pkgs/stdenv/generic/setup.sh: lint with ShellCheck

[ShamrockLee]

The behaviour of [[ -n/-z "${FOO[@]}" ]] is unspecified. Use [[ -n/-z "${FOO[*]-}" ]] instead.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[ShamrockLee]

@ofborg build stdenv
@ofborg build hello hello.tests

[wolfgangwalther]

We gotta be careful here, there was quite some discussion in #335666 around this part. Is this 100% the same as before?

[ShamrockLee]

I should remove the hyphens:

        if [[ -z "${nameref[*]}" && -n "$default" ]]; then

As the Bash Reference Manual doesn't specify the behavior of [[ -n "${arr[@]}" ]], let's experiment with the command if [[ -n "${foo[@]}" ]]; then echo yes; else echo no; fi; unset foo:

unset foo	foo=""	foo=" "	foo=" hi"	foo="hello hi"
no	no	yes	yes	yes

foo=()	foo=("")	foo=("" "")	foo=("" hi)	foo=("hello" "hi")
no	no	yes	yes	yes

According to the Bash Reference Manual,

Any element of an array may be referenced using ${name[subscript]}. ... If the word is double-quoted, ${name[*]} expands to a single word with the value of each array member separated by the first character of the IFS variable

This means the following conversion when the first character of the IFS variable is " ":

foo=()	foo=("")	foo=("" "")	foo=("" hi)	foo=("hello" "hi")
""	""	" "	" hi"	"hello hi"

It should be safe to say that [[ -n "${foo[@]}" ]] behaves like [[ -n "$foo[*]" ]], but only the latter is specified in the Bash Reference Manual.

[wolfgangwalther]

This should be good despite the eval error, which is related to the target branch at that time.