nixos-option: update manpage

pkgs/tools/nix/nixos-option/nixos-option.8

@@ -11,18 +11,35 @@
 .Nm
 .Op Fl r | -recursive
 .Op Fl I Ar path
+.Op Fl F | -flake Ar flake-uri
+.br
+.Op Fl -no-flake
+.Op Fl -show-trace
 .Ar option.name
 .
 .
 .
 .Sh DESCRIPTION
 This command evaluates the configuration specified in
-.Pa /etc/nixos/configuration.nix
-and returns the properties of the option name given as argument.
+.Ev NIXOS_CONFIG Ns
+,
+.Pa nixos-config
+in
+.Ev NIX_PATH
+(which by default is
+.Pa /etc/nixos/configuration.nix Ns
+),
+.Pa /etc/nixos/flake.nix
+or the file and attribute specified by the
+.Fl I
+or
+.Fl -flake
+parameter, and returns the properties of the option name given as argument.
 .
 .Pp
-When the option name is not an option, the command prints the list of attributes
-contained in the attribute set.
+When the option name is not an option but an attribute set, the command prints
+the list of attributes contained in it. When no option name is given, the
+command prints all top-level attributes in given NixOS configuration.
 .
 .
 .
@@ -32,14 +49,38 @@ contained in the attribute set.
 Print all the values at or below the specified path recursively.
 .
 .It Fl I Ar path
-This option is passed to the underlying
+Add an entry to the Nix expression search path. This option is passed to the
+underlying
 .Xr nix-instantiate 1
 invocation.
+.
+.It Fl -show-trace
+Print eval trace. This option is passed to the underlying
+.Xr nix-instantiate 1
+invocation.
+.
+.It Fl F , -flake Ar flake-uri
+Specify the flake containing NixOS configuration. It defaults to
+.Pa /etc/nixos/flake.nix Ns
+, if the flake exists, it must contain an output named
+.Ql nixosConfigurations. Ns Va name Ns
+\&. If
+.Va name
+is omitted, it defaults to the current host name.
+.
+.It Fl -no-flake
+Do not imply
+.Fl -flake
+if
+.Pa /etc/nixos/flake.nix
+exists. With this option, it is possible to show options in non-flake NixOS
+configurations even if the current NixOS systems uses flakes.
+.
 .El
 .
 .
 .
-.Sh ENVIRONMENT
+.Sh Ev ENVIRONMENT
 .Bl -tag -width indent
 .It Ev NIXOS_CONFIG
 Path to the main NixOS configuration module. Defaults to
@@ -60,19 +101,22 @@ initScript
 
 $ nixos-option boot.loader.grub.enable
 Value:
-true
+  true
 
 Default:
-true
+  true
+
+Type:
+  boolean
 
 Description:
-Whether to enable the GNU GRUB boot loader.
+  Whether to enable the GNU GRUB boot loader.
 
 Declared by:
-  "/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/nixos/modules/system/boot/loader/grub/grub.nix"
+  /nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/nixos/modules/system/boot/loader/grub/grub.nix
 
 Defined by:
-  "/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/nixos/modules/system/boot/loader/grub/grub.nix"
+  /nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/nixos/modules/system/boot/loader/grub/grub.nix
 .Ed
 .
 .