Add --warn-implicit-any

mypy/main.py

@@ -231,6 +231,10 @@ def add_invertible_flag(flag: str,
     add_invertible_flag('--warn-return-any', default=False, strict_flag=True,
                         help="warn about returning values of type Any"
                              " from non-Any typed functions")
+    add_invertible_flag('--warn-implicit-any', default=False,
+                        help='warn about implicit creation of type "Any" '
+                        "(experimental -- only warns in some limited circusmstances.)"
+                        )
     add_invertible_flag('--warn-unused-ignores', default=False, strict_flag=True,
                         help="warn about unneeded '# type: ignore' comments")
     add_invertible_flag('--show-error-context', default=False,

mypy/options.py

@@ -27,6 +27,7 @@ class Options:
         "show_none_errors",
         "warn_no_return",
         "warn_return_any",
+        "warn_implicit_any",
         "ignore_errors",
         "strict_boolean",
     }
@@ -70,6 +71,9 @@ def __init__(self) -> None:
         # declared with a precise type
         self.warn_return_any = False
 
+        # Warn about implicit creation of Any type (work in progress)
+        self.warn_implicit_any = False
+
         # Warn about unused '# type: ignore' comments
         self.warn_unused_ignores = False
 

mypy/semanal.py

@@ -3251,12 +3251,15 @@ def name_already_defined(self, name: str, ctx: Context) -> None:
         self.fail("Name '{}' already defined".format(name), ctx)
 
     def fail(self, msg: str, ctx: Context, serious: bool = False, *,
-             blocker: bool = False) -> None:
+             blocker: bool = False, implicit_any: bool = False) -> None:
         if (not serious and
                 not self.options.check_untyped_defs and
                 self.function_stack and
                 self.function_stack[-1].is_dynamic()):
             return
+        if implicit_any:
+            if not self.options.warn_implicit_any or self.cur_mod_node.is_stub:
+                return
         # In case it's a bug and we don't really have context
         assert ctx is not None, msg
         self.errors.report(ctx.get_line(), ctx.get_column(), msg, blocker=blocker)
@@ -3680,7 +3683,14 @@ def analyze(self, type: Type) -> None:
             analyzer = TypeAnalyserPass3(self.fail)
             type.accept(analyzer)
 
-    def fail(self, msg: str, ctx: Context, *, blocker: bool = False) -> None:
+    def fail(self, msg: str, ctx: Context, *, blocker: bool = False,
+             implicit_any: bool = False) -> None:
+        if implicit_any:
+            if not self.options.warn_implicit_any or self.errors.file.endswith('.pyi'):
+                return
+            # TempNode, so must have already reported in the first pass
+            if ctx.get_line() == -1:
+                return
         self.errors.report(ctx.get_line(), ctx.get_column(), msg)
 
     def fail_blocker(self, msg: str, ctx: Context) -> None:

mypy/typeanal.py

@@ -152,6 +152,7 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
             elif fullname == 'typing.Tuple':
                 if len(t.args) == 0 and not t.empty_tuple_index:
                     # Bare 'Tuple' is same as 'tuple'
+                    self.implicit_any('Tuple without type args', t)
                     return self.builtin_type('builtins.tuple')
                 if len(t.args) == 2 and isinstance(t.args[1], EllipsisType):
                     # Tuple[T, ...] (uniform, variable-length tuple)
@@ -174,6 +175,7 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
                 return self.analyze_callable_type(t)
             elif fullname == 'typing.Type':
                 if len(t.args) == 0:
+                    self.implicit_any('Type without type args', t)
                     return TypeType(AnyType(), line=t.line)
                 if len(t.args) != 1:
                     self.fail('Type[...] must have exactly one type argument', t)
@@ -183,6 +185,7 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
                 if self.nesting_level > 0:
                     self.fail('Invalid type: ClassVar nested inside other type', t)
                 if len(t.args) == 0:
+                    self.implicit_any('ClassVar without type args', t)
                     return AnyType(line=t.line)
                 if len(t.args) != 1:
                     self.fail('ClassVar[...] must have at most one type argument', t)
@@ -202,6 +205,7 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
                 act_len = len(an_args)
                 if exp_len > 0 and act_len == 0:
                     # Interpret bare Alias same as normal generic, i.e., Alias[Any, Any, ...]
+                    self.implicit_any('Generic type without type args', t)
                     return self.replace_alias_tvars(override, all_vars, [AnyType()] * exp_len,
                                                     t.line, t.column)
                 if exp_len == 0 and act_len == 0:
@@ -220,6 +224,7 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
                     # context. This is slightly problematic as it allows using the type 'Any'
                     # as a base class -- however, this will fail soon at runtime so the problem
                     # is pretty minor.
+                    self.implicit_any('Assigning value of type Any', t)
                     return AnyType()
                 # Allow unbound type variables when defining an alias
                 if not (self.aliasing and sym.kind == TVAR and
@@ -259,6 +264,7 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
                                             fallback=instance)
                 return instance
         else:
+            self.implicit_any('Fallback', t)
             return AnyType()
 
