fix: Treat NewType as their underlying runtime type

python/python-psi-impl/src/com/jetbrains/python/psi/types/PyTypeChecker.java

@@ -113,6 +113,26 @@ public static boolean match(@Nullable PyType expected,
       }
     }
 
+    // PY-85543: Treat typing.NewType instances as their underlying runtime type for assignability checks.
+    // NewType is only a static marker; at runtime it's the supertype, so unwrap it early.
+    if (actual instanceof PyTypingNewType typingNewType) {
+      if (expected instanceof PyTypingNewType && typingNewType.getAncestorTypes(context.context).contains(expected)) {
+        return Optional.of(true);
+      }
+
+      List<PyClassLikeType> superTypes = typingNewType.getSuperClassTypes(context.context);
+      if (!superTypes.isEmpty()) {
+        actual = superTypes.get(0);
+      }
+      else {
+        actual = new PyClassTypeImpl(typingNewType.getPyClass(), typingNewType.isDefinition());
+      }
+
+      if (Objects.equals(expected, actual)) {
+        return Optional.of(true);
+      }
+    }
+
     if (expected instanceof PyClassType) {
       Optional<Boolean> match = matchObject((PyClassType)expected, actual);
       if (match.isPresent()) {

python/testData/inspections/PyTypeCheckerInspection/NewTypeWithGenerics.py

@@ -0,0 +1,13 @@
+from typing import NewType, Dict, List
+
+KeyValue = NewType('KeyValue', Dict[str, int])
+
+def f(x: KeyValue):
+    pass
+
+kv = KeyValue({'a': 1})
+
+def g(x: Dict[str, str]):
+    pass
+
+g(<error descr="Expected type 'dict[str, str]', got 'KeyValue' instead">kv</error>)

python/testSrc/com/jetbrains/python/inspections/Py3TypeCheckerInspectionTest.java

@@ -1240,6 +1240,24 @@ def a_int_b_str(a: int, b: str) -> int:
                    res4 = twice(a_int_b_str, <warning descr="Expected type 'str', got 'int' instead">b=1</warning>, <warning descr="Expected type 'int', got 'str' instead">a="A"</warning>)""");
   }
 
+  // PY-85543
+  public void testNewTypeAcceptedByIntCallInsideFString() {
+    doTestByText("""
+                   from typing import NewType
+
+                   MyInt = NewType("MyInt", int)
+
+                   def test_():
+                       number = MyInt(10)
+                       q = f"{int(number)}"
+                   """);
+  }
+
+  // PY-85543
+  public void testNewTypeWithGenerics() {
+    doTest();
+  }
+
   // PY-50403
   public void testFunctionNotEnoughArgumentsToMatchWithParamSpec() {
     doTestByText("""