buildDubPackage: fix flag arrays not being expanded correctly

[CyberShadow]

Use concatTo to properly handle dubBuildFlags, dubTestFlags, and dubFlags. Previously these were used as "${var[@]}" but Nix lists become space-separated strings, not bash arrays, causing all flags to be concatenated into a single argument.

Motivating example:

          dubBuildFlags = [ "--config=mysql-integration" "-d=ASOCKETS_DEBUG_IDLE" ];

became:

            > Error Unknown build configuration: mysql-integration -d=ASOCKETS_DEBUG_IDLE                                                                                          

CC @TomaSajt

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

[SFrijters]

Somewhat related to #205690 - perhaps you could migrate the dub infrastructure to __structuredAttrs = true; instead, in which case the flags are actual arrays.

[CyberShadow]

That would be nice. @TomaSajt What do you think?

[TomaSajt]

I am not very experienced in bash array stuff.
As you noticed, I failed to properly migrate from nix to bash in #344744

I don't know how to use __structuredAttrs so I can't really so anything about whether it's better or not.

Does the current solution work with and without __structuredAttrs?
If yes, that's the ideal solution IMO, because the dub hooks are allowed to be used separately, without using buildDubPackage directly, and in those situations it's not guaranteed that __structuredAttrs is on.

[CyberShadow]

Does the current solution work with and without __structuredAttrs?

If you mean the solution in master right now, no; with this fix, it does seem to work with and without __structuredAttrs from looking at the code and a quick test. concatTo does the right thing in both situations.

[TomaSajt]

If that's the case, then LGTM.

[nixpkgs-ci]

Successfully created backport PR for release-25.11:

• [Backport release-25.11] buildDubPackage: fix flag arrays not being expanded correctly #487006