     def get_type_var_names(self, tp: Type) -> List[str]:
@@ -374,6 +380,7 @@ def analyze_callable_type(self, t: UnboundType) -> Type:
         fallback = self.builtin_type('builtins.function')
         if len(t.args) == 0:
             # Callable (bare). Treat as Callable[..., Any].
+            self.implicit_any('Callable without type args', t)
             ret = CallableType([AnyType(), AnyType()],
                                [nodes.ARG_STAR, nodes.ARG_STAR2],
                                [None, None],
@@ -492,6 +499,10 @@ def builtin_type(self, fully_qualified_name: str, args: List[Type] = None) -> In
     def tuple_type(self, items: List[Type]) -> TupleType:
         return TupleType(items, fallback=self.builtin_type('builtins.tuple', [AnyType()]))
 
+    def implicit_any(self, details: str, t: Type) -> None:
+        msg = 'Type Any created implicitly: ' + details
+        self.fail(msg, t, implicit_any=True)  # type: ignore
+
 
 class TypeAnalyserPass3(TypeVisitor[None]):
     """Analyze type argument counts and values of generic types.
@@ -522,6 +533,8 @@ def visit_instance(self, t: Instance) -> None:
         if len(t.args) != len(info.type_vars):
             if len(t.args) == 0:
                 # Insert implicit 'Any' type arguments.
+                if t.type.fullname() not in ('typing.Generator'):
+                    self.implicit_any('{} without type args'.format(t), t)
                 t.args = [AnyType()] * len(info.type_vars)
                 return
             # Invalid number of type parameters.
@@ -624,6 +637,10 @@ def visit_partial_type(self, t: PartialType) -> None:
     def visit_type_type(self, t: TypeType) -> None:
         pass
 
+    def implicit_any(self, details: str, t: Type) -> None:
+        msg = 'Type Any created implicitly: ' + details
+        self.fail(msg, t, implicit_any=True)  # type: ignore
+
 
 TypeVarList = List[Tuple[str, TypeVarExpr]]
 

test-data/unit/check-warnings.test

@@ -165,3 +165,42 @@ from typing import Any
 def g() -> Any: pass
 def f() -> Any: return g()
 [out]
+
+[case testWarnImplicitAny]
+# flags: --warn-implicit-any
+from typing import TypeVar, List, Tuple, Generic, Callable, Union
+
+T = TypeVar('T')
+U = TypeVar('U')
+A = TypeVar('A', str, int)
+
+class X(Generic[T]):
+    pass
+
+class Y(Generic[T, U]):
+    pass
+
+a1: Tuple  # E: Type Any created implicitly: Tuple without type args
+a2: Callable  # E: Type Any created implicitly: Callable without type args
+a4: list  # E: Type Any created implicitly: builtins.list without type args
+a5: List # E: Type Any created implicitly: builtins.list without type args
+a6: X  # E: Type Any created implicitly: __main__.X without type args
+a7: Y  # E: Type Any created implicitly: __main__.Y without type args
+
+def f(x: X) -> None:  # E: Type Any created implicitly: __main__.X without type args
+    pass
+
+def g() -> X:  # E: Type Any created implicitly: __main__.X without type args
+    pass
+
+b1: str
+b2: X[int]
+b3: Y[int, str]
+b4 = (1, 2)
+b5 = [1, 2]
+b6 = 'abc'
+
+Z = Union[A, X[A]]
+def q(z: Z) -> None: ...  # E: Type Any created implicitly: Generic type without type args
+
+[builtins fixtures/list.pyi]