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Diffstat (limited to 'nixos/doc/manual/development/assertions.xml')
-rw-r--r-- | nixos/doc/manual/development/assertions.xml | 74 |
1 files changed, 0 insertions, 74 deletions
diff --git a/nixos/doc/manual/development/assertions.xml b/nixos/doc/manual/development/assertions.xml deleted file mode 100644 index 32f90cf2e7c..00000000000 --- a/nixos/doc/manual/development/assertions.xml +++ /dev/null @@ -1,74 +0,0 @@ -<section xmlns="http://docbook.org/ns/docbook" - xmlns:xlink="http://www.w3.org/1999/xlink" - xmlns:xi="http://www.w3.org/2001/XInclude" - version="5.0" - xml:id="sec-assertions"> - <title>Warnings and Assertions</title> - - <para> - When configuration problems are detectable in a module, it is a good idea to - write an assertion or warning. Doing so provides clear feedback to the user - and prevents errors after the build. - </para> - - <para> - Although Nix has the <literal>abort</literal> and - <literal>builtins.trace</literal> - <link xlink:href="https://nixos.org/nix/manual/#ssec-builtins">functions</link> - to perform such tasks, they are not ideally suited for NixOS modules. Instead - of these functions, you can declare your warnings and assertions using the - NixOS module system. - </para> - - <section xml:id="sec-assertions-warnings"> - <title>Warnings</title> - - <para> - This is an example of using <literal>warnings</literal>. - </para> - -<programlisting> -<![CDATA[ -{ config, lib, ... }: -{ - config = lib.mkIf config.services.foo.enable { - warnings = - if config.services.foo.bar - then [ ''You have enabled the bar feature of the foo service. - This is known to cause some specific problems in certain situations. - '' ] - else []; - } -} -]]> -</programlisting> - </section> - - <section xml:id="sec-assertions-assertions"> - <title>Assertions</title> - - <para> - This example, extracted from the - <link xlink:href="https://github.com/NixOS/nixpkgs/blob/release-17.09/nixos/modules/services/logging/syslogd.nix"> - <literal>syslogd</literal> module </link> shows how to use - <literal>assertions</literal>. Since there can only be one active syslog - daemon at a time, an assertion is useful to prevent such a broken system - from being built. - </para> - -<programlisting> -<![CDATA[ -{ config, lib, ... }: -{ - config = lib.mkIf config.services.syslogd.enable { - assertions = - [ { assertion = !config.services.rsyslogd.enable; - message = "rsyslogd conflicts with syslogd"; - } - ]; - } -} -]]> -</programlisting> - </section> -</section> |