patches and low-level development discussion

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 = Configuring the Build
:page-parent: Development
:page-nav_order: 1
:example-caption: Test

// SPDX-FileCopyrightText: 2022 Unikie
// SPDX-License-Identifier: GFDL-1.3-no-invariants-or-later OR CC-BY-SA-4.0

Some aspects of a Spectrum build can be customised using a build
configuration file.

By default, this configuration file should be called config.nix and located in
the root of the Spectrum source tree, but this can be overridden by setting
`spectrum-config` in the
https://nixos.org/manual/nix/stable/command-ref/env-common.html#env-NIX_PATH[NIX_PATH]
to the path of the configuration file.

The configuration file should contain an attribute set.  The only
currently allowed attribute name is `pkgs`. It allows using a
custom Nixpkgs to evaluate Spectrum.

.config.nix to build Spectrum with a https://nixos.org/manual/nixpkgs/unstable/#sec-overlays-definition[Nixpkgs overlay]
[example]
[source,nix]
----
{
  pkgs = import <nixpkgs> {
    overlays = [
      (final: super: {
        weston = super.weston.overrideAttrs ({ patches ? [], ... }: {
          patches = patches ++ [
            path/to/weston.patch
          ];
        });
      })
    ];
  };
}
----