nixos/treewide: Fix incorrectly rendered examples

Many options define their example to be a Nix value without using
literalExample. This sometimes gets rendered incorrectly in the manual,
causing confusion like in https://github.com/NixOS/nixpkgs/issues/25516

This fixes it by using literalExample for such options. The list of
option to fix was determined with this expression:

  let
    nixos = import ./nixos { configuration = {}; };
    lib = import ./lib;
    valid = d: {
      # escapeNixIdentifier from https://github.com/NixOS/nixpkgs/pull/82461
      set = lib.all (n: lib.strings.escapeNixIdentifier n == n) (lib.attrNames d) && lib.all (v: valid v) (lib.attrValues d);
      list = lib.all (v: valid v) d;
    }.${builtins.typeOf d} or true;

    optionList = lib.optionAttrSetToDocList nixos.options;

  in map (opt: {
    file = lib.elemAt opt.declarations 0;
    loc = lib.options.showOption opt.loc;
  }) (lib.filter (opt: if opt ? example then ! valid opt.example else false) optionList)

which when evaluated will output all options that use a Nix identifier
that would need escaping as an attribute name.

5 files changed, 43 insertions, 31 deletions

diff --git a/nixos/modules/services/networking/3proxy.nix b/nixos/modules/services/networking/3proxy.nix
index 26aa1667946..ae8a4958ca9 100644
--- a/nixos/modules/services/networking/3proxy.nix
+++ b/nixos/modules/services/networking/3proxy.nix
@@ -334,10 +334,12 @@ in {
           nsrecord = mkOption {
             type = types.attrsOf types.str;
             default = { };
-            example = {
-              "files.local" = "192.168.1.12";
-              "site.local" = "192.168.1.43";
-            };
+            example = literalExample ''
+              {
+                "files.local" = "192.168.1.12";
+                "site.local" = "192.168.1.43";
+              }
+            '';
             description = "Adds static nsrecords.";
           };
         };
diff --git a/nixos/modules/services/networking/dnscache.nix b/nixos/modules/services/networking/dnscache.nix
index d123bca9321..d06032daecc 100644
--- a/nixos/modules/services/networking/dnscache.nix
+++ b/nixos/modules/services/networking/dnscache.nix
@@ -61,10 +61,12 @@ in {
           Table of {hostname: server} pairs to use as authoritative servers for hosts (and subhosts).
           If entry for @ is not specified predefined list of root servers is used.
         '';
-        example = {
-          "@" = ["8.8.8.8" "8.8.4.4"];
-          "example.com" = ["192.168.100.100"];
-        };
+        example = literalExample ''
+          {
+            "@" = ["8.8.8.8" "8.8.4.4"];
+            "example.com" = ["192.168.100.100"];
+          }
+        '';
       };
 
       forwardOnly = mkOption {
diff --git a/nixos/modules/services/networking/ndppd.nix b/nixos/modules/services/networking/ndppd.nix
index e015f76f622..77e979a8a42 100644
--- a/nixos/modules/services/networking/ndppd.nix
+++ b/nixos/modules/services/networking/ndppd.nix
@@ -43,7 +43,7 @@ let
       timeout = mkOption {
         type = types.int;
         description = ''
-          Controls how long to wait for a Neighbor Advertisment Message before 
+          Controls how long to wait for a Neighbor Advertisment Message before
           invalidating the entry, in milliseconds.
         '';
         default = 500;
@@ -51,7 +51,7 @@ let
       ttl = mkOption {
         type = types.int;
         description = ''
-          Controls how long a valid or invalid entry remains in the cache, in 
+          Controls how long a valid or invalid entry remains in the cache, in
           milliseconds.
         '';
         default = 30000;
@@ -142,7 +142,11 @@ in {
         messages, and respond to them according to a set of rules.
       '';
       default = {};
-      example = { eth0.rules."1111::/64" = {}; };
+      example = literalExample ''
+        {
+          eth0.rules."1111::/64" = {};
+        }
+      '';
     };
   };
 
diff --git a/nixos/modules/services/networking/strongswan.nix b/nixos/modules/services/networking/strongswan.nix
index 4ff9c486059..13a1a897c5e 100644
--- a/nixos/modules/services/networking/strongswan.nix
+++ b/nixos/modules/services/networking/strongswan.nix
@@ -4,7 +4,7 @@ let
 
   inherit (builtins) toFile;
   inherit (lib) concatMapStringsSep concatStringsSep mapAttrsToList
-                mkIf mkEnableOption mkOption types;
+                mkIf mkEnableOption mkOption types literalExample;
 
   cfg = config.services.strongswan;
 
@@ -79,19 +79,21 @@ in
     connections = mkOption {
       type = types.attrsOf (types.attrsOf types.str);
       default = {};
-      example = {
-        "%default" = {
-          keyexchange = "ikev2";
-          keyingtries = "1";
-        };
-        roadwarrior = {
-          auto       = "add";
-          leftcert   = "/run/keys/moonCert.pem";
-          leftid     = "@moon.strongswan.org";
-          leftsubnet = "10.1.0.0/16";
-          right      = "%any";
-        };
-      };
+      example = literalExample ''
+        {
+          "%default" = {
+            keyexchange = "ikev2";
+            keyingtries = "1";
+          };
+          roadwarrior = {
+            auto       = "add";
+            leftcert   = "/run/keys/moonCert.pem";
+            leftid     = "@moon.strongswan.org";
+            leftsubnet = "10.1.0.0/16";
+            right      = "%any";
+          };
+        }
+      '';
       description = ''
         A set of connections and their options for the ‘conn xxx’
         sections of the <filename>ipsec.conf</filename> file.
diff --git a/nixos/modules/services/networking/syncthing.nix b/nixos/modules/services/networking/syncthing.nix
index 5b3eb6f04b4..e717d78feed 100644
--- a/nixos/modules/services/networking/syncthing.nix
+++ b/nixos/modules/services/networking/syncthing.nix
@@ -169,12 +169,14 @@ in {
           description = ''
             folders which should be shared by syncthing.
           '';
-          example = {
-            "/home/user/sync" = {
-              id = "syncme";
-              devices = [ "bigbox" ];
-            };
-          };
+          example = literalExample ''
+            {
+              "/home/user/sync" = {
+                id = "syncme";
+                devices = [ "bigbox" ];
+              };
+            }
+          '';
           type = types.attrsOf (types.submodule ({ name, ... }: {
             options = {