Add more details for "Invalid type" errors (#7166)

Fixes #4030

This adds some more details to various `Invalid type` errors, and similar such as `Invalid type alias`, and `Invalid base class`. Unfortunately, `MessageBuilder` is not available in `typeanal.py`, so I put some error message formatting logic there.

Author: ilevkivskyi

mypy/newsemanal/semanal.py

@@ -1348,6 +1348,18 @@ def make_empty_type_info(self, defn: ClassDef) -> TypeInfo:
             info.set_line(defn)
         return info
 
+    def get_name_repr_of_expr(self, expr: Expression) -> Optional[str]:
+        """Try finding a short simplified textual representation of a base class expression."""
+        if isinstance(expr, NameExpr):
+            return expr.name
+        if isinstance(expr, MemberExpr):
+            return get_member_expr_fullname(expr)
+        if isinstance(expr, IndexExpr):
+            return self.get_name_repr_of_expr(expr.base)
+        if isinstance(expr, CallExpr):
+            return self.get_name_repr_of_expr(expr.callee)
+        return None
+
     def analyze_base_classes(
             self,
             base_type_exprs: List[Expression]) -> Optional[Tuple[List[Tuple[Type, Expression]],
@@ -1371,7 +1383,14 @@ def analyze_base_classes(
             try:
                 base = self.expr_to_analyzed_type(base_expr, allow_placeholder=True)
             except TypeTranslationError:
-                self.fail('Invalid base class', base_expr)
+                name = self.get_name_repr_of_expr(base_expr)
+                if isinstance(base_expr, CallExpr):
+                    msg = 'Unsupported dynamic base class'
+                else:
+                    msg = 'Invalid base class'
+                if name:
+                    msg += ' "{}"'.format(name)
+                self.fail(msg, base_expr)
                 is_error = True
                 continue
             if base is None:
@@ -1409,7 +1428,11 @@ def configure_base_classes(self,
                     self.fail(msg, base_expr)
                 info.fallback_to_any = True
             else:
-                self.fail('Invalid base class', base_expr)
+                msg = 'Invalid base class'
+                name = self.get_name_repr_of_expr(base_expr)
+                if name:
+                    msg += ' "{}"'.format(name)
+                self.fail(msg, base_expr)
                 info.fallback_to_any = True
             if self.options.disallow_any_unimported and has_any_from_unimported_type(base):
                 if isinstance(base_expr, (NameExpr, MemberExpr)):
@@ -1421,7 +1444,7 @@ def configure_base_classes(self,
                                    context=base_expr)
 
         # Add 'object' as implicit base if there is no other base class.
-        if (not base_types and defn.fullname != 'builtins.object'):
+        if not base_types and defn.fullname != 'builtins.object':
             base_types.append(self.object_type())
 
         info.bases = base_types
@@ -3186,7 +3209,7 @@ def visit_with_stmt(self, s: WithStmt) -> None:
             actual_targets = [t for t in s.target if t is not None]
             if len(actual_targets) == 0:
                 # We have a type for no targets
-                self.fail('Invalid type comment', s)
+                self.fail('Invalid type comment: "with" statement has no targets', s)
             elif len(actual_targets) == 1:
                 # We have one target and one type
                 types = [s.unanalyzed_type]
@@ -3196,10 +3219,10 @@ def visit_with_stmt(self, s: WithStmt) -> None:
                     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)
+                    self.fail('Incompatible number of types for "with" targets', s)
             else:
                 # We have multiple targets and one type
-                self.fail('Multiple types expected for multiple `with` targets', s)
+                self.fail('Multiple types expected for multiple "with" targets', s)
 
         new_types = []  # type: List[Type]
         for e, n in zip(s.expr, s.target):

