unittestCheckHook: handle unittestFlagsArray __structuredAttrs-agnostically

Take unittestFlags as the new and conforming interface.

Keep unittestFlagsArray as is.

doc/languages-frameworks/python.section.md

@@ -1433,7 +1433,7 @@ automatically add `pythonRelaxDepsHook` if either `pythonRelaxDeps` or
     unittestCheckHook
   ];
 
-  unittestFlagsArray = [
+  unittestFlags = [
     "-s" "tests" "-v"
   ];
 }

pkgs/development/interpreters/python/hooks/unittest-check-hook.sh

@@ -5,7 +5,14 @@ unittestCheckPhase() {
     echo "Executing unittestCheckPhase"
     runHook preCheck
 
-    eval "@pythonCheckInterpreter@ -m unittest discover $unittestFlagsArray"
+    local -a flagsArray=()
+
+    # Compatibility layer to the obsolete unittestFlagsArray
+    eval "flagsArray+=(${unittestFlagsArray[*]-})"
+
+    concatTo flagsArray unittestFlags
+    echoCmd 'unittest flags' "${flagsArray[@]}"
+    @pythonCheckInterpreter@ -m unittest discover "${flagsArray[@]}"
 
     runHook postCheck
     echo "Finished executing unittestCheckPhase"

pkgs/development/interpreters/python/mk-python-derivation.nix

@@ -108,6 +108,7 @@ let
     "disabledTests"
     "pytestFlags"
     "pytestFlagsArray"
+    "unittestFlags"
     "unittestFlagsArray"
     "outputs"
     "stdenv"
@@ -446,6 +447,9 @@ let
         // optionalAttrs (attrs ? pytestFlagsArray) {
           pytestFlagsArray = attrs.pytestFlagsArray;
         }
+        // optionalAttrs (attrs ? unittestFlags) {
+          unittestFlags = attrs.unittestFlags;
+        }
         // optionalAttrs (attrs ? unittestFlagsArray) {
           unittestFlagsArray = attrs.unittestFlagsArray;
         }