fix void check on decorated functions

Author: KotlinIsland

CHANGELOG.md

@@ -14,6 +14,7 @@
 ### Fixes
 - Render star args in error messages properly (#551)
 - The first argument to `cast` is analyzed as evaluated (#564)
+- Decorated functions that return `None` correctly warn when used (#572)
 
 ## [2.2.1]
 ### Fixes

mypy/checkexpr.py

@@ -688,10 +688,10 @@ def visit_call_expr_inner(self, e: CallExpr, allow_none_return: bool = False) ->
         if (
             not allow_none_return
             and isinstance(ret_type, NoneType)
-            and self.always_returns_none(e.callee)
+            # field lies about its return type and must be special-cased
+            and fullname != "dataclasses.field"
         ):
             self.chk.msg.does_not_return_value(callee_type, e)
-            return AnyType(TypeOfAny.from_error)
         return ret_type
 
     def check_str_format_call(self, e: CallExpr) -> None:
@@ -759,6 +759,8 @@ def always_returns_none(self, node: Expression) -> bool:
 
     def defn_returns_none(self, defn: SymbolNode | None) -> bool:
         """Check if `defn` can _only_ return None."""
+        if isinstance(defn, Decorator):
+            defn = defn.func
         if isinstance(defn, FuncDef):
             return isinstance(defn.type, CallableType) and isinstance(
                 get_proper_type(defn.type.ret_type), NoneType

test-data/unit/check-based-misc.test

@@ -154,3 +154,26 @@ def f():
     def guard(x: object) -> x is int:  # E: You need to put quotes around the entire type-guard, or enable `__future__.annotations`  [misc]
         ...
 [builtins fixtures/tuple.pyi]
+
+
+[case testUsingDecoratedNone]
+from typing import TypeVar, Callable
+T = TypeVar("T")
+def deco(t: T) -> T: ...
+@deco
+def f1(): ...
+
+a = f1()  # E: "f1" does not return a value  [func-returns-value]
+
+def becomes_none(f: object) -> Callable[[], None]: ...
+
+@becomes_none
+def f2() -> object: ...
+
+a = f2()  # E: "f2" does not return a value  [func-returns-value]
+def becomes_object(f: object) -> Callable[[], object]: ...
+
+@becomes_object
+def f3(): ...
+
+a = f3()

test-data/unit/check-bound.test

@@ -55,7 +55,7 @@ class C(Generic[T]):
         return self.t
 c1: C[None]
 c1.get()
-d = c1.get()
+d = c1.get()  # E: "get" of "C" does not return a value
 reveal_type(d)  # N: Revealed type is "None"
 
 
@@ -83,7 +83,7 @@ def f(g: Callable[[], T]) -> T:
     return g()
 def h() -> None: pass
 f(h)
-a = f(h)
+a = f(h)  # E: "f" does not return a value
 reveal_type(a)  # N: Revealed type is "None"
 
 

test-data/unit/check-expressions.test

@@ -1079,15 +1079,17 @@ class A:
 a: A
 o: object
 if int():
-    a = f()         # E: "f" does not return a value
+    a = f()         # E: "f" does not return a value \
+                    # E: Incompatible types in assignment (expression has type "None", variable has type "A")
 if int():
     o = a()         # E: Function does not return a value
 if int():
     o = A().g(a)    # E: "g" of "A" does not return a value
 if int():
     o = A.g(a, a)   # E: "g" of "A" does not return a value
 A().g(f())      # E: "f" does not return a value
-x: A = f()      # E: "f" does not return a value
+x: A = f()      # E: "f" does not return a value \
+                # E: Incompatible types in assignment (expression has type "None", variable has type "A")
 f()
 A().g(a)
 [builtins fixtures/tuple.pyi]
@@ -1104,7 +1106,8 @@ while f(): # E: "f" does not return a value
     pass
 def g() -> object:
     return f() # E: "f" does not return a value
-raise f() # E: "f" does not return a value
+raise f() # E: Exception must be derived from BaseException \
+          # E: "f" does not return a value
 [builtins fixtures/exception.pyi]
 
 [case testNoneReturnTypeWithExpressions]
@@ -1116,12 +1119,17 @@ class A:
 
 a: A
 [f()]       # E: "f" does not return a value
-f() + a     # E: "f" does not return a value
-a + f()     # E: "f" does not return a value
-f() == a    # E: "f" does not return a value
-a != f()    # E: "f" does not return a value
+f() + a     # E: "f" does not return a value \
+            # E: Unsupported left operand type for + ("None")
+a + f()     # E: "f" does not return a value \
+            # E: Unsupported operand types for + ("A" and "None")
+f() == a    # E: "f" does not return a value \
+            # E: Unsupported left operand type for == ("None")
+a != f()    # E: Unsupported left operand type for != ("A") \
+            # E: "f" does not return a value
 cast(A, f())
-f().foo     # E: "f" does not return a value
+f().foo     # E: "f" does not return a value \
+            # E: "None" has no attribute "foo"
 [builtins fixtures/list.pyi]
 
