[lldb-dev] [RFC]The future of pexpect

Davide Italiano via lldb-dev lldb-dev at lists.llvm.org
Mon Feb 25 13:15:32 PST 2019

On Fri, Feb 22, 2019 at 6:32 AM Pavel Labath <pavel at labath.sk> wrote:
> On 21/02/2019 19:48, Ted Woodward wrote:
> >
> >
> >> -----Original Message-----
> >> From: lldb-dev <lldb-dev-bounces at lists.llvm.org> On Behalf Of Pavel Labath
> >> via lldb-dev
> >> Sent: Thursday, February 21, 2019 8:35 AM
> >> To: Davide Italiano <dccitaliano at gmail.com>
> >> Cc: LLDB <lldb-dev at lists.llvm.org>
> >> Subject: [EXT] Re: [lldb-dev] [RFC]The future of pexpect
> >>
> >> On 21/02/2019 00:03, Davide Italiano wrote:
> >>> I found out that there are tests that effectively require
> >>> interactivity. Some of the lldb-mi ones are an example.
> >>> A common use-case is that of sending SIGTERM in a loop to make sure
> >>> `lldb-mi` doesn't crash and handle the signal correctly.
> >>>
> >>> This functionality is really hard to replicate in lit_as is_.
> >>> Any ideas on how we could handle this case?
> >>
> >> How hard is it to import a new version of pexpect which supports python3 and
> >> stuff?
> >>
> >> I'm not sure how the situation is on darwin, but I'd expect (:P) that most linux
> >> systems either already have it installed, or have an easy way to do so. So we
> >> may not even be able to get away with just using the system one and skipping
> >> tests when it's not present.
> >>
> >> BTW, for lldb-mi I would actually argue that it should *not* use pexpect :D.
> >> Interactivity is one thing, and I'm very much in favour of keeping that ability,
> >> but pexpect is not a prerequisite for that. For me, the main advantage of
> >> pexpect is that it emulates a real terminal. However, lldb-mi does not need
> >> that stuff. It doesn't have any command line editing capabilities or similar. It's
> >> expecting to communicate with an IDE over a pipe, and that's it.
> >>
> >> Given that, it should be fairly easy to rewrite the lldb-mi tests to work on top
> >> of the standard python "subprocess" library. While we're doing that, we might
> >> actually fix some of the issues that have been bugging everyone in the lldb-mi
> >> tests. At least for me, the most annoying thing was that when lldb-mi fails to
> >> produce the expected output, the test does not fail immediately, but instead
> >> the implementation of self.expect("^whatever") waits until the timeout
> >> expires, optimistically hoping that it will find some output that match the
> >> pattern.
> >>

Pavel, I think yours is a really nice idea.
I'm no python expert, but I found out making the conversion is
relatively simple.
I propose a proof-of-concept API and implementation here:


Comments appreciated! Once we agree on how this should look like, I do
recommend to have a new lldbMITest base class and incrementally start
moving the tests to it.
Once we're done, we can delete the old class.

Does this sound reasonable?


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