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# Copyright 2019 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# Load a Nix package set from a source specified in one of the following
# formats:
#
# 1. nixpkgs!$channel (e.g. nixpkgs!nixos-19.03)
# 2. git!$repo!$rev (e.g. git!git@github.com:NixOS/nixpkgs.git!master)
# 3. path!$path (e.g. path!/var/local/nixpkgs)
#
# '!' was chosen as the separator because `builtins.split` does not
# support regex escapes and there are few other candidates. It
# doesn't matter much because this is invoked by the server.
{ pkgSource, args ? { } }:
with builtins;
let
# If a nixpkgs channel is requested, it is retrieved from Github (as
# a tarball) and imported.
fetchImportChannel = channel:
let
url =
"https://github.com/NixOS/nixpkgs-channels/archive/${channel}.tar.gz";
in import (fetchTarball url) args;
# If a git repository is requested, it is retrieved via
# builtins.fetchGit which defaults to the git configuration of the
# outside environment. This means that user-configured SSH
# credentials etc. are going to work as expected.
fetchImportGit = url: rev:
let
# builtins.fetchGit needs to know whether 'rev' is a reference
# (e.g. a branch/tag) or a revision (i.e. a commit hash)
#
# Since this data is being extrapolated from the supplied image
# tag, we have to guess if we want to avoid specifying a format.
#
# There are some additional caveats around whether the default
# branch contains the specified revision, which need to be
# explained to users.
spec = if (stringLength rev) == 40 then {
inherit url rev;
} else {
inherit url;
ref = rev;
};
in import (fetchGit spec) args;
# No special handling is used for paths, so users are expected to pass one
# that will work natively with Nix.
importPath = path: import (toPath path) args;
source = split "!" pkgSource;
sourceType = elemAt source 0;
in if sourceType == "nixpkgs" then
fetchImportChannel (elemAt source 2)
else if sourceType == "git" then
fetchImportGit (elemAt source 2) (elemAt source 4)
else if sourceType == "path" then
importPath (elemAt source 2)
else
throw ("Invalid package set source specification: ${pkgSource}")
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