Fix crashes in class scoped imports (#12023)

Fixes #11045, fixes huggingface/transformers#13390
Fixes #10488
Fixes #7045
Fixes #7806
Fixes #11641
Fixes #11351
Fixes #10488

Co-authored-by: @A5rocks

mypy/semanal.py

@@ -48,10 +48,11 @@
   reduce memory use).
 """
 
+import copy
 from contextlib import contextmanager
 
 from typing import (
-    List, Dict, Set, Tuple, cast, TypeVar, Union, Optional, Callable, Iterator, Iterable
+    Any, List, Dict, Set, Tuple, cast, TypeVar, Union, Optional, Callable, Iterator, Iterable
 )
 from typing_extensions import Final, TypeAlias as _TypeAlias
 
@@ -78,7 +79,7 @@
     typing_extensions_aliases,
     EnumCallExpr, RUNTIME_PROTOCOL_DECOS, FakeExpression, Statement, AssignmentExpr,
     ParamSpecExpr, EllipsisExpr, TypeVarLikeExpr, implicit_module_attrs,
-    MatchStmt,
+    MatchStmt, FuncBase
 )
 from mypy.patterns import (
     AsPattern, OrPattern, ValuePattern, SequencePattern,
@@ -4798,7 +4799,38 @@ def add_imported_symbol(self,
                             module_hidden: bool) -> None:
         """Add an alias to an existing symbol through import."""
         assert not module_hidden or not module_public
-        symbol = SymbolTableNode(node.kind, node.node,
+
+        symbol_node: Optional[SymbolNode] = node.node
+
+        if self.is_class_scope():
+            # I promise this type checks; I'm just making mypyc issues go away.
+            # mypyc is absolutely convinced that `symbol_node` narrows to a Var in the following,
+            # when it can also be a FuncBase. Once fixed, `f` in the following can be removed.
+            # See also https://github.com/mypyc/mypyc/issues/892
+            f = cast(Any, lambda x: x)
+            if isinstance(f(symbol_node), (FuncBase, Var)):
+                # For imports in class scope, we construct a new node to represent the symbol and
+                # set its `info` attribute to `self.type`.
+                existing = self.current_symbol_table().get(name)
+                if (
+                    # The redefinition checks in `add_symbol_table_node` don't work for our
+                    # constructed Var / FuncBase, so check for possible redefinitions here.
+                    existing is not None
+                    and isinstance(f(existing.node), (FuncBase, Var))
+                    and f(existing.type) == f(symbol_node).type
+                ):
+                    symbol_node = existing.node
+                else:
+                    # Construct the new node
+                    constructed_node = copy.copy(f(symbol_node))
+                    assert self.type is not None  # guaranteed by is_class_scope
+                    constructed_node.line = context.line
+                    constructed_node.column = context.column
+                    constructed_node.info = self.type
+                    constructed_node._fullname = self.qualified_name(name)
+                    symbol_node = constructed_node
+
+        symbol = SymbolTableNode(node.kind, symbol_node,
                                  module_public=module_public,
                                  module_hidden=module_hidden)
         self.add_symbol_table_node(name, symbol, context)

