python3: fix overriding of interpreters, closes #163639

Overriding the interpreters did not work correctly. When overriding
packages would end up twice in the build time closure: one corresponding
to the overridden interpreter and one corresponding to the original
interpreter. The reason is that the override was not applied to the
interpreters in the spliced package sets.

pkgs/development/interpreters/python/cpython/default.nix

@@ -49,7 +49,7 @@
 , enableLTO ? stdenv.is64bit && stdenv.isLinux
 , reproducibleBuild ? false
 , pythonAttr ? "python${sourceVersion.major}${sourceVersion.minor}"
-}:
+} @ inputs:
 
 # Note: this package is used for bootstrapping fetchurl, and thus
 # cannot use fetchpatch! All mutable patches (generated by GitHub or
@@ -83,7 +83,10 @@ let
 
   tzdataSupport = tzdata != null && passthru.pythonAtLeast "3.9";
 
-  passthru = passthruFun rec {
+  passthru = let
+    # When we override the interpreter we also need to override the spliced versions of the interpreter
+    override = attr: let python = attr.override (inputs // { self = python; }); in python;
+  in passthruFun rec {
     inherit self sourceVersion packageOverrides;
     implementation = "cpython";
     libPrefix = "python${pythonVersion}";
@@ -91,11 +94,11 @@ let
     pythonVersion = with sourceVersion; "${major}.${minor}";
     sitePackages = "lib/${libPrefix}/site-packages";
     inherit hasDistutilsCxxPatch;
-    pythonOnBuildForBuild = pkgsBuildBuild.${pythonAttr};
-    pythonOnBuildForHost = pkgsBuildHost.${pythonAttr};
-    pythonOnBuildForTarget = pkgsBuildTarget.${pythonAttr};
-    pythonOnHostForHost = pkgsHostHost.${pythonAttr};
-    pythonOnTargetForTarget = pkgsTargetTarget.${pythonAttr} or {};
+    pythonOnBuildForBuild = override pkgsBuildBuild.${pythonAttr};
+    pythonOnBuildForHost = override pkgsBuildHost.${pythonAttr};
+    pythonOnBuildForTarget = override pkgsBuildTarget.${pythonAttr};
+    pythonOnHostForHost = override pkgsHostHost.${pythonAttr};
+    pythonOnTargetForTarget = if lib.hasAttr pythonAttr pkgsTargetTarget then (override pkgsTargetTarget.${pythonAttr}) else {};
   };
 
   version = with sourceVersion; "${major}.${minor}.${patch}${suffix}";