PEP 702 (@deprecated): improve the handling of explicit type annotati…

…ons of assignment statements (#17899)

Two improvements of the current PEP 702 implementation (deprecated):

* Analyse the explicit type annotations of "normal" assignment
statements (that have an rvalue).
* Dive into nested type annotations of assignment statements.

(I intend to continue working on PEP 702 and would prefer to do so in
small steps if this is okay for the maintainers/reviewers.)

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

mypy/checker.py

@@ -287,6 +287,18 @@ class PartialTypeScope(NamedTuple):
     is_local: bool
 
 
+class InstanceDeprecatedVisitor(TypeTraverserVisitor):
+    """Visitor that recursively checks for deprecations in nested instances."""
+
+    def __init__(self, typechecker: TypeChecker, context: Context) -> None:
+        self.typechecker = typechecker
+        self.context = context
+
+    def visit_instance(self, t: Instance) -> None:
+        super().visit_instance(t)
+        self.typechecker.check_deprecated(t.type, self.context)
+
+
 class TypeChecker(NodeVisitor[None], CheckerPluginInterface):
     """Mypy type checker.
 
@@ -2930,14 +2942,14 @@ def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
         Handle all kinds of assignment statements (simple, indexed, multiple).
         """
 
-        if isinstance(s.rvalue, TempNode) and s.rvalue.no_rhs:
+        if s.unanalyzed_type is not None:
             for lvalue in s.lvalues:
                 if (
                     isinstance(lvalue, NameExpr)
                     and isinstance(var := lvalue.node, Var)
-                    and isinstance(instance := get_proper_type(var.type), Instance)
+                    and (var.type is not None)
                 ):
-                    self.check_deprecated(instance.type, s)
+                    var.type.accept(InstanceDeprecatedVisitor(typechecker=self, context=s))
 
         # Avoid type checking type aliases in stubs to avoid false
         # positives about modern type syntax available in stubs such

test-data/unit/check-deprecated.test

@@ -102,7 +102,8 @@ def h() -> None: ...
 
 [case testDeprecatedClass]
 
-from typing_extensions import deprecated
+from typing import Callable, List, Optional, Tuple, Union
+from typing_extensions import deprecated, TypeAlias, TypeVar
 
 @deprecated("use C2 instead")
 class C: ...
@@ -114,10 +115,40 @@ C.missing()  # N: class __main__.C is deprecated: use C2 instead \
 C.__init__(c)  # N: class __main__.C is deprecated: use C2 instead
 C(1)  # N: class __main__.C is deprecated: use C2 instead \
       # E: Too many arguments for "C"
+
 D = C  # N: class __main__.C is deprecated: use C2 instead
 D()
 t = (C, C, D)  # N: class __main__.C is deprecated: use C2 instead
 
+u1: Union[C, int] = 1  # N: class __main__.C is deprecated: use C2 instead
+u1 = 1
+u2 = 1  # type: Union[C, int]  # N: class __main__.C is deprecated: use C2 instead
+u2 = 1
+
+c1 = c2 = C()  # N: class __main__.C is deprecated: use C2 instead
+i, c3 = 1, C()  # N: class __main__.C is deprecated: use C2 instead
+
+class E: ...
+
+x1: Optional[C]  # N: class __main__.C is deprecated: use C2 instead
+x2: Union[D, C, E]  # N: class __main__.C is deprecated: use C2 instead
+x3: Union[D, Optional[C], E]  # N: class __main__.C is deprecated: use C2 instead
+x4: Tuple[D, C, E]  # N: class __main__.C is deprecated: use C2 instead
+x5: Tuple[Tuple[D, C], E]  # N: class __main__.C is deprecated: use C2 instead
+x6: List[C]  # N: class __main__.C is deprecated: use C2 instead
+x7: List[List[C]]  # N: class __main__.C is deprecated: use C2 instead
+x8: List[Optional[Tuple[Union[List[C], int]]]]  # N: class __main__.C is deprecated: use C2 instead
+x9: Callable[[int], C]  # N: class __main__.C is deprecated: use C2 instead
+x10: Callable[[int, C, int], int]  # N: class __main__.C is deprecated: use C2 instead
+
+T = TypeVar("T")
+A1: TypeAlias = Optional[C]  # ToDo
+x11: A1
+A2: TypeAlias = List[Union[A2, C]]  # ToDo
+x12: A2
+A3: TypeAlias = List[Optional[T]]
+x13: A3[C]  # N: class __main__.C is deprecated: use C2 instead
+
 [builtins fixtures/tuple.pyi]