git: fix cygwin build

[corngood]

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.

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[me-and]

...I had the impression that Cygwin wasn't supported by Nixpkgs any more. And, as a maintainer for the Nixpkgs git package and the maintainer for the Git package for Cygwin, I probably ought to have known that!

I don't have a Cygwin Nix environment to test with (although maybe I should fix that). It seems likely to me that a more general fix would work better -- possibly some sort of hook that runs in stdenv to wrap ln where required -- but I've no objection to this change if it's a useful quick fix.

[corngood]

I don't have a Cygwin Nix environment to test with (although maybe I should fix that). It seems likely to me that a more general fix would work better -- possibly some sort of hook that runs in stdenv to wrap ln where required -- but I've no objection to this change if it's a useful quick fix.

This change is only actually required for cross-builds, because cygwin itself has its magical .exe suffix handling, so omitting the suffix still works there.

[me-and]

This change is only actually required for cross-builds, because cygwin itself has its magical .exe suffix handling, so omitting the suffix still works there.

Yeah, I figured as much! I was initially confused about why this was necessary given the magic .exe handling, but I could well believe the extension needs to be included when the symlink is being created in a non-Cygwin environment.

[corngood]

@me-and if you're interested in nixpkgs/cygwin stuff, the parent PR (#475998) has my next block of work, which is cross-building a stdenv bootstrap tarball.

It's been discussed a bit on https://matrix.to/#/#windows:nixos.org

[philiptaron]

Change looks fine to me, but I echo Adam's feedback that a cleanup pass when #nix-does-windows is checked in seems warranted.