Re: [PATCH] Introduce gdb_interact in testsuite

[Doug Evans <dje@google.com>]

On Thu, Jan 15, 2015 at 8:40 AM, Simon Marchi <simon.marchi@ericsson.com> wrote:
>
> gdb_interact is a small utility that we have found quite useful to debug
> test cases.
>
> Putting gdb_interact in a test suspends it and allows to interact with
> gdb to inspect whatever you want. You can then type ">>>" to resume the
> test execution. Of course, this is only for gdb devs. It wouldn't make
> sense to leave a gdb_interact permanently in a test case.
>
> When starting the interaction with the user, the script prints this
> banner:
>
> +------------------------------------------+
> | Script interrupted, you can now interact |
> | with by gdb. Type >>> to continue.       |
> +------------------------------------------+
>
> Notes:
> * When gdb is launched, the gdb_spawn_id variable (lib/gdb.exp) is
>   assigned -1. Given the name, I would expect it to contain the gdb
>   expect spawn id, which is needed for interact. I changed all places
>   that set gdb_spawn_id to -1 to set it to the actual gdb spawn id
>   instead.
>
> * When entering the "interact" mode, the last (gdb) prompt is already
>   eaten by expect, so it doesn't show up on the terminal. Subsequent
>   prompts do appear though. We tried to print "(gdb)" just before the
>   interact to replace it. However, it could be misleading if you are
>   debugging an MI test case, it makes you think that you are typing in a
>   CLI prompt, when in reality it's MI. In the end I decided that since
>   the feature is for developers who know what they're doing and that one
>   is normally consciously using gdb_interact, the script doesn't need
>   to babysit the user.
>
> * There are probably some quirks depending on where in the script
>   gdb_interact appears (e.g. it could interfere with following
>   commands and make them fail), but it works for most cases. Quirks can
>   always be fixed later.
>
> The idea and original implementation was contributed by Anders
> Granlund, a colleague of mine. Thanks to him.
>
> gdb/testsuite/ChangeLog:
>
>         * gdb.base/statistics.exp: Assign spawn id to gdb_spawn_id.
>         * gdb.base/valgrind-db-attach.exp: Same.
>         * gdb.base/valgrind-infcall.exp: Same.
>         * lib/mi-support.exp (default_mi_gdb_start): Same.
>         * lib/prompt.exp (default_prompt_gdb_start): Same.
>         * lib/gdb.exp (default_gdb_spawn): Same.
>         (gdb_interact): New.

[Apologies for the resend.]

I'm not sure why we're assigning -1 instead of a usable value,
but I can't find anything to suggest assigning a real id will
cause problems.

Plus given how trivial gdb_interact is, the patch is fine by me.

Another way such things are debugged is by first running tests
with TRANSCRIPT=y, and then massaging the transcript.N files
afterwards.  I'm all for adding more ways of debugging tests.
Thanks!