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

[Freddy Rietdijk]

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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