nixpkgs/pkgs/build-support/fetchmtn/builder.sh
Maximilian Bosch 8bc5104a6e
treewide: refactor .attrs.sh detection
When specifying the `builder` attribute in `stdenv.mkDerivation`, this
will be effectively transformed into

    builtins.derivation {
      builder = stdenv.shell;
      args = [ "-e" builder ];
    }

This also means that `default-builder.sh` is never sourced and as a
result it's not guaranteed that `$NIX_ATTRS_SH_FILE` is set to a correct
location[1].

Also, we need to source `.attrs.sh` to source `$stdenv`. So, the
following is done now:

* If `$NIX_ATTRS_SH_FILE` points to a correct location, then use it.
  Directly using `.attrs.sh` is problematic for `nix-shell(1)` usage
  (see previous commit for more context), so prefer the environment
  variable if possible.

* Otherwise, if `.attrs.sh` exists, then use it. See [1] for when this
  can happen.

* If neither applies, it can be assumed that `__structuredAttrs` is
  turned off and thus nothing needs to be done.

[1] It's possible that it doesn't exist at all - in case of Nix 2.3 or
    it can point to a wrong location on older Nix versions with a bug in
    `__structuredAttrs`.
2023-10-04 18:36:57 +02:00

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if [ -e "$NIX_ATTRS_SH_FILE" ]; then . "$NIX_ATTRS_SH_FILE"; elif [ -f .attrs.sh ]; then . .attrs.sh; fi
source $stdenv/setup
set -x
if ! [ -f "$cacheDB" ]; then
echo "Creating cache DB $cacheDB"
mtn --db "$cacheDB" db init
fi
echo "getting revision $selector";
done=;
for source in $dbs; do
if mtn pull --db "$cacheDB" "$source" "${branch}"; then
revision="$(mtn --db "$cacheDB" au toposort $(mtn --db "$cacheDB" au select "$selector") | tail -1)";
if [ -n "$revision" ]; then
if mtn --db "$cacheDB" au get_revision "$revision"; then
echo "found revision $revision"
done=1;
else
echo "revision $revision does not exist";
fi
else
echo "selector $selector does not match any revision";
fi
else
echo "pulling branch $branch wasn't successful";
fi;
if test -n "$done"; then
break;
fi;
done;
echo "checking out the revision $revision";
if test -n "$done"; then
mtn checkout --db "$cacheDB" -r "$revision" "$out" -b "${branch}"
else
echo "Needed revision still not found. Exiting";
exit 1;
fi;
echo "clearing _MTN in the output"
rm -rf "$out/_MTN"