forked from mirrors/nixpkgs
58 lines
1.6 KiB
XML
58 lines
1.6 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="chap-functions">
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<title>Functions reference</title>
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<para>
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The nixpkgs repository has several utility functions to manipulate Nix expressions.
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</para>
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<section xml:id="sec-pkgs-overridePackages">
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<title>pkgs.overridePackages</title>
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<para>
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This function inside the nixpkgs expression (<varname>pkgs</varname>)
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can be used to override the set of packages itself.
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</para>
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<para>
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Warning: this function is expensive and must not be used from within
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the nixpkgs repository.
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</para>
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<para>
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Example usage:
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<programlisting>let
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pkgs = import <nixpkgs> {};
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newpkgs = pkgs.overridePackages (self: super: {
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foo = super.foo.override { ... };
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};
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in ...</programlisting>
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</para>
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<para>
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The resulting <varname>newpkgs</varname> will have the new <varname>foo</varname>
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expression, and all other expressions depending on <varname>foo</varname> will also
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use the new <varname>foo</varname> expression.
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</para>
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<para>
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The behavior of this function is similar to <link
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linkend="sec-modify-via-packageOverrides">config.packageOverrides</link>.
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</para>
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<para>
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The <varname>self</varname> parameter refers to the final package set with the
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applied overrides. Using this parameter may lead to infinite recursion if not
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used consciously.
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</para>
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<para>
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The <varname>super</varname> parameter refers to the old package set.
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It's equivalent to <varname>pkgs</varname> in the above example.
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</para>
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</section>
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</chapter>
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