update-nix-fetchgit

This is a command-line utility for updating fetcher calls in Nix expressions. It has two primary purposes:

• Automating the process of keeping such expressions up-to-date with the latest sources

• Filling hashes automatically instead of copying from the error message¹.

The following fetchers are supported:

• fetchgit
• fetchgitPrivate
• fetchFromGitHub
• fetchFromGitLab
• builtins.fetchGit
• builtins.fetchTarball (Only updates the url when this is a archive fetch from GitHub)
• pkgs.haskellPackages.callHackageDirect (Only updates the hash)
• fetchurl (Only updates the hash)

The options deepClone, leaveDotGit, fetchSubmodules are also supported.

Additionally if the rev (for git fetches) or url attribute has a comment:

• pin: the revision or URL will not be updated, only the hash will be changed
• Anything else: the rev or url parameter will be updated to point to the revision pointed to by the branch or tag named in the comment. This is in the format expected by git ls-remote so if the expression has rev = _; # tags/v* it will be updated to the latest tag beginning with v, sorted by version.

Usage

As a command line tool

Pass the name of the files to be updated in place or pass no files to read and write to stdin and stdout (useful as a filter in an editor).

update-nix-fetchgit file1.nix file2.nix

update-nix-fetchgit <file1.nix >file1-updated.nix

It will update fetchers anywhere in the files, note that it is a purely syntactic match so complicated invocations of the fetchers may not be picked up; see ./src/Update/Nix/Updater.hs to look at the shapes of Nix expressions which are matched.

If you pass --only-commented only expressions which have a comment on the rev or url attribute will be updated. This can be useful for updating files en-mass with some control over which expressions are modified with a command like: fd .nix --exec update-nix-fetchgit --only-commented

Please open an issue if update-nix-fetchgit doesn't recognize a fetcher and you think it could.

From Vim

This VimScript will bind <leader>u to update the fetcher under the cursor.

The mnemonic is u for "it's unUsual to update things in this way"

" A helper to preserve the cursor location with filters
function! Preserve(command)
  let w = winsaveview()
  execute a:command
  call winrestview(w)
endfunction

" Update fetcher under cursor, note that this might take a little while if the
" fetched path is large.
autocmd FileType nix map <nowait> <leader>u :call Preserve("%!update-nix-fetchgit --location=" . line(".") . ":" . col("."))<CR>

Examples

Here are some examples of nix expressions which can be updated:

• Updating src and version

  { stdenv, fetchgit }:
  
  stdenv.mkDerivation rec {
    name = "foo-${version}";
    version = "2016-07-13";
    # ^ version will be updated to the date of the new revision
    src = fetchgit {
      url = "git://midipix.org/slibtool";
      rev = "4f56fd184ef6020626492a6f954a486d54f8b7ba";
      # ^ rev will be updated to the revision of HEAD
      sha256 = "0nmyp5yrzl9dbq85wyiimsj9fklb8637a1936nw7zzvlnzkgh28n";
      # ^ sha256 will be updated to the correct hash
    };
  }
  

• Following a branch fetched with builtins.fetchTarball

  { pkgs ? import (builtins.fetchTarball {
    url =
      "https://github.com/NixOS/nixpkgs/archive/foobar.tar.gz"; # nixos-unstable
      # ^ 'foobar' will be replaced with the revision pointed to by 'refs/heads/nixos-unstable'
    sha256 = "";
    # ^ sha256 will be updated to the correct hash
  }) { } }:
  
  myExpression
  

• Updating the hash (instead of trying to build and copying the hash from the error message)

  {
    upfind = import (pkgs.fetchFromGitHub {
      owner = "expipiplus1";
      repo = "upfind";
      rev = "cb451254f5b112f839aa36e5b6fd83b60cf9b9ae"; # pin
      # ^ This will not change because of the '# pin' comment
      sha256 = _;
      # ^ This will be updated
    }) { };
  }
  

Mechanism

When you run update-nix-fetchgit on a file, it will:

• Read the file and parse it as a Nix expression.
• Find all calls to fetchers.
• Run nix-prefetch-git or nix-prefetch-url (and a call to the GitHub API to get the commit date in the case of builtins.fetchTarball) to get information about the latest version.
• Update the corresponding rev, sha256, url, and version attributes for each repository.
• Overwrite the original input file or print to stdout

Any version attribute found in the file will be updated if it is in a set that contains (directly or indirectly) a Git fetch. The version attribute will be updated to the commit date of the latest HEAD commit in the Git repository, in the time zone of the committer, in "YYYY-MM-DD" format. If the set contains multiple Git fetches, the latest such date is used.

Building from source

The recommended way to build this program from source for development purposes is to download and run nix-shell in the top-level source directory and then run cabal build.

Authors

• expipiplus1 - I'm jophish on Freenode; say hi!
• DavidEGrayson

1: Don't deny you do it