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doc/manual: add note to allowSubstitutes advanced attribute

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Profpatsch 2019-12-03 18:01:45 +01:00
parent e59e2b2951
commit 7395e091c5
1 changed files with 13 additions and 2 deletions
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15
doc/manual/expressions/advanced-attributes.xml
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@ -325,12 +325,23 @@ big = "a very long string";
<varlistentry><term><varname>allowSubstitutes</varname></term>
<listitem><para>If this attribute is set to
<listitem>
<para>If this attribute is set to
<literal>false</literal>, then Nix will always build this
derivation; it will not try to substitute its outputs. This is
useful for very trivial derivations (such as
<function>writeText</function> in Nixpkgs) that are cheaper to
build than to substitute from a binary cache.</para></listitem>
build than to substitute from a binary cache.</para>
<note><para>You need to have a builder configured which satisfies
the derivation’s <literal>system</literal> attribute, since the
derivation cannot be substituted. Thus it is usually a good idea
to align <literal>system</literal> with
<literal>builtins.currentSystem</literal> when setting
<literal>allowSubstitutes</literal> to <literal>false</literal>.
For most trivial derivations this should be the case.
</para></note>
</listitem>
</varlistentry>