labath added inline comments.
================
Comment at: lldb/include/lldb/Interpreter/ScriptInterpreter.h:469
+
+ virtual int GetNumArgumentsForCallable(const char *callable_name) {
+ return -1;
----------------
labath wrote:
> lawrence_danna wrote:
> > jingham wrote:
> > > lawrence_danna wrote:
> > > > labath wrote:
> > > > > jingham wrote:
> > > > > > lawrence_danna wrote:
> > > > > > > labath wrote:
> > > > > > > > In light of varargs functions (`*args, **kwargs`), which are
> > > > > > > > fairly popular in python, the concept of "number of arguments
> > > > > > > > of a callable" does not seem that well defined. The current
> > > > > > > > implementation seems to return the number of fixed arguments,
> > > > > > > > which might be fine, but I think this behavior should be
> > > > > > > > documented. Also, it would be good to modernize this function
> > > > > > > > signature -- have it take a StringRef, and return a
> > > > > > > > `Expected<unsigned (?)>` -- ongoing work by @lawrence_danna
> > > > > > > > will make it possible to return errors from the python
> > > > > > > > interpreter, and this will make it possible to display those,
> > > > > > > > instead of just guessing that this is because the callable was
> > > > > > > > not found (it could in fact be because the named thing is not a
> > > > > > > > callable, of because resolving the name produced an exception,
> > > > > > > > ...).
> > > > > > > I just took a look at PythonCallable::GetNumArguments() and it's
> > > > > > > horribly broken.
> > > > > > >
> > > > > > > It doesn't even work for the simplest test case I could think of.
> > > > > > >
> > > > > > > ```
> > > > > > > auto builtins = PythonModule::Import("builtins");
> > > > > > > ASSERT_THAT_EXPECTED(builtins, llvm::Succeeded());
> > > > > > > auto hex = As<PythonCallable>(builtins.get().GetAttribute("hex"));
> > > > > > > ASSERT_THAT_EXPECTED(hex, llvm::Succeeded());
> > > > > > > EXPECT_EQ(hex.get().GetNumArguments().count, 1u);
> > > > > > > ```
> > > > > > >
> > > > > > > we should really re-write it to use inspect.signature.
> > > > > > Interesting. We use it for free functions (what you pass to the -F
> > > > > > option of `breakpoint command add`) and for the __init__ and
> > > > > > __call__ method in the little classes you can make up for scripted
> > > > > > thread plans and for the class version of Python implemented
> > > > > > command-line commands. We have tests for telling 3 vrs. 4 vrs. not
> > > > > > enough or too many, and they all pass. So it seems to work in the
> > > > > > cases we currently need it to work for...
> > > > > >
> > > > > > "inspect.signature" is python 3 only, and the python 2 equivalent
> > > > > > is deprecated. So it will take a little fancy footwork to use it
> > > > > > in the transition period.
> > > > > lol :)
> > > > >
> > > > > I would actually say that we should try not to use this
> > > > > function(ality) wherever possible. Making decisions based on the
> > > > > number of arguments the thing you're about to call takes sounds
> > > > > weird. I don't want to get too involved in this, but I was designing
> > > > > this, I'd just say that if one tries to pass arguments to the
> > > > > callback then the callback MUST take three arguments (or we'll abort
> > > > > processing the breakpoint command). If he wants his function to be
> > > > > called both with arguments and without, he can just add a default
> > > > > value to the third argument. (And if his function takes two
> > > > > arguments, but he still tries to pass something... well, it's his own
> > > > > fault).
> > > > >
> > > > > Anyway, feel free to ignore this comment, but I felt like I had to
> > > > > say something. :)
> > > > I completely agree with Pavel. Inspecting a function signature
> > > > before calling it is a big code smell in python. If there's a way to
> > > > avoid doing that introspection, that would be better.
> > > Unfortunately, we originally designed this interface to take three
> > > arguments, the frame pointer, the breakpoint location and the Python
> > > session dict. Then it became clear that it would be better to add this
> > > extra args argument (and in the case of Python based commands the
> > > ExecutionContext pointer). At that point we had three choices, abandon
> > > the improvement; switch to unconditionally passing the extra arguments,
> > > and break everybody's extant uses; or switch off of the number of
> > > arguments to decide whether the user had provided the old or new forms.
> > >
> > > My feeling about lldb Python scripts/commands etc. that people use in the
> > > debugger is that a lot of users don't know how they work at all, they
> > > just got them from somebody else; and many more figured out how to write
> > > them for some specific purpose, and then pretty much forgot how they
> > > worked. So suddenly breaking all these bits of functionality will result
> > > in folks just deciding that this affordance is not reliable and not worth
> > > their time, which would be a shame.
> > >
> > > So instead we accommodate both forms, which requires that we know which
> > > one the user provided. If you see a better way to do this, (and are
> > > willing to implement it because so far as I can see this method is going
> > > to work just fine) dig in, I'm not wedded to the particular approach.
> > > But I am not excited about penalizing our users because we didn't get the
> > > API design right the first time through.
> > makes sense.
> >
> > The only other way I can think of to solve it would be to have some
> > indication in the `break com add` command of what signature it expects from
> > the function. But that's really ugly too because now you're asking users
> > to understand yet another option.
> >
> > I put up https://reviews.llvm.org/D68995 this morning which adds
> > `inspect.signature` support for pythons that have it.
> >
> > Currently we have really gnarly ArgInfo tests like this:
> > ```
> > if (argc.count == 5 || argc.is_bound_method || argc.has_varargs)
> > pfunc(debugger_arg, PythonString(args), exe_ctx_arg,
> > cmd_retobj_arg, dict);
> > else
> > pfunc(debugger_arg, PythonString(args), cmd_retobj_arg, dict);
> > ```
> >
> > 😖
> >
> > I think if we replace `count` with `max_positional_args` we should be able
> > to replace that kindof test with just
> > ```
> > if (argc.max_positional_args < 5)
> > old_version
> > else
> > new_version
> > ```
> >
> >
> So, how about this: Put extra_args as the last argument, instead of inserting
> it in the middle (so the new signature becomes `frame, bp_loc, dict,
> extra_args` instead of `frame, bp_loc, extra_args, dict`. Then instead of
> ```
> if (arg_info.count == 3)
> result = pfunc(frame_arg, bp_loc_arg, dict);
> else if (arg_info.count == 4) {
> lldb::SBStructuredData *args_value = new
> lldb::SBStructuredData(args_impl);
> PythonObject args_arg(PyRefType::Owned,
> SBTypeToSWIGWrapper(args_value));
> result = pfunc(frame_arg, bp_loc_arg, args_arg, dict);
> ```
> we do:
> ```
> if (args_impl.was_specified())
> pfunc(frame_arg, bp_loc_arg, dict, args_arg)
> else
> pfunc(frame_arg, bp_loc_arg, dict);
> ```
> All existing scripts will not specify the extra arguments, so they will work
> as usual. New scripts which do pass extra arguments will have to use the new
> signature. New scripts can also put `args = None` in their python signature,
> so that they are callable both with and without arguments, should they so
> desire. (If we don't want to support the `=None` use case then we can even
> keep the arguments in the same order as in this patch.)
>
> Is there some reason why that would not work?
> The only other way I can think of to solve it would be to have some
> indication in the break com add command of what signature it expects from the
> function.
That's kind of what I'm getting at. I am hoping that the presence of the
`--key`, `--value` options can be used as an indicator of that signature.
(Though maybe I am misunderstanding something and I should shut up.)
Repository:
rLLDB LLDB
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D68671/new/
https://reviews.llvm.org/D68671
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