NixOS:config argument - Revision history

Raf: changed instances of pkgs.lib to more commonly available lib

2024-04-04T03:20:25Z

changed instances of pkgs.lib to more commonly available lib

← Older revision		Revision as of 03:20, 4 April 2024
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	<syntaxhighlight lang="nix">		<syntaxhighlight lang="nix">
	{config, pkgs, ...}:		{config, pkgs, lib ...}:

	{		{
	options = {		options = {
	foo = ~~pkgs.~~lib.mkOption {		foo = lib.mkOption {
	description = "...";		description = "...";
	};		};
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	<syntaxhighlight lang="nix">		<syntaxhighlight lang="nix">
	{config, pkgs, ...}:		{config, pkgs, lib, ...}:

	{		{
	options = {		options = {
	foo = ~~pkgs.~~lib.mkOption {		foo = lib.mkOption {
	default = false;		default = false;
	type = with ~~pkgs.~~lib.types; bool;		type = with lib.types; bool;
	description = "~~enable~~ foo";		description = "foo boolean option";
	};		};
	};		};
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	<syntaxhighlight lang="nix">		<syntaxhighlight lang="nix">
	{config, pkgs, ...}:		{config, pkgs, lib, ...}:

	{		{
	options = {		options = {
	foo = ~~pkgs.~~lib.mkOption {		foo = lib.mkOption {
	default = false;		default = false;
	type = with ~~pkgs.~~lib.types; bool;		type = with lib.types; bool;
	description = "~~enable~~ foo";		description = "foo boolean";
	};		};
	};		};

	config = ~~pkgs.~~lib.mkIf config.foo {		config = lib.mkIf config.foo {
	bar = 42;		bar = 42;
	};		};
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	<syntaxhighlight lang="nix">		<syntaxhighlight lang="nix">
	{config, pkgs, ...}:		{config, pkgs, lib, ...}:

	let		let
Line 89:		Line 89:
	in		in

	with ~~pkgs.~~lib; {		with lib; {
	options = {		options = {
	foo.bar.baz = {		foo.bar.baz = {

imported>Fricklerhandwerk: add category: NixOS

2022-08-04T08:29:48Z

add category: NixOS

← Older revision		Revision as of 08:29, 4 August 2022
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	[[Category:Reference]]		[[Category:Reference]]
			[[Category:NixOS]]

imported>Nix: recategorize

2021-09-20T00:35:10Z

recategorize

← Older revision		Revision as of 00:35, 20 September 2021
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	</syntaxhighlight>		</syntaxhighlight>

	[[Category:~~Discussion~~]]		[[Category:Reference]]

imported>Fadenb at 19:48, 22 August 2017

2017-08-22T19:48:03Z

← Older revision		Revision as of 19:48, 22 August 2017
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	[[Category:Discussion]]		[[Category:Discussion]]
	~~[[Category:Pages_with_syntax_highlighting_errors]]~~

imported>Fadenb: Syntax highlighting

2017-08-22T19:45:14Z

Syntax highlighting

← Older revision		Revision as of 19:45, 22 August 2017
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	The following code is used to support the explanation.		The following code is used to support the explanation.

	<~~pre~~>		<syntaxhighlight lang="nix">
	{config, pkgs, ...}:		{config, pkgs, ...}:

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	};		};
	}		}
	</~~pre~~>		</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.

	<~~pre~~>		<syntaxhighlight lang="nix">
	{config, pkgs, ...}:		{config, pkgs, ...}:

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	{};		{};
	}		}
	</~~pre~~>		</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:

	<~~pre~~>		<syntaxhighlight lang="nix">
	{config, pkgs, ...}:		{config, pkgs, ...}:

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	};		};
	}		}
	</~~pre~~>		</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.

	<~~pre~~>		<syntaxhighlight lang="nix">
	{config, pkgs, ...}:		{config, pkgs, ...}:

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	};		};
	}		}
	</~~pre~~>		</syntaxhighlight>

	[[Category:Discussion]]		[[Category:Discussion]]
	[[Category:Pages_with_syntax_highlighting_errors]]		[[Category:Pages_with_syntax_highlighting_errors]]

imported>Makefu at 19:24, 22 August 2017

2017-08-22T19:24:26Z

← Older revision		Revision as of 19:24, 22 August 2017
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	}		}
	</pre>		</pre>

			[[Category:Discussion]]
			[[Category:Pages_with_syntax_highlighting_errors]]

imported>Fadenb: Created page with "This argument gives access to the entire configuration of the system. It is computed from option declarations and option definitions defined inside all modules used for the s..."

2017-06-28T20:38:52Z

Created page with "This argument gives access to the entire configuration of the system. It is computed from option declarations and option definitions defined inside all modules used for the s..."

New page

This argument gives access to the entire configuration of the system. It is computed from option declarations and option definitions defined inside all modules used for the system.

== Simple Case ==

The following code is used to support the explanation.

<pre>
{config, pkgs, ...}:

{
options = {
foo = pkgs.lib.mkOption {
description = "...";
};
};

config = {
bar = config.foo;
};
}
</pre>

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.

Adding additional modules to the system may change the value of <code>config.foo</code> and may change the behavior of the previous module.

== Conditional Statements ==

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.

<pre>
{config, pkgs, ...}:

{
options = {
foo = pkgs.lib.mkOption {
default = false;
type = with pkgs.lib.types; bool;
description = "enable foo";
};
};

config =
if config.foo then
{ bar = 42; }
else
{};
}
</pre>

The previous module cause an infinite recursion:
* The <code>config</code> attribute is evaluated. This evaluation needs the result of the <code>if</code> statement.
* The <code>if</code> statement is evaluated. This evaluation needs the result of the condition.
* The condition (<code>config.foo</code>) is evaluated. This evaluation needs the result of the <code>config</code> argument.
* The <code>config</code> argument is evaluated. This evaluation needs the result of merging of all modules.
* The merge function of the modules is evaluated. This evaluation needs the evaluation of each module <code>config</code> attribute.

To avoid such infinite recursion, [[NixOS:Properties|properties]] have been introduced, thus the previous code should be rewritten in:

<pre>
{config, pkgs, ...}:

{
options = {
foo = pkgs.lib.mkOption {
default = false;
type = with pkgs.lib.types; bool;
description = "enable foo";
};
};

config = pkgs.lib.mkIf config.foo {
bar = 42;
};
}
</pre>

== Common Pattern ==

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.

<pre>
{config, pkgs, ...}:

let
cfg = config.foo.bar.baz;

# ...
in

with pkgs.lib; {
options = {
foo.bar.baz = {
enable = mkOption { /* ... */ };
option1 = mkOption { /* ... */ };
option2 = mkOption { /* ... */ };
option3 = mkOption { /* ... */ };
};
};

config = mkIf cfg.enable {
# ...
};
}
</pre>