mypy/newsemanal/typeanal.py

@@ -22,7 +22,7 @@
     TypeInfo, Context, SymbolTableNode, Var, Expression,
     nongen_builtins, check_arg_names, check_arg_kinds, ARG_POS, ARG_NAMED,
     ARG_OPT, ARG_NAMED_OPT, ARG_STAR, ARG_STAR2, TypeVarExpr,
-    TypeAlias, PlaceholderNode
+    TypeAlias, PlaceholderNode, SYMBOL_FUNCBASE_TYPES, Decorator, MypyFile
 )
 from mypy.typetraverser import TypeTraverserVisitor
 from mypy.tvar_scope import TypeVarScope
@@ -72,7 +72,7 @@ def analyze_type_alias(node: Expression,
     try:
         type = expr_to_unanalyzed_type(node)
     except TypeTranslationError:
-        api.fail('Invalid type alias', node)
+        api.fail('Invalid type alias: expression is not a valid type', node)
         return None
     analyzer = TypeAnalyser(api, tvar_scope, plugin, options, is_typeshed_stub,
                             allow_unnormalized=allow_unnormalized, defining_alias=True,
@@ -401,7 +401,29 @@ def analyze_unbound_type_without_type_info(self, t: UnboundType, sym: SymbolTabl
         # None of the above options worked. We parse the args (if there are any)
         # to make sure there are no remaining semanal-only types, then give up.
         t = t.copy_modified(args=self.anal_array(t.args))
-        self.fail('Invalid type "{}"'.format(name), t)
+        # TODO: Move this message building logic to messages.py.
+        notes = []  # type: List[str]
+        if isinstance(sym.node, Var):
+            # TODO: add a link to alias docs, see #3494.
+            message = 'Variable "{}" is not valid as a type'
+        elif isinstance(sym.node, (SYMBOL_FUNCBASE_TYPES, Decorator)):
+            message = 'Function "{}" is not valid as a type'
+            notes.append('Perhaps you need "Callable[...]" or a callback protocol?')
+        elif isinstance(sym.node, MypyFile):
+            # TODO: suggest a protocol when supported.
+            message = 'Module "{}" is not valid as a type'
+        elif unbound_tvar:
+            message = 'Type variable "{}" is unbound'
+            short = name.split('.')[-1]
+            notes.append(('(Hint: Use "Generic[{}]" or "Protocol[{}]" base class'
+                          ' to bind "{}" inside a class)').format(short, short, short))
+            notes.append('(Hint: Use "{}" in function signature to bind "{}"'
+                         ' inside a function)'.format(short, short))
+        else:
+            message = 'Cannot interpret reference "{}" as a type'
+        self.fail(message.format(name), t)
+        for note in notes:
+            self.note(note, t)
 
         # TODO: Would it be better to always return Any instead of UnboundType
         # in case of an error? On one hand, UnboundType has a name so error messages
@@ -422,7 +444,8 @@ def visit_deleted_type(self, t: DeletedType) -> Type:
         return t
 
     def visit_type_list(self, t: TypeList) -> Type:
-        self.fail('Invalid type', t)
+        self.fail('Bracketed expression "[...]" is not valid as a type', t)
+        self.note('Did you mean "List[...]"?', t)
         return AnyType(TypeOfAny.from_error)
 
     def visit_callable_argument(self, t: CallableArgument) -> Type:
@@ -457,9 +480,9 @@ def visit_tuple_type(self, t: TupleType) -> Type:
         if t.implicit and not self.allow_tuple_literal:
             self.fail('Syntax error in type annotation', t)
             if len(t.items) == 1:
-                self.note_func('Suggestion: Is there a spurious trailing comma?', t)
+                self.note('Suggestion: Is there a spurious trailing comma?', t)
             else:
-                self.note_func('Suggestion: Use Tuple[T1, ..., Tn] instead of (T1, ..., Tn)', t)
+                self.note('Suggestion: Use Tuple[T1, ..., Tn] instead of (T1, ..., Tn)', t)
             return AnyType(TypeOfAny.from_error)
         star_count = sum(1 for item in t.items if isinstance(item, StarType))
         if star_count > 1:
@@ -512,7 +535,7 @@ def visit_raw_expression_type(self, t: RawExpressionType) -> Type:
 
             self.fail(msg, t)
             if t.note is not None:
-                self.note_func(t.note, t)
+                self.note(t.note, t)
 
         return AnyType(TypeOfAny.from_error, line=t.line, column=t.column)
 
