Handle raise Exception(), None on Python2.7 (#11786)

Closes #11742
Related #11743
Related #11289
Related #11700

mypy/checker.py

@@ -3581,7 +3581,7 @@ def visit_raise_stmt(self, s: RaiseStmt) -> None:
         if s.expr:
             self.type_check_raise(s.expr, s)
         if s.from_expr:
-            self.type_check_raise(s.from_expr, s, True)
+            self.type_check_raise(s.from_expr, s, optional=True)
         self.binder.unreachable()
 
     def type_check_raise(self, e: Expression, s: RaiseStmt,
@@ -3590,24 +3590,94 @@ def type_check_raise(self, e: Expression, s: RaiseStmt,
         if isinstance(typ, DeletedType):
             self.msg.deleted_as_rvalue(typ, e)
             return
+
+        if self.options.python_version[0] == 2:
+            # Since `raise` has very different rule on python2, we use a different helper.
+            # https://github.com/python/mypy/pull/11289
+            self._type_check_raise_python2(e, s, typ)
+            return
+
+        # Python3 case:
         exc_type = self.named_type('builtins.BaseException')
-        expected_type = UnionType([exc_type, TypeType(exc_type)])
+        expected_type_items = [exc_type, TypeType(exc_type)]
         if optional:
-            expected_type.items.append(NoneType())
-        if self.options.python_version[0] == 2:
-            # allow `raise type, value, traceback`
-            # https://docs.python.org/2/reference/simple_stmts.html#the-raise-statement
-            # TODO: Also check tuple item types.
-            any_type = AnyType(TypeOfAny.implementation_artifact)
-            tuple_type = self.named_type('builtins.tuple')
-            expected_type.items.append(TupleType([any_type, any_type], tuple_type))
-            expected_type.items.append(TupleType([any_type, any_type, any_type], tuple_type))
-        self.check_subtype(typ, expected_type, s, message_registry.INVALID_EXCEPTION)
+            # This is used for `x` part in a case like `raise e from x`,
+            # where we allow `raise e from None`.
+            expected_type_items.append(NoneType())
+
+        self.check_subtype(
+            typ, UnionType.make_union(expected_type_items), s,
+            message_registry.INVALID_EXCEPTION,
+        )
 
         if isinstance(typ, FunctionLike):
             # https://github.com/python/mypy/issues/11089
             self.expr_checker.check_call(typ, [], [], e)
 
+    def _type_check_raise_python2(self, e: Expression, s: RaiseStmt, typ: ProperType) -> None:
+        # Python2 has two possible major cases:
+        # 1. `raise expr`, where `expr` is some expression, it can be:
+        #    - Exception typ
+        #    - Exception instance
+        #    - Old style class (not supported)
+        #    - Tuple, where 0th item is exception type or instance
+        # 2. `raise exc, msg, traceback`, where:
+        #    - `exc` is exception type (not instance!)
+        #    - `traceback` is `types.TracebackType | None`
+        # Important note: `raise exc, msg` is not the same as `raise (exc, msg)`
+        # We call `raise exc, msg, traceback` - legacy mode.
+        exc_type = self.named_type('builtins.BaseException')
+        exc_inst_or_type = UnionType([exc_type, TypeType(exc_type)])
+
+        if (not s.legacy_mode and (isinstance(typ, TupleType) and typ.items
+                or (isinstance(typ, Instance) and typ.args
+                    and typ.type.fullname == 'builtins.tuple'))):
+            # `raise (exc, ...)` case:
+            item = typ.items[0] if isinstance(typ, TupleType) else typ.args[0]
+            self.check_subtype(
+                item, exc_inst_or_type, s,
+                'When raising a tuple, first element must by derived from BaseException',
+            )
+            return
+        elif s.legacy_mode:
+            # `raise Exception, msg` case
+            # `raise Exception, msg, traceback` case
+            # https://docs.python.org/2/reference/simple_stmts.html#the-raise-statement
+            assert isinstance(typ, TupleType)  # Is set in fastparse2.py
+            if (len(typ.items) >= 2
+                    and isinstance(get_proper_type(typ.items[1]), NoneType)):
+                expected_type: Type = exc_inst_or_type
+            else:
+                expected_type = TypeType(exc_type)
+            self.check_subtype(
+                typ.items[0], expected_type, s,
+                'Argument 1 must be "{}" subtype'.format(expected_type),
+            )
+
+            # Typecheck `traceback` part:
+            if len(typ.items) == 3:
+                # Now, we typecheck `traceback` argument if it is present.
+                # We do this after the main check for better error message
+                # and better ordering: first about `BaseException` subtype,
+                # then about `traceback` type.
+                traceback_type = UnionType.make_union([
+                    self.named_type('types.TracebackType'),
+                    NoneType(),
+                ])
+                self.check_subtype(
+                    typ.items[2], traceback_type, s,
+                    'Argument 3 must be "{}" subtype'.format(traceback_type),
+                )
+        else:
+            expected_type_items = [
+                # `raise Exception` and `raise Exception()` cases:
+                exc_type, TypeType(exc_type),
+            ]
+            self.check_subtype(
+                typ, UnionType.make_union(expected_type_items),
+                s, message_registry.INVALID_EXCEPTION,
+            )
+
     def visit_try_stmt(self, s: TryStmt) -> None:
         """Type check a try statement."""
         # Our enclosing frame will get the result if the try/except falls through.

