patchtests: create an interactive gdb session with the 'debug' helper

> 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.

> 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
>  }

> 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",

> 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

> When the 'test_pause' helper function invokes the shell mid-test, it
> explicitly redirects the shell's stdout and stderr to file descriptors
> 3 and 4, which are the stdout and stderr of the tests (i.e. where they
> would be connected anyway without those redirections).  These file
> descriptors are only attached to the terminal in verbose mode, hence
> the restriction of 'test_pause' to work only with '-v'.
> 
> Redirect the shell's stdout and stderr to the test environment's
> original stdout and stderr, allowing it to work properly even in
> non-verbose mode, and the restriction can be lifted.
> 
> Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
> ---
>  t/test-lib-functions.sh | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)

> 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 redirected from
> /dev/null (for a good reason, see 781f76b15 (test-lib: redirect stdin
> of tests, 2011-12-15)).
> 
> Redirect gdb's standard file descriptors from/to the test
> environment's stdin, stdout and stderr in the 'debug' helper, thus
> creating an interactive gdb session (even in non-verbose mode), which
> is much, much more useful.
>
> [...]
>
>  debug () {
> -	 GIT_TEST_GDB=1 "$@"
> +	 GIT_TEST_GDB=1 "$@" <&6 >&5 2>&7
>  }

> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index 86d77c16d..23c29bce6 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -342,6 +342,7 @@ fi
>  
>  exec 5>&1
>  exec 6<&0
> +exec 7>&2

> 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 redirected from
> /dev/null (for a good reason, see 781f76b15 (test-lib: redirect stdin
> of tests, 2011-12-15)).
> 
> Redirect gdb's standard file descriptors from/to the test
> environment's stdin, stdout and stderr in the 'debug' helper, thus
> creating an interactive gdb session (even in non-verbose mode), which
> is much, much more useful.

> > 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.