 [case testNoneReturnTypeWithExpressions2]
@@ -1134,11 +1142,16 @@ class A:
 
 a: A
 b: bool
-f() in a   # E: "f" does not return a value  # E: Unsupported right operand type for in ("A")
-a < f()    # E: "f" does not return a value
-f() <= a   # E: "f" does not return a value
-a in f()   # E: "f" does not return a value
--f()       # E: "f" does not return a value
+f() in a   # E: "f" does not return a value \
+           # E: Unsupported right operand type for in ("A")
+a < f()    # E: Unsupported left operand type for < ("A") \
+           # E: "f" does not return a value
+f() <= a   # E: "f" does not return a value \
+           # E: Unsupported left operand type for <= ("None")
+a in f()   # E: Unsupported right operand type for in ("None") \
+           # E: "f" does not return a value
+-f()       # E: Unsupported operand type for unary - ("None") \
+           # E: "f" does not return a value
 not f()    # E: "f" does not return a value
 f() and b  # E: "f" does not return a value
 b or f()   # E: "f" does not return a value

test-data/unit/check-functions.test

@@ -2576,19 +2576,19 @@ from typing import TypeVar, Optional
 T = TypeVar('T')
 def X(val: T) -> T: ...
 x_in = None
-def Y(x: Optional[str] = X(x_in)): ...
+def Y(x: Optional[str] = X(x_in)): ...  # E: "X" does not return a value
 
-xx: Optional[int] = X(x_in)
+xx: Optional[int] = X(x_in)  # E: "X" does not return a value
 [out]
 
 [case testNoComplainInferredNoneStrict]
 from typing import TypeVar, Optional
 T = TypeVar('T')
 def X(val: T) -> T: ...
 x_in = None
-def Y(x: Optional[str] = X(x_in)): ...
+def Y(x: Optional[str] = X(x_in)): ...   # E: "X" does not return a value
 
-xx: Optional[int] = X(x_in)
+xx: Optional[int] = X(x_in)  # E: "X" does not return a value
 [out]
 
 [case testNoComplainNoneReturnFromUntyped]

test-data/unit/check-inference-context.test

@@ -963,7 +963,8 @@ class M(Generic[_KT, _VT]):
     def get(self, k: _KT, default: _T) -> _T: ...
 
 def f(d: M[_KT, _VT], k: _KT) -> _VT:
-    return d.get(k, None)  # E: Incompatible return value type (got "None", expected "_VT")
+    return d.get(k, None)  # E: "get" of "M" does not return a value \
+                           # E: Incompatible return value type (got "None", expected "_VT")
 
 [case testGenericMethodCalledInGenericContext2]
 from typing import TypeVar, Generic, Union

test-data/unit/check-inference.test

@@ -1180,7 +1180,8 @@ for e, f in [[]]:  # E: Need type annotation for "e" \
 [case testForStatementInferenceWithVoid]
 def f() -> None: pass
 
-for x in f(): # E: "f" does not return a value
+for x in f(): # E: "f" does not return a value \
+              # E: "None" has no attribute "__iter__" (not iterable)
     pass
 [builtins fixtures/for.pyi]
 
@@ -2119,6 +2120,8 @@ arr.append(arr.append(1))
 [builtins fixtures/list.pyi]
 [out]
 main:3: error: "append" of "list" does not return a value
+main:3: error: Argument 1 to "append" of "list" has incompatible type "None"; expected "int"
+
 
 -- Multipass
 -- ---------

test-data/unit/check-optional.test

@@ -119,7 +119,7 @@ reveal_type(z2)  # N: Revealed type is "Union[builtins.int, builtins.str, None]"
 
 [case testLambdaReturningNone]
 f = lambda: None
-x = f()
+x = f()  # E: Function does not return a value
 reveal_type(x)  # N: Revealed type is "None"
 
 [case testNoneArgumentType]
@@ -362,7 +362,8 @@ def g(x: Optional[int]) -> int:
   pass
 
 x = f()  # E: "f" does not return a value
-f() + 1  # E: "f" does not return a value
+f() + 1  # E: "f" does not return a value \
+         # E: Unsupported left operand type for + ("None")
 g(f())  # E: "f" does not return a value
 
 [case testEmptyReturn]

test-data/unit/check-overloading.test

@@ -1298,7 +1298,7 @@ def g(x: U, y: V) -> None:
          # N: Possible overload variants: \
          # N:     def [T <: str] f(x: T) -> T \
          # N:     def [T <: str] f(x: List[T]) -> None
-    a = f([x])
+    a = f([x])  # E: "f" does not return a value
     reveal_type(a)  # N: Revealed type is "None"
     f([y]) # E: Value of type variable "T" of "f" cannot be "V"
     f([x, y]) # E: Value of type variable "T" of "f" cannot be "object"

test-data/unit/check-protocols.test

@@ -1454,8 +1454,9 @@ class P2(Protocol):
 T = TypeVar('T')
 def f(x: Callable[[T, T], None]) -> T: pass
 def g(x: P, y: P2) -> None: pass
-x = f(g)
+x = f(g)  # E: "f" does not return a value
 reveal_type(x)  # N: Revealed type is "None"
+
 [case testMeetProtocolWithNormal]
 from typing import Protocol, Callable, TypeVar
 

test-data/unit/check-varargs.test

@@ -52,8 +52,10 @@ c: C
 
 f(c)       # E: Argument 1 to "f" has incompatible type "C"; expected "A"
 f(a, b, c) # E: Argument 3 to "f" has incompatible type "C"; expected "A"
-f(g())     # E: "g" does not return a value
-f(a, g())  # E: "g" does not return a value
+f(g())     # E: "g" does not return a value \
+           # E: Argument 1 to "f" has incompatible type "None"; expected "A"
+f(a, g())  # E: "g" does not return a value \
+           # E: Argument 2 to "f" has incompatible type "None"; expected "A"
 f()
 f(a)
 f(b)