python3Packages.mkPythonMetaPackage: init

This function exists create a meta package containing [metadata files](https://packaging.python.org/en/latest/specifications/recording-installed-packages/) to satisfy a dependency on a package, without it actually having been installed into the environment.

doc/languages-frameworks/python.section.md

@@ -361,6 +361,19 @@ modifications.
 
 Do pay attention to passing in the right Python version!
 
+#### `mkPythonMetaPackage` function {#mkpythonmetapackage-function}
+
+This will create a meta package containing [metadata files](https://packaging.python.org/en/latest/specifications/recording-installed-packages/) to satisfy a dependency on a package, without it actually having been installed into the environment.
+In nixpkgs this is used to package Python packages with split binary/source distributions such as [psycopg2](https://pypi.org/project/psycopg2/)/[psycopg2-binary](https://pypi.org/project/psycopg2-binary/).
+
+```nix
+mkPythonMetaPackage {
+  pname = "pscycopg2-binary";
+  inherit (psycopg2) optional-dependencies version meta;
+  dependencies = [ psycopg2 ];
+}
+```
+
 #### `python.buildEnv` function {#python.buildenv-function}
 
 Python environments can be created using the low-level `pkgs.buildEnv` function.

pkgs/development/interpreters/python/meta-package.nix

@@ -0,0 +1,58 @@
+{
+  buildPythonPackage,
+  lib,
+  hatchling,
+}:
+{
+  pname,
+  version,
+  dependencies ? [ ],
+  optional-dependencies ? { },
+  passthru ? { },
+  meta ? { },
+}:
+
+# Create a "fake" meta package to satisfy a dependency on a package, but don't actually build it.
+# This is useful for packages that have a split binary/source dichotomy like psycopg2/psycopg2-binary,
+# where we want to use the former, but some projects declare a dependency on the latter.
+
+buildPythonPackage {
+  inherit
+    pname
+    version
+    dependencies
+    optional-dependencies
+    meta
+    passthru
+    ;
+
+  pyproject = true;
+
+  # Make a minimal pyproject.toml that can be built
+  unpackPhase = ''
+    cat > pyproject.toml << EOF
+    [project]
+    name = "${pname}"
+    version = "${version}"
+    dependencies = ${builtins.toJSON (map lib.getName dependencies)}
+
+    [project.optional-dependencies]
+    ${lib.optionalString (optional-dependencies != { }) (
+      (lib.concatStringsSep "\n" (
+        lib.mapAttrsToList (
+          group: deps: group + " = " + builtins.toJSON (map lib.getName deps)
+        ) optional-dependencies
+      ))
+    )}
+
+    [tool.hatch.build.targets.wheel]
+    bypass-selection = true
+
+    [build-system]
+    requires = ["hatchling"]
+    build-backend = "hatchling.build"
+    EOF
+  '';
+
+  build-system = [ hatchling ];
+}

pkgs/development/interpreters/python/python-packages-base.nix

@@ -61,6 +61,8 @@ let
 
   removePythonPrefix = lib.removePrefix namePrefix;
 
+  mkPythonMetaPackage = callPackage ./meta-package.nix { };
+
   # Convert derivation to a Python module.
   toPythonModule = drv:
     drv.overrideAttrs( oldAttrs: {
@@ -97,6 +99,7 @@ in {
   inherit buildPythonPackage buildPythonApplication;
   inherit hasPythonModule requiredPythonModules makePythonPath disabled disabledIf;
   inherit toPythonModule toPythonApplication;
+  inherit mkPythonMetaPackage;
 
   python = toPythonModule python;