feat: allow specifying env for fetchPipMetadata

This helps for configuring pip with environment variables. See https://github.com/nix-community/dream2nix/discussions/697 for more context.

pip: remove callPackage

modules/dream2nix/pip/default.nix

@@ -122,7 +122,7 @@ in {
       # with the intention to keep modules independent.
       fetchPipMetadataScript = import ../../../pkgs/fetchPipMetadata/script.nix {
         inherit lib;
-        inherit (cfg) pypiSnapshotDate pipFlags pipVersion requirementsList requirementsFiles nativeBuildInputs;
+        inherit (cfg) env pypiSnapshotDate pipFlags pipVersion requirementsList requirementsFiles nativeBuildInputs;
         inherit (config.deps) writePureShellScript nix;
         inherit (config.paths) findRoot;
         inherit (nixpkgs) gitMinimal nix-prefetch-scripts python3 writeText;
@@ -141,7 +141,8 @@ in {
   # if any of the invalidationData changes, the lock file will be invalidated
   #   and the user will be promted to re-generate it.
   lock.invalidationData = {
-    pip = {
+    pip =
+      {
         inherit
           (config.pip)
           pypiSnapshotDate
@@ -152,7 +153,10 @@ in {
           ;
         # don't invalidate on bugfix version changes
         pythonVersion = lib.init (lib.splitVersion config.deps.python.version);
-    };
+      }
+      # including env conditionally to not invalidate all existing lockfiles
+      # TODO: refactor once compat is broken through something else
+      // (lib.optionalAttrs (config.pip.env != {}) config.pip.env);
   };
 
   pip = {

modules/dream2nix/pip/interface.nix

@@ -22,6 +22,18 @@ in {
     };
 
     # user interface
+    env = l.mkOption {
+      type = t.attrsOf t.str;
+      default = {};
+      description = ''
+        environment variables exported while locking
+      '';
+      example = lib.literalExpression ''
+        {
+          PIP_FIND_LINKS = "${config.deps.setuptools.dist}";
+        }
+      '';
+    };
     pypiSnapshotDate = l.mkOption {
       type = t.nullOr t.str;
       description = ''

pkgs/fetchPipMetadata/script.nix

@@ -26,6 +26,7 @@
   requirementsFiles ? [],
   pipFlags ? [],
   pipVersion ? "23.1",
+  env ? {},
   wheelVersion ? "0.40.0",
   nativeBuildInputs ? [],
   # maximum release date for packages
@@ -86,6 +87,12 @@
     writePureShellScript
     path
     ''
+      ${
+        lib.foldlAttrs
+        (acc: name: value: acc + "\nexport " + lib.toShellVar name value)
+        ""
+        env
+      }
       ${package}/bin/fetch_pip_metadata \
         --json-args-file ${args} \
         --project-root $(${findRoot})