modules: add support for module replacement with disabledModules

This is based on a prototype Nicolas B. Pierron worked on during a
discussion we had at FOSDEM.

A new version with a workaround for problems of the reverted original.
Discussion: https://github.com/NixOS/nixpkgs/commit/3f2566689
This commit is contained in:
Daiderd Jordan 2017-02-14 23:18:44 +01:00 committed by Vladimír Čunát
parent bb9a37a2a5
commit d88721e440
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9 changed files with 127 additions and 7 deletions

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@ -20,7 +20,8 @@ rec {
, prefix ? []
, # This should only be used for special arguments that need to be evaluated
# when resolving module structure (like in imports). For everything else,
# there's _module.args.
# there's _module.args. If specialArgs.modulesPath is defined it will be
# used as the base path for disabledModules.
specialArgs ? {}
, # This would be remove in the future, Prefer _module.args option instead.
args ? {}
@ -58,10 +59,7 @@ rec {
closed = closeModules (modules ++ [ internalModule ]) ({ inherit config options; lib = import ./.; } // specialArgs);
# Note: the list of modules is reversed to maintain backward
# compatibility with the old module system. Not sure if this is
# the most sensible policy.
options = mergeModules prefix (reverseList closed);
options = mergeModules prefix (reverseList (filterModules (specialArgs.modulesPath or "") closed));
# Traverse options and extract the option values into the final
# config set. At the same time, check whether all option
@ -87,6 +85,16 @@ rec {
result = { inherit options config; };
in result;
# Filter disabled modules. Modules can be disabled allowing
# their implementation to be replaced.
filterModules = modulesPath: modules:
let
moduleKey = m: if isString m then toString modulesPath + "/" + m else toString m;
disabledKeys = map moduleKey (concatMap (m: m.disabledModules) modules);
in
filter (m: !(elem m.key disabledKeys)) modules;
/* Close a set of modules under the imports relation. */
closeModules = modules: args:
let
@ -111,12 +119,13 @@ rec {
else {};
in
if m ? config || m ? options then
let badAttrs = removeAttrs m ["imports" "options" "config" "key" "_file" "meta"]; in
let badAttrs = removeAttrs m ["_file" "key" "disabledModules" "imports" "options" "config" "meta"]; in
if badAttrs != {} then
throw "Module `${key}' has an unsupported attribute `${head (attrNames badAttrs)}'. This is caused by assignments to the top-level attributes `config' or `options'."
else
{ file = m._file or file;
key = toString m.key or key;
disabledModules = m.disabledModules or [];
imports = m.imports or [];
options = m.options or {};
config = mkMerge [ (m.config or {}) metaSet ];
@ -124,9 +133,10 @@ rec {
else
{ file = m._file or file;
key = toString m.key or key;
disabledModules = m.disabledModules or [];
imports = m.require or [] ++ m.imports or [];
options = {};
config = mkMerge [ (removeAttrs m ["key" "_file" "require" "imports"]) metaSet ];
config = mkMerge [ (removeAttrs m ["_file" "key" "disabledModules" "require" "imports"]) metaSet ];
};
applyIfFunction = key: f: args@{ config, options, lib, ... }: if isFunction f then

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@ -99,6 +99,14 @@ checkConfigOutput 'true' "$@" ./define-enable.nix ./define-loaOfSub-if-foo-enabl
checkConfigOutput 'true' "$@" ./define-enable.nix ./define-loaOfSub-foo-if-enable.nix
checkConfigOutput 'true' "$@" ./define-enable.nix ./define-loaOfSub-foo-enable-if.nix
# Check disabledModules with config definitions and option declarations.
set -- config.enable ./define-enable.nix ./declare-enable.nix
checkConfigOutput "true" "$@"
checkConfigOutput "false" "$@" ./disable-define-enable.nix
checkConfigError "The option .*enable.* defined in .* does not exist" "$@" ./disable-declare-enable.nix
checkConfigError "attribute .*enable.* in selection path .*config.enable.* not found" "$@" ./disable-define-enable.nix ./disable-declare-enable.nix
checkConfigError "attribute .*enable.* in selection path .*config.enable.* not found" "$@" ./disable-enable-modules.nix
# Check _module.args.
set -- config.enable ./declare-enable.nix ./define-enable-with-custom-arg.nix
checkConfigError 'while evaluating the module argument .*custom.* in .*define-enable-with-custom-arg.nix.*:' "$@"

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@ -3,5 +3,6 @@
{
inherit (lib.evalModules {
inherit modules;
specialArgs.modulesPath = ./.;
}) config options;
}

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@ -0,0 +1,5 @@
{ lib, ... }:
{
disabledModules = [ ./declare-enable.nix ];
}

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@ -0,0 +1,5 @@
{ lib, ... }:
{
disabledModules = [ ./define-enable.nix ];
}

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@ -0,0 +1,5 @@
{ lib, ... }:
{
disabledModules = [ "define-enable.nix" "declare-enable.nix" ];
}

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@ -0,0 +1,75 @@
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id="sec-replace-modules">
<title>Replace Modules</title>
<para>Modules that are imported can also be disabled. The option
declarations and config implementation of a disabled module will be
ignored, allowing another to take it's place. This can be used to
import a set of modules from another channel while keeping the rest
of the system on a stable release.</para>
<para><literal>disabledModules</literal> is a top level attribute like
<literal>imports</literal>, <literal>options</literal> and
<literal>config</literal>. It contains a list of modules that will
be disabled. This can either be the full path to the module or a
string with the filename relative to the modules path
(eg. &lt;nixpkgs/nixos/modules&gt; for nixos).
</para>
<para>This example will replace the existing postgresql module with
the version defined in the nixos-unstable channel while keeping the
rest of the modules and packages from the original nixos channel.
This only overrides the module definition, this won't use postgresql
from nixos-unstable unless explicitly configured to do so.</para>
<programlisting>
{ config, lib, pkgs, ... }:
{
disabledModules = [ "services/databases/postgresql.nix" ];
imports =
[ # Use postgresql service from nixos-unstable channel.
# sudo nix-channel --add http://nixos.org/channels/nixos-unstable nixos-unstable
&lt;nixos-unstable/nixos/modules/services/databases/postgresql.nix&gt;
];
services.postgresql.enable = true;
}
</programlisting>
<para>This example shows how to define a custom module as a
replacement for an existing module. Importing this module will
disable the original module without having to know it's
implementation details.</para>
<programlisting>
{ config, lib, pkgs, ... }:
with lib;
let
cfg = config.programs.man;
in
{
disabledModules = [ "services/programs/man.nix" ];
options = {
programs.man.enable = mkOption {
type = types.bool;
default = true;
description = "Whether to enable manual pages.";
};
};
config = mkIf cfg.enabled {
warnings = [ "disabled manpages for production deployments." ];
};
}
</programlisting>
</section>

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@ -179,5 +179,6 @@ in {
<xi:include href="option-types.xml" />
<xi:include href="option-def.xml" />
<xi:include href="meta-attributes.xml" />
<xi:include href="replace-modules.xml" />
</chapter>

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@ -271,6 +271,16 @@ following incompatible changes:</para>
</para>
</listitem>
<listitem>
<para>
Modules can now be disabled by using <link
xlink:href="https://nixos.org/nixpkgs/manual/#sec-replace-modules">
disabledModules</link>, allowing another to take it's place. This can be
used to import a set of modules from another channel while keeping the
rest of the system on a stable release.
</para>
</listitem>
</itemizedlist>