Improve error message for dotted names resolved through variables or functions

mypy/semanal.py

@@ -6754,7 +6754,23 @@ def lookup_qualified(
                     # See https://github.com/python/mypy/pull/13468
                     if isinstance(node, ParamSpecExpr) and part in ("args", "kwargs"):
                         return None
-                    # Lookup through invalid node, such as variable or function
+                    if not suppress_errors and isinstance(node, (Var, FuncDef, Decorator)):
+                        # Attribute access through a variable or function cannot be
+                        # resolved by mypy. Give a more specific error than "Name ... is
+                        # not defined" so the user understands *why*.
+                        prefix = ".".join(parts[:i])
+                        if isinstance(node, (FuncDef, Decorator)):
+                            kind = "a function"
+                        else:
+                            kind = "a variable"
+                        self.fail(
+                            f'Name "{name}" is not defined'
+                            f' ("{prefix}" is {kind}, not a module or class)',
+                            ctx,
+                            code=codes.NAME_DEFINED,
+                        )
+                        return None
+                    # Lookup through invalid node
                     nextsym = None
                 if not nextsym or nextsym.module_hidden:
                     if not suppress_errors:

test-data/unit/check-namedtuple.test

@@ -1357,7 +1357,7 @@ from typing import NamedTuple
 class Test:
     def __init__(self, field) -> None:
         self.Item = NamedTuple("x", [(field, str)])  # E: NamedTuple type as an attribute is not supported
-        self.item: self.Item  # E: Name "self.Item" is not defined
+        self.item: self.Item  # E: Name "self.Item" is not defined ("self" is a variable, not a module or class)
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-namedtuple.pyi]
 

test-data/unit/check-newsemanal.test

@@ -2531,7 +2531,7 @@ from p.c import B
 [case testNewSemanticAnalyzerQualifiedFunctionAsType]
 import m
 
-x: m.C.a.b # E: Name "m.C.a.b" is not defined
+x: m.C.a.b # E: Name "m.C.a.b" is not defined ("m.C" is a function, not a module or class)
 
 [file m.py]
 def C(): pass
@@ -2569,8 +2569,7 @@ class C:
     class E: pass
 
     def f(self) -> None:
-        # TODO: Error message could be better
-        class D(self.E): # E: Name "self.E" is not defined
+        class D(self.E): # E: Name "self.E" is not defined ("self" is a variable, not a module or class)
             pass
 
 [case testNewAnalyzerShadowOuterDefinitionBasedOnOrderSinglePass]
@@ -2813,7 +2812,7 @@ class B: ...
 
 [case testNewAnalyzerImportAmbiguousWithTopLevelFunction]
 import a.b  # This works at runtime
-x: a.b.B  # E: Name "a.b.B" is not defined
+x: a.b.B  # E: Name "a.b.B" is not defined ("a.b" is a function, not a module or class)
 reveal_type(a.b)  # N: Revealed type is "def ()"
 [file a/__init__.py]
 import a.b

test-data/unit/check-semanal-error.test

@@ -61,6 +61,15 @@ main:3: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#varia
 main:3: error: Invalid base class "X"
 main:6: error: Incompatible types in assignment (expression has type "str", variable has type "int")
 
+[case testInvalidBaseClass3_AttributeAccess]
+class A:
+    pass
+class B:
+    def __init__(self) -> None:
+        self.a = A
+b = B()
+class C(b.a):  # E: Name "b.a" is not defined ("b" is a variable, not a module or class)
+    pass
 
 [case testInvalidNumberOfTypeArgs]
 from typing import TypeVar

test-data/unit/check-type-aliases.test

@@ -884,19 +884,19 @@ reveal_type(plausible_child_4)  # N: Revealed type is "def () -> builtins.int |
 
 # Use type aliases in a type alias context in an implausible way
 
-def weird_parent_1() -> p.NormalImplicit: pass   # E: Name "p.NormalImplicit" is not defined
-def weird_parent_2() -> p.NormalExplicit: pass   # E: Name "p.NormalExplicit" is not defined
-def weird_parent_3() -> p.SpecialImplicit: pass  # E: Name "p.SpecialImplicit" is not defined
-def weird_parent_4() -> p.SpecialExplicit: pass  # E: Name "p.SpecialExplicit" is not defined
+def weird_parent_1() -> p.NormalImplicit: pass   # E: Name "p.NormalImplicit" is not defined ("p" is a variable, not a module or class)
+def weird_parent_2() -> p.NormalExplicit: pass   # E: Name "p.NormalExplicit" is not defined ("p" is a variable, not a module or class)
+def weird_parent_3() -> p.SpecialImplicit: pass  # E: Name "p.SpecialImplicit" is not defined ("p" is a variable, not a module or class)
+def weird_parent_4() -> p.SpecialExplicit: pass  # E: Name "p.SpecialExplicit" is not defined ("p" is a variable, not a module or class)
 reveal_type(weird_parent_1)  # N: Revealed type is "def () -> Any"
 reveal_type(weird_parent_2)  # N: Revealed type is "def () -> Any"
 reveal_type(weird_parent_3)  # N: Revealed type is "def () -> Any"
 reveal_type(weird_parent_4)  # N: Revealed type is "def () -> Any"
 
-def weird_child_1() -> c.NormalImplicit: pass   # E: Name "c.NormalImplicit" is not defined
-def weird_child_2() -> c.NormalExplicit: pass   # E: Name "c.NormalExplicit" is not defined
-def weird_child_3() -> c.SpecialImplicit: pass  # E: Name "c.SpecialImplicit" is not defined
-def weird_child_4() -> c.SpecialExplicit: pass  # E: Name "c.SpecialExplicit" is not defined
+def weird_child_1() -> c.NormalImplicit: pass   # E: Name "c.NormalImplicit" is not defined ("c" is a variable, not a module or class)
+def weird_child_2() -> c.NormalExplicit: pass   # E: Name "c.NormalExplicit" is not defined ("c" is a variable, not a module or class)
+def weird_child_3() -> c.SpecialImplicit: pass  # E: Name "c.SpecialImplicit" is not defined ("c" is a variable, not a module or class)
+def weird_child_4() -> c.SpecialExplicit: pass  # E: Name "c.SpecialExplicit" is not defined ("c" is a variable, not a module or class)
 reveal_type(weird_child_1)  # N: Revealed type is "def () -> Any"
 reveal_type(weird_child_2)  # N: Revealed type is "def () -> Any"
 reveal_type(weird_child_3)  # N: Revealed type is "def () -> Any"