First, change the way in which our checkDerivation functions are call…

…ed so that they get access to either stdenv (for mkDerivation checks) or python (for buildPythonPackage checks), so that they know which interpreter/compiler they're using. Next, using this feature, implement a check for inconsistent versions of python in the same package, as suggested by @SuperSandro2000

lib/default.nix

@@ -41,8 +41,11 @@ rec {
             if builtins.elem namePosition namePositions
             then
               lib.recursiveUpdate originalDrv {
-                __nixpkgs-hammering-state = {
-                  reports = originalDrv.__nixpkgs-hammering-state.reports or [] ++ lib.filter ({ cond, ... }: cond) (check drv);
+                __nixpkgs-hammering-state =
+                let checkResult = check prev.stdenv drv;
+                in
+                {
+                  reports = originalDrv.__nixpkgs-hammering-state.reports or [] ++ lib.filter ({ cond, ... }: cond) checkResult;
                 };
               }
             else
@@ -62,9 +65,9 @@ rec {
     final:
     prev:
 
-    let pythonPackageOverrides = buildPythonPackage: self: super: {
+    let pythonPackageOverrides = python: self: super: {
       buildPythonPackage = drv:
-      let originalDrv = buildPythonPackage drv;
+      let originalDrv = python.pkgs.buildPythonPackage drv;
           namePosition =
           let
             pnamePosition = builtins.unsafeGetAttrPos "pname" drv;
@@ -74,8 +77,10 @@ rec {
         if builtins.elem namePosition namePositions
         then
         lib.recursiveUpdate originalDrv {
-          __nixpkgs-hammering-state = {
-            reports = originalDrv.__nixpkgs-hammering-state.reports or [] ++ lib.filter ({ cond, ... }: cond) (check drv);
+          __nixpkgs-hammering-state =
+            let checkResult = check python drv;
+            in {
+              reports = originalDrv.__nixpkgs-hammering-state.reports or [] ++ lib.filter ({ cond, ... }: cond) checkResult;
           };
         }
         else
@@ -100,7 +105,7 @@ rec {
     ];
     in
     lib.genAttrs pythonPackageSetNames (name: (builtins.getAttr name prev).override {
-      packageOverrides = pythonPackageOverrides (lib.getAttr name prev).pkgs.buildPythonPackage;
+      packageOverrides = pythonPackageOverrides (lib.getAttr name prev);
     });
 
     checkFor = check: let

overlays/attribute-ordering.nix

@@ -27,7 +27,7 @@ let
         builtins.listToAttrs
       ];
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     let
       getAttrLine = attr: (builtins.unsafeGetAttrPos attr drv).line;
 

overlays/build-tools-in-build-inputs.nix

@@ -15,7 +15,7 @@ let
     "pkg-config"
   ];
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     (map
       (tool: {
         name = "build-tools-in-build-inputs";

overlays/duplicate-check-inputs.nix

@@ -9,7 +9,7 @@ let
   inherit (import ../lib { inherit lib; }) checkFor;
   regex = "[[:space:]]*pytest[[:space:]]*";
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     lib.singleton {
         name = "duplicate-check-inputs";
 

overlays/explicit-phases.nix

@@ -15,7 +15,7 @@ let
     "install"
   ];
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     (map
       (phase: {
         name = "explicit-phases";

overlays/fixup-phase.nix

@@ -8,7 +8,7 @@ let
   inherit (prev) lib;
   inherit (import ../lib { inherit lib; }) checkMkDerivationFor;
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     lib.singleton {
       name = "fixup-phase";
       cond = drv ? fixupPhase;

overlays/meson-cmake.nix

@@ -8,7 +8,7 @@ let
   inherit (prev) lib;
   inherit (import ../lib { inherit lib; }) checkMkDerivationFor;
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     lib.singleton {
       name = "meson-cmake";
       cond = lib.elem prev.meson (drv.nativeBuildInputs or [ ]) && lib.elem prev.cmake (drv.nativeBuildInputs or [ ]);

