NixOS:config argument: Difference between revisions
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m changed instances of pkgs.lib to more commonly available lib |
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The following code is used to support the explanation. | The following code is used to support the explanation. | ||
< | <syntaxhighlight lang="nix"> | ||
{config, pkgs, ...}: | {config, pkgs, lib ...}: | ||
{ | { | ||
options = { | options = { | ||
foo = | foo = lib.mkOption { | ||
description = "..."; | description = "..."; | ||
}; | }; | ||
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}; | }; | ||
} | } | ||
</ | </syntaxhighlight> | ||
This snippet of code is a module which declare the option "<code>foo</code>" and define the option "<code>bar</code>". The option "<code>bar</code>" is defined with the value <code>config.foo</code>. This attribute <code>foo</code> of the <code>config</code> argument, is the result of the [[NixOS:Declaration#Evaluation|evaluation]] of the definitions and the declarations of the option "<code>foo</code>". Definitions of the option "<code>foo</code>" may exists in other module used by the system. | This snippet of code is a module which declare the option "<code>foo</code>" and define the option "<code>bar</code>". The option "<code>bar</code>" is defined with the value <code>config.foo</code>. This attribute <code>foo</code> of the <code>config</code> argument, is the result of the [[NixOS:Declaration#Evaluation|evaluation]] of the definitions and the declarations of the option "<code>foo</code>". Definitions of the option "<code>foo</code>" may exists in other module used by the system. | ||
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The process of module computation is highly recursive and may cause trouble when you want to add control flow statements. A common mistake is to use "<code>if</code>" or "<code>assert</code>" statements in the computation of a module. | The process of module computation is highly recursive and may cause trouble when you want to add control flow statements. A common mistake is to use "<code>if</code>" or "<code>assert</code>" statements in the computation of a module. | ||
< | <syntaxhighlight lang="nix"> | ||
{config, pkgs, ...}: | {config, pkgs, lib, ...}: | ||
{ | { | ||
options = { | options = { | ||
foo = | foo = lib.mkOption { | ||
default = false; | default = false; | ||
type = with | type = with lib.types; bool; | ||
description = " | description = "foo boolean option"; | ||
}; | }; | ||
}; | }; | ||
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{}; | {}; | ||
} | } | ||
</ | </syntaxhighlight> | ||
The previous module cause an infinite recursion: | The previous module cause an infinite recursion: | ||
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To avoid such infinite recursion, [[NixOS:Properties|properties]] have been introduced, thus the previous code should be rewritten in: | To avoid such infinite recursion, [[NixOS:Properties|properties]] have been introduced, thus the previous code should be rewritten in: | ||
< | <syntaxhighlight lang="nix"> | ||
{config, pkgs, ...}: | {config, pkgs, lib, ...}: | ||
{ | { | ||
options = { | options = { | ||
foo = | foo = lib.mkOption { | ||
default = false; | default = false; | ||
type = with | type = with lib.types; bool; | ||
description = " | description = "foo boolean"; | ||
}; | }; | ||
}; | }; | ||
config = | config = lib.mkIf config.foo { | ||
bar = 42; | bar = 42; | ||
}; | }; | ||
} | } | ||
</ | </syntaxhighlight> | ||
== Common Pattern == | == Common Pattern == | ||
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Often, the module declare options embedded inside an attribute set. To access these options, we add an attribute <code>cfg</code> as a shortcut notation. | Often, the module declare options embedded inside an attribute set. To access these options, we add an attribute <code>cfg</code> as a shortcut notation. | ||
< | <syntaxhighlight lang="nix"> | ||
{config, pkgs, ...}: | {config, pkgs, lib, ...}: | ||
let | let | ||
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in | in | ||
with | with lib; { | ||
options = { | options = { | ||
foo.bar.baz = { | foo.bar.baz = { | ||
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}; | }; | ||
} | } | ||
</ | </syntaxhighlight> | ||
[[Category: | [[Category:Reference]] | ||
[[Category: | [[Category:NixOS]] | ||