test-data/unit/check-classes.test

@@ -7134,3 +7134,112 @@ class B(A):  # E: Final class __main__.B has abstract attributes "foo"
 [case testUndefinedBaseclassInNestedClass]
 class C:
     class C1(XX): pass  # E: Name "XX" is not defined
+
+[case testClassScopeImportFunction]
+class Foo:
+    from mod import foo
+
+reveal_type(Foo.foo)  # N: Revealed type is "def (x: builtins.int, y: builtins.int) -> builtins.int"
+reveal_type(Foo().foo)  # E: Invalid self argument "Foo" to attribute function "foo" with type "Callable[[int, int], int]" \
+                        # N: Revealed type is "def (y: builtins.int) -> builtins.int"
+[file mod.py]
+def foo(x: int, y: int) -> int: ...
+
+[case testClassScopeImportVariable]
+class Foo:
+    from mod import foo
+
+reveal_type(Foo.foo)  # N: Revealed type is "builtins.int"
+reveal_type(Foo().foo)  # N: Revealed type is "builtins.int"
+[file mod.py]
+foo: int
+
+[case testClassScopeImportModule]
+class Foo:
+    import mod
+
+reveal_type(Foo.mod)  # N: Revealed type is "builtins.object"
+reveal_type(Foo.mod.foo)  # N: Revealed type is "builtins.int"
+[file mod.py]
+foo: int
+
+[case testClassScopeImportFunctionAlias]
+class Foo:
+    from mod import foo
+    bar = foo
+
+    from mod import const_foo
+    const_bar = const_foo
+
+reveal_type(Foo.foo)  # N: Revealed type is "def (x: builtins.int, y: builtins.int) -> builtins.int"
+reveal_type(Foo.bar)  # N: Revealed type is "def (x: builtins.int, y: builtins.int) -> builtins.int"
+reveal_type(Foo.const_foo)  # N: Revealed type is "builtins.int"
+reveal_type(Foo.const_bar)  # N: Revealed type is "builtins.int"
+[file mod.py]
+def foo(x: int, y: int) -> int: ...
+const_foo: int
+
+[case testClassScopeImportModuleStar]
+class Foo:
+    from mod import *
+
+reveal_type(Foo.foo)  # N: Revealed type is "builtins.int"
+reveal_type(Foo.bar)  # N: Revealed type is "def (x: builtins.int) -> builtins.int"
+reveal_type(Foo.baz)  # E: "Type[Foo]" has no attribute "baz" \
+                      # N: Revealed type is "Any"
+[file mod.py]
+foo: int
+def bar(x: int) -> int: ...
+
+[case testClassScopeImportFunctionNested]
+class Foo:
+    class Bar:
+        from mod import baz
+
+reveal_type(Foo.Bar.baz)  # N: Revealed type is "def (x: builtins.int) -> builtins.int"
+reveal_type(Foo.Bar().baz)  # E: Invalid self argument "Bar" to attribute function "baz" with type "Callable[[int], int]" \
+                            # N: Revealed type is "def () -> builtins.int"
+[file mod.py]
+def baz(x: int) -> int: ...
+
+[case testClassScopeImportUndefined]
+class Foo:
+    from unknown import foo  # E: Cannot find implementation or library stub for module named "unknown" \
+                             # N: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
+
+reveal_type(Foo.foo)  # N: Revealed type is "Any"
+reveal_type(Foo().foo)  # N: Revealed type is "Any"
+
+[case testClassScopeImportWithFollowImports]
+# flags: --follow-imports=skip
+class Foo:
+    from mod import foo
+
+reveal_type(Foo().foo)  # N: Revealed type is "Any"
+[file mod.py]
+def foo(x: int, y: int) -> int: ...
+
+[case testClassScopeImportVarious]
+class Foo:
+    from mod1 import foo
+    from mod2 import foo  # E: Name "foo" already defined on line 2
+
+    from mod1 import meth1
+    def meth1(self, a: str) -> str: ...  # E: Name "meth1" already defined on line 5
+
+    def meth2(self, a: str) -> str: ...
+    from mod1 import meth2  # E: Name "meth2" already defined on line 8
+
+class Bar:
+    from mod1 import foo
+
+import mod1
+reveal_type(Foo.foo)  # N: Revealed type is "def (x: builtins.int, y: builtins.int) -> builtins.int"
+reveal_type(Bar.foo)  # N: Revealed type is "def (x: builtins.int, y: builtins.int) -> builtins.int"
+reveal_type(mod1.foo)  # N: Revealed type is "def (x: builtins.int, y: builtins.int) -> builtins.int"
+[file mod1.py]
+def foo(x: int, y: int) -> int: ...
+def meth1(x: int) -> int: ...
+def meth2(x: int) -> int: ...
+[file mod2.py]
+def foo(z: str) -> int: ...

test-data/unit/check-modules.test

@@ -131,9 +131,9 @@ def f() -> None: pass
 [case testImportWithinClassBody2]
 import typing
 class C:
-    from m import f
+    from m import f  # E: Method must have at least one argument
     f()
-    f(C) # E: Too many arguments for "f"
+    f(C) # E: Too many arguments for "f" of "C"
 [file m.py]
 def f() -> None: pass
 [out]

test-data/unit/check-newsemanal.test

@@ -2722,7 +2722,7 @@ import m
 
 [file m.py]
 class C:
-    from mm import f
+    from mm import f  # E: Method must have at least one argument
     @dec(f)
     def m(self): pass
 
@@ -2742,7 +2742,7 @@ import m
 
 [file m/__init__.py]
 class C:
-    from m.m import f
+    from m.m import f  # E: Method must have at least one argument
     @dec(f)
     def m(self): pass
 

test-data/unit/semanal-modules.test

@@ -568,7 +568,7 @@ MypyFile:1(
     ImportFrom:2(_x, [y])
     AssignmentStmt:3(
       NameExpr(z* [m])
-      NameExpr(y [_x.y]))))
+      NameExpr(y [__main__.A.y]))))
 
 [case testImportInClassBody2]
 class A: