Re: [PATCH] Test the interaction between GDBHISTSIZE and .gdbinit

[Patrick Palka <patrick at parcs dot ath dot cx>]

On Thu, Jun 18, 2015 at 8:44 AM, Patrick Palka <patrick@parcs.ath.cx> wrote:
> On Thu, Jun 18, 2015 at 5:06 AM, Pedro Alves <palves@redhat.com> wrote:
>> On 06/17/2015 09:17 PM, Patrick Palka wrote:
>>> The value inside the GDBHISTSIZE environment variable, only if valid,
>>> should override setting the history size through one's .gdbinit file.
>>
>> Thanks, looks good.
>>
>>> +    unset -nocomplain env(GDBHISTSIZE)
>>>      array set env [array get old_env]
>>
>> Though this unset looks unnecessary, given that the following line
>> restores the whole array.
>
> It turns out that
>
>     array set env [array get old_env]
>
> does not completely restore the env array to its original state.  What
> it seems to do is to reset each pre-existing environment variable
> (existing in the saved env array) to its original value.  New
> environment variables that were set inside the env array in the
> meantime do not get unset after restoring.  So e.g. after doing
>
>     array set old_env [array get env]
>     set env(SOME_NEW_VAR) foo
>     array set env [array get old_env]
>
> the environment variable SOME_NEW_VAR=foo will still be in the env
> array.  So this "array set env" trick is insufficient.  That is why
> the unset of GDBHISTSIZE is necessary there.
>
> To make the pattern of "temporarily altering global variables,
> restoring their original value afterwards" more convenient and less
> error-prone, I've been thinking about introducing a new tcl proc that
> acts as a wrapper for saving/restoring a specified list of variables.
> Its use would look something like:
>
>     save_vars { INTERNAL_GDBFLAGS env(GDBHISTSIZE) env(HOME) } {
>         append INTERNAL_GDBFLAGS " -nx"
>         unset -nocomplain env(GDBHISTSIZE)
>         unset -nocomplain env(HOME)
>         gdb_test ....
>         more_gdb_test ...
>     }
>
> which guarantees that after the body has finished executing, the given
> list of variables will have their contents restored to their original
> values.  What do you think about this?

Here is an implementation of save_vars (bad name I know) which can
successfully replace the manual saving/restoring of globals done in
gdbinit-history.exp, gdbhistsize-history.exp and readline.exp.  (TCL
sure is cool.)

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