Currently stdenv requires Bash 4.x that was released in 2009. This
change bumps the required version to Bash 5.x (2019, 5 years ago).
See https://mywiki.wooledge.org/BashFAQ/061 for more details.
Using a relatively modern Bash version allows us to rely on newer
features (e.g. ${var@a}) and remove workarounds for older quirks (e.g.
https://stackoverflow.com/a/7577209, “old bash empty array problem”).
Note that many setup hooks are using features added after 4.0 version,
e.g. makeWrapper uses ${var@Q} from 4.4, but some even require >5.0,
e.g. cargoBuildHook uses ${var@U} from 5.1.
The previously used pattern was introduced in #318614, but technically
leaked the default flags into the global scope. While this would
probably not make much of a practical difference, making concatTo
support default values is a much cleaner approach.
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
```
