If an alias is already defined in all-packages.nix, we want to throw
an error to make it obvious that something is wrong. Otherwise there
is no way to realize that the alias is shadowing the real definition.
Note that a bunch of non-python packages use this attribute already.
Some of those are clearly unaware of the fact that this attribute does
not exists in stdenv because they define it but don't to add it to
their `bulidInputs` :)
Also note that I use `buildInputs` here and only handle regular
builds because python and haskell builders do it this way and I'm not
sure how to properly handle the cross-compilation case.
As in:
$ nix eval -f . bash
Also remove the glibc propagation inherit that made these necessary,
stages handle propagating libc themselves (apparently) and
AFAICT no hashes are changed as a result of this.
... binutils and gcc add it already anyway.
Without this it's easy to get cross-toolchain paths longer than 256
chars and nix-daemon will then fail to commit them to /nix/store on XFS.
upstream issue:
https://bugs.python.org/issue31940
There are two PR's proposed to fix this,
but both seem to be stalling waiting for review.
I previously used what appears to be the favored
of the two approaches[1] to fix this,
with plan of keeping it musl-only until PR was merged.
However, while writing up a commit message
explaining the problem and why it needed fixing...
I investigated a bit and found it increasingly
hard to justify anything other than ...
simply not using lchmod.
Here's what I found:
* lchmod is non-POSIX, seems BSD-only these days
* Functionality of lchmod isn't supported on Linux
* best scenario on Linux would be an error
* POSIX does provide lchmod-esque functionality
with fchmodat(), which AFAICT is generally preferred.
* Python intentionally overlooks fchmodat()[2]
electing instead to use lchmod() behavior
as a proxy for whether fchmodat() "works".
I'm not sure I follow their reasoning...
* both glibc and musl provide lchmod impls:
* glibc returns ENOSYS "not implemented"
* musl implements lchmod with fchmodat(),
and so returns EOPNOTSUPP "op not supported"
* Python doesn't expect EOPNOTSUPP from lchmod,
since it's not valid on BSD's lchmod.
* "configure" doesn't actually check lchmod usefully,
instead checks for glibc preprocessor defines
to indicate if the function is just a stub[3];
somewhat fittingly, if the magic macros are defined
then the next line of the C source is "choke me",
causing the compiler to trip, fall, and point
a finger at whatever is near where it ends up.
(somewhat amusing, but AFAIK effective way to get an error :P)
I'm leaving out links to threads on mailing lists and such,
but for now I hope I've convinced you
(or to those reading commit history: explained my reasons)
that this is a bit of a mess[4].
And so instead of making a big mess messier,
and with hopes of never thinking about this again,
I propose we simply tell Python "don't use lchmod" on Linux.
[1] https://github.com/python/cpython/pull/4783
[2] 28453feaa8/Lib/os.py (L144)
[3] 28453feaa8/configure (L2198)
[4] Messes happen, no good intention goes unpunished :).
