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

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{stdenv, git}:
{url, rev ? "HEAD", md5 ? "", sha256 ? "", leaveDotGit ? false }:
/* NOTE:
fetchgit has one problem: git fetch only works for refs.
This is because fetching arbitrary (maybe dangling) commits may be a security risk
and checking whether a commit belongs to a ref is expensive. This may
change in the future when some caching is added to git (?)
Usually refs are either tags (refs/tags/*) or branches (refs/heads/*)
Cloning branches will make the hash check fail when there is an update.
But not all patches we want can be accessed by tags.
The workaround is getting the last n commits so that it's likly that they
still contain the hash we want.
for now : increase depth iteratively (TODO)
real fix: ask git folks to add a
git fetch $HASH contained in $BRANCH
facility because checking that $HASH is contained in $BRANCH is less
expensive than fetching --depth $N.
Even if git folks implemented this feature soon it may take years until
server admins start using the new version?
*/
stdenv.mkDerivation {
name = "git-export";
builder = ./builder.sh;
fetcher = ./nix-prefetch-git;
buildInputs = [git];
outputHashAlgo = if sha256 == "" then "md5" else "sha256";
outputHashMode = "recursive";
outputHash = if sha256 == "" then md5 else sha256;
inherit url rev leaveDotGit;
impureEnvVars = [
# We borrow these environment variables from the caller to allow
# easy proxy configuration. This is impure, but a fixed-output
# derivation like fetchurl is allowed to do so since its result is
# by definition pure.
"http_proxy" "https_proxy" "ftp_proxy" "all_proxy" "no_proxy"
];
}