nixpkgs/pkgs/build-support/fetchgitlocal/default.nix

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{ runCommand, git, nix }: src:
let
srcStr = toString src;
# Adds the current directory (respecting ignored files) to the git store, and returns the hash
gitHashFile = runCommand "put-in-git" {
nativeBuildInputs = [ git ];
dummy = builtins.currentTime; # impure, do every time
preferLocalBuild = true;
} ''
cd ${srcStr}
ROOT=$(git rev-parse --show-toplevel) # path to repo
cp $ROOT/.git/index $ROOT/.git/index-user # backup index
git reset # reset index
git add . # add current directory
# hash of current directory
# remove trailing newline
git rev-parse $(git write-tree) \
| tr -d '\n' > $out
mv $ROOT/.git/index-user $ROOT/.git/index # restore index
'';
gitHash = builtins.readFile gitHashFile; # cache against git hash
nixPath = runCommand "put-in-nix" {
nativeBuildInputs = [ git ];
preferLocalBuild = true;
} ''
mkdir $out
# dump tar of *current directory* at given revision
git -C ${srcStr} archive --format=tar ${gitHash} \
| tar xvf - -C $out
'';
in nixPath