Merge pull request #125604 from ryantm/md-assertions

nixos/doc: convert assertions and warnings section to CommonMark
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# Warnings and Assertions {#sec-assertions}
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.
Although Nix has the `abort` and `builtins.trace` [functions](https://nixos.org/nix/manual/#ssec-builtins) 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.
## Warnings {#sec-assertions-warnings}
This is an example of using `warnings`.
```nix
{ 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 [];
}
}
```
## Assertions {#sec-assertions-assetions}
This example, extracted from the [`syslogd` module](https://github.com/NixOS/nixpkgs/blob/release-17.09/nixos/modules/services/logging/syslogd.nix) shows how to use `assertions`. 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.
```nix
{ config, lib, ... }:
{
config = lib.mkIf config.services.syslogd.enable {
assertions =
[ { assertion = !config.services.rsyslogd.enable;
message = "rsyslogd conflicts with syslogd";
}
];
}
}
```

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<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>

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@ -182,7 +182,7 @@ in {
<xi:include href="option-declarations.xml" />
<xi:include href="option-types.xml" />
<xi:include href="option-def.xml" />
<xi:include href="assertions.xml" />
<xi:include href="../from_md/development/assertions.section.xml" />
<xi:include href="meta-attributes.xml" />
<xi:include href="importing-modules.xml" />
<xi:include href="replace-modules.xml" />

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<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" 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 language="bash">
{ 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-assetions">
<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 language="bash">
{ config, lib, ... }:
{
config = lib.mkIf config.services.syslogd.enable {
assertions =
[ { assertion = !config.services.rsyslogd.enable;
message = &quot;rsyslogd conflicts with syslogd&quot;;
}
];
}
}
</programlisting>
</section>
</section>