Interpret tuple default parameter value as a weak type (PY-10967)

python/src/com/jetbrains/python/psi/impl/PyNamedParameterImpl.java

@@ -239,7 +239,7 @@ public class PyNamedParameterImpl extends PyPresentableElementImpl<PyNamedParame
             final PyType type = context.getType(defaultValue);
             if (type != null && !(type instanceof PyNoneType)) {
               if (type instanceof PyTupleType) {
-                return PyTypeParser.getTypeByName(this, "collections.Iterable");
+                return PyUnionType.createWeakType(type);
               }
               return type;
             }

python/src/com/jetbrains/python/psi/impl/PyTargetExpressionImpl.java

@@ -208,7 +208,7 @@ public class PyTargetExpressionImpl extends PyPresentableElementImpl<PyTargetExp
           final PyAssignmentStatement assignment = (PyAssignmentStatement)nextParent;
           final PyExpression value = assignment.getAssignedValue();
           if (value != null) {
-            final PyType assignedType = context.getType(value);
+            final PyType assignedType = PyTypeChecker.toNonWeakType(context.getType(value), context);
             if (assignedType instanceof PyTupleType) {
               final PyType t = getTypeFromTupleAssignment((PyTupleExpression)parent, (PyTupleType)assignedType);
               if (t != null) {

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

@@ -215,6 +215,17 @@ public class PyTypeChecker {
     return false;
   }
 
+  @Nullable
+  public static PyType toNonWeakType(@Nullable PyType type, @NotNull TypeEvalContext context) {
+    if (type instanceof PyUnionType) {
+      final PyUnionType unionType = (PyUnionType)type;
+      if (unionType.isWeak()) {
+        return unionType.excludeNull(context);
+      }
+    }
+    return type;
+  }
+
   public static boolean hasGenerics(@Nullable PyType type, @NotNull TypeEvalContext context) {
     final Set<PyGenericType> collected = new HashSet<PyGenericType>();
     collectGenerics(type, context, collected, new HashSet<PyType>());

python/testSrc/com/jetbrains/python/PyTypeTest.java

@@ -805,6 +805,13 @@ public class PyTypeTest extends PyTestCase {
            "expr = iter(xs).next()\n");
   }
 
+  // PY-10967
+  public void testDefaultTupleParameterMember() {
+    doTest("int",
+           "def foo(xs=(1, 2)):\n" +
+           "  expr, foo = xs\n");
+  }
+
   private static TypeEvalContext getTypeEvalContext(@NotNull PyExpression element) {
     return TypeEvalContext.userInitiated(element.getContainingFile()).withTracing();
   }