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Diffstat (limited to 'doc/overlays.xml')
| -rw-r--r-- | doc/overlays.xml | 93 |
1 files changed, 19 insertions, 74 deletions
diff --git a/doc/overlays.xml b/doc/overlays.xml index bff2339ca933..26a888368abf 100644 --- a/doc/overlays.xml +++ b/doc/overlays.xml @@ -3,47 +3,32 @@ xml:id="chap-overlays"> <title>Overlays</title> <para> - This chapter describes how to extend and change Nixpkgs using overlays. - Overlays are used to add layers in the fixed-point used by Nixpkgs to compose - the set of all packages. + This chapter describes how to extend and change Nixpkgs using overlays. Overlays are used to add layers in the fixed-point used by Nixpkgs to compose the set of all packages. </para> <para> - Nixpkgs can be configured with a list of overlays, which are applied in - order. This means that the order of the overlays can be significant if - multiple layers override the same package. + Nixpkgs can be configured with a list of overlays, which are applied in order. This means that the order of the overlays can be significant if multiple layers override the same package. </para> <!--============================================================--> <section xml:id="sec-overlays-install"> <title>Installing overlays</title> <para> - The list of overlays can be set either explicitly in a Nix expression, or - through <literal><nixpkgs-overlays></literal> or user configuration - files. + The list of overlays can be set either explicitly in a Nix expression, or through <literal><nixpkgs-overlays></literal> or user configuration files. </para> <section xml:id="sec-overlays-argument"> <title>Set overlays in NixOS or Nix expressions</title> <para> - On a NixOS system the value of the <literal>nixpkgs.overlays</literal> - option, if present, is passed to the system Nixpkgs directly as an - argument. Note that this does not affect the overlays for non-NixOS - operations (e.g. <literal>nix-env</literal>), which are - <link xlink:href="#sec-overlays-lookup">looked</link> up independently. + On a NixOS system the value of the <literal>nixpkgs.overlays</literal> option, if present, is passed to the system Nixpkgs directly as an argument. Note that this does not affect the overlays for non-NixOS operations (e.g. <literal>nix-env</literal>), which are <link xlink:href="#sec-overlays-lookup">looked</link> up independently. </para> <para> - The list of overlays can be passed explicitly when importing nixpkgs, for - example <literal>import <nixpkgs> { overlays = [ overlay1 overlay2 ]; - }</literal>. + The list of overlays can be passed explicitly when importing nixpkgs, for example <literal>import <nixpkgs> { overlays = [ overlay1 overlay2 ]; }</literal>. </para> <para> - Further overlays can be added by calling the <literal>pkgs.extend</literal> - or <literal>pkgs.appendOverlays</literal>, although it is often preferable - to avoid these functions, because they recompute the Nixpkgs fixpoint, - which is somewhat expensive to do. + Further overlays can be added by calling the <literal>pkgs.extend</literal> or <literal>pkgs.appendOverlays</literal>, although it is often preferable to avoid these functions, because they recompute the Nixpkgs fixpoint, which is somewhat expensive to do. </para> </section> @@ -58,30 +43,20 @@ <orderedlist> <listitem> <para> - First, if an - <link xlink:href="#sec-overlays-argument"><varname>overlays</varname> - argument</link> to the Nixpkgs function itself is given, then that is - used and no path lookup will be performed. + First, if an <link xlink:href="#sec-overlays-argument"><varname>overlays</varname> argument</link> to the Nixpkgs function itself is given, then that is used and no path lookup will be performed. </para> </listitem> <listitem> <para> - Otherwise, if the Nix path entry - <literal><nixpkgs-overlays></literal> exists, we look for overlays at - that path, as described below. + Otherwise, if the Nix path entry <literal><nixpkgs-overlays></literal> exists, we look for overlays at that path, as described below. </para> <para> - See the section on <literal>NIX_PATH</literal> in the Nix manual for - more details on how to set a value for - <literal><nixpkgs-overlays>.</literal> + See the section on <literal>NIX_PATH</literal> in the Nix manual for more details on how to set a value for <literal><nixpkgs-overlays>.</literal> </para> </listitem> <listitem> <para> - If one of <filename>~/.config/nixpkgs/overlays.nix</filename> and - <filename>~/.config/nixpkgs/overlays/</filename> exists, then we look - for overlays at that path, as described below. It is an error if both - exist. + If one of <filename>~/.config/nixpkgs/overlays.nix</filename> and <filename>~/.config/nixpkgs/overlays/</filename> exists, then we look for overlays at that path, as described below. It is an error if both exist. </para> </listitem> </orderedlist> @@ -92,15 +67,12 @@ <itemizedlist> <listitem> <para> - If the path is a file, then the file is imported as a Nix expression and - used as the list of overlays. + If the path is a file, then the file is imported as a Nix expression and used as the list of overlays. </para> </listitem> <listitem> <para> - If the path is a directory, then we take the content of the directory, - order it lexicographically, and attempt to interpret each as an overlay - by: + If the path is a directory, then we take the content of the directory, order it lexicographically, and attempt to interpret each as an overlay by: <itemizedlist> <listitem> <para> @@ -109,8 +81,7 @@ </listitem> <listitem> <para> - Importing a top-level <filename>default.nix</filename> file, if it is - a directory. + Importing a top-level <filename>default.nix</filename> file, if it is a directory. </para> </listitem> </itemizedlist> @@ -120,12 +91,7 @@ </para> <para> - Because overlays that are set in NixOS configuration do not affect - non-NixOS operations such as <literal>nix-env</literal>, the - <filename>overlays.nix</filename> option provides a convenient way to use - the same overlays for a NixOS system configuration and user configuration: - the same file can be used as <filename>overlays.nix</filename> and imported - as the value of <literal>nixpkgs.overlays</literal>. + Because overlays that are set in NixOS configuration do not affect non-NixOS operations such as <literal>nix-env</literal>, the <filename>overlays.nix</filename> option provides a convenient way to use the same overlays for a NixOS system configuration and user configuration: the same file can be used as <filename>overlays.nix</filename> and imported as the value of <literal>nixpkgs.overlays</literal>. </para> <!-- TODO: Example of sharing overlays between NixOS configuration @@ -139,9 +105,7 @@ <title>Defining overlays</title> <para> - Overlays are Nix functions which accept two arguments, conventionally called - <varname>self</varname> and <varname>super</varname>, and return a set of - packages. For example, the following is a valid overlay. + Overlays are Nix functions which accept two arguments, conventionally called <varname>self</varname> and <varname>super</varname>, and return a set of packages. For example, the following is a valid overlay. </para> <programlisting> @@ -158,38 +122,19 @@ self: super: </programlisting> <para> - The first argument (<varname>self</varname>) corresponds to the final - package set. You should use this set for the dependencies of all packages - specified in your overlay. For example, all the dependencies of - <varname>rr</varname> in the example above come from - <varname>self</varname>, as well as the overridden dependencies used in the - <varname>boost</varname> override. + The first argument (<varname>self</varname>) corresponds to the final package set. You should use this set for the dependencies of all packages specified in your overlay. For example, all the dependencies of <varname>rr</varname> in the example above come from <varname>self</varname>, as well as the overridden dependencies used in the <varname>boost</varname> override. </para> <para> - The second argument (<varname>super</varname>) corresponds to the result of - the evaluation of the previous stages of Nixpkgs. It does not contain any of - the packages added by the current overlay, nor any of the following - overlays. This set should be used either to refer to packages you wish to - override, or to access functions defined in Nixpkgs. For example, the - original recipe of <varname>boost</varname> in the above example, comes from - <varname>super</varname>, as well as the <varname>callPackage</varname> - function. + The second argument (<varname>super</varname>) corresponds to the result of the evaluation of the previous stages of Nixpkgs. It does not contain any of the packages added by the current overlay, nor any of the following overlays. This set should be used either to refer to packages you wish to override, or to access functions defined in Nixpkgs. For example, the original recipe of <varname>boost</varname> in the above example, comes from <varname>super</varname>, as well as the <varname>callPackage</varname> function. </para> <para> - The value returned by this function should be a set similar to - <filename>pkgs/top-level/all-packages.nix</filename>, containing overridden - and/or new packages. + The value returned by this function should be a set similar to <filename>pkgs/top-level/all-packages.nix</filename>, containing overridden and/or new packages. </para> <para> - Overlays are similar to other methods for customizing Nixpkgs, in particular - the <literal>packageOverrides</literal> attribute described in - <xref linkend="sec-modify-via-packageOverrides"/>. Indeed, - <literal>packageOverrides</literal> acts as an overlay with only the - <varname>super</varname> argument. It is therefore appropriate for basic - use, but overlays are more powerful and easier to distribute. + Overlays are similar to other methods for customizing Nixpkgs, in particular the <literal>packageOverrides</literal> attribute described in <xref linkend="sec-modify-via-packageOverrides"/>. Indeed, <literal>packageOverrides</literal> acts as an overlay with only the <varname>super</varname> argument. It is therefore appropriate for basic use, but overlays are more powerful and easier to distribute. </para> </section> </chapter> |