···

       
31
       
 
       


     

       
32
       
 
       
This is in contrast to `config._module.args`, which is only available after all `imports` have been resolved.

     

       
33
       
 
       


     

       
0
       
 
       

     

       
0
       
 
       

     

       
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0
       
 
       

     

       
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0
       
 
       

     

       
34
       
 
       
#### `class` {#module-system-lib-evalModules-param-class}

     

       
35
       
 
       


     

       
36
       
 
       
If the `class` attribute is set and non-`null`, the module system will reject `imports` with a different `_class` declaration.

     

···

       
31
       
 
       


     

       
32
       
 
       
This is in contrast to `config._module.args`, which is only available after all `imports` have been resolved.

     

       
33
       
 
       


     

       
34
       
+
       
::: {.warning}

     

       
35
       
+
       
You may be tempted to use `specialArgs.lib` to provide extra library functions. Doing so limits the interoperability of modules, as well as the interoperability of Module System applications.

     

       
36
       
+
       


     

       
37
       
+
       
`lib` is reserved for the Nixpkgs library, and should not be used for custom functions.

     

       
38
       
+
       


     

       
39
       
+
       
Instead, you may create a new attribute in `specialArgs` to provide custom functions.

     

       
40
       
+
       
This clarifies their origin and avoids incompatibilities.

     

       
41
       
+
       
:::

     

       
42
       
+
       


     

       
43
       
 
       
#### `class` {#module-system-lib-evalModules-param-class}

     

       
44
       
 
       


     

       
45
       
 
       
If the `class` attribute is set and non-`null`, the module system will reject `imports` with a different `_class` declaration.

     

···

       
24
       
 
       


     

       
25
       
 
       
        - `lib.nixos` for other NixOS-provided functionality, such as [`runTest`](https://nixos.org/manual/nixos/unstable/#sec-call-nixos-test-outside-nixos)

     

       
26
       
 
       
      */

     

       
0
       
 
       

     

       
0
       
 
       

     

       
27
       
 
       
      lib = lib.extend (final: prev: {

     

       
28
       
 
       


     

       
29
       
 
       
        /**

     

···

       
24
       
 
       


     

       
25
       
 
       
        - `lib.nixos` for other NixOS-provided functionality, such as [`runTest`](https://nixos.org/manual/nixos/unstable/#sec-call-nixos-test-outside-nixos)

     

       
26
       
 
       
      */

     

       
27
       
+
       
      # DON'T USE lib.extend TO ADD NEW FUNCTIONALITY.

     

       
28
       
+
       
      # THIS WAS A MISTAKE. See the warning in lib/default.nix.

     

       
29
       
 
       
      lib = lib.extend (final: prev: {

     

       
30
       
 
       


     

       
31
       
 
       
        /**

     

···

       
5
       
 
       
 */

     

       
6
       
 
       
let

     

       
7
       
 
       


     

       
8
       
-
       
  inherit (import ./fixed-points.nix { inherit lib; }) makeExtensible;

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
0
       
 
       

     

       
9
       
 
       


     

       
10
       
-
       
  lib = makeExtensible (self: let

     

       
11
       
 
       
    callLibs = file: import file { lib = self; };

     

       
12
       
 
       
  in {

     

       
13
       
 
       


     

···

       
5
       
 
       
 */

     

       
6
       
 
       
let

     

       
7
       
 
       


     

       
8
       
+
       
  # A copy of `lib.makeExtensible'` in order to document `extend`.

     

       
9
       
+
       
  # It has been leading to some trouble, so we have to document it specially.

     

       
10
       
+
       
  makeExtensible' =

     

       
11
       
+
       
    rattrs:

     

       
12
       
+
       
    let self = rattrs self // {

     

       
13
       
+
       
          /**

     

       
14
       
+
       
            Patch the Nixpkgs library

     

       
15
       
+
       


     

       
16
       
+
       
            The name `extends` is a bit misleading, as it doesn't actually extend the library, but rather patches it.

     

       
17
       
+
       
            It is merely a consequence of being implemented by `makeExtensible`.

     

       
18
       
+
       


     

       
19
       
+
       
            # Inputs

     

       
20
       
+
       


     

       
21
       
+
       
            - An "extension function" `f` that returns attributes that will be updated in the returned Nixpkgs library.

     

       
22
       
+
       


     

       
23
       
+
       
            # Output

     

       
24
       
+
       


     

       
25
       
+
       
            A patched Nixpkgs library.

     

       
26
       
+
       


     

       
27
       
+
       
            :::{.warning}

     

       
28
       
+
       
            This functionality is intended as an escape hatch for when the provided version of the Nixpkgs library has a flaw.

     

       
29
       
+
       


     

       
30
       
+
       
            If you were to use it to add new functionality, you will run into compatibility and interoperability issues.

     

       
31
       
+
       
            :::

     

       
32
       
+
       
          */

     

       
33
       
+
       
          extend = f: lib.makeExtensible (lib.extends f rattrs);

     

       
34
       
+
       
        };

     

       
35
       
+
       
    in self;

     

       
36
       
 
       


     

       
37
       
+
       
  lib = makeExtensible' (self: let

     

       
38
       
 
       
    callLibs = file: import file { lib = self; };

     

       
39
       
 
       
  in {

     

       
40