mypy/fastparse2.py

@@ -665,19 +665,23 @@ def visit_With(self, n: ast27.With) -> WithStmt:
                         typ)
         return self.set_line(stmt, n)
 
+    # 'raise' [test [',' test [',' test]]]
     def visit_Raise(self, n: ast27.Raise) -> RaiseStmt:
+        legacy_mode = False
         if n.type is None:
             e = None
         else:
             if n.inst is None:
                 e = self.visit(n.type)
             else:
+                legacy_mode = True
                 if n.tback is None:
                     e = TupleExpr([self.visit(n.type), self.visit(n.inst)])
                 else:
                     e = TupleExpr([self.visit(n.type), self.visit(n.inst), self.visit(n.tback)])
 
         stmt = RaiseStmt(e, None)
+        stmt.legacy_mode = legacy_mode
         return self.set_line(stmt, n)
 
     # TryExcept(stmt* body, excepthandler* handlers, stmt* orelse)

mypy/nodes.py

@@ -1302,16 +1302,19 @@ def accept(self, visitor: StatementVisitor[T]) -> T:
 
 
 class RaiseStmt(Statement):
-    __slots__ = ('expr', 'from_expr')
+    __slots__ = ('expr', 'from_expr', 'legacy_mode')
 
     # Plain 'raise' is a valid statement.
     expr: Optional[Expression]
     from_expr: Optional[Expression]
+    # Is set when python2 has `raise exc, msg, traceback`.
+    legacy_mode: bool
 
     def __init__(self, expr: Optional[Expression], from_expr: Optional[Expression]) -> None:
         super().__init__()
         self.expr = expr
         self.from_expr = from_expr
+        self.legacy_mode = False
 
     def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_raise_stmt(self)

test-data/unit/check-python2.test

@@ -68,18 +68,89 @@ A.f(1)
 A.f('') # E: Argument 1 to "f" of "A" has incompatible type "str"; expected "int"
 [builtins_py2 fixtures/staticmethod.pyi]
 
-[case testRaiseTuple]
-import typing
-raise BaseException, "a"
-raise BaseException, "a", None
-[builtins_py2 fixtures/exception.pyi]
-
 [case testRaiseTupleTypeFail]
 import typing
 x = None # type: typing.Type[typing.Tuple[typing.Any, typing.Any, typing.Any]]
 raise x # E: Exception must be derived from BaseException
 [builtins_py2 fixtures/exception.pyi]
 
+[case testRaiseTupleOfThreeOnPython2]
+from types import TracebackType
+from typing import Optional, Tuple, Type
+
+e = None  # type: Optional[TracebackType]
+
+# Correct raising several items:
+
+raise BaseException
+raise BaseException(1)
+raise (BaseException,)
+raise (BaseException(1),)
+raise BaseException, 1
+raise BaseException, 1, e
+raise BaseException, 1, None
+
+raise Exception
+raise Exception(1)
+raise Exception()
+raise Exception(1), None
+raise Exception(), None
+raise Exception(1), None, None
+raise Exception(1), None, e
+raise (Exception,)
+raise (Exception(1),)
+raise Exception, 1
+raise Exception, 1, e
+raise Exception, 1, None
+
+# Errors:
+
+raise int, 1  # E: Argument 1 must be "Type[builtins.BaseException]" subtype
+raise int, None  # E: Argument 1 must be "Union[builtins.BaseException, Type[builtins.BaseException]]" subtype
+raise Exception(1), 1  # E: Argument 1 must be "Type[builtins.BaseException]" subtype
+raise Exception(1), 1, None # E: Argument 1 must be "Type[builtins.BaseException]" subtype
+raise Exception, 1, 1  # E: Argument 3 must be "Union[types.TracebackType, None]" subtype
+raise int, 1, 1  # E: Argument 1 must be "Type[builtins.BaseException]" subtype \
+                 # E: Argument 3 must be "Union[types.TracebackType, None]" subtype
+
+# Correct raising tuple:
+
+t1 = (BaseException,)
+t2 = (Exception(1), 2, 3, 4)  # type: Tuple[Exception, int, int, int]
+t3 = (Exception,)  # type: Tuple[Type[Exception], ...]
+t4 = (Exception(1),)  # type: Tuple[Exception, ...]
+
+raise t1
+raise t2
+raise t3
+raise t4
+
+# Errors:
+
+raise t1, 1, None  # E: Argument 1 must be "Type[builtins.BaseException]" subtype
+raise t2, 1        # E: Argument 1 must be "Type[builtins.BaseException]" subtype
+raise t3, 1, e     # E: Argument 1 must be "Type[builtins.BaseException]" subtype
+raise t4, 1, 1     # E: Argument 1 must be "Type[builtins.BaseException]" subtype \
+                   # E: Argument 3 must be "Union[types.TracebackType, None]" subtype
+
+w1 = ()
+w2 = (1, Exception)
+w3 = (1,)  # type: Tuple[int, ...]
+
+raise w1  # E: Exception must be derived from BaseException
+raise w2  # E: When raising a tuple, first element must by derived from BaseException
+raise w3  # E: When raising a tuple, first element must by derived from BaseException
+
+# Bare raise:
+
+try:
+    pass
+except Exception:
+    raise  # ok
+[builtins_py2 fixtures/exception.pyi]
+[file types.pyi]
+class TracebackType: pass
+
 [case testTryExceptWithTuple]
 try:
     None