d9168e3e4d
Some upcoming changes might require the Nix build to be split into multiple separate nix-build invocations of different expressions, thus splitting this out is useful. It also fixes an issue where `build-image/default.nix` might be called in an environment where no Nix channels are configured.
73 lines
2.7 KiB
Nix
73 lines
2.7 KiB
Nix
# Copyright 2019 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# https://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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# Load a Nix package set from a source specified in one of the following
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# formats:
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#
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# 1. nixpkgs!$channel (e.g. nixpkgs!nixos-19.03)
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# 2. git!$repo!$rev (e.g. git!git@github.com:NixOS/nixpkgs.git!master)
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# 3. path!$path (e.g. path!/var/local/nixpkgs)
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#
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# '!' was chosen as the separator because `builtins.split` does not
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# support regex escapes and there are few other candidates. It
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# doesn't matter much because this is invoked by the server.
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{ pkgSource, args ? { } }:
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with builtins;
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let
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# If a nixpkgs channel is requested, it is retrieved from Github (as
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# a tarball) and imported.
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fetchImportChannel = channel:
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let
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url =
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"https://github.com/NixOS/nixpkgs-channels/archive/${channel}.tar.gz";
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in import (fetchTarball url) args;
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# If a git repository is requested, it is retrieved via
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# builtins.fetchGit which defaults to the git configuration of the
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# outside environment. This means that user-configured SSH
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# credentials etc. are going to work as expected.
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fetchImportGit = url: rev:
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let
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# builtins.fetchGit needs to know whether 'rev' is a reference
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# (e.g. a branch/tag) or a revision (i.e. a commit hash)
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#
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# Since this data is being extrapolated from the supplied image
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# tag, we have to guess if we want to avoid specifying a format.
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#
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# There are some additional caveats around whether the default
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# branch contains the specified revision, which need to be
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# explained to users.
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spec = if (stringLength rev) == 40 then {
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inherit url rev;
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} else {
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inherit url;
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ref = rev;
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};
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in import (fetchGit spec) args;
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# No special handling is used for paths, so users are expected to pass one
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# that will work natively with Nix.
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importPath = path: import (toPath path) args;
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source = split "!" pkgSource;
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sourceType = elemAt source 0;
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in if sourceType == "nixpkgs" then
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fetchImportChannel (elemAt source 2)
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else if sourceType == "git" then
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fetchImportGit (elemAt source 2) (elemAt source 4)
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else if sourceType == "path" then
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importPath (elemAt source 2)
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else
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throw ("Invalid package set source specification: ${pkgSource}")
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