Fix interaction of list comprehension shadowing and binders (#7476)

Binders are keyed by "literal_hash" which uses the name of the
variable as part of the key. Use the Var node instead so that
shadowing works.

Fixes mypyc/mypyc#695 but also was a bug separate from mypyc.

Author: msullivan

mypy/literals.py

@@ -113,7 +113,10 @@ def visit_star_expr(self, e: StarExpr) -> Key:
         return ('Star', literal_hash(e.expr))
 
     def visit_name_expr(self, e: NameExpr) -> Key:
-        return ('Var', e.name)
+        # N.B: We use the node itself as the key, and not the name,
+        # because using the name causes issues when there is shadowing
+        # (for example, in list comprehensions).
+        return ('Var', e.node)
 
     def visit_member_expr(self, e: MemberExpr) -> Key:
         return ('Member', literal_hash(e.expr), e.name)

mypyc/test-data/run.test

@@ -4633,3 +4633,15 @@ with assertRaises(TypeError, "errored formatting real type!"):
 
 with assertRaises(TypeError, "tuple[int, native.A] object expected; got tuple[int, int]"):
     g((20, 30))
+
+[case testComprehensionShadowBinder]
+def foo(x: object) -> object:
+    if isinstance(x, list):
+        return tuple(x for x in x), x
+    return None
+
+[file driver.py]
+from native import foo
+
+assert foo(None) == None
+assert foo([1, 2, 3]) == ((1, 2, 3), [1, 2, 3])

test-data/unit/check-lists.test

@@ -77,3 +77,11 @@ reveal_type(b)  # N: Revealed type is 'builtins.list[builtins.int*]'
 c = [*a, 0]
 reveal_type(c)  # N: Revealed type is 'builtins.list[builtins.int*]'
 [builtins fixtures/list.pyi]
+
+[case testComprehensionShadowBinder]
+# flags: --strict-optional
+def foo(x: object) -> None:
+    if isinstance(x, str):
+        [reveal_type(x) for x in [1, 2, 3]]  # N: Revealed type is 'builtins.int*'
+
+[builtins fixtures/isinstancelist.pyi]