--update-data should not touch xfail tests (#15337)

Author: ikonst

mypy/test/testupdatedata.py

@@ -46,6 +46,9 @@ def test_update_data(self) -> None:
             [case testWrong]
             s: str = 42  # E: wrong error
 
+            [case testXfail-xfail]
+            s: str = 42  # E: wrong error
+
             [case testWrongMultiline]
             s: str = 42  # E: foo \
                          # N: bar
@@ -101,6 +104,9 @@ def test_update_data(self) -> None:
         [case testWrong]
         s: str = 42  # E: Incompatible types in assignment (expression has type "int", variable has type "str")
 
+        [case testXfail-xfail]
+        s: str = 42  # E: wrong error
+
         [case testWrongMultiline]
         s: str = 42  # E: Incompatible types in assignment (expression has type "int", variable has type "str")
 

mypy/test/update_data.py

@@ -10,6 +10,8 @@
 def update_testcase_output(
     testcase: DataDrivenTestCase, actual: list[str], *, incremental_step: int
 ) -> None:
+    if testcase.xfail:
+        return
     collector = testcase.parent
     assert isinstance(collector, DataFileCollector)
     for fix in _iter_fixes(testcase, actual, incremental_step=incremental_step):