meta.pkgConfigModules: Init convention

See docs.

Follow-up work:

- Existing packages should be converted

- `defaultPkgConfigPackages` should assert on `meta.pkgConfigModules`
  and let `tests.pkg-config` alone test the build results.

CC @sternenseemann

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

1 files changed, 45 insertions, 3 deletions

diff --git a/doc/languages-frameworks/pkg-config.section.md b/doc/languages-frameworks/pkg-config.section.md
index ee0a471be3e5..eecc84b4c1aa 100644
--- a/doc/languages-frameworks/pkg-config.section.md
+++ b/doc/languages-frameworks/pkg-config.section.md
@@ -4,6 +4,48 @@
 
 Nixpkgs provides a couple of facilities for working with this tool.
 
- - A [setup hook](#setup-hook-pkg-config) bundled with in the `pkg-config` package, to bring a derivation's declared build inputs into the environment.
- - The [`validatePkgConfig` setup hook](https://nixos.org/manual/nixpkgs/stable/#validatepkgconfig), for packages that provide pkg-config modules.
- - The `defaultPkgConfigPackages` package set: a set of aliases, named after the modules they provide. This is meant to be used by language-to-nix integrations. Hand-written packages should use the normal Nixpkgs attribute name instead.
+## Writing packages providing pkg-config modules
+
+Packages should set `meta.pkgConfigProvides` with the list of package config modules they provide.
+They should also use `testers.testMetaPkgConfig` to check that the final built package matches that list.
+Additionally, the [`validatePkgConfig` setup hook](https://nixos.org/manual/nixpkgs/stable/#validatepkgconfig), will do extra checks on to-be-installed pkg-config modules.
+
+A good example of all these things is zlib:
+
+```
+{ pkg-config, testers, ... }:
+
+stdenv.mkDerivation (finalAttrs: {
+  ...
+
+  nativeBuildInputs = [ pkg-config validatePkgConfig ];
+
+  passthru.tests.pkg-config = testers.testMetaPkgConfig finalAttrs.finalPackage;
+
+  meta = {
+    ...
+    pkgConfigModules = [ "zlib" ];
+  };
+})
+```
+
+## Accessing packages via pkg-config module name
+
+### Within Nixpkgs
+
+A [setup hook](#setup-hook-pkg-config) is bundled in the `pkg-config` package to bring a derivation's declared build inputs into the environment.
+This will populate environment variables like `PKG_CONFIG_PATH`, `PKG_CONFIG_PATH_FOR_BUILD`, and `PKG_CONFIG_PATH_HOST` based on:
+
+ - how `pkg-config` itself is depended upon
+
+ - how other dependencies are depended upon
+
+For more details see the section on [specifying dependencies in general](#ssec-stdenv-dependencies).
+
+Normal pkg-config commands to look up dependencies by name will then work with those environment variables defined by the hook.
+
+### Externally
+
+The `defaultPkgConfigPackages` package set is a set of aliases, named after the modules they provide.
+This is meant to be used by language-to-nix integrations.
+Hand-written packages should use the normal Nixpkgs attribute name instead.