@@ -722,6 +745,9 @@ def analyze_type(self, t: Type) -> Type:
     def fail(self, msg: str, ctx: Context) -> None:
         self.fail_func(msg, ctx)
 
+    def note(self, msg: str, ctx: Context) -> None:
+        self.note_func(msg, ctx)
+
     @contextmanager
     def tvar_scope_frame(self) -> Iterator[None]:
         old_scope = self.tvar_scope

mypy/semanal.py

@@ -2864,10 +2864,10 @@ def visit_with_stmt(self, s: WithStmt) -> None:
                     types = s.unanalyzed_type.items
                 else:
                     # But it's the wrong number of items
-                    self.fail('Incompatible number of types for `with` targets', s)
+                    self.fail('Incompatible number of types for "with" targets', s)
             else:
                 # We have multiple targets and one type
-                self.fail('Multiple types expected for multiple `with` targets', s)
+                self.fail('Multiple types expected for multiple "with" targets', s)
 
         new_types = []  # type: List[Type]
         for e, n in zip(s.expr, s.target):

test-data/unit/check-basic.test

@@ -325,13 +325,14 @@ import e
 1+'no'  # E: Unsupported operand types for + ("int" and "str")
 
 [case testModuleAsTypeNoCrash]
+# flags: --new-semantic-analyzer
 import mock
 from typing import Union
 
 class A: ...
 class B: ...
 
-x: Union[mock, A]  # E: Invalid type "mock"
+x: Union[mock, A]  # E: Module "mock" is not valid as a type
 
 if isinstance(x, B):
     pass
@@ -340,13 +341,14 @@ if isinstance(x, B):
 [out]
 
 [case testModuleAsTypeNoCrash2]
+# flags: --new-semantic-analyzer
 import mock
 from typing import overload, Any, Union
 
 @overload
 def f(x: int) -> int: ...
 @overload
-def f(x: str) -> Union[mock, str]: ...  # E: Invalid type "mock"
+def f(x: str) -> Union[mock, str]: ...  # E: Module "mock" is not valid as a type
 def f(x):
     pass
 

test-data/unit/check-classes.test

@@ -4833,12 +4833,13 @@ reveal_type(Arc1[MyDestr]())  # N: Revealed type is '__main__.Arc1[__main__.MyDe
 [typing fixtures/typing-full.pyi]
 
 [case testSixMetaclassErrors]
+# flags: --new-semantic-analyzer
 import six
 class M(type): pass
 class A(object): pass
 def f() -> type: return M
-class C1(six.with_metaclass(M), object): pass  # E: Invalid base class
-class C2(C1, six.with_metaclass(M)): pass  # E: Invalid base class
+class C1(six.with_metaclass(M), object): pass  # E: Unsupported dynamic base class "six.with_metaclass"
+class C2(C1, six.with_metaclass(M)): pass  # E: Unsupported dynamic base class "six.with_metaclass"
 class C3(six.with_metaclass(A)): pass  # E: Metaclasses not inheriting from 'type' are not supported
 @six.add_metaclass(A)  # E: Argument 1 to "add_metaclass" has incompatible type "Type[A]"; expected "Type[type]" \
                        # E: Metaclasses not inheriting from 'type' are not supported

test-data/unit/check-columns.test

@@ -69,32 +69,34 @@ if int():
     (f(b=object())) # E:6: Unexpected keyword argument "b" for "f"
 
 [case testColumnInvalidType]
+# flags: --new-semantic-analyzer
 from typing import Iterable
 
 bad = 0
 
-def f(x: bad): # E:10: Invalid type "__main__.bad"
-    y: bad # E:8: Invalid type "__main__.bad"
+def f(x: bad): # E:10: Variable "__main__.bad" is not valid as a type
+    y: bad # E:8: Variable "__main__.bad" is not valid as a type
 
 if int():
-    def g(x): # E:5: Invalid type "__main__.bad"
+    def g(x): # E:5: Variable "__main__.bad" is not valid as a type
         # type: (bad) -> None
-        y = 0  # type: bad  # E:9: Invalid type "__main__.bad"
+        y = 0  # type: bad  # E:9: Variable "__main__.bad" is not valid as a type
 
