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Re: [PATCH] tests: create an interactive gdb session with the 'debug' helper




On Fri, Mar 17, 2017 at 3:55 PM, Jeff King <peff@xxxxxxxx> wrote:
> On Fri, Mar 17, 2017 at 03:46:46PM +0100, SZEDER Gábor wrote:
>
>> The 'debug' test helper is supposed to facilitate debugging by running
>> a command of the test suite under gdb.  Unfortunately, its usefulness
>> is severely limited, because that gdb session is not interactive,
>> since the test's, and thus gdb's standard input is attached to
>> /dev/null (for a good reason, see 781f76b15 (test-lib: redirect stdin
>> of tests, 2011-12-15)).
>>
>> Re-attach the original standard input in the debug helper, thus
>> creating an interactive gdb session, which is much much more useful.
>
> Yeah, I think I've had to do a similar hack manually. This is an obvious
> improvement. Though...
>
>> diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
>> index bd357704c..9567dc986 100644
>> --- a/t/test-lib-functions.sh
>> +++ b/t/test-lib-functions.sh
>> @@ -154,7 +154,7 @@ test_pause () {
>>  #
>>  # Example: "debug git checkout master".
>>  debug () {
>> -      GIT_TEST_GDB=1 "$@"
>> +      GIT_TEST_GDB=1 "$@" <&6
>>  }
>
> Your stderr and stdout may be redirected, too. That's usually not a big
> problem because you'll be using "-v",

Yeah, I didn't consider using this helper in non-verbose mode at all,
and the resulting behaviour is not quite pleasant, indeed: gdb starts
in interactive mode, but as its stdout goes straight to /dev/null the
user has no idea, and gdb does not quit on Ctrl-C.  A possible
solution would be to forbid using the 'debug' helper without '-v',
like in the 'test_pause' helper just above.

However...

> but perhaps this should add:
>
>   >&3 2>&4
>
> to be on the safe side. That covers running without "-v", as well as
> cases where the test script is redirecting output

That wouldn't buy us much.  First, file descriptors 3 and 4 are the
test's stdout and stderr, i.e. any process started within the test
would be connected to those fds anyway without those explicit
redirections.  Second, fds 3 and 4 are redirected to /dev/null in
non-verbose mode, so it would still not work without '-v'.

Perhaps you meant '>&5 2>&7' here (and in the bash example in the
commit message of 781f76b15 (test-lib: redirect stdin of tests,
2011-12-15), for that matter)?  Those redirections do in fact make
'debug' work even without '-v'.  Furthermore, those redirections do
make 'test_pause' work without '-v', too.

So this is what v2 will do, then.

Gábor