nixos: nixos/doc/manual/development/option-def.xml to CommonMark

4 files changed, 196 insertions, 100 deletions

diff --git a/nixos/doc/manual/development/option-def.section.md b/nixos/doc/manual/development/option-def.section.md
new file mode 100644
index 00000000000..91b24cd4a3a
--- /dev/null
+++ b/nixos/doc/manual/development/option-def.section.md
@@ -0,0 +1,91 @@
+# Option Definitions {#sec-option-definitions}
+
+Option definitions are generally straight-forward bindings of values to
+option names, like
+
+```nix
+config = {
+  services.httpd.enable = true;
+};
+```
+
+However, sometimes you need to wrap an option definition or set of
+option definitions in a *property* to achieve certain effects:
+
+## Delaying Conditionals {#sec-option-definitions-delaying-conditionals .unnumbered}
+
+If a set of option definitions is conditional on the value of another
+option, you may need to use `mkIf`. Consider, for instance:
+
+```nix
+config = if config.services.httpd.enable then {
+  environment.systemPackages = [ ... ];
+  ...
+} else {};
+```
+
+This definition will cause Nix to fail with an "infinite recursion"
+error. Why? Because the value of `config.services.httpd.enable` depends
+on the value being constructed here. After all, you could also write the
+clearly circular and contradictory:
+
+```nix
+config = if config.services.httpd.enable then {
+  services.httpd.enable = false;
+} else {
+  services.httpd.enable = true;
+};
+```
+
+The solution is to write:
+
+```nix
+config = mkIf config.services.httpd.enable {
+  environment.systemPackages = [ ... ];
+  ...
+};
+```
+
+The special function `mkIf` causes the evaluation of the conditional to
+be "pushed down" into the individual definitions, as if you had written:
+
+```nix
+config = {
+  environment.systemPackages = if config.services.httpd.enable then [ ... ] else [];
+  ...
+};
+```
+
+## Setting Priorities {#sec-option-definitions-setting-priorities .unnumbered}
+
+A module can override the definitions of an option in other modules by
+setting a *priority*. All option definitions that do not have the lowest
+priority value are discarded. By default, option definitions have
+priority 1000. You can specify an explicit priority by using
+`mkOverride`, e.g.
+
+```nix
+services.openssh.enable = mkOverride 10 false;
+```
+
+This definition causes all other definitions with priorities above 10 to
+be discarded. The function `mkForce` is equal to `mkOverride 50`.
+
+## Merging Configurations {#sec-option-definitions-merging .unnumbered}
+
+In conjunction with `mkIf`, it is sometimes useful for a module to
+return multiple sets of option definitions, to be merged together as if
+they were declared in separate modules. This can be done using
+`mkMerge`:
+
+```nix
+config = mkMerge
+  [ # Unconditional stuff.
+    { environment.systemPackages = [ ... ];
+    }
+    # Conditional stuff.
+    (mkIf config.services.bla.enable {
+      environment.systemPackages = [ ... ];
+    })
+  ];
+```
diff --git a/nixos/doc/manual/development/option-def.xml b/nixos/doc/manual/development/option-def.xml
deleted file mode 100644
index 50a705d0cb8..00000000000
--- a/nixos/doc/manual/development/option-def.xml
+++ /dev/null
@@ -1,99 +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-option-definitions">
- <title>Option Definitions</title>
-
- <para>
-  Option definitions are generally straight-forward bindings of values to
-  option names, like
-<programlisting>
-config = {
-  services.httpd.enable = true;
-};
-</programlisting>
-  However, sometimes you need to wrap an option definition or set of option
-  definitions in a <emphasis>property</emphasis> to achieve certain effects:
- </para>
-
- <simplesect xml:id="sec-option-definitions-delaying-conditionals">
-  <title>Delaying Conditionals</title>
-  <para>
-   If a set of option definitions is conditional on the value of another
-   option, you may need to use <varname>mkIf</varname>. Consider, for instance:
-<programlisting>
-config = if config.services.httpd.enable then {
-  environment.systemPackages = [ <replaceable>...</replaceable> ];
-  <replaceable>...</replaceable>
-} else {};
-</programlisting>
-   This definition will cause Nix to fail with an “infinite recursion”
-   error. Why? Because the value of
-   <option>config.services.httpd.enable</option> depends on the value being
-   constructed here. After all, you could also write the clearly circular and
-   contradictory:
-<programlisting>
-config = if config.services.httpd.enable then {
-  services.httpd.enable = false;
-} else {
-  services.httpd.enable = true;
-};
-</programlisting>
-   The solution is to write:
-<programlisting>
-config = mkIf config.services.httpd.enable {
-  environment.systemPackages = [ <replaceable>...</replaceable> ];
-  <replaceable>...</replaceable>
-};
-</programlisting>
-   The special function <varname>mkIf</varname> causes the evaluation of the
-   conditional to be “pushed down” into the individual definitions, as if
-   you had written:
-<programlisting>
-config = {
-  environment.systemPackages = if config.services.httpd.enable then [ <replaceable>...</replaceable> ] else [];
-  <replaceable>...</replaceable>
-};
-</programlisting>
-  </para>
- </simplesect>
-
- <simplesect xml:id="sec-option-definitions-setting-priorities">
-  <title>Setting Priorities</title>
-  <para>
-   A module can override the definitions of an option in other modules by
-   setting a <emphasis>priority</emphasis>. All option definitions that do not
-   have the lowest priority value are discarded. By default, option definitions
-   have priority 1000. You can specify an explicit priority by using
-   <varname>mkOverride</varname>, e.g.
