The crystal package's default version is currently 1.16.

However, this version becomes unusable once 1.17 or higher is introduced.
Additionally, we are unable to pin the specific version of crystal in other packages.

Follow-up: #399318

> nix run nixpkgs#crystal -- --version
Crystal 1.16.3 (2025-05-12)

LLVM: 18.1.8
Default target: x86_64-unknown-linux-gnu

> nix run nixpkgs#crystal_1_15 -- --version
Crystal 1.15.1 (2025-02-04)

LLVM: 18.1.8
Default target: x86_64-unknown-linux-gnu

> nix run nixpkgs#crystal_1_16 -- --version
error: flake 'flake:nixpkgs' does not provide attribute 'apps.x86_64-linux.crystal_1_16', 'packages.x86_64-linux.crystal_1_16', 'legacyPackages.x86_64-linux.crystal_1_16' or 'crystal_1_16'
       Did you mean one of crystal_1_11, crystal_1_12, crystal_1_14, crystal_1_15 or crystal_1_2?

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.

@david50407
@manveru
@peterhoeg
@donovanglover
@straight-shoota

Add a 👍 reaction to pull requests you find important.