-z: Iterable[bad] # E:13: Invalid type "__main__.bad"
-h: bad[int] # E:4: Invalid type "__main__.bad"
+z: Iterable[bad] # E:13: Variable "__main__.bad" is not valid as a type
+h: bad[int] # E:4: Variable "__main__.bad" is not valid as a type
 
 [case testColumnInvalidType_python2]
+# flags: --new-semantic-analyzer
 from typing import Iterable
 
 bad = 0
 
 if int():
-    def g(x): # E:5: Invalid type "__main__.bad"
+    def g(x): # E:5: Variable "__main__.bad" is not valid as a type
         # type: (bad) -> None
-        y = 0  # type: bad  # E:9: Invalid type "__main__.bad"
+        y = 0  # type: bad  # E:9: Variable "__main__.bad" is not valid as a type
 
-    z = ()  # type: Iterable[bad] # E:5: Invalid type "__main__.bad"
+    z = ()  # type: Iterable[bad] # E:5: Variable "__main__.bad" is not valid as a type
 
 [case testColumnFunctionMissingTypeAnnotation]
 # flags: --disallow-untyped-defs

test-data/unit/check-custom-plugin.test

@@ -496,12 +496,12 @@ from mod import declarative_base, Column, Instr, non_declarative_base
 Bad1 = non_declarative_base()
 Bad2 = Bad3 = declarative_base()
 
-class C1(Bad1): ...  # E: Invalid type "__main__.Bad1" \
-                     # E: Invalid base class
-class C2(Bad2): ...  # E: Invalid type "__main__.Bad2" \
-                     # E: Invalid base class
-class C3(Bad3): ...  # E: Invalid type "__main__.Bad3" \
-                     # E: Invalid base class
+class C1(Bad1): ...  # E: Variable "__main__.Bad1" is not valid as a type \
+                     # E: Invalid base class "Bad1"
+class C2(Bad2): ...  # E: Variable "__main__.Bad2" is not valid as a type \
+                     # E: Invalid base class "Bad2"
+class C3(Bad3): ...  # E: Variable "__main__.Bad3" is not valid as a type \
+                     # E: Invalid base class "Bad3"
 [file mod.py]
 from typing import Generic, TypeVar
 def declarative_base(): ...

test-data/unit/check-functions.test

@@ -1720,6 +1720,7 @@ def Arg(x, y): pass
 F = Callable[[Arg(int, 'x')], int]  # E: Invalid argument constructor "__main__.Arg"
 
 [case testCallableParsingFromExpr]
+# flags: --new-semantic-analyzer
 from typing import Callable, List
 from mypy_extensions import Arg, VarArg, KwArg
 import mypy_extensions
@@ -1737,12 +1738,12 @@ J = Callable[[VarArg(), KwArg()], int] # ok
 K = Callable[[VarArg(), int], int] # E: Required positional args may not appear after default, named or var args
 L = Callable[[Arg(name='x', type=int)], int] # ok
 # I have commented out the following test because I don't know how to expect the "defined here" note part of the error.
-# M = Callable[[Arg(gnome='x', type=int)], int]   E: Invalid type alias   E: Unexpected keyword argument "gnome" for "Arg"
+# M = Callable[[Arg(gnome='x', type=int)], int]   E: Invalid type alias: expression is not a valid type   E: Unexpected keyword argument "gnome" for "Arg"
 N = Callable[[Arg(name=None, type=int)], int] # ok
-O = Callable[[List[Arg(int)]], int]  # E: Invalid type alias  # E: Value of type "int" is not indexable  # E: Type expected within [...] # E: The type "Type[List[Any]]" is not generic and not indexable
+O = Callable[[List[Arg(int)]], int]  # E: Invalid type alias: expression is not a valid type  # E: Value of type "int" is not indexable  # E: Type expected within [...] # E: The type "Type[List[Any]]" is not generic and not indexable
 P = Callable[[mypy_extensions.VarArg(int)], int] # ok
-Q = Callable[[Arg(int, type=int)], int]  # E: Invalid type alias  # E: Value of type "int" is not indexable  # E: "Arg" gets multiple values for keyword argument "type"
-R = Callable[[Arg(int, 'x', name='y')], int]  # E: Invalid type alias  # E: Value of type "int" is not indexable  # E: "Arg" gets multiple values for keyword argument "name"
+Q = Callable[[Arg(int, type=int)], int]  # E: Invalid type alias: expression is not a valid type  # E: Value of type "int" is not indexable  # E: "Arg" gets multiple values for keyword argument "type"
+R = Callable[[Arg(int, 'x', name='y')], int]  # E: Invalid type alias: expression is not a valid type  # E: Value of type "int" is not indexable  # E: "Arg" gets multiple values for keyword argument "name"
 
