This fixes the regression introduced by c47a1e701d
on Darwin. The creation of the file using `install` and process
substitution does not work on Darwin, you get the following complain:
```
install: skipping file '/dev/fd/63', as it was replaced while being copied
```
Fixes#335016
Instead of checking for __structuredAttrs everywhere, it's easier to
just set the default value via parameter expansion and then hand the
array construction off to "concatTo".
Once more setup-hooks will be made structuredAttrs-aware, this pattern
will reduce the use of this implementation detail even more.
structuredAttrs was used here to make an assumption about the type of
the named variables passed as arguments. This can be done better by
looking at the actual types of those variables.
This gives a bit more backwards compatibility as well: Once you turn to
structuredAttrs, you should still be able to pass a bare string instead
of a list and have it behave as a whitespace-separated string like
before.
When running `nix develop` for a package, Nix records the stdenv
environment with NIX_LOG_FD set. That is, when the actual development
shell runs, it uses the functions that attempt to log to NIX_LOG_FD, but
this variable is not actually set.
As a workaround, check whether NIX_LOG_FD is set at runtime.
Example (before this change):
```console
$ nix develop --file . bash
$ echo "${NIX_LOG_FD-unset}"
unset
$ runPhase unpackPhase
bash: "$NIX_LOG_FD": Bad file descriptor
Running phase: unpackPhase
unpacking source archive /nix/store/v28dv6l0qk3j382kp40bksa1v6h7dx9p-bash-5.2.tar.gz
bash: "$NIX_LOG_FD": Bad file descriptor
source root is bash-5.2
bash: "$NIX_LOG_FD": Bad file descriptor
setting SOURCE_DATE_EPOCH to timestamp 1663942708 of file bash-5.2/y.tab.h
```
After this change:
```console
$ nix develop --file . bash
$ runPhase unpackPhase
Running phase: unpackPhase
unpacking source archive /nix/store/v28dv6l0qk3j382kp40bksa1v6h7dx9p-bash-5.2.tar.gz
source root is bash-5.2
setting SOURCE_DATE_EPOCH to timestamp 1663942708 of file bash-5.2/y.tab.h
```
Without the change `runPhase` fails on tarballs like
`diffoscope-269` that contain single top-level `-269` root as:
diffoscope> unpacking source archive /nix/store/p620nidkm73vrp0z6kk5krmrm4vg7bxd-diffoscope-269.tar.bz2
diffoscope> source root is -269
diffoscope> setting SOURCE_DATE_EPOCH to timestamp 1717143039 of file ./-269/tests/utils/versions.py
diffoscope> chmod: invalid mode: ‘-269’
diffoscope> Try 'chmod --help' for more information.
Currently `diffoscope-269` has a `sourceRoot = "./-269";` workaround to
bypass the failure.
Most Linux distributions are enabling this these days and it does
protect against real world vulnerabilities as demonstrated by
CVE-2018-16864 and CVE-2018-16865.
Fix#53753.
Information on llvm version support gleaned from
6609892a2d68e07da3e5092507a730
Information on gcc version support a lot harder to gather,
but both 32bit and 64bit arm do appear to be supported
based on the test suite.
A second take at eb28e5e72e, which was reverted for the extra logging
during the internals of `nix-shell -p`. This commit does the same
logging, but to $NIX_LOG_FD instead, which is echoed during any normal
build, but not during the internals of `nix-shell -p`.
[1]: eb28e5e72e
