vimPlugins.vim-colorschemes: add overlay to address hash issue

[malob]

Motivation for this change

As discussed in #157609, the source for vim-colorschemes contains two files with who's name only differ by the case:

• colors/darkBlue.vim
• colors/darkblue.vim

This results in update.py generating a different hash for the plugin depending on whether the file system of the system it's run on is case-sensitive or not. This mainly comes up on Darwin systems.

There's an issue on the upstream repo (flazz/vim-colorschemes#186) as well as a PR to fix the issue (flazz/vim-colorschemes#181).

Unfortunately the owner of the repo hasn't been active for over a year, so waiting for the PR to land probably isn't a viable solution :(

This PR is a proposed hack to address the issue.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 22.05 Release Notes (or backporting 21.11 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
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[malob]

Result of nixpkgs-review pr 157622 run on aarch64-darwin 1

1 package built:

• spacevim

[malob]

Result of nixpkgs-review pr 157622 run on x86_64-linux 1

1 package built:

• spacevim

[malob]

Result of nixpkgs-review pr 157622 run on aarch64-darwin 1

1 package built:

• spacevim

[malob]

Result of nixpkgs-review pr 157622 run on x86_64-linux 1

1 package built:

• spacevim

[jonringer]

I think the hash would need to be recomputed as well

[jonringer]

Suggested change

	postFetch = srcOld.postFetch + lib.optionalString (!stdenv.isDarwin) ''
	postFetch = (srcOld.postFetch or "") + lib.optionalString (!stdenv.isDarwin) ''

[malob]

@jonringer, I updated the PR with the change you suggested.

I initially thought the same thing about the hash, however, the current hash in nixpkgs is based off the source being downloaded on a darwin system. Given the override does nothing on darwin systems, the hash is the same. When I was testing this to ensure the hashes were the same on both systems I set the sha265 hash for the vim-colorschemes source to "" in generated.nix, to see what hashes Nix expected on each system.

On my Mac:

error: hash mismatch in fixed-output derivation '/nix/store/6yy77dsf8j3dmsia15w1xmbmxh2w1742-source.drv':
         specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
            got:    sha256-5Y29LUC1cddrX/mwLQoMTWxRcvXHYrgRo+s5IKRx+k4=

On my NixOS machine:

error: hash mismatch in fixed-output derivation '/nix/store/7hzr62y9l08j1c37flskx890p0h489dk-source.drv':
         specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
            got:    sha256-5Y29LUC1cddrX/mwLQoMTWxRcvXHYrgRo+s5IKRx+k4=

The expected hash is the same as the current hash in generated.nix:

❯ nix hash to-sri --type sha256 0kpsf6j20fgblc8vhqn7ymr52v2d1h52vc7rbxmxfwdm80nvv3g5
sha256-5Y29LUC1cddrX/mwLQoMTWxRcvXHYrgRo+s5IKRx+k4=

[SuperSandro2000]

The or "" is only added to prevent evaluation errors if the overwriten Derivation for some reason no longer contain postFetch.

[malob]

That's what I assumed yeah.

[jonringer]

LGTM

Result of nixpkgs-review pr 157622 run on x86_64-linux 1

2 packages built:

• spacevim
• tests.vim.test_vim_with_vim_nix