When adding patches in this manner you should be reasonably sure that the used URL is stable. Patches referencing open pull requests will change when the PR is updated and code forges (such as GitHub) usually garbage collect commits that are no longer reachable due to rebases/amends.

### Vendoring patches

In the following cases, a `.patch` file _should_ be added to Nixpkgs repository, instead of retrieved:

- solves problems unique to packaging in Nixpkgs
- cannot be fetched easily
- has a high chance to disappear in the future due to unstable or unreliable URLs

The latter avoids link rot when the upstream abandons, squashes or rebases their change, in which case the commit may get garbage-collected.

```nix
{
  patches = [ ./0001-add-missing-include.patch ];
}
```

If you do need to do create this sort of patch file, one way to do so is with git:

1. Move to the root directory of the source code you're patching.

    ```ShellSession
    $ cd the/program/source
    ```

2. If a git repository is not already present, create one and stage all of the source files.

    ```ShellSession
    $ git init
    $ git add .
    ```

3. Edit some files to make whatever changes need to be included in the patch.

4. Use git to create a diff, and pipe the output to a patch file:

    ```ShellSession
    $ git diff -a > nixpkgs/pkgs/the/package/0001-changes.patch
    ```

## Deprecating/removing packages

There is currently no policy when to remove a package.

Before removing a package, one should try to find a new maintainer or fix smaller issues first.

### Steps to remove a package from Nixpkgs

We use jbidwatcher as an example for a discontinued project here.

1. Have Nixpkgs checked out locally and up to date.
1. Create a new branch for your change, e.g. `git checkout -b jbidwatcher`
1. Remove the actual package including its directory, e.g. `git rm -rf pkgs/applications/misc/jbidwatcher`
1. Remove the package from the list of all packages (`pkgs/top-level/all-packages.nix`).
1. Add an alias for the package name in `pkgs/top-level/aliases.nix` (There is also `pkgs/applications/editors/vim/plugins/aliases.nix`. Package sets typically do not have aliases, so we can't add them there.)

    For example in this case:

    ```nix
    {
      jbidwatcher = throw "jbidwatcher was discontinued in march 2021"; # added 2021-03-15
    }
    ```

    The throw message should explain in short why the package was removed for users that still have it installed.

1. Test if the changes introduced any issues by running `nix-env -qaP -f . --show-trace`. It should show the list of packages without errors.
1. Commit the changes. Explain again why the package was removed. If it was declared discontinued upstream, add a link to the source.

    ```ShellSession
    $ git add pkgs/applications/misc/jbidwatcher/default.nix pkgs/top-level/all-packages.nix pkgs/top-level/aliases.nix
    $ git commit
    ```

    Example commit message:

    ```
    jbidwatcher: remove

    project was discontinued in march 2021. the program does not work anymore because ebay changed the login.

    https://web.archive.org/web/20210315205723/http://www.jbidwatcher.com/
    ```

1. Push changes to your GitHub fork with `git push`
1. Create a pull request against Nixpkgs. Mention the package maintainer.

This is how the pull request looks like in this case: [https://github.com/NixOS/nixpkgs/pull/116470](https://github.com/NixOS/nixpkgs/pull/116470)

## Package tests

To run the main types of tests locally:

- Run package-internal tests with `nix-build --attr pkgs.PACKAGE.passthru.tests`
- Run [NixOS tests](https://nixos.org/manual/nixos/unstable/#sec-nixos-tests) with `nix-build --attr nixosTests.NAME`, where `NAME` is the name of the test listed in `nixos/tests/all-tests.nix`
- Run [global package tests](https://nixos.org/manual/nixpkgs/unstable/#sec-package-tests) with `nix-build --attr tests.PACKAGE`, where `PACKAGE` is the name of the test listed in `pkgs/test/default.nix`
- See `lib/tests/NAME.nix` for instructions on running specific library tests