 [builtins fixtures/dict.pyi]
 

test-data/unit/check-generics.test

@@ -722,6 +722,7 @@ reveal_type(f('a'))  # N: Revealed type is '__main__.D[builtins.str*]'
 main:15: error: Argument 1 to "D" has incompatible type "int"; expected "Tuple[T, T]"
 
 [case testGenericTypeAliasesSubclassingBad]
+# flags: --new-semantic-analyzer
 from typing import TypeVar, Generic, Tuple, Union
 T = TypeVar('T')
 class Node(Generic[T]):
@@ -733,7 +734,7 @@ UNode = Union[int, Node[T]]
 
 class C(TupledNode): ... # Same as TupledNode[Any]
 class D(TupledNode[T]): ...
-class E(Generic[T], UNode[T]): ... # E: Invalid base class
+class E(Generic[T], UNode[T]): ... # E: Invalid base class "UNode"
 
 reveal_type(D((1, 1))) # N: Revealed type is '__main__.D[builtins.int*]'
 [builtins fixtures/list.pyi]
@@ -962,6 +963,7 @@ O[int]  # E: Bad number of arguments for type alias, expected: 0, given: 1  # E:
 [out]
 
 [case testAliasesInClassBodyNormalVsSubscripted]
+# flags: --new-semantic-analyzer
 from typing import Union, Type, Iterable
 
 class A: pass
@@ -976,9 +978,9 @@ class C:
         b = int  # E: Cannot assign multiple types to name "b" without an explicit "Type[...]" annotation
     if int():
         c = int
-    def f(self, x: a) -> None: pass  # E: Invalid type "__main__.C.a"
+    def f(self, x: a) -> None: pass  # E: Variable "__main__.C.a" is not valid as a type
     def g(self, x: b) -> None: pass
-    def h(self, x: c) -> None: pass  # E: Invalid type "__main__.C.c"
+    def h(self, x: c) -> None: pass  # E: Variable "__main__.C.c" is not valid as a type
     x: b
     reveal_type(x)  # N: Revealed type is 'Union[builtins.int, builtins.str]'
 [out]

test-data/unit/check-incremental.test

@@ -2180,6 +2180,7 @@ tmp/b.py:1: error: Module 'c' has no attribute 'x'
 tmp/b.py:1: error: Module 'c' has no attribute 'x'
 
 [case testCacheDeletedAfterErrorsFound2]
+# flags: --new-semantic-analyzer
 import a
 [file a.py]
 from b import x
@@ -2195,9 +2196,11 @@ from b import x
 1 + 1
 [out]
 [out2]
-tmp/b.py:2: error: Invalid type "c.C"
+tmp/b.py:2: error: Function "c.C" is not valid as a type
+tmp/b.py:2: note: Perhaps you need "Callable[...]" or a callback protocol?
 [out3]
-tmp/b.py:2: error: Invalid type "c.C"
+tmp/b.py:2: error: Function "c.C" is not valid as a type
+tmp/b.py:2: note: Perhaps you need "Callable[...]" or a callback protocol?
 
 [case testCacheDeletedAfterErrorsFound3]
 import a