[Nix-dev] wrapProgram: also pass name as NIX_PROGRAM_NAME

[Freddy Rietdijk]

If a Python script is run, then `sys.argv[0]` is set to the script name (or
path, depending on platform). Some scripts use this name or path to start a
new instance of itself. Unfortunately, exec -a doesn't set `sys.argv[0]`.
Therefore, when running a wrapped Python script, `sys.argv[0]` points not
to the wrapped script, but to the original one.

On Mon, May 22, 2017 at 9:41 AM, zimbatm <zimbatm at zimbatm.com> wrote:

> Hi Freddy,
>
> Can you expand a bit on why this is a problem? If a program is executed
> using python I would expect this to be reflected in the process name. Argv0
> would contain a path to python and argv1 the path to the script.
>
> Cheers,
> z
>
> On Fri, 19 May 2017, 12:35 Freddy Rietdijk, <freddyrietdijk at fridh.nl>
> wrote:
>
>> Hi,
>>
>> When we create a wrapper we use `exec -a` so that the wrapped program
>> uses the name of the original program. This isn't respected by all
>> programs, e.g. Python ignores this. If I am correct this is the case with
>> all interpreters. How do we handle this with other interpreters?
>>
>> Currently we 'solve' the issue for Python by patching the scripts setting
>> `sys.argv[0]` to the original script name, including the full path. This is
>> sufficient for scripts that call themselves, however, it is troublesome
>> when such a script is wrapped in another derivation, because when the
>> script now calls itself, it will call the unwrapped version.
>>
>> Therefore, I propose we set an environment variable `NIX_PROGRAM_NAME`
>> that the scripts check for. To prevent creating yet another `wrapProgram`
>> variant I propose we extend `wrapProgram` to always set this variable.
>>
>> This, however, doesn't solve the issue with nested wrappers yet, because
>> if we would use `set`, it would still refer to the name passed by the
>> innermost wrapper. Either we try and update wrappers, or, which has my
>> preference, we do not use `set` but use `prefix` and make the script pick
>> the last item from the list.
>>
>> What do you think? I like to also refer to the following gist where I've
>> been documenting some of the issues and how we can rewrite the Python infra
>> to solve those issues.
>> https://gist.github.com/FRidh/c3e974e34eac738405af699786b462d5
>>
>>
>> Freddy
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>> nix-dev at lists.science.uu.nl
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>>
>
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