, self.default_cmd_name)
-        return super(DefaultGroup, self).parse_args(ctx, args)
+        updated_args = super(DefaultGroup, self).parse_args(ctx, args)
+        if separator_index is not None:
+            breakpoint()
+        return updated_args
 
     def get_command(self, ctx, cmd_name):
         if cmd_name not in self.commands:
diff --git a/test.py b/test.py
index f90b80d..1e23b50 100644
--- a/test.py
+++ b/test.py
@@ -28,6 +28,32 @@ def bar():
 r = CliRunner()
 
 
+@click.group(cls=DefaultGroup, default="baz", invoke_without_command=True)
+def cli_with_argument_and_option():
+    pass
+
+
+@cli_with_argument_and_option.command()
+@click.argument("argument")
+@click.option("--option")
+def baz(argument, option):
+    click.echo(f"baz: argument: {argument}, option: {option}")
+
+
+def test_cli_with_argument_and_option():
+    result = r.invoke(
+        cli_with_argument_and_option, ["argument", "--option", "option"]
+    )
+    assert result.output == "baz: argument: argument, option: option\n"
+    # Now try with a -- prefixed argument
+    result2 = r.invoke(
+        cli_with_argument_and_option, ["--", "--starts-with-hyphens"]
+        , catch_exceptions=False
+    )
+    assert result2.output == "baz: argument: --starts-with-hyphens, option: None\n"
+
+
+
 def test_default_command_with_arguments():
     assert r.invoke(cli, ['--foo', 'foooo']).output == 'foooo\n'
     assert 'no such option' in r.invoke(cli, ['-x']).output.lower()