-<programlisting>
-services.openssh.enable = mkOverride 10 false;
-</programlisting>
-   This definition causes all other definitions with priorities above 10 to be
-   discarded. The function <varname>mkForce</varname> is equal to
-   <varname>mkOverride 50</varname>.
-  </para>
- </simplesect>
-
- <simplesect xml:id="sec-option-definitions-merging">
-  <title>Merging Configurations</title>
-  <para>
-   In conjunction with <literal>mkIf</literal>, it is sometimes useful for a
-   module to return multiple sets of option definitions, to be merged together
-   as if they were declared in separate modules. This can be done using
-   <varname>mkMerge</varname>:
-<programlisting>
-config = mkMerge
-  [ # Unconditional stuff.
-    { environment.systemPackages = [ <replaceable>...</replaceable> ];
-    }
-    # Conditional stuff.
-    (mkIf config.services.bla.enable {
-      environment.systemPackages = [ <replaceable>...</replaceable> ];
-    })
-  ];
-</programlisting>
-  </para>
- </simplesect>
-</section>
diff --git a/nixos/doc/manual/development/writing-modules.xml b/nixos/doc/manual/development/writing-modules.xml
index 245c49dbb7e..ac9617f4ea0 100644
--- a/nixos/doc/manual/development/writing-modules.xml
+++ b/nixos/doc/manual/development/writing-modules.xml
@@ -181,7 +181,7 @@ in {
  </example>
  <xi:include href="../from_md/development/option-declarations.section.xml" />
  <xi:include href="../from_md/development/option-types.section.xml" />
- <xi:include href="option-def.xml" />
+ <xi:include href="../from_md/development/option-def.section.xml" />
  <xi:include href="../from_md/development/assertions.section.xml" />
  <xi:include href="meta-attributes.xml" />
  <xi:include href="importing-modules.xml" />
diff --git a/nixos/doc/manual/from_md/development/option-def.section.xml b/nixos/doc/manual/from_md/development/option-def.section.xml
new file mode 100644
index 00000000000..8c9ef181aff
--- /dev/null
+++ b/nixos/doc/manual/from_md/development/option-def.section.xml
@@ -0,0 +1,104 @@
+<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-option-definitions">
+  <title>Option Definitions</title>
+  <para>
+    Option definitions are generally straight-forward bindings of values
+    to option names, like
+  </para>
+  <programlisting language="bash">
+config = {
+  services.httpd.enable = true;
+};
+</programlisting>
+  <para>
+    However, sometimes you need to wrap an option definition or set of
+    option definitions in a <emphasis>property</emphasis> to achieve
+    certain effects:
+  </para>
+  <section xml:id="sec-option-definitions-delaying-conditionals">
+    <title>Delaying Conditionals</title>
+    <para>
+      If a set of option definitions is conditional on the value of
+      another option, you may need to use <literal>mkIf</literal>.
+      Consider, for instance:
+    </para>
+    <programlisting language="bash">
+config = if config.services.httpd.enable then {
+  environment.systemPackages = [ ... ];
+  ...
+} else {};
+</programlisting>
+    <para>
+      This definition will cause Nix to fail with an <quote>infinite
+      recursion</quote> error. Why? Because the value of
+      <literal>config.services.httpd.enable</literal> depends on the
+      value being constructed here. After all, you could also write the
+      clearly circular and contradictory:
+    </para>
+    <programlisting language="bash">
+config = if config.services.httpd.enable then {
+  services.httpd.enable = false;
+} else {
+  services.httpd.enable = true;
+};
+</programlisting>
+    <para>
+      The solution is to write:
+    </para>
+    <programlisting language="bash">
+config = mkIf config.services.httpd.enable {
+  environment.systemPackages = [ ... ];
+  ...
+};
+</programlisting>
+    <para>
+      The special function <literal>mkIf</literal> causes the evaluation
+      of the conditional to be <quote>pushed down</quote> into the
+      individual definitions, as if you had written:
+    </para>
+    <programlisting language="bash">
+config = {
+  environment.systemPackages = if config.services.httpd.enable then [ ... ] else [];
+  ...
+};
+</programlisting>
+  </section>
+  <section xml:id="sec-option-definitions-setting-priorities">
+    <title>Setting Priorities</title>
+    <para>
+      A module can override the definitions of an option in other
+      modules by setting a <emphasis>priority</emphasis>. All option
+      definitions that do not have the lowest priority value are
+      discarded. By default, option definitions have priority 1000. You
+      can specify an explicit priority by using
+      <literal>mkOverride</literal>, e.g.
+    </para>
+    <programlisting language="bash">
+services.openssh.enable = mkOverride 10 false;
+</programlisting>
+    <para>
+      This definition causes all other definitions with priorities above
+      10 to be discarded. The function <literal>mkForce</literal> is
+      equal to <literal>mkOverride 50</literal>.
+    </para>
+  </section>
+  <section xml:id="sec-option-definitions-merging">
+    <title>Merging Configurations</title>
+    <para>
+      In conjunction with <literal>mkIf</literal>, it is sometimes
+      useful for a module to return multiple sets of option definitions,
+      to be merged together as if they were declared in separate
+      modules. This can be done using <literal>mkMerge</literal>:
+    </para>
+    <programlisting language="bash">
+config = mkMerge
+  [ # Unconditional stuff.
+    { environment.systemPackages = [ ... ];
+    }
+    # Conditional stuff.
+    (mkIf config.services.bla.enable {
+      environment.systemPackages = [ ... ];
+    })
+  ];
+</programlisting>
+  </section>
+</section>