New semantic analyzer: Copy, don't modify, unanalyzed types (#7094)

Fixes #6951.

Author: ilevkivskyi

mypy/newsemanal/semanal.py

@@ -3131,7 +3131,7 @@ def visit_with_stmt(self, s: WithStmt) -> None:
             elif isinstance(s.unanalyzed_type, TupleType):
                 # We have multiple targets and multiple types
                 if len(actual_targets) == len(s.unanalyzed_type.items):
-                    types = s.unanalyzed_type.items
+                    types = s.unanalyzed_type.items.copy()
                 else:
                     # But it's the wrong number of items
                     self.fail('Incompatible number of types for `with` targets', s)

test-data/unit/check-newsemanal.test

@@ -2717,6 +2717,16 @@ class N(NamedTuple):
         b
 [builtins fixtures/tuple.pyi]
 
+[case testWithMultipleTargetsDeferred]
+a: A
+
+class A:
+    def __enter__(self) -> int: pass
+    def __exit__(self, x, y, z): pass
+
+with A() as x, A() as y:  # type: int, int
+    pass
+
 [case testNewAnalyzerLessErrorsNeedAnnotation]
 from typing import TypeVar, Optional