fetchGit fails when trying to fetch from a repository that doesn't have master

[knedlsepp]

When trying to fetch a git revision of a repository that doesn't have a master branch, I get the following error

fatal: Couldn't find remote ref master

Example:

cat << EOF | nix repl
builtins.fetchGit {
  url = https://github.com/conradsnicta/armadillo-code;
  rev = "8696c7ef3a7e66e92558b438182b7ee5878f028f";
}
EOF

This can be resolved by additionally specifying the branch which includes the commit as ref:

cat << EOF | nix repl
builtins.fetchGit {
  url = https://github.com/conradsnicta/armadillo-code;
  ref = "unstable";
  rev = "8696c7ef3a7e66e92558b438182b7ee5878f028f";
}
EOF

While the issue itself is solvable via specifying the ref, this behavior is however rather surprising.

[dtzWill]

I suspect this means that fetchgit on a url with a default branch other than master won't work. IIRC the code sets ref to master if not otherwise set.

Perhaps this should be "HEAD" instead? (untested)

[dtzWill]

Yes, problem happens with bare URL too, as in builtins.fetchGit https://github.com/conradsnicta/armadillo-code.

HEAD seems reasonable and seems to work.

This would change the behavior but AFAICT it's not documented to prefer "master" so hopefully that's not a problem.

Change is trivial if it's what we want: dtzWill@51efd3b

[knedlsepp]

Thanks for the quick diagnosis. I guess there is a strong argument for HEAD.

[eqyiel]

I've been seeing an issue that may be related, fetchGit doesn't appear to work for revisions that aren't in master.

For example, this is the output when trying to fetch a revision from a different branch:

❯ nix-build --expr 'with import <nixpkgs> {}; callPackage ./default.nix {}' --no-out-link
fatal: not a tree object
error: program 'git' failed with exit code 128
(use '--show-trace' to show detailed location information)

[eqyiel]

Can be reproduced like this using some old unmerged nixpkgs branch: https://github.com/NixOS/nixpkgs/tree/gnu-kfreebsd

❯ nix repl
Welcome to Nix version 2.1pre6149_b37f5ae3. Type :? for help.

nix-repl> builtins.fetchGit { url = "https://github.com/NixOS/nixpkgs.git"; rev = "3dc6915610c1267331a95a3b533f3a0f2e69b81d"; }
fetching Git repository 'https://github.com/NixOS/nixpkgs.git'warning: no common commits
fatal: not a tree object
error: program 'git' failed with exit code 128

nix-repl> builtins.fetchGit { url = "https://github.com/NixOS/nixpkgs.git"; rev = "3dc6915610c1267331a95a3b533f3a0f2e69b81d"; ref = "gnu-kfreebsd"; }
tar: This does not look like a tar archive
tar: Exiting with failure status due to previous errors
error: interrupted by the user

nix-repl>

[manveru]

I've got the same issue with not a tree object. For some reason doing the same fetchGit from nix repl instead of nix build fetches the correct revision.

[eqyiel]

@shlevy could this be re-opened?

[graham-at-target]

fetching Git repository 'https://github.com/NixOS/nixpkgs.git'
{ outPath = "/nix/store/kq2lk2v3alv4yhb0y8ayblp50qxbhpbq-source"; rev = "3dc6915610c1267331a95a3b533f3a0f2e69b81d"; revCount = 9035; shortRev = "3dc6915"; }```

Works for me, so I think this can be closed.

[fogti]

I think I also ran into this (see also: https://cl.tvl.fyi/c/depot/+/4552/1):

[zseri@orca:~/devel/depot]$ nix-build --no-out-link --attr "tools.depot-scanner" "$DEPOT_ROOT" --show-trace
fatal: couldn't find remote ref refs/heads/master
error: program 'git' failed with exit code 128

       … while fetching the input 'git+https://github.com/google/go-genproto?rev=83cc0476cb11ea0da33dacd4c6354ab192de6fe6'

in
nix-env (Nix) 2.6.0pre20211223_af553b2