overlays/missing-phase-hooks.nix

@@ -15,7 +15,7 @@ let
     "install"
   ];
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     (map
       (phase:
         let

overlays/patch-phase.nix

@@ -8,7 +8,7 @@ let
   inherit (prev) lib;
   inherit (import ../lib { inherit lib; }) checkMkDerivationFor;
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     lib.singleton {
       name = "patch-phase";
       cond = drv ? patchPhase;

overlays/python-explicit-check-phase.nix

@@ -9,7 +9,7 @@ let
   inherit (import ../lib { inherit lib; }) checkBuildPytonPackageFor;
   regex = "[[:space:]]*pytest[[:space:]]*";
 
-  checkDerivation = drv:
+  checkDerivation = python: drv:
     lib.singleton {
         name = "python-explicit-check-phase";
         cond = (drv ? checkPhase) && (builtins.match regex drv.checkPhase) != null;

overlays/python-imports-check-typo.nix

@@ -15,7 +15,7 @@ let
     "pythonCheckImports"
   ];
 
-  checkDerivation = drv:
+  checkDerivation = python: drv:
     (map
       (incorrectSpelling: {
         name = "python-imports-check-typo";

overlays/python-include-tests.nix

@@ -8,7 +8,7 @@ let
   inherit (prev) lib;
   inherit (import ../lib { inherit lib; }) checkBuildPytonPackageFor;
 
-  checkDerivation = drv:
+  checkDerivation = python: drv:
     lib.singleton {
         name = "python-include-tests";
         cond = let

overlays/python-inconsistent-interpreters.nix

@@ -0,0 +1,39 @@
+{ builtAttrs
+, packageSet
+, namePositions
+}@attrs:
+
+final: prev:
+let
+  inherit (prev) lib;
+  inherit (import ../lib { inherit lib; }) checkBuildPytonPackageFor;
+
+  checkDerivation = python: drv:
+      let
+            propagatedBuildInputs = lib.attrByPath ["propagatedBuildInputs"] [] drv;
+            checkInputs = lib.attrByPath ["checkInputs"] [] drv;
+            runtimeInputs = checkInputs ++ propagatedBuildInputs;
+            inputPythonInterpreters = map (p: p.pythonModule) (builtins.filter (p: p ? pythonModule) runtimeInputs);
+            allPythonInterpreters = lib.unique (inputPythonInterpreters ++ [python]);
+        in
+    lib.singleton {
+        name = "python-inconsistent-interpreters";
+        cond = lib.length allPythonInterpreters > 1;        
+        msg = let
+            allPythonNames = map (p: p.name) allPythonInterpreters;
+            sources = ["buildPythonPackage"] ++ 
+                (if (lib.length propagatedBuildInputs) > 0 then ["propagatedBuildInputs"] else []) ++
+                (if (lib.length checkInputs) > 0 then ["checkInputs"] else []);            
+        in            
+        ''
+          Between ${lib.concatStringsSep " and " sources}, this derivation seems
+          to be simultaneously trying to use packages from multiple different python package sets.
+          Mixing package sets like this is not supported.
+
+          Detected pythons:
+
+            ${lib.concatStringsSep "\n  " allPythonNames}
+        '';
+    };
+  in
+checkBuildPytonPackageFor checkDerivation attrs final prev

overlays/unclear-gpl.nix

@@ -21,7 +21,7 @@ let
     "lgpl3"
   ];
 
-  checkDerivation = drv:
+  checkDerivation = python: drv:
     (map
       (license: {
         name = "unclear-gpl";

overlays/unnecessary-parallel-building.nix

@@ -8,7 +8,7 @@ let
   inherit (prev) lib;
   inherit (import ../lib { inherit lib; }) checkMkDerivationFor;
 
-  checkDerivation = drv:
+  checkDerivation = stdenv: drv:
     lib.singleton {
       name = "unnecessary-parallel-building";
       cond =